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Sample records for bentonite deposit cabo

  1. Selection of bentonite deposits

    International Nuclear Information System (INIS)

    The selection of bentonite deposits is to offer a supply base of backfill/buffer materials for high-level radioactive waste repository in China. In this paper the comprehensive evaluation criteria were discussed first, then a comprehensive comment on bentonite deposits in China was given. The properties of geographic distribution, origin, reserves and ore quality of bentonite deposits were also discussed. The comprehensive comparison studies on 12 large-sized bentonite deposits was presented. Based on the results obtained Gaomiaozi bentonite deposit, Inner Mongolia, was recommended as the first choice of backfill/buffer materials for repository in China. (author)

  2. Occurrence of Fe–Mg-rich smectites and corrensite in the Morrón de Mateo bentonite deposit (Cabo de Gata region, Spain): A natural analogue of the bentonite barrier in a radwaste repository

    OpenAIRE

    Pelayo Bayón, Marta; García Romero, Emilia; Labajo Rodillana, Miguel A.; Pérez del Villar Guillén, L.

    2011-01-01

    The Morrón de Mateo bentonite deposit is being studied as a natural analogue of the thermal and geochemical effects on a bentonite barrier in a deep geological repository of high level radioactive wastes. This bentonite deposit and its host rocks were intruded by a rhyodacitic volcanic dome that induced a hydrothermal metasomatic process affecting the biocalcarenite beds close to the dome. In this work, the mineralogical and chemical features of the clay minerals of the hydrotherm...

  3. Occurrence of Fe-Mg-rich smectites and corrensite in the Morron de Mateo bentonite deposit (Cabo de Gata region, Spain): A natural analogue of the bentonite barrier in a radwaste repository

    International Nuclear Information System (INIS)

    Highlights: → A hydrothermal process transformed Fe-Mg smectites into corrensite. → This transformation was favoured by the intrusion of the Morron de Mateo dome. → The intrusion caused a temperature increased and a supply of Fe-Mg rich solutions. → The system can be a good natural analogue of bentonite barrier in a radwaste disposal. → Experimental studies of stability of bentonite are in agreement with the results. - Abstract: The Morron de Mateo bentonite deposit is being studied as a natural analogue of the thermal and geochemical effects on a bentonite barrier in a deep geological repository of high level radioactive wastes. This bentonite deposit and its host rocks were intruded by a rhyodacitic volcanic dome that induced a hydrothermal metasomatic process affecting the biocalcarenite beds close to the dome. In this work, the mineralogical and chemical features of the clay minerals of the hydrothermally altered pyroclastic (white tuffs) and epiclastic rocks (mass flow), located in the NE sector of the Morron de Mateo deposit are described. White tuffs have a high content of phyllosilicates, mainly composed of dioctahedral smectites, while mass flow have a higher proportion of inherited minerals, the neoformed phyllosilicates are dioctahedral smectites and an interlayer chlorite/smectite mineral of corrensite type. The chemical composition of smectites reflects the different nature of the parent rocks, in such a way that smectites from white tuffs have a quite homogeneous chemical composition and their structural formulae correspond to montmorillonite type, while smectites from mass flow show more chemical variability, higher Fe and Mg contents and a mean structural formulae corresponding to Fe-Mg-rich beidellite and/or to an intermediate smectite member between beidellite and saponite. In addition, chemical composition and textural features of corrensite-like clay minerals in relation to Fe-Mg-rich smectites in the samples have also been studied

  4. Chemical and Mineralogical Features of Smectite from the Morron de Mateo Bentonite Deposit (Cabo de Gata, Almeria) in Relation to the Parent Rocks and the Alteration Processes Occurred After the Bentonite Formation: Analogies and Implications for the Engineered Clayey Barrier of a Deep Geological Rad waste Repository

    International Nuclear Information System (INIS)

    The Morron de Mateo bentonite deposit is being studied as a natural analogue of the thermal and geochemical effects on the clayey barrier of a Deep Geological Rad waste Repository (DGRR) after its closure, in relation to the radioactive decay of the fission products and the container corrosion. This bentonite deposit and their host rocks were intruded by a rhyodacitic volcanic dome that induced a hydrothermal metasomatic process affecting the bioclastic calcarenite beds close to the dome. Bentonite from the NE sector of the deposit have been chemically and mineralogically characterized. Pyroclastic rocks (white tuffs), epyclastic rocks (mass flow) and andesitic breccia all of them hydrothermally altered, have been studied at the site. Samples are composed of feldspars, quartz and amphybols, as inherited minerals, and phyllosilicates, zeolites, crystoballite and calcite, as new formed minerals. White tuffs have the highest phyllosilicate contents, mainly dioctahedral smectite of montmorillonite type. Epyclastic rocks and andesitic breccia have a highest proportion of inherited minerals, the new formed phillosilicates being di octahedral smectite of beidellite type and an ordered interlayer chlorite/smectite mineral, of corrensite type. Smectite from the epyclastic rocks have higher Fe and Mg contents and chemical variability, as a consequence of nature of their parent rocks. The presence of corrensite in the epyclastic rocks suggests that in the Morron de Mateo area a propilitic alteration process occurred after bentonite formation, which transformed Fe-Mg-rich smectite into corrensite. This transformation was probably favoured by the sub volcanic intrusion, which also produced a temperature increase in the geological media and a supply of Fe-Mg-rich solutions, which also were the responsible for the metasomatic transformations observed in the calcarenite beds. (Author) 57 refs

  5. Na-smectite s in the Cala de Tomate bentonite deposit (Spain): a natural analogue of the salinity effect on the bentonite barrier of a rad waste disposal

    Energy Technology Data Exchange (ETDEWEB)

    Perez del Villar, L.; Pelayo, M.; Fernandez, A.M.; Cozar, J.S. [CIEMAT - Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas (CIEMAT/DIRE/CEAGP), Madrid (Spain); Delgado, A.; Reyes, E. [Ciencias de la Tierra y Quimica Ambiental Estacion Experimental del Zaidin Dpt., Granada (Spain); Fernandez-Soler, J.M. [Granada Univ., Dpt. de Mineralogia y Petrologia (Spain); Tsige, M. [Facultad de Ciencias Geologicas, Dpt. de Geodinamica, Madrid (Spain)

    2005-07-01

    Within the framework of the ENRESA programme for the assessment of the long-term behaviour of the bentonite-engineered barrier for a deep radwaste geological repository, analogue studies on several bentonite deposits are conducted at CIEMAT. Among these analogue studies, the thermal effect induced by volcanic intrusions on bentonite deposits is highlighted. In the Cabo de Gata volcanic region, there are several analogue scenarios where these studies have been performed, such as the Cala de Tomate bentonite deposit that was intruded by a pyroxene andesite volcanic dome. However, geological, mineralogical, physicochemical, geochemical and stable isotopic data obtained from the smectites do not allow to establish any analogy with the thermal effect expected on the bentonite-engineered barrier of a deep geological repository after burial. Thus, the bentonitisation processes took place after the intrusion of the dome, as a result of meteoric diagenesis intensively developed on faulting zone affecting the parent pyroclastic acid tuffs. This faulting process occurred after the dome intrusion. However, the physicochemical characteristics of these smectites, specially the exchangeable cations, allow to consider this bentonite deposit as a natural analogue of the saline effect on the clayey barrier. This analogy has been established because Na-smectites are present in this deposit and, up to our present knowledge, it is the first time that these smectites occur naturally in the Cabo de Gata-La Serrata de Nijar volcanic region. As a consequence, the main objectives of this work are: i) to characterise these smectites; ii) to establish their genesis and processes affecting them after their formation and iii) to identify the effects on the bentonite-engineered barrier should it were affected by a Na-rich saline waterfront. (authors)

  6. Chemical and Mineralogical Features of Smectite from the Morron de Mateo Bentonite Deposit (Cabo de Gata, Almeria) in Relation to the Parent Rocks and the Alteration Processes Occurred After the Bentonite Formation: Analogies and Implications for the Engineered Clayey Barrier of a Deep Geological Rad waste Repository; Naturaleza de las Esmectitas del Yacimiento de Morron de Mateo (Cabo de Gata, Almeria) en Relacion con la Roca Madre y con los Procesos Posteriores a la Bentonitizacion: Implicaciones Analogicas para la Barrera de Ingenieria de un Almacenamiento Geologico de Residuos Radiactivos

    Energy Technology Data Exchange (ETDEWEB)

    Pelayo, M.; Labajo, M. A.; Garcia Romero, L.; Perez del Villar, L.

    2009-10-12

    The Morron de Mateo bentonite deposit is being studied as a natural analogue of the thermal and geochemical effects on the clayey barrier of a Deep Geological Rad waste Repository (DGRR) after its closure, in relation to the radioactive decay of the fission products and the container corrosion. This bentonite deposit and their host rocks were intruded by a rhyodacitic volcanic dome that induced a hydrothermal metasomatic process affecting the bioclastic calcarenite beds close to the dome. Bentonite from the NE sector of the deposit have been chemically and mineralogically characterized. Pyroclastic rocks (white tuffs), epyclastic rocks (mass flow) and andesitic breccia all of them hydrothermally altered, have been studied at the site. Samples are composed of feldspars, quartz and amphybols, as inherited minerals, and phyllosilicates, zeolites, crystoballite and calcite, as new formed minerals. White tuffs have the highest phyllosilicate contents, mainly dioctahedral smectite of montmorillonite type. Epyclastic rocks and andesitic breccia have a highest proportion of inherited minerals, the new formed phillosilicates being di octahedral smectite of beidellite type and an ordered interlayer chlorite/smectite mineral, of corrensite type. Smectite from the epyclastic rocks have higher Fe and Mg contents and chemical variability, as a consequence of nature of their parent rocks. The presence of corrensite in the epyclastic rocks suggests that in the Morron de Mateo area a propilitic alteration process occurred after bentonite formation, which transformed Fe-Mg-rich smectite into corrensite. This transformation was probably favoured by the sub volcanic intrusion, which also produced a temperature increase in the geological media and a supply of Fe-Mg-rich solutions, which also were the responsible for the metasomatic transformations observed in the calcarenite beds. (Author) 57 refs.

  7. Mineralogy and geochemistry of bauxite and bentonite deposits from Mozambique

    NARCIS (Netherlands)

    Dos Muchangos, A.C.

    2000-01-01

    Results of mineralogical and geochemical studies of bauxites, kaolinitic clays and bentoniteS from Mozambique are presented in this thesis. The bauxite and kaolinitic clay deposits in Penhalonga area (in the central western part of Mozambique) are associated with Precambrian magmatic rocks and the b

  8. Characterization of bentonite clay from “Greda” deposit

    Directory of Open Access Journals (Sweden)

    Nadežda Stanković

    2011-06-01

    Full Text Available Based on mineralogical and technological investigations of the deposit “Greda” important characteristics of bentonite clay were determined. Representative samples of the deposit were characterized with X-ray diffraction, low-temperature nitrogen adsorption, chemical analysis, differential thermal analysis and scanning electron microscopy. It was determined that the main mineral is montmorillonite and in subordinate quantities kaolinite, quartz and pyrite. The chemical composition generally shows high silica and alumina contents in all samples and small quantities of Fe3+, Ca2+ and Mg2+ cations. Based on technological and mineralogical research, bentonite from this deposit is a high-quality raw material for use in the ceramic industry.

  9. Sorption of strontium on bentonites from Slovak deposits

    International Nuclear Information System (INIS)

    Sorption on bentonite from different Slovak deposits / Jelsovy potok, Kopernica and Lieskove has been investigated under various experimental conditions, such as contact time, pH, sorbate concentrations, presence of complementary cation. The sorption of strontium from aqueous solutions was investigated using a radiometric determination of distribution coefficient, Kd. The individual solutions were labelled with radiotracer. Radiation stability has been investigated, the higher sorption parameters were observed for the irradiated bentonites /tab.l/ , which can be explained by the increase of specific surface and change of solubility of the irradiated samples of bentonite. The presence of complementary cations, Na+, K+, NH4+, Ca2+, Mg2+ and Ba2+ depresses the sorption of Sr on bentonite. In the case of bentonite Kopernica the effectiveness in reducing the sorption of strontium by cations followed the order K+ 4+ + 2+ 2+ 2+. Results indicate that the sorption of Sr+ on bentonite will be affected by the presence of high concentrations of various salts in the waste water effluents. (author)

  10. DEPOSITS AND MINING POTENTIAL OF BENTONITE IN CROATIA

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    Mario Klanfar

    2012-07-01

    Full Text Available Bentonite is one of the materials that is planed to be used for buffering and backfilling in spent nuclear fuel repositories, within deep crystalline rock. There are several locations in Croatia that bentonite deposits and occurrences are found on. Some were exploited in past, and others were more or less explored. This paper presents overview of bentonite deposits, basic properties and potential resources, and mining practices in Croatia. Largest exploited deposits are found in area of Poljanska luka, Gornja Jelenska and Bednja. Surface and underground methods (drift and fill, sublevel caving were used during exploitation. In the area of Svilaja and Lika are found potentially valuable deposits that were never exploited. Montmorilonite content ranges form 20-50% to 57-89%. Most deposits contain bentonite beds with thickness 0,4-1,6 m, and have plunge 10°-30°. Few exceptions are nearly horizontal and thick more than 5 m and even 12 m. One is declined at 70° and up to 40m thick. Proven reserves are about 2,3 Mt with some level of uncertainty. Average production per mine during exploitation period can be assumed to be several thousands t/y.

  11. Experimental study on bentonite gel migration from a deposition hole

    International Nuclear Information System (INIS)

    The experimental study on bentonite gel migration from a deposition hole into a surrounding joint has been performed by using a transparent acrylic resin cell with a slot. Cylindrical blocks of pure bentonite and a bentonite-sand mixture have been used as the buffer material, and the slot width simulating the joint aperture is set between 0.3 to 1.5 mm. The time-dependence displacement of migrating gel fronts in the slots and the swelling pressure of the sample in the core, which simulate a deposition hole, have been measured. It has been observed that the migrating gel front separates two distinct zones, and the displacement of the front is proportional to the square-root of time before the separation. With wider slots, the swelling pressure of the sample in the core has rapidly decreased. Applying theoretical models to the experimental results, the viscosity of the migrating gel in the slot (ca. 200 MPa·s) and the diffusion coefficient of bentonite clay (ca. 3 x 10-11m2/s) have been obtained. (author)

  12. Backfilling of deposition tunnels: Use of bentonite pellets

    International Nuclear Information System (INIS)

    The state of knowledge related to use of bentonite pellets as part of backfill or other gap filling components in repository applications is reviewed. How the pellets interact with adjacent sealing materials and the surrounding rock mass is a critical aspect in determining backfill behaviour. The key features and processes that determine how the pellet component of the KBS-3V deposition tunnel backfill will behave are discussed and recommendations related to what additional information needs to be developed are provided. Experiences related to pellet material composition, size, shape, placement options and more importantly, the density to which they can be placed all indicate that there are significant limitations to the achievable as-placed density of bentonite pellet fill. Low as-placed density of the pellet fill component of the backfill is potentially problematic as the outermost regions of tunnel backfill will be the first region of the backfill to be contacted by water entering the tunnels. It is also through this region that initial water movement along the length of the deposition tunnels will occur. This will greatly influence the operations in a tunnel, especially with respect to situations where water is exiting the downstream face of still open deposition tunnels. Pellet-filled regions are also sensitive to groundwater salinity, susceptible to development of piping features and subsequent mechanical erosion by through flowing water, particularly in the period preceding deposition tunnel closure. A review of the experiences of various organisations considering use of bentonite-pellet materials as part of buffer or backfill barriers is provided in this document. From this information, potential options and limitations to use of pellets or pellet-granule mixtures in backfill are identified. Of particular importance is identification of the apparent upper-limits of dry density to which such materials can to be placed in the field. These bounds will

  13. Backfilling of deposition tunnels: Use of bentonite pellets

    Energy Technology Data Exchange (ETDEWEB)

    Dixon, David (Atomic Energy of Canada Limited (Canada)); Sanden, Torbjoern (Clay Technology AB (Sweden)); Jonsson, Esther (Swedish Nuclear Fuel and Waste Mangaement Co. (Sweden)); Hansen, Johanna (Posiva Oy (Finland))

    2011-02-15

    The state of knowledge related to use of bentonite pellets as part of backfill or other gap filling components in repository applications is reviewed. How the pellets interact with adjacent sealing materials and the surrounding rock mass is a critical aspect in determining backfill behaviour. The key features and processes that determine how the pellet component of the KBS-3V deposition tunnel backfill will behave are discussed and recommendations related to what additional information needs to be developed are provided. Experiences related to pellet material composition, size, shape, placement options and more importantly, the density to which they can be placed all indicate that there are significant limitations to the achievable as-placed density of bentonite pellet fill. Low as-placed density of the pellet fill component of the backfill is potentially problematic as the outermost regions of tunnel backfill will be the first region of the backfill to be contacted by water entering the tunnels. It is also through this region that initial water movement along the length of the deposition tunnels will occur. This will greatly influence the operations in a tunnel, especially with respect to situations where water is exiting the downstream face of still open deposition tunnels. Pellet-filled regions are also sensitive to groundwater salinity, susceptible to development of piping features and subsequent mechanical erosion by through flowing water, particularly in the period preceding deposition tunnel closure. A review of the experiences of various organisations considering use of bentonite-pellet materials as part of buffer or backfill barriers is provided in this document. From this information, potential options and limitations to use of pellets or pellet-granule mixtures in backfill are identified. Of particular importance is identification of the apparent upper-limits of dry density to which such materials can to be placed in the field. These bounds will

  14. Bentonite-like material sealing to high-level radioactive wastes storage

    International Nuclear Information System (INIS)

    Among the most used materials for sealing of radioactive waste storage, bentonite shows a high number of advantages because of its plasticity, thermal and hydraulic conductivity, etc. The paper makes a review on different Spanish deposits of bentonite and their stability. Most of studies are focussed on the volcanic region at Cabo de Gata (Almeria). That area offers the most productive hydrothermal bentonite deposits in Spain

  15. Bentonite deposits as a natural analogue to long-term barriers in a final repository of nuclear waste

    International Nuclear Information System (INIS)

    The geology of bentonite occurrences in Almeria (Spain) and Wyoming (USA) were studied in order to find suitable natural analogue to the longterm mechanical behaviour of the bentonite barrier in the final nuclear waste disposal. The study is based on literature review over both occurrence areas and on fieldwork observations from Almeria, Spain. The deposit areas differ from each other by age, deposition environment, exchangeable cation chemistry, alteration condition, occurrence and deformational features. One of the most important deformational feature in Almeria bentonites was the existence of Tertiary (Middle and Upper Miocene, 6-15.5 Ma old) bentonite intrusion inside/over younger Quaternary (Pleistocene Superior, 0.01-0.72 Ma old) sediments. This was a result of the confining pressure of overlying volcanic rocks and sediments and the high plasticity behaviour of bentonites. According to this observation, the pressure effect in final nuclear waste repositories requires further investigations. The bentonites in Wyoming have survived weathering and shearing without losing their expandability or other properties typical of smectite-rich materials. (orig.)

  16. Chemical signature of two Permian volcanic ash deposits within a bentonite bed from Melo, Uruguay.

    Science.gov (United States)

    Calarge, Liane M; Meunier, Alain; Lanson, Bruno; Formoso, Milton L L

    2006-09-01

    A Permian bentonite deposit at Melo, Uruguay is composed of a calcite-cemented sandstone containing clay pseudomorphs of glass shards (0-0.50 m) overlying a pink massive clay deposit (0.50-2.10 m). The massive bed is composed of two layers containing quartz and smectite or pure smectite respectively. The smectite is remarkably homogeneous throughout the profile: it is a complex mixed layer composed of three layer types whose expandability with ethylene glycol (2EG 1EG or 0EG sheets in the interlayer zone which correspond to low-, medium- and high-charge layers respectively) varies with the cation saturating the interlayer zone. The smectite homogeneity through the profile is the signature of an early alteration process in a lagoonal water which was over saturated with respect to calcite. Compaction during burial has made the bentonite bed a K-depleted closed system in which diagenetic illitization was inhibited. Variations in major, REE and minor element abundances throughout the massive clay deposit suggest that it originated from two successive ash falls. The incompatible element abundances are consistent with that of a volcanic glass fractionated from a rhyolite magma formed in a subduction/collision geological context. PMID:16936941

  17. Bentonite deposits in china and its possible use as buffer material for China high level radioactive waste repository

    International Nuclear Information System (INIS)

    Radioactive waste is produced from a wide range of nuclear activities and the safe disposal of radioactive waste is a key issue of the nuclear industry worldwide. In China, the work related to radioactive waste disposal is managed by the China National Nuclear Corporation (CNNC). In 1985, CNNC proposed an R and D program called DGD program for the Deep Geological Disposal of HLW. The objective of the program is to build a granite-hosted national geological repository between 2030 and 2040, which is able to dispose of vitrified waste, transuranic waste and small amount of CANDU spent fuel. The concept of geological disposal of high level radioactive waste in China is based on a multi-barrier system which combines an isolating geological environment with an engineered barrier system. The buffer/backfill material is one of the main engineered barriers for HLW repository. The basic requirement of the buffer is to restrict radionuclide migration by restricting groundwater movement, providing a high sorption capacity for dissolved nuclides and acting as a filter for radionuclide - bearing colloids. To ensure safety over the long timescales of interest, it is necessary to demonstrate that no significant detrimental impacts on the physical properties of the buffer material. In parallel, it is also necessary to demonstrate the feasibility of manufacturing and installing the buffer. Natural clay is a material that can satisfy all the above functions, to a greater or lesser extent. Among the types of natural clay, bentonite, when compacted, is considered as a superior barrier because (1) it has exceptionally low water permeability to control the movement of water in buffer, (2) it fills void spaces in the buffer and fractures in the host rock as it swells upon water uptake, (3) it has the ability to exchange cations and to adsorb cationic radioelement. There are 84 main bentonite deposits discovered in China. In order to select a bentonite deposit for China high level waste

  18. Chemical signature of two Permian volcanic ash deposits within a bentonite bed from Melo, Uruguay

    Directory of Open Access Journals (Sweden)

    Liane M. Calarge

    2006-09-01

    Full Text Available A Permian bentonite deposit at Melo, Uruguay is composed of a calcite-cemented sandstone containing clay pseudomorphs of glass shards (0-0.50 m overlying a pink massive clay deposit (0.50-2.10m. The massive bed is composed of two layers containing quartz and smectite or pure smectite respectively. The smectite is remarkably homogeneous throughout the profile: it is a complex mixed layer composed of three layer types whose expandability with ethylene glycol (2EG 1EG or 0EG sheets in the interlayer zone which correspond to low-, medium- and high-charge layers respectively varies with the cation saturating the interlayer zone. The smectite homogeneity through the profile is the signature of an early alteration process in a lagoonal water which was over saturated with respect to calcite. Compaction during burial has made the bentonite bed a K-depleted closed system in which diagenetic illitization was inhibited. Variations in major, REE and minor element abundances throughout the massive clay deposit suggest that it originated from two successive ash falls. The incompatible element abundances are consistent with that of a volcanic glass fractionated from a rhyolite magma formed in a subduction/collision geological context.Um depósito Permiano de bentonita em Melo, Uruguai,é composto por um arenito com cimento calcítico contendo pseudomorfos de argila sobre detritos vítreos(0-0.50 m superpostos a um deposito maciço de argila rosado (0.50-2.10 m. A camada maciça é composta por dois níveis contendo quartzo e esmectita ou esmectita pura, respectivamente. A homogeneidade de esmectita ao longo do perfil é notável: trata-se de um interestratificado composto de três tipos de camadas, cuja expansibilidade com etileno-glicol (folhas 2EG, 1EG ou 0EG na zona interfoliar correspondentes a camadas com baixa, média e alta carga, respectivamente variam com o tipo de cátion que satura a zona interfoliar. A homogeneidade da esmectita ao longo do perfil

  19. BENTONITE PROCESSING

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    Anamarija Kutlić

    2012-07-01

    Full Text Available Bentonite has vide variety of uses. Special use of bentonite, where its absorbing properties are employed to provide water-tight sealing is for an underground repository in granites In this paper, bentonite processing and beneficiation are described.

  20. Characterisation of bentonite from Hliník nad Hronom deposit (Jastrabá Formation of the Štiavnica stratovolcano, Western Carpathians

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    Peter Uhlík

    2012-05-01

    Full Text Available The Hliník nad Hronom bentonite deposit is situated in Jastrabá Formation on the NW margin of the Štiavnické vrchy Mts. Geological exploration was realised in the deposit at the end of eighties. The bentonite was described as lower quality. The deposit is very rarely operated. The purpose of presented study was characterisation of the bentonite predominately by actual X-ray diffraction techniques and infrared spectroscopy and comparison of the Hliník nad Hronom deposit with other Western Carpathian bentonites. Studied bentonite and bentonized rhyolitic tuff from Hliník nad Hronom were composed of 30–53 wt % of Al-Mg montmorillonite, 19–45 wt % of opal-C or opal-CT, mostly less than 14 wt % of volcanic glass and less than 10 wt % of K-feldspar. Also illite, biotite, kaolinite and other were determined as minor and trace mineral phases. Cation-exchange capacity (CEC of bulk rock samples ranged from 30 to 65 meq/100g. CEC was significantly higher in clay fraction (85–95 meq/100g that is in good correlation with presence of almost pure montmorillonite. The BWA analysis of montmorillonite 001 XRD peaks was performed to calculate the mean crystallite size and the crystallite size distribution. Surface controlled crystal growth mechanism was determined for Hliník nad Hronom´s montmorillonite according to calculated parameters of lognormal particle thickness distribution (α and β2, similarly as for other Western Carpathian smectites. The mean thickness of smectite particles from Hliník nad Hronom (about 6.78 nm belongs to the lowest values that were calculated for Western Carpathian smectites. Based on the presented results and previous knowledge, we can assume that the deposit originated in lacustrine environment. The insufficient fluid flow rate caused the precipitation of high amount of opal-C or/and opal-CT. The crystallisation temperature of smectites was low, only 20–50°C, at the bentonitization of rhyolitic tuff of Hliník nad

  1. The saturation and resulting swelling pressure of a deposition hole-tunnel system filled with bentonite under consideration of the excavation disturbed zone (EDZ) with the help of the two phase flow theory

    International Nuclear Information System (INIS)

    The water saturation of the Bentonite buffer around the Cu canister in the deposition hole of the project 'Prototype Repository - ASPO' is significant with respect to the type of the bentonite and the spread of temperature. A fundamental question is how fast does the initially unsaturated bentonite becomes saturated with water and can sufficient water penetrate from the host granite rock into all areas of the bentonite. There are two possible paths, one being the path through the tunnel and the other hydraulically active fractures intersected by the deposition hole. The ingress of water is however immediately halted by the swelling of the bentonite. A path via the undisturbed compacted granite is deemed negligible due to its low permeability of K -23 m2. The inflowing water is distributed over the excavation disturbed zone EDZ, created during the construction of the deposition hole, Since the degree of disturbance of the granite is not unequivocally known, a time-dependent parameter study using appropriate permeability values was performed to consider the width of the EDZ. The non-steady state hydraulic behaviour of the system is controlled by the saturation of the bentonite, The calculations were performed using the Rockflow computer software, described below. (author)

  2. Final report of the rock sealing project - Sealing of the near-field rock around deposition holes by use of bentonite grouts

    International Nuclear Information System (INIS)

    Test 1 of the rock sealing project comprised determ ination of the hydraulic properties of the rock around large-diameter holes like canister deposition holes or TBM tunnels and attempts were made to seal the fractures intersecting such holes with bentonite slurry. The heater holes from the buffer mass test which are 76 cm in diameter, were used and injection made from inside the holes with a specially designed device using dynamic injection technique. The hydraulic properties of the surrounding rock were tested by use of the same device before and after the injections, as well as after a 3 months heat pulse. The results were interpreted by applying a special derived grout flow model and by analyzing the rock response through different calculation techniques, as well as by localizing the injected grout by rock excavation. The experiments showed that grouting of fractured rock by using the applied technique can give very significant sealing. (au)

  3. Effectiveness of use of Nanostructure Minerals – Bentonite of Taganskiy Deposit for Waste Water Clearing in Metallurgy Industry

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    Sharbanu Muzdybayeva

    2014-10-01

    Full Text Available The currently used traditional method of waste water treatment based on the precipitation of heavy metals by iron hydroxide formed at the time of neutralization (liming / bleach(active chlorine doesn’t correspondent to the standards of maximum permissible concentration (MPC in practical meaning. In this regard, the urgent task is the use of natural materials as sorbents due to the relatively high sorption capacity, selectivity, having cation-exchange properties and the possibility of almost complete removal of heavy metal ions. Another important factor is their relatively low cost and availability (sometimes as alocal material. We believe that the use of scientific-based combinations of different ways in waste water treatment based on the success of modern chemistry allows opening newand perspective opportunities in this area.Key Words: Waste Water, Metallurgy, Bentonite, Zeolites, Groundwater

  4. Earthquake induced rock shear through a deposition hole. Modelling of three model tests scaled 1:10. Verification of the bentonite material model and the calculation technique

    International Nuclear Information System (INIS)

    Three model shear tests of very high quality simulating a horizontal rock shear through a deposition hole in the centre of a canister were performed 1986. The tests and the results are described by /Boergesson 1986/. The tests simulated a deposition hole in the scale 1:10 with reference density of the buffer, very stiff confinement simulating the rock, and a solid bar of copper simulating the canister. The three tests were almost identical with exception of the rate of shear, which was varied between 0.031 and 160 mm/s, i.e. with a factor of more than 5,000 and the density of the bentonite, which differed slightly. The tests were very well documented. Shear force, shear rate, total stress in the bentonite, strain in the copper and the movement of the top of the simulated canister were measured continuously during the shear. After finished shear the equipment was dismantled and careful sampling of the bentonite with measurement of water ratio and density were made. The deformed copper 'canister' was also carefully measured after the test. The tests have been modelled with the finite element code Abaqus with the same models and techniques that were used for the full scale scenarios in SR-Site. The results have been compared with the measured results, which has yielded very valuable information about the relevancy of the material models and the modelling technique. An elastic-plastic material model was used for the bentonite where the stress-strain relations have been derived from laboratory tests. The material model is made a function of both the density and the strain rate at shear. Since the shear is fast and takes place under undrained conditions, the density is not changed during the tests. However, strain rate varies largely with both the location of the elements and time. This can be taken into account in Abaqus by making the material model a function of the strain rate for each element. A similar model, based on tensile tests on the copper used in the scale

  5. Microbial communities in bentonite formations and their interactions with uranium

    International Nuclear Information System (INIS)

    Highlights: • Microbial diversity of Spanish bentonites was studied. • High number of aerobe and facultative anaerobe microbes were isolated from bentonites. • Natural bentonite microbes are able to tolerate high U concentrations. • U is immobilized by the cells of the strain Rhodotorula mucilaginosa BII-R8 as U(VI) phosphates. - Abstract: A reliable performance assessment of deep geological disposal of nuclear waste depends on better knowledge of radionuclide interactions with natural microbes of geological formations (granitic rock, clay, salts) used to host these disposal systems. In Spain, clay deposits from Cabo de Gata region, Almeria, are investigated for this purpose. The present work characterizes the culture-dependent microbial diversity of two bentonite samples (BI and BII) recovered from Spanish clay deposits. The evaluation of aerobe and facultative anaerobe microbial populations shows the presence of a high number of cultivable bacteria (e.g. Stenotrophomonas, Micrococcus, Arthrobacter, Kocuria, Sphingomonas, Bacillus, Pseudomonas, etc.) affiliated to three phyla Proteobacteria, Actinobacteria, and Firmicutes. In addition, a pigmented yeast strain BII-R8 related to Rhodotorula mucilaginosa was also recovered from these formations. The minimal inhibitory concentrations of uranium for the growth of these natural isolates were found to range from 4 to 10.0 mM. For instance, strain R. mucilaginosa BII-R8 was shown to tolerate up to 8 mM of U. Flow cytometry studies indicated that the high U tolerance of this yeast isolate is a biologically mediated process. Microscopically dense intracellular and cell wall-bound precipitates were observed by Scanning Transmission Electron Microscopy-High-Angle Annular Dark-Field (STEM-HAADF). Energy Dispersive X-ray (EDX) element-distribution maps showed the presence of U and P within these accumulates, indicating the ability of cells to precipitate U as U(VI) phosphate minerals. Fundamental understanding of the

  6. Diffusion of humic colloids in compacted bentonite

    International Nuclear Information System (INIS)

    In Sweden, as in many other countries, compacted bentonite will surround the encapsulated spent nuclear fuel in a deep bedrock repository. Bentonite gives mechanical support and minimizes the water flow over the deposition holes. The retardation for cationic radionuclides escaping a faulted canister is high in saturated compacted bentonite, since cationic radionuclides sorbs strongly on the bentonite surface, and the only plausible transport mechanism is diffusion. Sorption and diffusion of radionuclides in the bentonite barrier has been extensively studied, and sorption and diffusion coefficients are well established. There is a lack of knowledge as well as data for effects of colloids on radionuclide mobility and transport in the bentonite barrier. In a deep bedrock repository, colloids, particles in the size range of 1-1000 nm, will be present, however in very low concentrations. The colloids origin from eroded bedrock and filling material, mineral oxides, clay, degraded organic compounds and micro-organisms etc. The bentonite barrier is regarded to be an efficient filtering barrier for colloids. With the widely spread micro-structure with pores in between the montmorillonite flakes in the size range of nm, and the inter particle voids partly gel filled of sizes, colloid transport seems unlikely. In a Japanese diffusion study on gold colloids no breakthrough of the colloids was detected. However, to reject the possibility of enhancement of transport of radionuclides by colloids, more data from diffusion studies on other types of colloids in compacted bentonite are needed. Therefore diffusion experiments of Humic Colloids (HC), in the size range of 1-10 nm, were performed. (author)

  7. Dependencies of the speed of adsorption 60Co(II) from the time on the bentonite from a deposit Jelsovy potok

    International Nuclear Information System (INIS)

    Adsorption of cobalt on selected sorbents was studied by radioindicator method in a batch experimental arrangement. Distribution coefficients and adsorption percentage were determined for bentonite - cobalt system as a function of time mixing. For adsorption study there were selected bentonite from the alder creek area. Their main advantages are rapid ion exchange and low permeability. They are also considered as the most promising candidates in multi barrier system in repositories of radioactive waste and spent nuclear fuel. Cobalt solution at two concentrations was stirred from 15 min to 24 h. The experiment results showed that the adsorption is a time dependent process. Rapid adsorption of cobalt in the beginning and later very slow adsorption indicates two adsorption mechanisms, which are ion exchange and adsorption followed by a slow penetration of cobalt into the crystal grid of montmorillonite, the main component of bentonite. The time to reach the adsorption equilibrium was 4 hours. (authors)

  8. Depósitos cuaternarios de la costa atlántica fueguina, entre los cabos Peñas y Ewan Quaternary deposits of the Fuegian Atlantic coast between Peñas and Ewan capes

    Directory of Open Access Journals (Sweden)

    G.G. Bujalesky

    2006-03-01

    Full Text Available La zona litoral del noreste de Tierra del Fuego situada entre los cabos Peñas y Ewan fue afectada por procesos vinculados a las glaciaciones y transgresiones del Cuaternario. El área estuvo libre de hielo, al menos, desde hace unos 1,5 Ma. Los depósitos glacifluviales fueron retrabajados por los procesos litorales y dieron origen a playas de grava durante los episodios interglaciales. En el área se reconocieron cuatro niveles de playas de grava del Pleistoceno. Los dos niveles más jóvenes e inferiores corresponden a los estadíos isotópicos 18O 5e (Formación La Sara, 7 m sobre la berma de tormenta actual y 7 (Formación Shaiwaal, 12 m s.b.t.. Los niveles superiores se corresponderían a episodios interglaciales más antiguos que el estadío isotópico 18O 11 (Formación Viamonte, 38 m s.b.t. y Formación Najmishk, 53 m s.b.t.. Estas son las playas elevadas del Pleistoceno más australes del mundo. Durante el Holoceno, el desarrollo de las planicies de cordones litorales de grava comenzó a obturar los estuarios interiores de las entrantes costeras de la ensenada de la Colonia y de la desembocadura del río Fuego hace unos 5000 años A.P. Estas planicies de cordones muestran características regresivas. No revelan erosión, reciclado de sedimentos (canibalismo y retroceso litoral, como el resto de las formas litorales de la costa atlántica septentrional de Tierra del Fuego.The littoral zone of north-eastern Tierra del Fuego located between Cabo Peñas and Cabo Ewan was affected by processes related to the Quaternary glaciations and marine transgressions. This was a free-ice area at least since 1.5 Ma B.P. Glacifluvial deposits were re-worked by litoral processes that formed gravel beaches during highstands of the sea level. Four levels of Pleistocene gravel beaches were recognized in the area. The younger and lower levels would probably correspond to the oxygen isotope stage 5e (La Sara Formation, altitude about 7 m above the present

  9. Swelling characteristics of Gaomiaozi bentonite and its prediction

    Directory of Open Access Journals (Sweden)

    De'an Sun

    2014-04-01

    Full Text Available Gaomiaozi (GMZ bentonite has been chosen as a possible matrix material of buffers/backfills in the deep geological disposal to isolate the high-level radioactive waste (HLRW in China. In the Gaomiaozi deposit area, calcium bentonite in the near surface zone and sodium bentonite in the deeper zone are observed. The swelling characteristics of GMZ sodium and calcium bentonites and their mixtures with sand wetted with distilled water were studied in the present work. The test results show that the relationship between the void ratio and swelling pressure of compacted GMZ bentonite-sand mixtures at full saturation is independent of the initial conditions such as the initial dry density and water content, but dependent on the ratio of bentonite to sand. An empirical method was accordingly proposed allowing the prediction of the swelling deformation and swelling pressure with different initial densities and bentonite-sand ratios when in saturated conditions. Finally, the swelling capacities of GMZ Na- and Ca-bentonites and Kunigel Na-bentonite are compared.

  10. Long-time stability following freezing and thawing of concrete and bentonite in deposition of low- and intermediate-level radioactive waste in SFR 1

    International Nuclear Information System (INIS)

    This document describes the effect of freezing on the concrete and bentonite barriers in SFR 1. The document constitutes one of the references describing the degradation of barriers in a long-time perspective and is used in the safety analysis SFR 1 SAR-08

  11. Bentonite porewater chemistry

    International Nuclear Information System (INIS)

    Porewater composition in a compacted bentonite is dependent on the composition of the surrounding groundwater, and on the characteristics of the bentonite itself. Two mechanisms through which bentonite influences the respective porewater composition are distinguished: surface chemical reactions (ion exchange, surface complexation) on smectite and dissolution of minerals and soluble impurities included in bentonite. This report provides the results of different activities related to the definition of porewater chemistry through the use of geochemical models: 1) review of thermodynamic model on ion exchange reaction, 2) modeling of bentonite-water interactions under aerobic conditions, 3) performance of sensitivity analyses of key parameters in the bentonite model, 4) model simulation of bentonite porewater chemistry in the engineered barrier system under repository conditions. Experimental information of bentonite-water interaction allowed the determination of soluble impurities in the bentonite, and the knowledge of these impurities is important for predictive modeling. For the impurities of Kunigel-V1, 0.38% of CaSO4, 0.0011% of NaCl and 0.0044% of KCl were determined. The sensitivity analyses resulted in that the presence of calcite, CaSO4 and pyrite strongly influences the pH in the compacted bentonite, and the pH in compacted bentonite is buffered by the acid/base equilibria at the Na-smectite surface as well. Through the model calculations, some remarks on the expected trends for the long term behavior can be made like that the pH in compacted bentonite is expected to increase with increasing number of water exchange cycles, as long as CaCO3 contributes to the pH buffering capacity, due to slow depletion of the soluble impurities in the bentonite. The pH of the porewater, however, lies in all cases (but in the presence of CaCo3) between 5.6 and 9.5. Based on the findings discussed above, a large number of calculations were carried out to support the definition

  12. Influence of selected factors on strontium sorption on bentonites

    International Nuclear Information System (INIS)

    Sorption on bentonite will play an important role in retarding the migration of radionuclides from a waste repository. Bentonite is a natural clay and one of the most promising candidates for use as a buffer material in the geological disposal systems for high-level nuclear waste. It is intended to isolate metal canisters with highly radioactive waste products from the surrounding rocks because of its ability to retard the movement of radionuclides by sorption. Bentonite is characterized by low permeability, water swelling capability and excellent sorption potential for cationic radionuclides. To correctly assess the sorption potential of radionuclides on bentonite is essential for the development of predictive migration models. The sorption of strontium on bentonite from different Slovak deposits - Jelsovy potok, Kopernica and Lieskovec has been investigated under various experimental conditions, such as contact time, sorbate concentrations, presence of complementary cation. Sorption was studied using the batch technique. The uptake of Sr was rapid and equilibrium was reached almost instantaneously. The instantaneous uptake may be due to adsorption and/or exchange of the metal with some ions on the surface of the adsorbent. The best sorption characteristics distinguish bentonite Kopernica, sorption capacity for Sr of the fraction under 45 mm is 0,48 mmol·g-1 for Sr. The highest values of distribution coefficient were reached for the bentonite Jelsovy potok. Radiation stability has been investigated, the higher sorption parameters were observed for the irradiated bentonites, which can be explained by the increase of specific surface of the bentonite samples. The presence of complementary cations depresses the sorption of Sr on bentonite. Cations Ca2+ exhibit higher effect on cesium sorption than the Na2+ ions. Results indicate that the sorption of Sr2+ on bentonite will be affected by the presence of high concentrations of various salts in the waste water

  13. Copper/bentonite interaction

    International Nuclear Information System (INIS)

    The prediction of the processes and rate of corrosion of the KBS 2 copper canisters must be based on a proper scenario, which involves the physical state of the bentonite surrounding the canisters, and the chemical interaction between copper and bentonite. Literature data suggest slow Cu migration and Cu exchanging originally adsorbed cations. Two tests involving copper/bentonite contacts for 3 - 6 months in boreholes have yielded certain valuable information. Thus, Cu ion migration is indeed very slow and where it yields a sufficiently high concentration, it is associated with replacement of originally adsorbed Na ions, which should result in an increased permeability. In one of the tests the copper was separated from the bentonite by a partly air-filled slot. These conditions caused the formation of copper oxides and hydroxides which intermingled with the bentonite that expanded to fill the slot. Due to the low solubility of these copper compounds, the Cu ion concentration was too low to produce ion exchange during the time of observation. (Author)

  14. Porewater chemistry in compacted bentonite

    International Nuclear Information System (INIS)

    In this study, the porewater chemistry in compacted bentonite, considered as an engineered barrier in the repository of spent fuel, has been studied in interaction experiments. Many parameters, like the composition and density of bentonite, composition of the solution, bentonite-to-water ratio (B/W), surrounding conditions and experimental time have been varied in the experiments. At the end of the interaction the equilibrating solution, the porewaters squeezed out of the bentonite samples, and bentonites themselves were analyzed to give information for the interpretation and modelling of the interaction. Equilibrium modelling was performed with the HYDRAQL/CE computer code

  15. Effects of silica sol on bentonite

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. Compacted bentonite will be used in Sweden as an engineered barrier in the disposal of nuclear waste, mainly due to bentonites sorption and swelling capacity, where the latter property is warranted in order to seal possible future intersecting fractures. However during the actual construction and deposition period other grouting agents must be used in order to seal already existing fractures. In Sweden Silica sol is currently being investigated in situ at Aespoe Hard Rock Laboratory as a fine fracture (< 100 μm) grouting agent by injection. During this period, there is a plausible risk of Silica sol coming into contact with bentonite. The effect of Silica sol, either in colloidal form or as a gel, on the chemical and physical properties of bentonite has not been properly addressed and has to be further investigated. The Silica sol (Meyco MP320, EKA Chemicals) consists of amorphous SiO2 particles, average size approximately 20 nm. Due to the small particle size Silica sol can penetrate and seal finer fractures than more coarse grouting agents commonly used. Upon injection NaCl (approx 0.3 M) is used as a gel accelerator, leading to a hydrological barrier in the form of a ductile gel after < 1 hour, which then hardens with time (months) increasing its strength significantly, depending on water content, ionic strength and temperature. Upon aggregation, either due to high ionic strength or drying, the silica colloids aggregate seemingly irreversible forming siloxane bonds by condensation of the silanol surface groups. These silanol groups can react at the montmorillonite edges in a similar way. In a worst case scenario the Silica sol would act as an inorganic glue, creating a pillared montmorillonite or modify the edges of the clay particles. Such effects would irreversibly reduce the overall swelling capacity of the affected bentonite. An experimental program has been developed to characterize the Silica sol

  16. Long term mineralogical properties of bentonite/quartz buffer substance

    International Nuclear Information System (INIS)

    This report shows results from investigations concerning properties in bentonitebased buffersubstances which are suggested to be used when high level radioactive wastes from nuclear powerplants are to be stored finally. Recommended material characteristica of the bentonite to be used are summerized. In an attempt to find geological evidence for bentonite to loose its desireable properties there were no such findings at the temperatures, groundwater situations and pressures which are to be expected at the actual depositing depth (500 m) for a considerable period of time. Concerning biological activity and then specially the mobility and activity of bacteria the conclusion is that there will be little or no influence from them either there is bentonite-sand or compacted pure bentonite in the buffer mass

  17. Educar para a diversidade : Cabo Verde

    OpenAIRE

    Ramos, Natália; Ferreira, Lígia Évora

    1997-01-01

    Recursos Educativos - Humanidades O videograma pretende dar a visão geral dos aspetos geográficos, sociodemográficos e culturais de Cabo Verde e da situação dos cabo-verdianos em Portugal. Produção do Centro de Estudos das Migrações e das Relações Interculturais, Universidade Aberta.

  18. Stability of bentonite gels in crystalline rock

    International Nuclear Information System (INIS)

    The present, extended study comprises a derivation of a simple rock model as a basis for calculation of the penetration rate of bentonite and of the groundwater flow rate, which is a determinant of the erodibility of the protruding clay film. This model, which is representative of a gross permeability of about 10-8 - 10-9 m/s, implies a spectrum of slot-shaped joints with apertures ranging between 0.1 and 0.5 mm. It is concluded that less than 2percent of the highly compacted bentonite will be lost into traversing joints in 106 years. A closer analysis, in which also Poiseuille retardation and short-term experiments were taken into account, even suggests that the penetration into the considered joints will be less than that. The penetration rate is expected to be 1 decimeter in a few hundred years. The risk of erosion by flowing groundwater was estimated by comparing clay particle bond strength, evaluated from viscometer tests, and theoretically derived drag forces, the conclusion being that the maximum expected water flow rate in the widest joints of the rock model (4 times 10-4 m/s) is not sufficient to disrupt the gel front or the large individual clay flocs that may exist at this front. The experiments support the conclusion that erosion will not be a source of bentonite loss. A worst case scenario with a shear zone being developed across deposition holes is finally considered and in addition to this, the conditions in the fracture-rich tunnel floor at the upper end of the deposition holes are also analysed. This study shows that even if the rock is much more fractured than normal conditions would imply, the bentonite loss is expected to be very moderate and without substantial effect on the barrier functions of the remaining clay cores in the deposition holes. (author)

  19. Gas Transport in Bentonite

    Energy Technology Data Exchange (ETDEWEB)

    Villar, M. V.; Gutierre-Rodrigo, V.; Martin, P. I.; Romero, F. J.; Barcala, J. M.

    2013-07-01

    The gas permeability of the Spanish FEBEX bentonite compacted at dry densities of between 1.4 and 1.8 g/cm{sup 3} with high water contents was measured for different confining, injection and back pressures. The results were compared with results obtained in previous investigations for lower degrees of saturation. It was checked that gas permeability was greatly affected by dry density, decreasing about three orders of magnitude when it increased from 1.5 to 1.8 g/cm{sup 3} for similar water content. The increase of water content caused also a decrease in gas permeability. It was found that both gas permeability and the relative gas permeability were mainly related to the accessible porosity. These relationships could be fitted to potential expressions with exponents between 3 and 4, as well as the relationship between intrinsic permeability and void ratio. For gas pressures below 1.2 MPa no effect of the injection or confining pressures on the value of permeability was detected. For a given confining pressure the permeability value decreased as the effective pressure increased, especially if the increase in effective pressure was due to a decrease in gas back pressure. It was checked that the Klinkenberg effect was not significant for this material in the range of pressures applied in the tests. The gas breakthrough pressure values in FEBEX saturated bentonite were determined for different dry densities. They increased clearly with dry density and were always higher than the swelling pressure of the bentonite. In high density samples gas flow tended to stop abruptly after breakthrough, whereas in lower density samples gas flow decreased gradually until a given pressure gradient was reached. The permeabilities computed after breakthrough (which usually did not stabilise) were inversely related to dry density. This would indicate that, even if the flow took place predominantly through preferential pathways that sometimes closed quickly after breakthrough and others

  20. UO22+ sorption on bentonite

    International Nuclear Information System (INIS)

    The capacity of bentonite and purified bentonite to remove UO22+ ions from aqueous solutions has been investigated. The UO22+ uptake in these clays was determined for 0.2 and 0.002M uranyl nitrate solutions. It was found that under these conditions (0.2M) the maximum UO22+ uptake was 1.010±0.070 meq UO22+/g of bentonite and 0.787±0.020 meq UO22+/g of purified bentonite. In purified bentonite UO22+ sorption is irreversible up to 50 hours as no desorption was observed. Such is not the case in the natural bentonite. X-ray diffraction, thermal analyses, and transmission electron microscopy were used to characterize the solids. The uranium content was determined by neutron activation analysis. (author)

  1. Portal do Conhecimento de Cabo Verde

    OpenAIRE

    Carvalho, José; Rodrigues, Eloy; Príncipe, Pedro; Corsino, Paulo

    2014-01-01

    Poster apresentado na "5ª Conferência Luso-Brasileira sobre Acesso Aberto", Coimbra, Portugal, 06 - 08 de outubro de 2014. O Portal do Conhecimento de Cabo Verde é uma iniciativa do Ministério do Ensino Superior, Ciência e Inovação de Cabo Verde, que em conjunto com o NOSI – Núcleo Operacional para a Sociedade da Informação e a Universidade do Minho, desenvolveram um ponto único de pesquisa da produção científica de Cabo Verde e a disponibilização de uma biblioteca digital. Este serviç...

  2. Lot A2 test, THC modelling of the bentonite buffer

    Science.gov (United States)

    Itälä, Aku; Olin, Markus; Lehikoinen, Jarmo

    Finnish spent nuclear fuel is planned to be disposed of deep in the crystalline bedrock of the Olkiluoto island. In such a repository, the role of the bentonite buffer is considered to be central. The initially unsaturated bentonite emplaced around a spent-fuel canister will become fully saturated by the groundwater from the host rock. In order to assess the long-term safety of a deep repository, it is essential to determine how temperature influences the chemical stability of bentonite. The aim of this study was to achieve an improved understanding of the factors governing the thermo-hydro-chemical evolution of the bentonite buffer subject to heat generation from the disposed fuel and in contact with a highly permeable rock fracture intersecting a canister deposition hole. TOUGHREACT was used to model a test known as the long-term test of buffer material adverse-2, which was conducted at the Äspö hard rock laboratory in Sweden. The results on the evolution of cation-exchange equilibria, bentonite porewater chemistry, mineralogy, and saturation of the buffer are presented and discussed. The calculated model results show similarity to the experimental results. In particular, the spatial differences in the saturation and porewater chemistry of the bentonite buffer were clearly visible in the model.

  3. Lot A2 test, THC modelling of the bentonite buffer

    International Nuclear Information System (INIS)

    Finnish spent nuclear fuel is planned to be disposed of deep in the crystalline bedrock of the Olkiluoto island. In such a repository, the role of the bentonite buffer is considered to be central. The initially unsaturated bentonite emplaced around a spent-fuel canister will become fully saturated by the groundwater from the host rock. In order to assess the long-term safety of a deep repository, it is essential to determine how temperature influences the chemical stability of bentonite. The aim of this study was to achieve an improved understanding of the factors governing the thermo-hydro-chemical evolution of the bentonite buffer subject to heat generation from the disposed fuel and in contact with a highly permeable rock fracture intersecting a canister deposition hole. TOUGHREACT was used to model a test known as the long-term test of buffer material adverse-2, which was conducted at the Aespoe hard rock laboratory in Sweden. The results on the evolution of cation-exchange equilibria, bentonite pore water chemistry, mineralogy, and saturation of the buffer are presented and discussed. The calculated model results show similarity to the experimental results. In particular, the spatial differences in the saturation and pore water chemistry of the bentonite buffer were clearly visible in the model. (authors)

  4. Bentonite erosion. Final report

    International Nuclear Information System (INIS)

    Low saline water may reach KBS-3 repository depth, e.g. during periods of glaciation. Under such aqueous conditions, the montmorillonite part of the bentonite buffer might transform into a sol and thereby be transported away with flowing water in fractures. The primary aim with this report is to improve the understanding of the basic principles for this possible montmorillonite particle release. The report includes experimental and theoretical work performed at Clay Technology. Natural bentonite and ion-exchanged purified montmorillonite from three different geographical origins, Wyoming (U.S.), Milos (Greece) and Kutch (India) have been studied. Experimental and/or theoretical investigations have been performed with respect to: - Free swelling ability; - Rheological properties; - Rate of bentonite loss into fractures; - Filtering; - Ion exchange; - Sol formation ability; - Ion diffusion; - Mass loss due to erosion. The performed erosion experiments show that erosion does not occur in a mixed calcium/sodium montmorillonite with at least 20% calcium in exchange positions, when the external solution contains above 4 mM charge equivalents. This result is in agreement with the presented conceptual view of sol formation and measured equilibrium properties in mixed calcium/sodium montmorillonite. The findings imply that the buffer will be stable for non-glacial conditions. However, erosion due to sol formation cannot be ruled out for glacial conditions.

  5. Bentonite erosion. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Birgersson, Martin; Boergesson, Lennart; Hedstroem, Magnus; Karnland, Ola; Nilsson, Ulf (Clay Technology AB, Lund (Sweden))

    2009-12-15

    Low saline water may reach KBS-3 repository depth, e.g. during periods of glaciation. Under such aqueous conditions, the montmorillonite part of the bentonite buffer might transform into a sol and thereby be transported away with flowing water in fractures. The primary aim with this report is to improve the understanding of the basic principles for this possible montmorillonite particle release. The report includes experimental and theoretical work performed at Clay Technology. Natural bentonite and ion-exchanged purified montmorillonite from three different geographical origins, Wyoming (U.S.), Milos (Greece) and Kutch (India) have been studied. Experimental and/or theoretical investigations have been performed with respect to: - Free swelling ability; - Rheological properties; - Rate of bentonite loss into fractures; - Filtering; - Ion exchange; - Sol formation ability; - Ion diffusion; - Mass loss due to erosion. The performed erosion experiments show that erosion does not occur in a mixed calcium/sodium montmorillonite with at least 20% calcium in exchange positions, when the external solution contains above 4 mM charge equivalents. This result is in agreement with the presented conceptual view of sol formation and measured equilibrium properties in mixed calcium/sodium montmorillonite. The findings imply that the buffer will be stable for non-glacial conditions. However, erosion due to sol formation cannot be ruled out for glacial conditions.

  6. Los depósitos de bentonita de Barda Negra y cerro Bandera, departamento Zapala, provincia del Neuquén, Argentina Bentonite deposits of Barda Negra and Cerro Bandera, Zapala Department, Neuquén Province, Argentina

    Directory of Open Access Journals (Sweden)

    A. Impiccini

    2002-09-01

    Full Text Available Las bentonitas de la región nordpatagónica pueden ser agrupadas en dos distritos mineralogenéticos caracterizados desde el punto de vista geológico, geográfico y estratigráfico. En este trabajo se considera a las bentonitas terciarias localizadas en la región occidental, en el departamento Zapala, provincia del Neuquén. Los depósitos consisten en estratos lenticulares, subhorizontales, de 2 a 15 metros de espesor, la mayoría de ellos aflorantes. Están incluidos en la Formación Collón Curá, una secuencia miocena continental donde alternan tobas y areniscas. Los cuerpos de arcilla son productos de alteración de materiales piroclásticos vítreos en ambientes húmedos confinados, tales como cuerpos de agua someros. Los análisis por difracción de rayos X muestran que prevalece una esmectita dioctaédrica - montmorillonita - como único mineral arcilloso en la mayoría de los depósitos. Los minerales accesorios son cuarzo, feldespato, plagioclasa y cristobalita (ópalo-CT, y en menor proporción, ceolitas y yeso. El Na+ es el ión intercambiable dominante, junto con Ca++, Mg++ y K+. El contenido en Fe2O3 es muy alto. Estas bentonitas son buenos agentes ligantes en arenas de moldeo para fundición, pero sus propiedades reológicas y el test de filtrado no cumplen exactamente con las normas API para lodos de perforación de petróleo.Bentonites from the North Patagonia region can be grouped in two mineralogenic districts distinguishable on geological, geographical, and stratigraphical criteria. In this paper, we consider the Tertiary bentonites located in the western region, Zapala Department, Neuquén Province. The deposits occur in sub-horizontal lenticular beds, 2 to 15 m in thickness, most of which crop out at the surface. They lie within the Collón Curá Formation, a Miocene continental sequence of alternating tuffs and sandstones. The clay bodies are alteration products of pyroclastic glassy materials in confined wet

  7. Bentonite erosion. Laboratory studies

    International Nuclear Information System (INIS)

    This report covers the laboratory studies that have been performed at Nuclear Chemistry, KTH in the project 'Bentonite Erosion'. Many of the experiments in this report were performed to support the work of the modelling group and were often relatively simple. One of the experiment series was performed to see the impact of gravity and concentration of mono- and di-valent cations. A clay suspension was prepared in a test tube. A net was placed in contact with the suspension, the test tube was filled with solutions of different concentrations and the system was left overnight to settle. The tube was then turned upside down and the behaviour was visually observed. Either the clay suspension fell through the net or stayed on top. By using this method surprisingly sharp determinations of the Critical Coagulation (Flocculation) Concentration (CCC/CFC) could be made. The CCC/CFC of Ca2+ was for sodium montmorillonite determined to be between 1 and 2 mM. An artificial fracture was manufactured in order to simulate the real case scenario. The set-up was two Plexiglas slabs separated by 1 mm thick spacers with a bentonite container at one side of the fracture. Water was pumped with a very low flow rate perpendicular to bentonite container and the water exiting the fracture was sampled and analyzed for colloid content. The bentonite used was treated in different ways. In the first experiment a relatively montmorillonite rich clay was used while in the second bentonite where only the readily soluble minerals had been removed was used. Since Plexiglas was used it was possible to visually observe the bentonite dispersing into the fracture. After the compacted bentonite (1,000 kg/m3) had been water saturated the clay had expanded some 12 mm out into the fracture. As the experiment progressed the clay expanded more out into the fracture and seemed to fractionate in two different phases with less material in the outmost phase. A dark rim which was later analyzed to contain mostly

  8. Bentonite erosion. Laboratory studies

    Energy Technology Data Exchange (ETDEWEB)

    Jansson, Mats (Div. of Nuclear Chemistry, Royal Inst. of Technology, Stockholm (Sweden), School of Chemical Science and Engineering)

    2009-11-15

    This report covers the laboratory studies that have been performed at Nuclear Chemistry, KTH in the project 'Bentonite Erosion'. Many of the experiments in this report were performed to support the work of the modelling group and were often relatively simple. One of the experiment series was performed to see the impact of gravity and concentration of mono- and di-valent cations. A clay suspension was prepared in a test tube. A net was placed in contact with the suspension, the test tube was filled with solutions of different concentrations and the system was left overnight to settle. The tube was then turned upside down and the behaviour was visually observed. Either the clay suspension fell through the net or stayed on top. By using this method surprisingly sharp determinations of the Critical Coagulation (Flocculation) Concentration (CCC/CFC) could be made. The CCC/CFC of Ca2+ was for sodium montmorillonite determined to be between 1 and 2 mM. An artificial fracture was manufactured in order to simulate the real case scenario. The set-up was two Plexiglas slabs separated by 1 mm thick spacers with a bentonite container at one side of the fracture. Water was pumped with a very low flow rate perpendicular to bentonite container and the water exiting the fracture was sampled and analyzed for colloid content. The bentonite used was treated in different ways. In the first experiment a relatively montmorillonite rich clay was used while in the second bentonite where only the readily soluble minerals had been removed was used. Since Plexiglas was used it was possible to visually observe the bentonite dispersing into the fracture. After the compacted bentonite (1,000 kg/m3) had been water saturated the clay had expanded some 12 mm out into the fracture. As the experiment progressed the clay expanded more out into the fracture and seemed to fractionate in two different phases with less material in the outmost phase. A dark rim which was later analyzed to contain

  9. Adsorption of cesium and strontium on natrified bentonites

    International Nuclear Information System (INIS)

    The influence of chemical activation-natrification of bentonites on adsorption of Cs and Sr was studied with regards to utilization of bentonites for depositing high-level radioactive waste and spent nuclear fuel. Bentonite samples from three Slovak deposits in three different grain-size (15, 45 and 250 μm), natural and natrified forms (Na-bentonites); under various experimental conditions, such as contact time, adsorbent and adsorbate concentration have been studied. When comparing the Na-bentonites and their natural analogues, the highest adsorbed Cs and Sr amounts were reached on the natrified samples. After the Sr adsorption a drop in the pH equilibrium value was observed together with the increase of the initial Sr concentration. A disadvantage of the natrified bentonite forms is formation of colloid particles. After 2 h of phase mixing a gentle turbidity was observed as well as formation of a gel-like form. The above findings were confirmed by observing the particle distribution in dry and wet dispersion and centrifugation at two different speeds. Natrification as a technological process of bentonite quality improvement cannot be applied when constructing a long-term repository for high-level radioactive waste and spent nuclear fuel. The main problem of natrification is a technological process which leads to a significant pH increase. Alkaline environment in combination with the K presence and increased temperature in the vicinity of radio-active waste can lead to a rapid illitization of smectite and loss of the original adsorption qualities. Moreover, sodium additions are a significant point of uncertainty since it is not possible to state what amount of Na enters the interlayer space and what amount stays in the inter-partition space. (author)

  10. Long-term stability of bentonite. A literature review

    International Nuclear Information System (INIS)

    for divalent cations and it is not as easily eroded or dissolved in case of diluted groundwater or in case of high pH. Although the information on cementation by thermal effects from natural bentonite occurrences may not be directly applicable to the repository conditions, they show that very high temperatures have affected the bentonites and for long periods of time and there is still unaltered montmorillonite in those deposits. Natural occurrences of bentonite and smectite provide information on the bentonite behaviour in varying conditions. How to adapt this information in the predicting the buffer behaviour is a challenging task. To be able to make a direct comparison between different natural occurrences and the buffer, more detailed information would be needed on density/compaction rate, saturation degrees, pressure conditions, chemical conditions, and duration of the thermal events for the natural bentonites as these are well known for the buffer. (orig.)

  11. Wyoming bentonites. Evidence from the geological record to evaluate the suitability of bentonite as a buffer material during the long-term underground containment of radioactive wastes

    Energy Technology Data Exchange (ETDEWEB)

    Smellie, J. [Conterra AB (Sweden)

    2001-12-01

    In the Swedish programme for the deep, geological disposal of radioactive wastes, bentonite is planned to be used as a barrier material to reduce groundwater flow and minimise radionuclide migration into the geosphere. One of the possible threats to long-term bentonite stability is the gradual incursion of saline water into the repository confines which may reduce the swelling capacity of the bentonite, even to the extent of eliminating the positive effects of mixing bentonite into backfill materials. Important information may be obtained from the study of analogous processes in nature (i.e. natural analogue or natural system studies) where bentonite, during its formation, has been in long-term contact with reducing waters of brackish to saline character. Type bentonites include those mined from the Clay Spur bed at the top of the Cretaceous Mowry Formation in NE Wyoming and demarcated for potential use as a barrier material (e.g. MX-80 sodium bentonite) in the Swedish radioactive waste programme. This bentonite forms part of the Mowry Shale which was deposited in a southern embayment of the late Albian Western Interior Cretaceous sea (Mowry Sea). The question is whether these bentonite deposits show evidence of post-deposition alteration caused by the sea water in which they were deposited, and/or, have they been altered subsequently by contact with waters of increasing salinity? Bentonites are the product of pyroclastic fall deposits thought to be generated by the type of explosive, subaerial volcanic activity characteristic of Plinian eruptive systems. In Wyoming the overall composition of the original ash varied from dacite to rhyolite, or latite to trachyte. The ash clouds were carried to high altitudes and eastwards by the prevailing westerly winds before falling over the shallow Mowry Sea and forming thin but widespread and continuous horizons on sea floor muds and sands. Whilst bentonites were principally wind-transported, there is evidence of some water

  12. Wyoming bentonites. Evidence from the geological record to evaluate the suitability of bentonite as a buffer material during the long-term underground containment of radioactive wastes

    International Nuclear Information System (INIS)

    In the Swedish programme for the deep, geological disposal of radioactive wastes, bentonite is planned to be used as a barrier material to reduce groundwater flow and minimise radionuclide migration into the geosphere. One of the possible threats to long-term bentonite stability is the gradual incursion of saline water into the repository confines which may reduce the swelling capacity of the bentonite, even to the extent of eliminating the positive effects of mixing bentonite into backfill materials. Important information may be obtained from the study of analogous processes in nature (i.e. natural analogue or natural system studies) where bentonite, during its formation, has been in long-term contact with reducing waters of brackish to saline character. Type bentonites include those mined from the Clay Spur bed at the top of the Cretaceous Mowry Formation in NE Wyoming and demarcated for potential use as a barrier material (e.g. MX-80 sodium bentonite) in the Swedish radioactive waste programme. This bentonite forms part of the Mowry Shale which was deposited in a southern embayment of the late Albian Western Interior Cretaceous sea (Mowry Sea). The question is whether these bentonite deposits show evidence of post-deposition alteration caused by the sea water in which they were deposited, and/or, have they been altered subsequently by contact with waters of increasing salinity? Bentonites are the product of pyroclastic fall deposits thought to be generated by the type of explosive, subaerial volcanic activity characteristic of Plinian eruptive systems. In Wyoming the overall composition of the original ash varied from dacite to rhyolite, or latite to trachyte. The ash clouds were carried to high altitudes and eastwards by the prevailing westerly winds before falling over the shallow Mowry Sea and forming thin but widespread and continuous horizons on sea floor muds and sands. Whilst bentonites were principally wind-transported, there is evidence of some water

  13. Study of caesium sorption on Na and Ca-Mg bentonites using batch and diffusion experiments

    International Nuclear Information System (INIS)

    In most deep geological repository concepts sorption of radionuclides on bentonite represents a very important process in retarding radionuclide migration into geosphere. Despite a huge amount of studies concerning caesium sorption on bentonites, there are still some problems requiring deeper clarification. One of the most important issues is the difference between distribution coefficients (Kd) obtained using batch and diffusion experiments. The results of a comprehensive study of caesium sorption on Na bentonite (industrial sorbent Volclay KWK 20-80, Suedchemie, Germany) and Ca-Mg bentonite (raw bentonite, Rokle deposit, Czech Republic) using both of these methods suggest that the reasons of this difference can originate from different sources connected with conditions of experiments and the ways of their evaluation. The main uncertainties of caesium sorption on two different bentonites using the batch method were described and the influence on sorption has been demonstrated. Detailed mineralogical and chemical analysis of bentonite samples confirmed the differences in mineral composition and physical-chemical properties of selected bentonite types. These data are necessary for better understanding of their sorption behaviour and for sorption results evaluation. The results suggest that caesium-selective minerals present in bentonites as admixtures can govern the sorption behaviour of caesium on different bentonites at its trace concentrations. At higher concentrations, the ion exchange on non-selective sites dominates the sorption and can be well-described using sorption isotherms and ion-exchange models. It also follows from the performed experiments that the caesium sorption on studied bentonites cannot be described using the simple Kd method that is often used to evaluate distribution coefficients from diffusion experiments. The uncertainties of evaluation of sorption coefficients from diffusion experiments can also be connected with the way of diffusion

  14. Long-time stability following freezing and thawing of concrete and bentonite in deposition of low- and intermediate-level radioactive waste in SFR 1; Laangtidsstabilitet till foeljd av frysning och tining av betong och bentonit vid foervaring av laag- och medelaktivt kaernavfall i SFR 1

    Energy Technology Data Exchange (ETDEWEB)

    Emborg, Mats; Jonasson, Jan-Erik; Knutsson, Sven (Luleaa Univ. of Technology, Dept. of Civil, Mining and Environmental Engineering (SE))

    2007-10-15

    This document describes the effect of freezing on the concrete and bentonite barriers in SFR 1. The document constitutes one of the references describing the degradation of barriers in a long-time perspective and is used in the safety analysis SFR 1 SAR-08

  15. Comments regarding the bentonite barrier - SR 97 Post-closure safety

    International Nuclear Information System (INIS)

    This review only deals with the role of the bentonite for ensuring the integrity of the canister from the start and throughout the lifetime of the repository. It seems as the technical reports in question deliver convincing data and answers to most of the questions that can be raised concerning the bentonite and the interplay between the different processes at hand. However, there is one area where further analysis and discussions seem inevitable. This area is related to the thermo-hydrological behavior of the bentonite, especially during the first phase of the repository. This is discussed in some detail below. The bentonite is compacted to a high density before installation and has a degree of saturation of about 80 % when it is placed in the bedrock and around the canister. The bentonite is then expected to gradually increase its water content by uptake of water from the surrounding bedrock. Thereby, the bentonite will swell and completely fill the gap between the canister and the bentonite and between the bentonite and the bedrock as well as exert radial pressure on the canister itself. It is well known that the hydraulic conductivity and the heat conductivity of the bentonite to a large extent depend on the degree of saturation. In the reports it is obvious that the pore pressure in the surrounding bedrock is expected to be large, close to 500 kPa. This high pressure, together with the suction in the bentonite, is expected to result in a rather quick saturation of the bentonite around the canister. The same processes are expected to rather quickly saturate the backfill, consisting of a mixture of crushed bedrock and bentonite in the tunnels above the deposition holes. These processes have been analyzed by means of finite element analysis. The time required is comparatively short and the resulting temperatures in the bentonite close to the canister will be acceptable. Questions can, however, be raised regarding the boundary conditions assumed for the pressures

  16. Bentonite in the repository - Manufacture of bentonite blocks. A literature study; Bentonit i slutfoervaret - Tillverkning av bentonitblock. En litteraturstudie

    Energy Technology Data Exchange (ETDEWEB)

    Hultgren, Aa. [NFC Konsult, Nykoeping (Sweden)

    1995-09-01

    Activities in nuclear power countries are reviewed, concerning developments in the use of bentonite for backfilling in nuclear waste repositories, in particular regarding manufacture of bentonite-blocks. Only one report was found which in detail describes the manufacture of highly compacted blocks of bentonite. Use of bentonite for sealing boreholes etc in the oil- and gas industry was also covered in the literature study. 19 refs, 3 tabs.

  17. Study of cesium and strontium adsorption on slovak bentonite

    International Nuclear Information System (INIS)

    Bentonite is a natural clay and one of the most promising candidates for use as a buffer material in the geological disposal systems for high-level radioactive waste and spent nuclear fuel. It is intended to isolate metal canisters with highly radioactive waste products from the surrounding rocks because of its ability to retard the movement of radionuclides by adsorption. Slovak Republic avails of many significant deposits of bentonite. Adsorption of Cs and Sr on five Slovak bentonite of deposits (Jelsovy potok, Kopernica, Lieskovec, Lastovce and Dolna Ves) and montmorillonite K10 (Sigma-Aldrich) has been studied with the using batch of radiometric techniques. Natural, irradiated and natrified samples, in three different kinds of grain size: 15, 45 and 250 μm have been used in the experiments. The adsorptions of Cs and Sr on bentonite under various experimental conditions, such as contact time, adsorbent and adsorbate concentrations, pH after adsorption and effect of pH change, chemical modification, competitive ions and organic agents on the adsorption have been studied. The Kd have been determined for adsorbent-Cs/Sr solution system as a function of contact time and adsorbate and adsorbent concentration. The data have been interpreted in terms of Langmuir isotherm. The adsorption of Cs and Sr has increased with increasing metal concentrations. Adsorption of Cs and Sr has been suppressed by presence of organic agents; and of bivalent cations more than univalent cations. By adsorption on natrified samples colloidal particles and pH value increase have been formed. Adsorption experiments carried out show that the most suitable materials intended for use as barriers surrounding a canister of spent nuclear fuel are bentonite of the Jelsovy potok and Kopernica deposits. (author)

  18. Equilibria in saturated bentonite

    International Nuclear Information System (INIS)

    It has been proposed that smectite clays, the predominant minerals in bentonite, are metastable solid solutions whose compositional heterogeneity prevents strict adherence to fixed ion activities and activity ratios characterizing invariant equilibria among stoichiometric phases. This is analysis of exceptionally well-constrained experimental data using a solid solution model defined by the phase rule and estimated ideal site-mixing are approached among smectite solid solutions and coexist metastably with respect to aSiO2(aq). Irreducible uncertainties are generated in the model by analytical and conceptual deficiencies in understanding compositional variability in smectite. However, their estimated effects on smectite's stability are relatively small, and are comparable to the effects of experimental uncertainty in standard Gibbs energies on the stabilities of stoichiometric minerals. An alternate analysis of the data further confirms that smectite does not behave like a stoichiometric phase. Ion-exchange models for this clay mineral may therefore be thermodynamically ill defined because stoichiometric behavior is assumed implicitly under limiting conditions of fixed sites. Ion exchange is a pragmatic simplification enabling empirical analysis of some experimental data. However, its empirical, rather than thermodynamic, basis should not be overextended to conditions that are beyond an experimentally calibrated range

  19. Research on bed layer made from bentonite for system of radioactive waste storage

    International Nuclear Information System (INIS)

    Nowadays, bentonite is widely used in many different fields such as environment, building, nanocomposite material and so on. Vietnam has huge reserve of bentonite. Montmorillonite of bentonite deposit in BinhThuan and Lam Dong ore ranges from 25 to 45 %. This project presents the results of research on the bed layer made from bentonite for system of radioactive waste storage. Our project has also researched the absorption capability of UO22+, Th4+ and heavy metals such as Pb2+ and Cd2+ on BinhThuan and Lam Dong bentonite in different conditions such as absorption time, pH of solution, concentration, amount of absorbent, etc. The swelling characteristic, the endosmosis of BinhThuan and Lam Dong bentonite have been identified. Our experiments showed that the bed layer made from BinhThuan and Lam Dong bentonite with size: (100 x 100 x 10) mm, additives Na2SiO3 is widely used for system of radioactive waste storage. (author)

  20. Multiple scenarios of bentonite alteration

    International Nuclear Information System (INIS)

    Performance assessment for TRU waste repositories has shown that soluble and poorly sorbing nuclides such as I-129 and C-14 dominate the dose. These nuclides are expected to migrate with groundwater flow, hence hydraulic conditions and their evolution with time in the repository are key issues for repository safety. Cementitious material will be used for waste packaging, backfilling and structural material in a TRU waste repository. Bentonite is also expected to be used for some TRU wastes to provide the function of a hydraulic barrier in the disposal system. There is concern that the coexistence of cementitious material and bentonite cause the alteration of smectite due to interaction with hyperalkaline leachates and consequent deleterious perturbation of the function of bentonite as a hydraulic barrier. Many research studies have been performed to identify possible mechanisms of cement-bentonite interaction. However, uncertainties still exist in our understanding of the precise chemical scheme of bentonite alteration in highly alkaline conditions, especially the space and time variation of secondary mineral occurrences. In order to reflect this uncertainty, multiple scenarios of bentonite alteration were developed based on the possible mineralogical changes derived from knowledge of both experiments and observation of natural systems. It was focused that the mineral reaction involving hyperalkaline fluids would thermodynamically depend on the variable chemical condition in bentonite buffer and that kinetics would be important as well as thermodynamic stability in controlling their occurrence, i.e., the kinetic controls may operate to remain metastable minerals over the long term. The mineralogical consequences of the interaction between clays and alkaline fluids are summarized as follows. Clay → C-S-H gel and other solids which can rapidly precipitate. Clay and gel → illite. Clay and gel → metastable zeolite. Clay and gel → metastable zeolite → stable

  1. Larry Jacobs: Jacobs Farm/Del Cabo

    OpenAIRE

    Reti, Irene H.

    2010-01-01

    Larry Jacobs is the co-founder of Jacobs Farm/Del Cabo with his wife, Sandra Belin. He was born in 1950 in the San Fernando Valley near Los Angeles, California. As a young man, he owned and managed a tree nursery. When aphids infested some of his trees, a pesticide inspector sold him Metasystox to apply with a backpack sprayer. Jacobs temporarily became very ill from pesticide exposure. Vowing never to apply pesticides again, he searched for alternatives. Jacobs was lucky to find a mentor in ...

  2. Bentonite THM behaviour mock-up studies

    International Nuclear Information System (INIS)

    Nuclear waste disposal rely on multi-barrier system. Engineered Barrier Systems make use of swelling clay buffer set in place unsaturated in deposition hole. After waste emplacement, buffer hydrates and swells, being submitted to the heat from nuclear waste decay. In order to characterize the THM behaviour of swelling clays under temperatures exceeding 100 C, Andra has gathered research laboratories, CEA/LECBA, Eurogeomat and EDF/CPM to conduct experimental a d modelling studies. The analysis of the state of art led to the definition of mock-up tests to evaluate effects of high temperatures and high thermal gradients on the heat and mass transfer, and the stress-strain behaviour of initially unsaturated MX80 bentonite during a thermal loading at constant volume for both closed and opened system. This paper presents the first mock-up tests and their experimental result. (authors)

  3. Gas transport through saturated bentonite and interfaces

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. The aim of this investigation was the determination of the gas transport properties of saturated compacted bentonite and its interfaces. The bentonite used was the Spanish FEBEX bentonite, which is mainly composed of montmorillonite (more than 90%). For a dry density of 1.6 g/cm3 the saturated permeability of the bentonite is about 5.10-14 m/s, with deionised water used as percolating fluid. The saturated swelling pressure for the same dry density has a value of about 6 MPa. To perform the gas breakthrough tests a series of stainless steel cells were designed and manufactured. The cells consisted of a body, in which the cylindrical sample was inserted, pistons with o-rings at both ends of the samples and threaded caps. The samples, of 3.8 and 5.0 cm in diameter and 2.5 or 5.0 in height, were obtained by uniaxial compaction of the bentonite with its hygroscopic water content directly inside the cell body. Saturation with deionised water was accomplished by applying injection pressures of between 2 and 10 bar. The water content of the bentonite after saturation was higher than 27% for all the dry densities. Once the samples saturated, the filters on top and bottom of the samples were replaced by dry ones, the cells were again closed, and they were connected to a setup specially designed to measure breakthrough pressure. It consisted of two stainless steel deposits connected to the ends of the cell. One of the deposits was pressurised with nitrogen at 2 bar, whereas vacuum was applied to the other one. The pressures were measured by means of pressure transmitters. If no changes in pressure were recorded during 24 h, the injection pressure in the upstream deposit was increased by 2 bar and kept constant for 24 h. The process was repeated until gas started to flow through the sample. The time required for the completion of a particular experiment was determined by the conditions of the sample being studied. Although

  4. Pore water chemistry of Rokle Bentonite (Czech Republic)

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. With inflowing the groundwater to Deep Geological Repository (DGR), the interaction of this water with engineering barrier materials will alter both, barrier materials and also the groundwater. One of the most important alterations represents the formation of bentonite pore water that will affect a number of important processes, e.g. corrosion of waste package materials, solubility of radionuclides, diffusion and sorption of radionuclides. The composition of bentonite pore water is influenced primarily by the composition of solid phase (bentonite), liquid phase (inflowing groundwater), the gaseous phase (partial pressure of CO2), bentonite compaction and the rate of groundwater species diffusion through bentonite. Also following processes have to be taken into account: dissolution of admixtures present in the bentonite (particularly well soluble salts, e.g. KCl, NaCl, gypsum), ion exchange process and protonation and deprotonation of surface hydroxyl groups on clay minerals. Long-term stability of mineral phases and possible mineral transformation should not be neglected as well. In the Czech Republic, DGR concept takes local bentonite into account as material for both buffer and backfill. The candidate bentonite comes from the Rokle deposit (NW Bohemia) and represents complex mixture of (Ca,Mg)-Fe-rich montmorillonite, micas, kaolinite and other mineral admixtures (mainly Ca, Mg, Fe carbonates, feldspars and iron oxides). The mineralogical and chemical characteristics were published previously. This bentonite is different in composition and properties from worldwide studied Na-bentonite (e.g. MX-80, Volclay) or Na-Ca bentonite (e.g. Febex). This fact leads to the need of investigation of Rokle bentonite in greater detail to verify its suitability as a buffer and backfill in DGR. Presented task is focused on the study of pore water evolution. Our approach for this study consists in modeling the pore water using

  5. Organophilic bentonites based on Argentinean and Brazilian bentonites: part 2: potential evaluation to obtain nanocomposites

    Directory of Open Access Journals (Sweden)

    L. B. Paiva

    2012-12-01

    Full Text Available This work describes the preparation of composites of polypropylene and organophilic bentonites based on Brazilian and Argentinean bentonites. During the processing of the samples in a twin screw microextruder, torque and pressures of the extruder were accompanied and the viscosity values were calculated. No significant changes in the torque, pressure and viscosity were found for composites prepared with different bentonites. The samples were characterized by XRD and TEM to evaluate the structure and dispersion of the organophilic bentonites. Composites with exfoliated, partially exfoliated and intercalated structures were obtained and correlations between the intrinsic properties of the sodium clays and organophilic bentonites and their influence on the composites were studied. The cation exchange capacity of the sodium bentonites and the swelling capacity of the organophilic bentonites were the most important properties to obtain exfoliated structures in composites. All bentonites showed the potential to obtain polymer nanocomposites, but the ones from Argentina displayed the best results.

  6. Bentonite in the repository - Manufacture of bentonite blocks. A literature study

    International Nuclear Information System (INIS)

    Activities in nuclear power countries are reviewed, concerning developments in the use of bentonite for backfilling in nuclear waste repositories, in particular regarding manufacture of bentonite-blocks. Only one report was found which in detail describes the manufacture of highly compacted blocks of bentonite. Use of bentonite for sealing boreholes etc in the oil- and gas industry was also covered in the literature study. 19 refs, 3 tabs

  7. Preparation of bentonites for laboratory investigations

    International Nuclear Information System (INIS)

    A project study on behalf of Nagra for high radioactive waste disposal in deep geological formations as well as literature studies have shown that bentonite could be a suitable filling and sealing material. The Institute for Foundation and Soil Mechanics of the Swiss Institute of Technology has been given a contract by Nagra to investigate different bentonites. The investigations concentrate on the Na-bentonite MX-80 from Wyoming, which is foreseen by the Swedes, and on the geographically more favorable Ca-bentonite Montigel from Bavaria. Montigel powder and granulate, which show certain manufacturing advantages, were investigated. The quality of the bentonites was examined especially to ascertain whether the bentonites were homogeneous with respect to composition and properties. Montmorillonite, carbonate, oxidizing substances and exchangeable ions were quality content criteria for bentonite. The investigations showed that these bentonites are typical Na- and Ca-bentonites. A representative sample of 500 kg weight (250 kg for Montigel K) was largely homogeneous. The samples were analysed by x-rays and thermoanalysis. Additionally grain size, carbonate content, methylene blue value, yield point, exchange capacity and exchangeable ions were determined. 5 refs., 2 figs., 2 tabs

  8. Anti-fouling effect of bentonite suspension in ultrafiltration of oil/water emulsion.

    Science.gov (United States)

    Panpanit, S; Visvanathan, C; Muttamara, S

    2002-03-01

    The effect on membrane fouling resistance during ultrafilration of oil/water emulsion with the presence of bentonite suspension is experimentally evaluated. The fouling resistance was analyzed as a function of different membrane types and bentonite concentration. The total membrane fouling was categorized into reversible and irreversible, by adopting an appropriate chemical cleaning technique. The results revealed a 40% flux augmentation with the increase of bentonite concentration up to an optimum value of 300 mg l(-1) for cellulose acetate membrane. Further increase of bentonite concentration led to particle deposition on the membrane surface and reduced the flux. The polysulfone membrane did not show a similar flux improvement. This could be due to its high hydrophobicity. The absorption of oil/water emulsion on bentonite increased TOC removal rate from 65% to 80%, and this effect was the major cause of reduction in gel layer formation on the membrane surface. The extent of irreversible fouling of the hydrophilic cellulose acetate membrane was much smaller than that of the polysulfone membrane. These experiments demonstrated that, presence of bentonite could induce transformation of irreversible fouling caused by oil emulsion to reversible fouling, which could be periodically chemically cleaned. PMID:11999987

  9. Pertechnetate diffusion in GMZ bentonite

    International Nuclear Information System (INIS)

    99Tc is an important radionuclides related to repository safety assessment. The mobility pertechnetate (TcO4-) can be reduced to immobility technetium(IV) hydrous oxides (TcO2 · nH2O) by Fe(II)-bearing minerals. In China, Gaomiaozi (GMZ) bentonite is regarded as the favorable candidate backfilling material for the HLW repository, which is contained some FeO. The diffusion behavior of 99Tc was investigated in GMZ bentonite by through- and out-diffusion methods. The effective diffusion coefficient (De), the accessible porosity (εacc), apparent diffusion coefficient (Da) and distribution coefficient (Kd) were decreased with the increasing of dry density. The De values were (2.8 ± 0.2) x 10-11 m2/s and (3.5 ± 0.2) x 10-12 m2/s at dry density of 1,600 and 1,800 kg/m3, respectively. It was indicated that the dominating species was TcO4- during the diffusion processing. While, out-diffusion results showed that part of TcO4- may be reduced by Fe(II). The relationship of De and εacc could be described by Archie's law with exponent n = 2.4 for 99Tc diffusion in GMZ bentonite. Furthermore, the relationship between Da and dry density (ρ) was exponential. (author)

  10. Bentonite erosion by dilute waters in initially saturated bentonite

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. One scenario of interest for the long-term safety assessment of a spent nuclear fuel repository involves the loss of bentonite buffer material through contact with dilute groundwater at a transmissive fracture interface (SKB 2011, Posiva 2012a). The scenario is based on the stable colloids at low ionic strength: - the cohesive forces of bentonite decrease in low-salinity conditions, and colloids start to dominate and are able to leave the gel-like bentonite on the groundwater bentonite boundary; - after colloid formation, groundwater may carry away the only just released clay colloids; - low-salinity events are most probable during post-glacial conditions, when also pressure gradients are high, causing elevated flow velocity, which may enhance colloidal transport. Therefore, it is very important from the point of view of repository safety assessment to be able to estimate how much bentonite may be lost during a post-glacial event, when the groundwater salinity and velocity, as well as the duration of the event are fixed. It is possible that more than one event will hit the same canister and buffer, and that several canisters and buffers may be jeopardized. The results in the issue so far may be divided into modelling attempts and experimental work. The modelling has been based on two main guidelines: external (Birgersson et al., 2009) and internal friction models (Neretnieks et al., 2009). However, these models have not been validated for erosion, probably due to lack of suitable laboratory data. The latter approach is more ambitious due to lack of fitting parameters, though the internal friction model itself may be varied. The internal friction model has proven to be time-consuming to solve numerically. This work indicates that experiments carried out by Schatz et al. (2012) differ significantly from the predictions obtained from Neretnieks' model. We present our numerical modelling results based on a set of

  11. The bentonite industry in North America

    International Nuclear Information System (INIS)

    The Canadian Nuclear Fuel Waste Management Program is studying a concept for the disposal of nuclear fuel waste at a depth of 500 to 1000 m below the surface in stable crystalline rock of the Canadian Shield. The waste containers would be surrounded by a clay-based buffer material, composed of equal proportions of bentonite clay and silica sand. In the reference disposal concept, some 1.9 x 105 Mg of used fuel would be emplaced. This would require 2.5 x 106 Mg of bentonite. A review of the bentonite industry in North America was carried out to establish the availability of sufficient high-quality material. There are proven reserves of sodium bentonite clay in excess of 1.5 x 108 Mg, and vast supplies are known to exist but not yet proven. The Canadian conceptual disposal vault would require 6 x 104 Mg of sodium bentonite each year for 40 years. The bentonite industry of North America has an installed annual production capacity of 2 x 107 Mg. A disposal vault would therefore require approximately 2% of the industry capacity. A number of commercial products have been screened for potential suitability for use as a component of the buffer. Ten currently marketed bentonite products have been identified as meeting the initial quality standards for the buffer, and two non-commercial bentonites have been identified as having the potential for use in a disposal vault. (Author) (14 figs., 7 tabs., 18 refs.)

  12. THE IMPACT OF LABORATORY AIR TEMPERATURE AND RELATIVE HUMIDITY ON BENTONITE WATER ABSORPTION CAPACITY

    Directory of Open Access Journals (Sweden)

    Helena Strgar

    2011-12-01

    Full Text Available Bentonite, which is a mineral component of geosynthetic clay liners, has important physical and chemical properties that ensure very small hydraulic permeability. The main component of bentonite is a clay mineral called sodium montmorillonite whose very low permeability is due to its ability to swell. The deposits of bentonite are spread all over the world, however, only a very small number of those deposits satisfies all the quality and durability demands that must be met if the bentonite is to be used in the sealing barriers. Depending on the location of installation and their purpose, geosynthetic clay liners must meet certain requirements. Their compatibility with the prescribed criterion is confirmed through various laboratory procedures. Amongst them are tests examining the index indicators (free swell index, fluid loss index, and water absorption capacity. This paper presents results regarding the impact of laboratory air temperature and relative humidity of the testing area on the water absorption capacity. This is one of the criteria that bentonite must satisfy during the quality and durability control of the mineral component of geosynthetic clay liner (the paper is published in Croatian.

  13. Transient nuclide release through the bentonite barrier -SKB 91

    International Nuclear Information System (INIS)

    A study of near-field radionuclide migration is presented. The study has been performed in the context of the SKB91 study which is a comprehensive performance assessment of disposal of spent fuel. The objective of the present study has been to enable the assessment of which nuclides can be screened out because they decay to insignificant levels already in the near-field of the repository. A numerical model has been used which describes the transient transport of radionuclides through a small hole in a HLW canister imbedded in bentonite clay into a fracture in the rock outside the bentonite. Calculations for more than twenty nuclides, nuclides with both high and low solubility have been made. The effect of sorption in the bentonite backfill is included. The size of the penetration hole was assumed to be constant up to time when the calculations were terminated, 500000 year after the deposition. The mass transport rate is controlled by diffusion. The model is three dimensional. The report describes the geometry of the modelled system, the assumptions concerning the transport resistances at the boundary conditions, the handling of the source term and obtained release curves. (au)

  14. Design and emplacement of bentonite barriers

    International Nuclear Information System (INIS)

    Bentonite is a well known sealing and buffer material for waste disposals in hard rock conditions. Bentonite was also tested as a sealing material for rock salt formations. Under salt conditions the hydraulic conductivity is higher and the swelling pressure is lower then under freshwater conditions using the same bentonite dry density. Because rock salt conditions are more ambitious for bentonite, the new research results of material design and emplacement technology are very useful for applications under freshwater conditions. Commercial available bentonites were tested by measurements of hydraulic conductivity and swelling pressure at various dry densities. The result is the required emplacement dry density for each bentonite. Following an industrial production process for high compacted bentonite materials with low initial water content was developed. Bentonite blocks for drift sealings and compacts / granules for bulk mixtures for shaft sealings have been successful tested in large scale in situ tests in salt mines. Since 1998 about 500 t of bentonite blocks have been produced by the company Preiss-Daimler Industries GmbH - Feuerfestwerke Wetro. The blocks have a standard size of (250 x 125 x 62,5) mm. A proper fit of the blocks to the rock contour can be formed by sawing. The emplacement as dry brickwork is simple and reliable for the rough conditions in underground mines. The recent shaft sealing systems consist of a binary mixture of air dry compacted bentonite compacts and granules (moisture content 7 - 10 %). This material design and the production technology were developed in cooperation with the K and S Group. Both components of the bulk mixture (compacts and granules) are now produced at the plant 'Bergmannssegen-Hugo' (K and S Group). This material defines the actual best state of the art for bentonite sealing materials for long term stable shaft sealing systems, especially under difficult conditions like in salt mines. Since 2004 about 3000 t of

  15. Properties of Bentonite Enhanced Loess and Laterite

    Institute of Scientific and Technical Information of China (English)

    刘阳生; 白庆中; 聂永丰

    2004-01-01

    Loess and laterite distributed widely in the northern and southern China cannot be directly used as the natural barrier to isolate the solid waste because of their high hydraulic conductivity. In this paper, they are enhanced by bentonite to improve their hydraulic performance. The impact of bentonite content and water content on compressive strength of the compacted soil was investigated. The effects of bentonite content, water content, dry density and hydraulic gradient on the hydraulic conductivity were studied in detail. For the laterite and the laterite with 8% of bentonite, the experimental results of hydraulic conductivity can be applied in the engineering design. However, for the loess and the bentonite enhanced loess, those of hydraulic conductivity can not be directly applied in the engineering design because their hydraulic performance does not comply with the Darcy's law. These experimental results have to be carefully modified before application.

  16. Diffusion, sorption, and retardation processes of anions in bentonite and organo-bentonites for multibarrier systems

    Science.gov (United States)

    Schampera, Birgit; Dultz, Stefan

    2013-04-01

    The low permeability, high cation exchange capacity (CEC) and plasticity of bentonites favor their use in multibarrier systems of waste deposits [1]. Bentonites have a high CEC but their ability to sorb anions is very low. There is, however, need for retardation of anions and organic pollutants in many applications. Bentonites, modified with certain organic cations, have the capacity to sorb anions and non-polar organic compounds in addition to cations. Investigations on organically modified clays address a wide variety of applications including immobilization of pollutants in contaminated soils, waste water treatment and in situ placement for the protection of ground water [2]. Many experiments on anion and cation sorption of organo-clays were conducted in the batch mode which does not reflect solid-liquid ratios and material densities in barrier systems. Diffusion experiments on compacted clays allow the evaluation of transport processes and sorption of pollutants at conditions relevant for repositories. For organo-clays only few diffusion studies are published e.g. [3] measured the diffusion of tritium and [4] the diffusion of H2O in bentonite and organo-bentonites. The organic cation hexadecylpyridinium (HDPy) was added to Wyoming bentonite (MX-80) in amounts corresponding to 2-400 % of the CEC. The uptake of organic cations was determined by the C-content, XRD and IR-spectroscopy. Wettability was analyzed by the contact angle. Physical, chemical and mineralogical properties of clays were characterized. Diffusion experiments were carried out in situ in a cell attached to the ATR-unit of a FTIR-spectrometer. For H2O-diffusion the compacted organo-clays are saturated first with D2O, afterwards H2O is supplied to the surface at the top of the clay platelet. Anion-diffusion was conducted with NO3--solution instead of H2O only having characteristic IR band positions at 1350 cm-1. Three different concentrations (0.25M, 0.5M and 1M) were used. Additional batch

  17. Magmatism and cenozoic tectonism in the Cabo Frio region, RJ, Brazil

    International Nuclear Information System (INIS)

    The western portion of the Campos Basin is limited by a hinge line that bounds the deposition of pre-Aptian sediments in the offshore region. The Cabo Frio arch corresponds to a platform with smaller relative subsidence, where Tertiary sediments are deposited directly on shallow basement rocks. Towards the continental slope of the Cabo Frio region, tectonic activity is also observed in the post-Aptian sequence, particularly in the region between the Santos and Campos basins, where a very large graben trends parallel to the pre-Aptian limit of the basin, and is controlled by faults that-affect Upper Miocene rocks. Eastwards of this region, an array of antithetic faults trends in a NE direction. These faults, apparently detaching an the Aptian salt, show unique geometric patterns. The rupturing of Pangea in the Lower Cretaceous is marked by widespread outpouring of mafic magmas in Campos and Santos basins. Radiometric age determinations for this volcanism show a mean of about 139 M.a. After the rift phase, another volcanic episode is observed in the Cabo Frio region, with K/Ar radiometric dating of about 50 M.a. Volcanic mounds are observed within the Eocene sedimentary sequence. An Eocene volcanic episode is characterized by the presence of volcaniclassic rocks, including autoclastic, hydroclastic, epiclastic and pyroclastic sediments. This tectonic episode is also identified within other stratigraphic intervals in the sedimentary column. (author)

  18. Bentonite mat demonstration. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Serrato, M.G.

    1994-12-30

    The Bentonite Mat Demonstration was developed to provide the Environmental Restoration Department with field performance characteristics and engineering data for an alternative closure cover system configuration. The demonstration was initiated in response to regulatory concerns regarding the use of an alternative cover system for future design configurations. These design considerations are in lieu of the US Environmental Protection Agency (EPA) Recommended Design for Closure Cover Systems and specifically a single compacted kaolin clay layer with a hydraulic conductivity of 1 {times} 10{sup {minus}7} cm/sec. This alternative configuration is a composite geosynthetic material hydraulic barrier consisting from bottom to top: 2 ft compacted sandy clay layer (typical local Savannah River Site soil type) that is covered by a bentonite mat--geosynthetic clay liner (GCL) and is overlaid by a 40 mil High Density Polyethylene (HDPE) geomembrane--flexible membrane liner. This effort was undertaken to obtain and document the necessary field performance/engineering data for future designs and meet regulatory technical requirements for an alternative cover system configuration. The composite geosynthetic materials hydraulic barrier is the recommended alternative cover system configuration for containment of hazardous and low level radiological waste layers that have a high potential of subsidence to be used at the Savannah River Site (SRS). This alternative configuration mitigates subsidence effects in providing a flexible, lightweight cover system to maintain the integrity of the closure. The composite geosynthetic materials hydraulic barrier is recommended for the Sanitary Landfill and Low Level Radiological Waste Disposal Facility (LLRWDF) Closures.

  19. Assessment Criteria of Bentonite Binding Properties

    Directory of Open Access Journals (Sweden)

    S. Żymankowska-Kumon

    2012-09-01

    Full Text Available The criteria, with which one should be guided at the assessment of the binding properties of bentonites used for moulding sands, areproposed in the paper. Apart from the standard parameter which is the active bentonite content, the unrestrained growth indicator should be taken into account since it seems to be more adequate in the estimation of the sand compression strength. The investigations performed for three kinds of bentonites, applied in the Polish foundry plants, subjected to a high temperature influences indicate, that the pathway of changes of the unrestrained growth indicator is very similar to the pathway of changes of the sand compression strength. Instead, the character of changes of the montmorillonite content in the sand in dependence of the temperature is quite different. The sand exhibits the significant active bentonite content, and the sand compression strength decreases rapidly. The montmorillonite content in bentonite samples was determined by the modern copper complex method of triethylenetetraamine (Cu(II-TET. Tests were performed for bentonites and for sands with those bentonites subjected to high temperatures influences in a range: 100-700ºC.

  20. Effectiveness of fracture sealing with bentonite grouting

    International Nuclear Information System (INIS)

    Bentonite is known to have an extremely low permeability and a self-healing ability. It has therefore been selected as a major sealing component in several repository concepts. Bentonite grouts have the following advantages, (1) small particle size, can be injected into small fractures or voids, (2) suitable water absorption properties, can produce gels at low concentrations, and (3) stable physical and chemical properties, may have considerable longevity. Bentonite fracture grouting tests are performed on a model made of circular acrylic plates with outer diameter of 30 cm and central injection hole of 2.5 cm diameter. Suspension with bentonite concentration of 15% to 31% have been injected into fractures with apertures of 9 to 90 microns under injection pressures less than 0.6 MPa. Grouting reduces the hydraulic conductivities of the fractures from the 10-1 to the 10-5 cm/s level. When the suspension is thin enough and the fracture is very small, channeling develops in the grouted fractures. Preliminary results indicate that the permeability of a grouted fracture does not increase with time in more than 125 days. The flow properties of bentonite suspensions, viscosity, shear stress, yield stress and gelation, are investigated. Water flow through ungrouted fractures and movement of water in bentonite grout are studies. The physical stability or bleeding capacity of bentonite suspensions is determined. 122 refs., 56 figs., 10 tabs

  1. Marine magnetic survey between Cabo da Roca and Cabo Espichel (near Lisbon, Portugal): first results

    Science.gov (United States)

    Neres, Marta; Terrinha, Pedro; Calado, António; Miranda, Miguel; Madureira, Pedro

    2016-04-01

    We present a magnetic survey conducted in the offshore region between Cabo da Roca and Sesimbra (mouth of Tagus River, Portugal). Strong magnetic anomalies are recognized in this area since a first marine survey in 1958 (Allan, 1965) and by further aeromagnetic survey (c.f. Silva et al, 2000). The anomalies have been linked to Cretaceous magmatic events related to the Upper Cretaceous Sintra magmatic complex and Lisbon volcanic complex, but their geometry and extension has yet not been resolved. The aim of the present survey was to unravel the location, geometry and type of the magnetic sources, thus contributing for the characterization of the main magmatic and tectonic features in the region. The survey was conducted in two legs (October 2014 and June 2015), consisting of 27 lines and 6 tielines, extending up to 40 km from the coast. The line spacing was 1 mile for the main lines and 5-6 miles for the tielines. The bathymetry of the surveyed area varies from very shallow (about 10 m) to near 3000 m. Total field was measured with a G-882 Cesium marine magnetometer of Geometrics (self-oscillating split-beam Cesium vapor), with frequency of acquisition of 10 Hz. Layback was real-time corrected using the acquisition software. Noise was removed by despike in Magpick software (Geometrics), and further processing was done using Oasis montaj (Geosoft) software. Data were subtracted of IGRF values and levelled by tielines to retrieve the final map of anomalies. Several punctual and linear anomalies with varying amplitude and wavenumber were identified, which cannot be explained by bathymetric variation; therefore they must then be due to the presence of higher susceptibility, likely volcanic rocks, and to structural inheritance associated with rifting and Alpine orogeny. The highest anomaly corresponds to the Cabo Raso positive magnetic anomaly, with maximum and minimum of 2800 nT and -1350 nT, respectively. This anomaly, already surveyed in 1958, has been compared to a

  2. Quality assurance of the bentonite material

    International Nuclear Information System (INIS)

    This report describes a quality assurance chain for the bentonite material acquisition for a nuclear waste disposal repository. Chemical, mineralogical and geotechnical methods, which may be applied in quality control of bentonite are shortly reviewed. As a case study, many of the presented control studies were performed for six different bentonite samples. Chemical analysis is a very reliable research method to control material homogeneity, because the accuracy and repeatability of the study method is extremely good. Accurate mineralogical study of bentonite is a complicated task. X-ray diffractometry is the best method to identify smectite minerals, but quantitative analysis of smectite content remains uncertain. To obtain a better quantitative analysis, development of techniques based on automatic image analysis of SEM images is proposed. General characteristics of bentonite can be obtained by rapid indicator tests, which can be done on the place of reception. These tests are methylene blue test giving information on the cation exchange capacity, swelling index and determination of water absorption. Different methods were used in the determination of cation exchange capacity (CEC) of bentonite. The results indicated differences both between methodologies and between replicate determinations for the same material and method. Additional work should be done to improve the reliability and reproducibility of the methodology. Bentonite contains water in different modes. Thus, different determination methods are used in bentonite studies and they give somewhat dissimilar results. Clay research use frequently the so-called consistency tests (liquid limit, plastic limit and plasticity index). This study method does, however, not seem to be very practical in quality control of bentonite. Therefore, only the determination of liquid limit with fall-cone method is recommended for quality control. (orig.)

  3. Activation of wine bentonite with gamma rays

    International Nuclear Information System (INIS)

    The action of gamma rays on wine bentonite as well as influence of its adsorption and technologic qualities on the composition and stability of wines against protein darkening and precipitation has been studied. The experiments were carried out with wine bentonite produced in the firm Bentonite and irradiated with doses of 0.4, 0.6, 0.8 and 1.0 MR. White and red wines have been treated with irradiated bentonite under laboratory conditions at 1.0 g/dm3. All samples are treated at the same conditions. The flocculation rate of the sediment was determined visually. Samples have been taken 24 h later from the cleared wine layers. The following parameters have been determined: clarification, filtration rate, phenolic compounds, calcium, colour intensity, total extracted substances, etc. The volume of the sediment has been determined also. The control samples have been taken from the same unirradiated wines. The results showed better and faster clarification in on the third, the 20th and the 24th hours with using of gamma-irradiated at doses 0.8 and 1.0 MR. The sediment was the most compact and its volume - the smallest compared to the samples treated with bentonite irradiated with doses of 0.6 and 0.4 MR. This ensures a faster clarification and better filtration of treated wines. The bentonite activated with doses of 0.8 and 1.0 MR adsorbs the phenolic compounds and the complex protein-phenolic molecules better. In the same time it adsorbs less extracted substances compared to untreated bentonite and so preserves all organoleptic properties of wine. The irradiated bentonite adsorbs less the monomers of anthocyan compounds which ensures brighter natural colour of wine. The gamma-rays activation consolidates calcium in the crystal lattice of bentonite particles and in this way eliminates the formation of crystal precipitates

  4. A Educação Musical em Cabo Verde

    Directory of Open Access Journals (Sweden)

    Alcides J. D. Lopes

    2012-09-01

    Full Text Available O presente artigo pretende abordar o tema A Educação Musical em Cabo Verde partindo de uma análise dos dados publicados e de entrevistas realizadas com personalidades relevantes ao tema.

  5. Cabo Rojo National Wildlife Refuge: Comprehensive Conservation Plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This Comprehensive Conservation Plan (CCP) was written to guide management on Cabo Rojo NWR for the next 15 years. This plan outlines the Refuge vision and purpose...

  6. Mechanical stability of bentonite buffer system for high level nuclear waste

    International Nuclear Information System (INIS)

    According to present plans, high level nuclear waste in Finland is going to be disposed of in bedrock at a depth of several hundred metres. The spent fuel containers will be placed in boreholes drilled in the floors of deposition tunnels with engineered clay buffer, which is made of bentonite blocks. The tunnels will be filled with a mixture of bentonite and crushed rock. For stability calculations a thermomechanical model for compressed bentonite is needed. In the study a thermomechanically consistent model for reversible processes for swelling clays is presented. Preliminary calculations were performed and they show that uncertainty in material parameter values causes significantly different results. Therefore, measurements that are consistent with the model are needed

  7. Modelling Iron-Bentonite Interactions

    Science.gov (United States)

    Watson, C.; Savage, D.; Benbow, S.; Wilson, J.

    2009-04-01

    The presence of both iron canisters and bentonitic clay in some engineered barrier system (EBS) designs for the geological disposal of high-level radioactive wastes creates the potential for chemical interactions which may impact upon the long-term performance of the clay as a barrier to radionuclide migration. Flooding of potential radionuclide sorption sites on the clay by ferrous ions and conversion of clay to non-swelling sheet silicates (e.g. berthierine) are two possible outcomes deleterious to long-term performance. Laboratory experimental studies of the corrosion of iron in clay show that corrosion product layers are generally thin ( 250 °C) are dominated by chlorite, whereas lower temperatures produce berthierine, odinite, cronstedtite, or Fe-rich smectite. Unfortunately, the inevitable short-term nature of laboratory experimental studies introduces issues of metastability and kinetics. The sequential formation in time of minerals in natural systems often produces the formation of phases not predicted by equilibrium thermodynamics. Evidence from analogous natural systems suggests that the sequence of alteration of clay by Fe-rich fluids will proceed via an Ostwald step sequence. The computer code, QPAC, has been modified to incorporate processes of nucleation, growth, precursor cannibalisation, and Ostwald ripening to address the issues of the slow growth of bentonite alteration products. This, together with inclusion of processes of iron corrosion and diffusion, has enabled investigation of a representative model of the alteration of bentonite in a typical EBS environment. Simulations with fixed mineral surface areas show that berthierine dominates the solid product assemblage, with siderite replacing it at simulation times greater than 10 000 years. Simulations with time-dependent mineral surface areas show a sequence of solid alteration products, described by: magnetite -> cronstedtite -> berthierine -> chlorite. Using plausible estimates of mineral

  8. Mechanisms and models for bentonite erosion

    Energy Technology Data Exchange (ETDEWEB)

    Neretnieks, Ivars; Longcheng Liu; Moreno, Luis (Dept. of Chemical Engineering and Technology, School of Chemical Science and Engineering, Royal Inst. of Technology, KTH, Stockholm (Sweden))

    2009-12-15

    There are concerns that the bentonite buffer surrounding the canisters with spent nuclear fuel may erode when non-saline groundwaters seep past the buffer. This is known to happen if the water content of ions is below the critical coagulation concentration CCC. Above the CCC the smectite forms a coherent gel, which does not release particles. One main effort in this study has been directed to assess under which conditions the pore water composition of the gel at the gel/water interface could be lower than the CCC. Another main effort has been directed to understanding the behaviour of expansive gel when the pore water is below the CCC. We have developed a Dynamic model for sodium gel expansion in fractures where the gel soaks up non-saline water as it expands. The model is based on a force balance between and on smectite particles, which move in the water. The Dynamic model of gel expansion showing the evolution in time and space of a gel was successfully tested against expansion experiments in test tubes. The expansion was measured with high resolution and in great detail over many months by Magnetic Resonance Imaging. The model also predicted the gel expansion through filters with very narrow pores well. A gel viscosity model of dilute gels was derived, which accounts for ion concentration influence as well as the volume fraction of smectite in the gel. The model accounts for the presence of the DDL, which seemingly makes the particles larger so that they interact at lower particle densities. Simulations were performed for a case where the gel expands outward into the fracture that intersects the deposition hole. Fresh groundwater approaches and passes the gel/water interface. Smectite colloids move out into the water due to the repulsive forces between the particle and by Brownian motion (effect included in the Dynamic model). The dilute gel/sol is mobilised and flows downstream in a thin region where the viscosity is low enough to permit flow. Sodium diffuses

  9. Mechanisms and models for bentonite erosion

    International Nuclear Information System (INIS)

    There are concerns that the bentonite buffer surrounding the canisters with spent nuclear fuel may erode when non-saline groundwaters seep past the buffer. This is known to happen if the water content of ions is below the critical coagulation concentration CCC. Above the CCC the smectite forms a coherent gel, which does not release particles. One main effort in this study has been directed to assess under which conditions the pore water composition of the gel at the gel/water interface could be lower than the CCC. Another main effort has been directed to understanding the behaviour of expansive gel when the pore water is below the CCC. We have developed a Dynamic model for sodium gel expansion in fractures where the gel soaks up non-saline water as it expands. The model is based on a force balance between and on smectite particles, which move in the water. The Dynamic model of gel expansion showing the evolution in time and space of a gel was successfully tested against expansion experiments in test tubes. The expansion was measured with high resolution and in great detail over many months by Magnetic Resonance Imaging. The model also predicted the gel expansion through filters with very narrow pores well. A gel viscosity model of dilute gels was derived, which accounts for ion concentration influence as well as the volume fraction of smectite in the gel. The model accounts for the presence of the DDL, which seemingly makes the particles larger so that they interact at lower particle densities. Simulations were performed for a case where the gel expands outward into the fracture that intersects the deposition hole. Fresh groundwater approaches and passes the gel/water interface. Smectite colloids move out into the water due to the repulsive forces between the particle and by Brownian motion (effect included in the Dynamic model). The dilute gel/sol is mobilised and flows downstream in a thin region where the viscosity is low enough to permit flow. Sodium diffuses

  10. Gas migration through bentonite clay

    International Nuclear Information System (INIS)

    Hydrogen gas produced by irradiation of pore water in the highly compacted bentonite that surrounds the copper canisters according to the KBS 2 and 3 concepts, may escape from the clay/copper interface if the gas pressure is higher than the groundwater pressure. A reasonable physical model predicts that gas may penetrate wider capillary passages that actually exist in the very dense clay, although these passages are still of microscopic size. In the large majority of the clay voids, the capillary action is sufficient, however, to resist gas penetration, and this suggests that a possible mechanism of gas migration is that of a finger-like pattern of tortuous gas passages extending from the canisters if radiolysis takes place at all. Two series of experiments have been run at gas pressures up to about 10 MPa. Nitrogen as well as hydrogen were used in these tests which seem to confirm, in principle, the validity of the physical model. (authors)

  11. Results of bentonite grouting experiment

    International Nuclear Information System (INIS)

    The Bentonite grouting, which will not solidify, is mainly expected to reduce the hydraulic conductivity of underground water in the expected damage zone by filling the fractures or cracks, so the evaluation of the degree of hydraulic conductivity, stability and the improvement area becomes important. The study and basic experiments for sealing of the adits have been promoted, up to now, from the aspects of the characteristics and long term stability of candidate materials, and design and construction (Pusch et al., 1987; Tanai and Masuda, 1991). However, in Japan, the application examples of clay type materials for grouting are extremely few and is limited to the construction experience of the national oil underground storage at Kuji (Miyanaga and Ebara, 1993), with the exception of some test cases (Boergesson et al., 1991) from overseas. This report summarize basic characteristics of the clay type material relevant to the hydraulic conductivity, from the result of the clay grouting experiment conducted at the rock site. (author)

  12. Purification of bentonitics of the city Cubati-PB to obtaining organoclays for use in oil-based drilling fluids

    International Nuclear Information System (INIS)

    In Boa Vista, PB, are located deposits of bentonite clays commonly used in the preparation of drilling fluids. The disorderly exploitation of the deposits of Boa Vista is causing the depletion of these clays, which will cause a very serious problem for the national oil industry. This work aims to characterize new deposits of bentonite clays Cubati, PB, for the development of organoclay from its refining using a hydrocyclone for use in oil based drilling fluids. The characterization of samples of the clays was performed through the techniques: AG, XRD, EDX, TGA and DTA. The characterization is typical of bentonite for the purification process was determined the best configuration of the hydrocyclone, and the environment organic diesel fuel, the best affinity was obtained with clays organophilizated with surfactant Praepagen WB. (author)

  13. Effect of bentonites on fluorometric selenium determination

    International Nuclear Information System (INIS)

    Bentonites in feeds cause error in the analysis for Se by the AOAC (3.097-3.101) fluorometric method for Se in plants. The error apparently results from the binding of the piazselenol by insoluble residue from the bentonite. This effect is avoided by diluting digests to volume after reduction with HCl, centrifuging or allowing to stand, and analyzing a portion of the clear supernatant liquid. Insoluble residues present after digestion of plant materials do not appear to cause a similar error

  14. Thermal cycling: impact on bentonite permeability

    OpenAIRE

    Zihms, S.G.; Harrington, J. F.

    2015-01-01

    Due to its favourable properties, in particular, low permeability and swelling capacity, bentonite has been favoured as an engineered-barrier and backfill material for the geological storage of radioactive waste. To ensure its safe long-term performance it is important to understand any changes in these properties when the material is subject to heat-emitting waste. As such, this study investigates the hydraulic response of bentonite under multi-step thermal loading subject to a constant-volu...

  15. Erosion of bentonite by flow and colloid diffusion

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. Bentonite intrusion into a fracture intersecting the canister deposition hole is modelled. The model describes the expansion of the bentonite within the fracture. It accounts for the repulsive electrostatic double-layer forces, the attractive van der Waals forces and friction forces between the particles and the water. The model also takes into account the diffusion of the colloid particles in the smectite sol. The buffer contains sodium in the pore water in much higher concentrations than the approaching seeping groundwater in the fracture has. Diffusion of sodium outward in the expanding gel is accounted for as this strongly influences the double layer force and the viscosity of the gel/sol. The gel/ sol is considered to be a fluid with a varying viscosity that is strongly dependent on the bentonite volume fraction in the gel and the sodium concentration in the water. Two different geometries were modelled; a rectangular and a cylindrical showing the flow in a fracture intersecting the deposition hole with the canister. The rectangular geometry was used to gain experience with the processes and mechanisms and how they interact since the cylindrical geometry was somewhat less stable numerically and more time consuming. In the rectangular geometry a fracture 1 metre long in the flow direction was modelled. In both geometries the fracture depth (extent from the deposition hole) was selected sufficiently large to ensure that the water velocity, near this border was nearly the same as the approaching water velocity and that the smectite concentration there was vanishingly small. It was found that the velocity of the fluid drops considerably where the bentonite volume fraction is larger than 1-2%. This is due to the strong increase in viscosity with increasing bentonite volume fraction. The loss of smectite as it is carried away by the slowly flowing fluid was found to be proportional to the square root of the seeping

  16. Removal of oil from water by bentonite

    International Nuclear Information System (INIS)

    Many materials, included activated carbon, peat, coal, fiberglass, polypropylene, organoclay and bentonite have been used for removing oils and grease from water. However, bentonite has been used only rarely for this purpose. In this study Na-bentonite was used to remove oil from oil-in-water emulsions of various kinds such as standard mineral oil, cutting oils, refinery effluent and produced water from production wells at Estevan, Saskatchewan. Removal efficiencies obtained were 85 to 96 per cent for cutting oils, 84 to 86 per cent for produced water and 54 to 87 per cent for refinery effluent. Bentonite proved to be more effective in the removal of oil from oil-in-water emulsions than from actual waste waters; up to 96 percent from oil-in-water emulsions to only 87 per cent from actual waste water. The percentage of oil removed was found to be a function of the amount of bentonite added and the adsorption time up to the equilibrium time. Result also showed that the Langmuir, Freundlich and BET isotherms are well suited to describe the adsorption of oil by bentonite from the various oily waters employed in this study. 15 refs

  17. Seafloor mapping of the southeast Iberian margin (from Cabo de Palos to Cabo de Gata)

    Science.gov (United States)

    Lastras, Galderic; Leon, César; Elvira, Elena; Pascual, Laura; Muñoz, Araceli; de Cárdenas, Enrique; Acosta, Juan; Canals, Miquel

    2014-05-01

    We present the multibeam bathymetry and derived maps of the southeast Iberian margin from Cabo de Palos to Cabo de Gata, 37º35'N to 35º45'N and 2º10'W to 0º20'E, from the coastline down to the Algero-Balearic abyssal plain at depths exceeding 2600 m. The edition of of the maps is carried out within the Complementary Action VALORPLAT ("Scientific valorisation of multibeam bathymetry data from the Spanish continental shelf and slope"), funded by the Spanish Ministry of Economy and Competitivity. The multibeam bathymetry data of the slope and abyssal plain were obtained during different surveys in 2004, 2006 and 2007 on board R/V Vizconde de Eza with a Simrad EM300 multibeam echo-sounder as part of the CAPESME Project, a collaboration between the Spanish Institute of Oceanography (IEO) and General Secretariat of Fisheries (SGP), primarily aiming at creating maps of the fishing grounds of the Mediterranean continental margins of Spain. Multibeam bathymetry data from the continental shelf were obtained within the ESPACE project, also in a cooperative frame between IEO and SGP. The map series is constituted by a general map at 1:400,000 scale and 14 detailed maps at 1:75,000 scale, which include inset maps on slope gradients and seafloor nature (rock or sediment type), the later obtained with rock dredges and Shipeck sediment dredges. Both the detailed maps and the general map are available in paper print, and the whole collection is also distributed in an edited USB. The geological features displayed in the different maps include the continental shelf, with abundant geomorphic features indicative of past sea-level changes, the continental slope carved by the Palos, Tiñoso, Cartagena Este, Cartagena Oeste, Águilas, Almanzora, Alias, Garrucha and Gata submarine canyons, the Mazarrón, Palomares and Al-Mansour escarpments, the Abubácer, Maimonides and Yusuf ridges, the Águilas and Al-Mansour seamounts, and the Algero-Balearic abyssal plain where prominent

  18. Determination of trace elements by instrumental neutron activation analysis in Anatolian bentonitic clays

    Science.gov (United States)

    Güngör, N.; Tulun, T.; Alemdar, A.

    1998-08-01

    Instrumental Neutron Activation Analysis (INAA) was carried out for the determination of trace elements in non-swelling type bentonitic clays. Samples were irradiated in Triga Mark II type of reactor at the Nuclear Institute of Technical University of Istanbul. Irradiation was performed in two steps for "short and long lived" isotopes. The γ spectra of short lived isotopes were interpreted with respect to Al, Ca, Mg, Na, K, Ti, Mn, V qualitatively and that of long lived isotopes with respect to Sc, Cr, Br, Sb, Cs, La, Ce, Sm, Yb, Hf quantitatively. The relative richness of the trace elements (Al, Ti, Ca, Mg, Na, K) observed in the Sampo 90 program was obtained using Atomic Absorption technique by normalizing its value to that of sodium. The silicon content of samples was determined by gravimetry. The results indicated that Sample I contained relatively higher amount of REE, Sb, Ca and Na than Sample II. The amount of Sc, Cr and Br were about similar in both samples. Concentrations of La, Ce, Sm and Yb are higher than REE abundances found in all natural waters. These results suggest that Ca-bentonite samples are representative of primary deposition environment. In addition, the Sc content of both the samples indicates that Ca-bentonite deposits originated from continental crust. The relatively high amount of REE might bring about porosity problems in the use of Ca-bentonite in cement and concrete production.

  19. Exchangeability of bentonite buffer and backfill materials

    International Nuclear Information System (INIS)

    Clay-based buffer and tunnel backfill materials are important barriers in the KBS-3 repository concept for final disposal of spent nuclear fuel in Finland. One issue that is relevant to material properties is the degree to which different bentonite compositions can be regarded as interchangeable. In Posiva's current repository design, the reference bentonite composition is MX-80, a sodium montmorillonite dominated clay. Posiva would like to be able to use bentonite with Ca-montmorillonite as the dominant clay mineral. However, at this stage, it is not clear what supporting data need to be acquired/defined to be able to place the state of knowledge of Ca-bentonite at the same level as that of Na-bentonite. In this report, the concept of bentonite exchangeability has been evaluated through consideration of how bentonite behaviour may be affected in six key performance-relevant properties, namely (1) mineralogical composition and availability of materials, (2) hydraulic conductivity, (3) mechanical and rheological properties, (4) long-term alteration, (5) colloidal properties, and (6) swelling pressure. The report evaluates implications for both buffer and backfill. Summary conclusions are drawn from these sections to suggest how bentonite exchangeability may be addressed in regulatory assessments of engineered barrier design for a future geological repository for spent fuel in Finland. Some important conclusions are: (a) There are some fundamental differences between Ca- and Na-bentonites such as colloidal behaviour, pore structure and long-term alteration that could affect the exchangeability of these materials as buffer or backfill materials and which should be further evaluated; (b) Additional experimental data are desirable for some issues such as long-term alteration, hydraulic properties and swelling behaviour, (c) The minor mineral content of bentonites is very variable, both between different bentonites and within the same bentonite type, it is not clear

  20. Pore water chemistry of the febex bentonite

    International Nuclear Information System (INIS)

    The knowledge of pore water chemistry in the clay barrier is essential for performance assessment purposes in a nuclear waste repository, since the pore water composition controls the processes involved in the release and transport of the radionuclides. The methodology followed to define the representative composition of the FEBEX bentonite pore water is presented in this paper. A series of bentonite-water interaction tests have been performed with the aim of providing a database on the main chemical parameters of the bentonite. These tests were carried out both with high solid to liquid (s:l) ratios (squeezing tests) and low s:l ratios (aqueous extracts tests). The exchangeable cations have also been analyzed to determine the selectivity coefficient of the exchange reactions. To complete the data set, a physical and mineralogical characterization of the bentonite was made. The most significant bentonite-water interaction processes controlling the chemistry of the system was identified. The ion concentrations basically depend on the s:l ratio of the system, and the pore water composition is controlled by the dissolution of chlorides, dissolution/precipitation of carbonates and sulphates and the cation exchange reactions in the smectite. The bentonite/water system was modelled with the PHREEQC2 program to obtain the best possible estimation of the pore water composition for initial conditions of water content (=14%), after checking the conceptual model with the experimental results. The model predictions fitted satisfactorily with the experimental data at low s:l ratios. At high s:l ratios, the modelled results agree adequately, except for the sulphate content, which could be affected by the effective porosity, anion exclusion or stagnant zones not taken into account in the model. According to the model, the FEBEX bentonite pore water at 14% moisture is a sodium-chloride type, with an ionic strength of 0.25 M and pH of 7.78. Copyright (2001) Material Research

  1. Microbial activity in bentonite buffers. Literature study

    Energy Technology Data Exchange (ETDEWEB)

    Ratto, M.; Itavaara, M.

    2012-07-01

    The proposed disposal concept for high-level radioactive wastes involves storing the wastes underground in copper-iron containers embedded in buffer material of compacted bentonite. Hydrogen sulphide production by sulphate-reducing prokaryotes is a potential mechanism that could cause corrosion of waste containers in repository conditions. The prevailing conditions in compacted bentonite buffer will be harsh. The swelling pressure is 7-8 MPa, the amount of free water is low and the average pore and pore throat diameters are small. This literature study aims to assess the potential of microbial activity in bentonite buffers. Literature on the environmental limits of microbial life in extreme conditions and the occurrence of sulphatereducing prokaryotes in extreme environments is reviewed briefly and the results of published studies characterizing microbes and microbial processes in repository conditions or in relevant subsurface environments are presented. The presence of bacteria, including SRBs, has been confirmed in deep groundwater and bentonite-based materials. Sulphate reducers have been detected in various high-pressure environments, and sulphate-reduction based on hydrogen as an energy source is considered a major microbial process in deep subsurface environments. In bentonite, microbial activity is strongly suppressed, mainly due to the low amount of free water and small pores, which limit the transport of microbes and nutrients. Spore-forming bacteria have been shown to survive in compacted bentonite as dormant spores, and they are able to resume a metabolically active state after decompaction. Thus, microbial sulphide production may increase in repository conditions if the dry density of the bentonite buffer is locally reduced. (orig.)

  2. Microbial activity in bentonite buffers. Literature study

    International Nuclear Information System (INIS)

    The proposed disposal concept for high-level radioactive wastes involves storing the wastes underground in copper-iron containers embedded in buffer material of compacted bentonite. Hydrogen sulphide production by sulphate-reducing prokaryotes is a potential mechanism that could cause corrosion of waste containers in repository conditions. The prevailing conditions in compacted bentonite buffer will be harsh. The swelling pressure is 7-8 MPa, the amount of free water is low and the average pore and pore throat diameters are small. This literature study aims to assess the potential of microbial activity in bentonite buffers. Literature on the environmental limits of microbial life in extreme conditions and the occurrence of sulphatereducing prokaryotes in extreme environments is reviewed briefly and the results of published studies characterizing microbes and microbial processes in repository conditions or in relevant subsurface environments are presented. The presence of bacteria, including SRBs, has been confirmed in deep groundwater and bentonite-based materials. Sulphate reducers have been detected in various high-pressure environments, and sulphate-reduction based on hydrogen as an energy source is considered a major microbial process in deep subsurface environments. In bentonite, microbial activity is strongly suppressed, mainly due to the low amount of free water and small pores, which limit the transport of microbes and nutrients. Spore-forming bacteria have been shown to survive in compacted bentonite as dormant spores, and they are able to resume a metabolically active state after decompaction. Thus, microbial sulphide production may increase in repository conditions if the dry density of the bentonite buffer is locally reduced. (orig.)

  3. Ion diffusion in compacted bentonite

    International Nuclear Information System (INIS)

    In the study, a two-dimensional molecular-level diffusion model, based on a modified form of the Gouy-Chapman (GC) theory of the electrical double layers, for hydrated ionic species in compacted bentonite was developed. The modifications to the GC theory, which forms the very kernel of the diffusion model, stem from various non-conventional features: ionic hydration, dielectric saturation, finite ion-sizes and specific adsorption. The principal objectives of the study were met. With the aid of the consistent diffusion model, it is a relatively simple matter to explain the experimentally observed macroscopic exclusion for anions as well as the postulated, but greatly controversial, surface diffusion for cations. From purely theoretical grounds, it was possible to show that the apparent diffusivities of cations, anions and neutral molecules (i) do not exhibit order-or-magnitude differences, and (ii) are practically independent of the solution ionic strength used and, consequently, of the distribution coefficient, Kd, unless they experience specific binding onto the substrate surface. It was also of interest to investigate the equilibrium anionic concentration distribution in the pore geometry of the GMM model as a function of the solution ionic strength, and to briefly speculate its consequences to diffusion. An explicit account of the filter-plate effect was taken by developing a computerised macroscopic diffusion model, which is based upon the very robust and efficient Laplace Transform Finite-Difference technique. Finally, the inherent limitations as well as the potential fields of applications of the models were addressed. (orig.)

  4. Enhancement of the bentonite sorption properties

    Energy Technology Data Exchange (ETDEWEB)

    Mockovciakova, Annamaria, E-mail: mocka@saske.sk [Institute of Geotechnics, Slovak Academy of Sciences Watsonova 45, 04354 Kosice (Slovakia); Orolinova, Zuzana [Institute of Geotechnics, Slovak Academy of Sciences Watsonova 45, 04354 Kosice (Slovakia); Skvarla, Jiri [Institute of Montaneous Sciences and Environmental Protection, Technical University in Kosice, Park Komenskeho 19, 04200 Kosice (Slovakia)

    2010-08-15

    The almost monomineral fraction of bentonite rock-montmorillonite was modified by magnetic particles to enhance its sorption properties. The method of clay modification consists in the precipitation of magnetic nanoparticles, often used in preparing of ferrofluids, on the surface of clay. The influence of the synthesis temperature (20 and 85 deg. C) and the weight ratio of bentonite/iron oxides (1:1 and 5:1) on the composite materials properties were investigated. The obtained materials were characterized by the X-ray diffraction method and Moessbauer spectroscopy. Changes in the surface and pore properties of the magnetic composites were studied by the low nitrogen adsorption method and the electrokinetic measurements. The natural bentonite and magnetic composites were used in sorption experiments. The sorption of toxic metals (zinc, cadmium and nickel) from the model solutions was well described by the linearized Langmuir and Freundlich sorption model. The results show that the magnetic bentonite is better sorbent than the unmodified bentonite if the initial concentration of studied metals is very low.

  5. Migration behavior of iodine in compacted bentonite

    International Nuclear Information System (INIS)

    When the wastes that include I-129 dispose, compacted bentonite would be used as buffer material as well as for HLW disposal. Therefore in this study diffusion experiments were carried out to investigate the migration behavior of iodine in compacted bentonite. Bentonite used in this study consists of more than 95 % of sodium montmorillonite. Bentonite powder was compacted into a cylinder with a diameter of 10 mm and a height of 10 mm with a varied dry density. After saturated with water including 0.01 M of NaCl for one month, approximately 10 micro liters of tracer solution I- or IO3- were spiked on a surface of compacted bentonite respectively. The constant boundary concentrations and the diffusion coefficients of I- and IO3- were determined by the penetration method. Iodine profiles showed typical shape of error function complement. The constant boundary concentration of I- is several times larger than that of IO3-. This could be cause by geometrical limitation and/or anion exclusion of montmorillonite because IO3- is larger than I- and montmorillonite has negative surface charge. Apparent diffusion coefficients of I- and IO3- were obtained in the range of 27.0 to 192.9 μm2/s and 9.8 to 117.4 μm2/s, respectively. (author)

  6. Bentonite-amended soil special study

    International Nuclear Information System (INIS)

    This special study was conducted to assess the viability of soil with a high percentage of bentonite added as an infiltration barrier in the cover of Uranium Mill Tailings Remedial Action (UMTRA) Project disposal cells. To achieve maximum concentration limits (MCLs) at several UMTRA Project sites, covers with a very low permeability are needed. If alternate concentration limits (ACLs) are the appropriate site groundwater compliance strategy, the US Department of Energy (DOE) is required to demonstrate, among other things, that the infiltration to the disposal cell is as low as reasonably achievable, and hence that the cover has a very low permeability. When the study discussed here was begun, the lowest permeability element available was CLAYMAXR, a manufactured liner material constructed of natural material (bentonite clay) between two geosynthetics.The strength of soil-bentonite mixes was measured to see if they could be placed on sideslopes and not pose stability problems. Also evaluated were the hydraulic conductivities of soil-bentonite mixes. If the strengths and permeabilities of soils with a high percentage of bentonite are favorable, the soils may be used as infiltration barriers in current cover designs without changing pile geometries. The scope of work for this study called for a literature review and a two-phased laboratory testing program. This report presents the results of the literature review and the first phase of the testing program

  7. Formulaçao de um elemento finito de cabo incorporando o efeito do atrito (Elemento de cabos escorregando)

    OpenAIRE

    Pauletti, Ruy M.; Paulo M. Pimenta

    1995-01-01

    O trabalho apresenta a formulacáo geometricamente exata e a implementaçao computacional de um elemento finito de cabo que permite o escorregamento em presenca de atrito. O novo elemento fornece procedimentos naturais para simular o processo de montagem e a resposta aos carregamentos de estruturas de cabos em geral, além de ter campos promissores de aplicaçáo no modelamento de estruturas de concreto protendido e no estudo de oscilaçoes auto-excitáveis. Resultados de exemplos elementares sáo di...

  8. Sealing performance of bentonite and bentonite/crushed rock borehole plugs

    Energy Technology Data Exchange (ETDEWEB)

    Ouyang, S.; Daemen, J.J.K. [Arizona Univ., Tucson, AZ (United States). Dept. of Mining and Geological Engineering

    1992-07-01

    This study includes a systematic investigation of the sealing performance of bentonite and bentonite/crushed rock plugs. American Colloid C/S granular bentonite and crushed Apache Leap tuff have been mixed to prepare samples for laboratory flow testing. Bentonite weight percent and crushed tuff gradation are the major variables studied. The sealing performance assessments include high injection pressure flow tests, polyaxial flow tests, high temperature flow tests, and piping tests. The results indicate that a composition to yield a permeability lower than 5 {times} 10{sup {minus}8} cm/s would have at least 25% bentonite by weight mixed with well-graded crushed rock. Hydraulic properties of the mixture plugs may be highly anisotropic if significant particle segregation occurs during sample installation and compaction. Temperature has no significant effect on the sealing performance within the test range from room temperature to 600{degree}C. Piping damage to the sealing performance is small if the maximum hydraulic gradient does not exceed 120 and 280 for samples with a bentonite content of 25 and 35%, respectively. The hydraulic gradients above which flow of bentonite may take place are deemed critical. Analytical work includes the introduction of bentonite occupancy percentage and water content at saturation as two major parameters for plug design. A permeability model is developed for the prediction of permeability in clays, especially in view of the difficulties in obtaining this property experimentally. A piping model is derived based on plastic flow theory. This piping model permits the estimation of critical hydraulic gradients at which flow of bentonite takes place. The model can also be used to define the maximum allowable pore diameter of a protective filter layer.

  9. Sorption of metals on zeolites and bentonite

    International Nuclear Information System (INIS)

    This contribution presents the recently obtained results on the sorption of heavy metals by natural microporous materials (especially zeolites and bentonite) of different origin. The sorption of caesium and strontium from its aqueous solutions by ten clinoptilolite-mordenite-containing sedimentary materials from Slovakia, Bulgaria, Ukraine and Greece and bentonite was investigated a batch-type procedure and radiotracer techniques. The experimental results provide information on suitability of the individual materials for the treatment of radioactive waste and their application as backfills in potential nuclear waste repositories. Furthermore, the sorption of cadmium, mercury and zinc-ions by zeolites and bentonite was investigated using batch techniques and radioactive tracers. Uptake values and distribution coefficients were calculated in order to study the suitability of these materials for utilization in the environmental technology (i.g. treatment of industrial waste). (author)

  10. Analysis of the effect of vibrations on the bentonite buffer in the canister hole

    Energy Technology Data Exchange (ETDEWEB)

    Jonsson, Martin (AaF- Berg och Maetteknik, Stockholm (Sweden)); Hakami, Hossein; Ekneligoda, Thushan (Itasca Geomekanik AB, Solna (Sweden))

    2009-09-15

    During the construction of a final repository for spent nuclear fuel in crystalline rock, blasting activities in certain deposition tunnels will occur at the same time as the deposition of canisters containing the waste is going on in another adjacent access tunnel. In fact, the deposition consists of several stages after the drilling of the deposition hole. The most vulnerable stage from a vibration point of view is when the bentonite buffer is placed in the deposition hole but the canister has not been placed yet. During this stage, a hollow column of bentonite blocks remains free to vibrate inside the deposition hole. The goal of this study was to investigate the displacement of the bentonite blocks when exposed to the highest vibration level that can be expected during the drill and blast operations. In order to investigate this, a three dimensional model in 3DEC, capable of capturing the dynamic behaviour of the bentonite buffer was set up. To define the vibration levels, which serve as input data for the 3DEC model, an extensive analysis of the recorded vibrations from the TASQ - tunnel was carried out. For this purpose, an upper expected vibration limit was defined. This was done outgoing from the fact that the planned charging for the construction of the geological repository will lie in the interval 2 to 4 kg. Furthermore, at the first stage for this study, it was decided that the vibration should be conservatively evaluated for 30 m distance. Using these data, it was concluded that the maximum vibration level that can be expected will be approximately 60 mm/s. After simplifying the vibration signal, a sinusoidal wave with the amplitude 60 mm/s was applied at the bottom of the column and it was assumed that the vibrations only affect the bentonite buffer in one direction (horizontal direction). From this simulation, it was concluded that hardly any displacements occurred. However, when applying the same sinusoidal wave both in the horizontal and the

  11. Analysis of the effect of vibrations on the bentonite buffer in the canister hole

    International Nuclear Information System (INIS)

    During the construction of a final repository for spent nuclear fuel in crystalline rock, blasting activities in certain deposition tunnels will occur at the same time as the deposition of canisters containing the waste is going on in another adjacent access tunnel. In fact, the deposition consists of several stages after the drilling of the deposition hole. The most vulnerable stage from a vibration point of view is when the bentonite buffer is placed in the deposition hole but the canister has not been placed yet. During this stage, a hollow column of bentonite blocks remains free to vibrate inside the deposition hole. The goal of this study was to investigate the displacement of the bentonite blocks when exposed to the highest vibration level that can be expected during the drill and blast operations. In order to investigate this, a three dimensional model in 3DEC, capable of capturing the dynamic behaviour of the bentonite buffer was set up. To define the vibration levels, which serve as input data for the 3DEC model, an extensive analysis of the recorded vibrations from the TASQ - tunnel was carried out. For this purpose, an upper expected vibration limit was defined. This was done outgoing from the fact that the planned charging for the construction of the geological repository will lie in the interval 2 to 4 kg. Furthermore, at the first stage for this study, it was decided that the vibration should be conservatively evaluated for 30 m distance. Using these data, it was concluded that the maximum vibration level that can be expected will be approximately 60 mm/s. After simplifying the vibration signal, a sinusoidal wave with the amplitude 60 mm/s was applied at the bottom of the column and it was assumed that the vibrations only affect the bentonite buffer in one direction (horizontal direction). From this simulation, it was concluded that hardly any displacements occurred. However, when applying the same sinusoidal wave both in the horizontal and the

  12. MANU. Purchase of Bentonite. Process Description

    International Nuclear Information System (INIS)

    The aim of this study is to describe the entire bentonite purchasing process accurately. This will enable efficient and focused use of information related to the purchasing phase and to each individual bentonite batch. This work continues from the work started in the report by Ahonen et al. (2008), Quality Assurance of the Bentonite Material, Posiva Working Report 2008-33. The current work includes a short enquiry for all relevant and at the time known producers or re-sellers of bentonite. Questions about relevant products suitable for civil engineering use, more specifically nuclear waste disposal site use, were asked together with test methods, typical test results and test standards. The following aspects and opinions have been processed from the results that were obtained during the project. Each seller/producer has a quality management system, QMS (typically ISO 9001), and ability to perform the basic tests, but there is not an established common set of properties to be tested. Some producers are willing to test according to customers' specifications. Posiva could arrange a network of capable laboratories to carry out tests according to its selected standards. This activity should then be accredited with a reasonable testing volume. Before starting the purchase of bentonite at a large scale, Posiva should go through negotiations and audits with each seller in order to make sure that both parties are testing with the same methods and both understand the range where the values of key parameters may lie. A database is needed for gathering statistically relevant information from the bentonite material parameters over the long run. This is needed for determining the limits within which the material parameters should remain in order to be acceptable. Posiva is encouraged to create a process to optimize the test types and the amount of tests should be identified for immediate and long term use. This process ensures the required quality and costs involved. (orig.)

  13. Erosion properties and dispersion-flocculation behavior of bentonite particles

    International Nuclear Information System (INIS)

    Experimental and theoretical studies have been performed to clarify the ability of flowing groundwater in contact with bentonite to generate bentonite colloidal particles and disperse such colloids. This information is required to determine (a) the long-term stability of bentonite as a buffer material for borehole disposal of radioactive wastes in deep geologic media and (b) the potential influence of bentonite colloidal particles on radionuclide transport, specifically for use in scenario analyses in the performance assessment of waste disposal. In this study, the minimum groundwater velocity required to erode particles of Na-bentonite or Ca-bentonite from a bentonite surface in contact with groundwater was derived from shear strengths of aqueous bentonite gel suspensions, as determined by viscometer tests. The shear strengths were used to estimate the corresponding shear force on bentonite particle-particle bonds, using an estimated value for the number of initial bentonite particle-particle bonds in the experimental systems studied. The derived shear force was converted to corresponding groundwater velocity by using Stokes' equation and simplifying assumptions. The results indicate that groundwater velocities in a range of about 10-5 to 10-4 m/s would be required to initiate bentonite erosion. This range is higher than the groundwater flow velocity generally found in deep geologic media in Japan. In addition, known groundwater electrolyte concentrations were compared with theoretical estimates of aqueous electrolyte concentrations required to flocculate colloidal bentonite particles (for example 1 x 10-3 mol/l Na+). The comparison indicates that, even if erosion of bentonite occurred, the colloidal bentonite particles formed would flocculate. As a result, this study has shown that the effect of bentonite colloids on radionuclide transport is likely to be negligible in the performance assessment of radioactive waste disposal in deep geologic media

  14. Ion diffusion in compacted bentonite

    Energy Technology Data Exchange (ETDEWEB)

    Lehikoinen, J. [VTT Chemical Technology, Espoo (Finland)

    1999-03-01

    In the study, a two-dimensional molecular-level diffusion model, based on a modified form of the Gouy-Chapman (GC) theory of the electrical double layers, for hydrated ionic species in compacted bentonite was developed. The modifications to the GC theory, which forms the very kernel of the diffusion model, stem from various non-conventional features: ionic hydration, dielectric saturation, finite ion-sizes and specific adsorption. The principal objectives of the study were met. With the aid of the consistent diffusion model, it is a relatively simple matter to explain the experimentally observed macroscopic exclusion for anions as well as the postulated, but greatly controversial, surface diffusion for cations. From purely theoretical grounds, it was possible to show that the apparent diffusivities of cations, anions and neutral molecules (i) do not exhibit order-or-magnitude differences, and (ii) are practically independent of the solution ionic strength used and, consequently, of the distribution coefficient, K{sub d}, unless they experience specific binding onto the substrate surface. It was also of interest to investigate the equilibrium anionic concentration distribution in the pore geometry of the GMM model as a function of the solution ionic strength, and to briefly speculate its consequences to diffusion. An explicit account of the filter-plate effect was taken by developing a computerised macroscopic diffusion model, which is based upon the very robust and efficient Laplace Transform Finite-Difference technique. Finally, the inherent limitations as well as the potential fields of applications of the models were addressed. (orig.) 45 refs.

  15. Preparation and characterization of bentonite organo clay

    International Nuclear Information System (INIS)

    Bentonite clays organically modified have great potential use for environmental remediation, especially in the separation of organic compounds from the water. The aim of this work was the preparation of organophilic clays from 'Verde-Lodo' bentonite clay with the quaternary ammonium salts cetyl-pyridinium chloride and benzalkonium chloride. The materials obtained were characterized by XRD, thermogravimetric analyses, Helium picnometry, SEM and energy dispersive X-ray techniques. The results show consistently successful synthesis of the organoclay through the increase in the basal spacing, as well as salt elimination picks and presence of carbon and chlorine in the modified clays; they are inexistent elements in the natural clay. (author)

  16. Retention of chromium by modified Al-Bentonite

    OpenAIRE

    Volzone C.; Garrido L. B.

    2002-01-01

    Retention of chromium (III) from a tanning wastewater by modified Al-bentonites was studied. One bentonite from San Juan province, Argentina, was used. Al-bentonite was prepared by contact of bentonite with hydrolyzed OH-Al solutions (0.10 M in Al) for 24 hours. The modified Al-bentonites were obtained by: a) treatment with 0.5 M sodium chloride; b) with 0.5 M sodium chloride adjusted at pH 8; and c) treatment with an hexametaphosphate solution after sodium addition. Then, the samples were dr...

  17. Equipment for deployment of canisters with spent nuclear fuel and bentonite buffer in horizontal holes

    International Nuclear Information System (INIS)

    The study presents the predesign of equipment for the deployment of canisters in long horizontal holes. The canisters are placed in the centre of the hole and are surrounded by a bentonite buffer. In thE study the canisters are assumed to have a diameter of 1.6 m and a length of 5.9 m, including the hemispherical ends. Their total weight is 60 tonnes. The bentonite buffer after homogenization is 400 mm thick, making a total package diameter of 2.4 m. The deployment system consists of four wagons for handling The canisters and the bentonite blocks. To ensure safe emplacement, every part is installed separately in its final position. This also makes it possible to use small clearances between the canisters and the bentonite blocks and between the blocks and the rock wall. With small clearances, backfilling can be avoided. Another basic design idea is that the wagons are equipped with wheels, which are in direct contact with the rock walls. Thus, rails, which have to be removed as the deployment progresses, are unnecessary. To minimize the time taken for deploying one canister, the wagons are designed so that only three trips from the service area to the deposit area are needed. Due to the radiation in the vicinity of the canisters, the wagons have to be teleoperated

  18. Equipment for deployment of canisters with spent nuclear fuel and bentonite buffer in horisontal holes

    International Nuclear Information System (INIS)

    This study presents the predesign of equipment for the deployment of canisters in long horizontal holes. The canisters are placed in the centre of the hole and are surrounded by a bentonite buffer. In this study the canisters are assumed to have a diameter of 1.6 m and a length of 5.9 m, including the hemispherical ends. Their total weight is 60 tonnes. The bentonite buffer after homogenization is 400 mm thick, making a total package diameter of 2.4 m. The deployment system consists of four wagons for handling the canisters and the bentonite blocks. To ensure safe emplacement, every part is installed separately in its final position. This also makes it possible to use small clearances between the canisters and the bentonite blocks and between the blocks and the rock wall. With small clearances, backfilling can be avoided. Another basic design idea is that the wagons are equipped with wheels, which are in direct contact with the rock walls. Thus, rails, which have to be removed as the deployment progresses, are unnecessary. To minimize the time taken for deploying one canister, the wagons are designed so that only three trips from the service area to the deposit area are needed. Due to the radiation in the vicinity of the canisters, the wagons have to be teleoperated. (au)

  19. Manufacture and homogeneity of highly dense bentonite samples

    International Nuclear Information System (INIS)

    A project study on behalf of Nagra for high radioactive waste disposal in deep geological formations as well as literature studies have shown that bentonite could be a suitable filling and sealing material. The Institute for Foundation and Soil Mechanics of the Swiss Institute of Technology is under contract by Nagra to investigate different bentonites. The investigations concentrate on the Na-bentonite MX-80 from Wyoming, which is foreseen by the Swedes, and on the geographically more favorable Ca-bentonite Montigel from Bavaria. Montigel powder and granulate, which show certain manufacturing advantages, were investigated. Numerous experiments, mostly for manufacturing of sample bodies for swelling experiments, were performed and evaluated with the aim to clarify the condensation properties of bentonites in a highly dense field. Especially the relationship between water content, pressure and attained dry density for the three bentonites: MX-80 (granulate), Montigel (powder) and Montigel K (granulate) were investigated. It was shown that the delivery water contents of the three bentonites favorably lie within the 8-10 % necessary to prepare high density samples with dry densities of about 2.0 Mg/m3. The comparison of the three bentonites shows that both bentonites in granular form allow lower pressures at condensation than the bentonite in powder form. Based on x-ray and pressure porosimetry investigations the high density bentonites are largely homogeneous sample bodies considering their density and pore radius distribution. 15 figs., 2 tabs

  20. Bentonite as a waste isolation pilot plant shaft sealing material

    Energy Technology Data Exchange (ETDEWEB)

    Daemen, J.; Ran, Chongwei [Univ. of Nevada, Reno, NV (United States)

    1996-12-01

    Current designs of the shaft sealing system for the Waste Isolation Pilot Plant (WIPP) propose using bentonite as a primary sealing component. The shaft sealing designs anticipate that compacted bentonite sealing components can perform through the 10,000-year regulatory period and beyond. To evaluate the acceptability of bentonite as a sealing material for the WIPP, this report identifies references that deal with the properties and characteristics of bentonite that may affect its behavior in the WIPP environment. This report reviews published studies that discuss using bentonite as sealing material for nuclear waste disposal, environmental restoration, toxic and chemical waste disposal, landfill liners, and applications in the petroleum industry. This report identifies the physical and chemical properties, stability and seal construction technologies of bentonite seals in shafts, especially in a saline brine environment. This report focuses on permeability, swelling pressure, strength, stiffness, longevity, and densification properties of bentonites.

  1. Bentonite as a waste isolation pilot plant shaft sealing material

    International Nuclear Information System (INIS)

    Current designs of the shaft sealing system for the Waste Isolation Pilot Plant (WIPP) propose using bentonite as a primary sealing component. The shaft sealing designs anticipate that compacted bentonite sealing components can perform through the 10,000-year regulatory period and beyond. To evaluate the acceptability of bentonite as a sealing material for the WIPP, this report identifies references that deal with the properties and characteristics of bentonite that may affect its behavior in the WIPP environment. This report reviews published studies that discuss using bentonite as sealing material for nuclear waste disposal, environmental restoration, toxic and chemical waste disposal, landfill liners, and applications in the petroleum industry. This report identifies the physical and chemical properties, stability and seal construction technologies of bentonite seals in shafts, especially in a saline brine environment. This report focuses on permeability, swelling pressure, strength, stiffness, longevity, and densification properties of bentonites

  2. Estudio de "las capas del cabo ladrillero superior" en el cabo homónimo, mioceno inferior de la cuenca austral, tierra del fuego Study of "The Upper Cabo Ladrillero Beds" in the homonym locality, Lower Miocene of the Austral Basin, Tierra del Fuego

    Directory of Open Access Journals (Sweden)

    Estefanía P Tudisca

    2012-03-01

    Austral or Magallanes foreland basin infill crop out. This locality contains Lower Mocene deposits informally named "Cabo Ladrillero beds" and "Cabo San Pablo beds" being the "upper Cabo Ladrillero beds" analyzed in this paper. This locality is situated around ten kilometers to the north of the emerging orogenic front (Punta Gruesa locality where four facies association have been defined from gravitationally-driven supra batial to prograding and shallowing upward deltaic wedges. Deformed and massive beds by liquefaction processes and resedimentation are connected with abundant clastic dykes and synsedimentary faults. The statistic study suggests they are associated tectonic activity related to a transtensive episode rather than tectonic quiescence sometimes suggested in previous works. We conclude that microfossils documented in the area and used as a tool to support a deep marine environment are situated in underlying stratigraphic intervals that form part of the Desdémona Formation and the "lower Cabo Ladrillero beds" cropping out to the south of the study area. Sedimentological evidence are not conclusive respect to the batimetry but absence of classical turbidites, hyperpycnal flows and abundant deformed and resedimented deposits are more compatible with deltaic deposits, with high detritus supply generating unstable slopes rather than deep marine depositional settings, suggesting a more complex depositional evolution than the foraminiferal-based framework dominant in the literature.

  3. Sealing performance assessments of bentonite and bentonite/crushed rock plugs

    International Nuclear Information System (INIS)

    Bentonite and mixtures of bentonite and crushed rock are potential sealing materials for high level nuclear waste repositories. The materials have been used to form cap layers to reduce infiltration for mined waste tailings and can also be used to construct clay liners for municipal as well as industrial waste managements. American Colloid C/S granular dentonite and Apache Leap tuff have been mixed to prepare samples for laboratory flow testing. Bentonite weight percent and crushed tuff gradation are the major variables studied. The sealing performance assessments include high injection pressure flow tests, polyaxial flow tests, high temperature flow tests, and piping tests. The results indicate that an appropriate composition would have at least 25% bentonite by weight mixed with well-graded crushed rock. Hydraulic properties of the mixture plugs may be highly anisotropic if significant particle segregation occurs during sample installation and compaction. Temperature has no negative effects on the sealing performance within the test range from room temperature to 60C. The piping damage to the sealing performance is small if the maximum hydraulic gradient does not exceed 120 and 280 for 25 and 35% bentonite content, respectively. The hydraulic gradients above which flow of bentonite may take place are deemed critical. Analytical work includes the introduction of bentonite occupancy percentage and water content at saturation as two major parameters for the plug design. A permeability model developed is useful for the prediction of permeability in clays. A piping model permits the estimation of critical hydraulic gradient allowed before the flow of bentonite takes place. It can also be used to define the maximum allowable pore diameter of a protective filter layer

  4. Application of thermo-mechanically treated drill cuttings as an alternative to bentonite in spud muds

    OpenAIRE

    Taghiyev, Farid

    2014-01-01

    Drill cuttings recovered after drilling with OBM today are treated and deposited at onshore facilities. The TWMA Company offers a new technology, which recovers drilled subsurface materials together with oil and water rests. Due to the similarity between subsurface rock mineralogy and conventional bentonite used in the drilling fluid industry an extended laboratory study was carried out to evaluate the possibility of spud mud development using thermo-mechanically treated drill cuttings. Pr...

  5. Ion-migration through bentonite/zeolite and bentonite/quartz sand mixture

    International Nuclear Information System (INIS)

    In the geological disposal system of the high level radioactive wastes radionuclides begin leaching from the waste form when the canister is degraded by corrosion. The buffer materials, as one of the engineered barriers can retard the migration of the radionuclides to the biosphere. In this study, the diffusivity of radionuclides has been obtained in the compacted clay materials, such as mixtures of bentonite-zeolite, and bentonite-quartz sand for buffer materials. For the bentonite and zeolite mixture, Kd-value for cesium has been increasing with zeolite contents. The increase in the Kd-value has also been obtained for strontium, though the inclination is found to be smaller than that for cesium. In the case of bentonite and quartz sand mixture, the Kd-value has increased with quartz content (up to 70%), though the increasing rate is smaller than that in the zeolite mixture. The purpose of the quartz sand mixing is to improve the thermal conductivity of the buffer materials. It is to be noted that the sorption capability of bentonite and quartz sand mixture is found to be a little bit larger than that of bentonite. As for cesium, the Kd-values obtained in diffusion experiment agree well with those from batch experiments within a factor of 2, while for strontium good agreement has not been obtained

  6. Chemical evolution of bentonite buffer in a KBS-3 type spent fuel repository from thermal to post glacial phase

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. The very long-term interaction between the bentonite buffer and ground waters present in a KBS-3 spent fuel repository has not been studied systematically, although this evolution is the base scenario in safety-case studies. In long-term safety considerations one must take into account all successive disturbances a bentonite buffer may have experienced (even short-term ones), as the effects of these are often irreversible. The interaction starts soon after the installation of bentonite blocks, when water is intruding into a deposition hole. The initially partially dry compacted bentonite starts to saturate and swell under the temperature gradient resulting from the heat formed by decaying radionuclides inside a copper canister. However, heat formation will decrease with time and bentonite will achieve full saturation after about one thousand years. The groundwater composition is estimated to change during the first 100,000 years from saline to extremely dilute, the latter likely encountered during the post-glacial phase. The bentonite is in contact with groundwater through a water-conducting fracture and possibly through excavation damaged and spalling zones formed around the deposition hole. An interesting question is the extent to which this coupling can slow down chemical changes in bentonite. Another important process affecting the evolution is the chemical alteration of the primary minerals in bentonite (i.e. montmorillonite and the accessory minerals). Swelling and other mechanical phenomena are important during the saturation of the buffer, but implementing these to our reactive transport models is beyond the scope of this paper. The implementing remains, however, the final aim. In this work, 2D reactive transport (TOUGHREACT v. 1.0) and some 3D COMSOL Multiphysics (COMSOL 2008) model calculations have been carried out on the chemical evolution of bentonite buffer from the operational phase of the repository

  7. Preparation and characterization of bentonite clay for formation of nanocomposites

    International Nuclear Information System (INIS)

    This study we used the linear medium density polyethylene (PELMD) as polymer matrix and introduced, as reinforcement to increase the mechanical and thermal properties, the green bentonite deposit of Boa Vista/PB, rich montmorillonite (MMT), previously characterized by XRD, that passed by three stages of purification. The first stage was to clean by washing and filtering for removal of coarse material (sand and organic matter), followed by an acid attack. In the second, we used the quaternary ammonium surfactant, in order to increase the distance between the layers of MMT, and the third was removed from the wastewater, using absolute ethanol, finishing the purification of process. Then, the clay was introduced into the polymer matrix by polymerization in solution by intercalation and characterized by XRD. The results showed a partial exfoliation, satisfying the increasing properties. (author)

  8. Purification of bentonite clays from the district of Cubati, PB, for other uses; Purificacao de argilas bentoniticas do municipio de Cubati, PB para usos diversos

    Energy Technology Data Exchange (ETDEWEB)

    Costa, M.R.; Araujo, J.P.; Silva, I.A.; Cardoso, M.A.; Silva, C.D.; Neves, G.A.; Ferreira, H.C., E-mail: jullymrc@gmail.com [Universidade Federal de Campina Grande (UFCG/CCT/UAEMa), PB (Brazil). Unidade Academica de Engenharia de Materiais

    2012-07-01

    The state of Paraiba is responsible for the increased production of crude bentonite in the country, coming from one of the largest mines of Brazil, located in Boa Vista, PB. Recently, in the regions of Cubati and Pedra Lavrada, PB, found new deposits of bentonite that could expand the state reserves. The paper aims at the characterization and development of clay purified using the techniques of screening and hydrocycloning, from bentonite clay recently discovered in the city of Cubati, PB, for various uses. The sample characterization was performed through techniques: granulometric analysis by laser diffraction, X-ray diffraction and chemical analysis by X-ray fluorescence and thermogravimetric and differential thermogravimetric analysis. The results showed that the samples are typical of bentonite clay, and that the purification process using only the hydrocycloning shows better results. (author)

  9. Brasil e Cabo Verde: duas margens do mesmo mar

    Directory of Open Access Journals (Sweden)

    Oliveira, Vera Lúcia de

    2010-01-01

    Full Text Available Fala-se, neste artigo, das relações entre Cabo Verde e Brasil, relações antigas, que derivam não só do fato dos dois países terem feito parte do antigo império colonial português, mas das muitas afinidades geográficas, culturais, linguísticas e literárias que aproximam estas duas nações irmãs

  10. The Cabo Mondego section as a possible Bajocian boundary stratotype

    OpenAIRE

    Rocha, Rogério B; Henriques, María Helena Paiva; Soares, Antonio; Mouterde, René; Caloo, Brigitte; Ruget, Christiane; Fernández López, Sixto Rafael

    1990-01-01

    The Cabo Mondego section situated on the Atlantic coast, 160 km north of Lisbon, presents characteristics of a good boundary stratotype section (G.S.S.P.). The outcrop is easily accessible and well exposed near the sea where the erosion process is continuous. The section shows a thick succession of clay limestones with a regular sedimentation and belongs to a sedimenrary basin whose palaeogeography is already well established. The variety and abundance of cephalopods p...

  11. Ga migration through MX-80 bentonite

    International Nuclear Information System (INIS)

    Highly compacted bentonite is known to let gas ghrough at a very low rate but earlier invetigations have indicated the possible existence of a critical gas pressure at which the gas forms highly conductive passages through the clay. The present study was primarily aimed at testing the hypothesis of the critical pressure concept by measuring the gas pressure, and by trying to identify microstructural evidence of how gas percolates clay. Eight tests were run with MX-80 bentonite saturated with strongly brackish NAGRA water, the density of the water saturated bentonite ranging from 1.7 to somewhat more than 2.1 t/m3. In all the tests it was observed that gas break-through, manifested by largely increased conductivity, took place at a gas pressure of the same order of magnitude as the swelling pressure. One of the samples was analysed with respect to the microstructure and it revealed the existence of discrete gas-filled voids, some of which released gas when the trimmed clay specimen was placed into the embedding substance used for the microstructural analysis. This confirms that gas percolates through a number of narrow passages that are formed when the gas pressure is sufficiently high. In soft and medium-dense bentonite the 'capillary retention' is probably the major resistance to gas propagation, while in dense bentonite the penetrating gas has to make its way by displacing clay aggregates. In the latter case the critical gas pressure is therefore logically very high and close to the swelling pressure. (author)

  12. Mineralogy and sealing properties of various bentonites and smectite-rich clay materials

    International Nuclear Information System (INIS)

    The present work includes a coherent study of Wyoming bentonite with respect to the most relevant properties for use in a repository, and a parallel study of other potential buffer and tunnel backfilling materials. The reason for this is twofold; to quantify the effect of mineralogical variations on the various important sealing properties of bentonite, and to verify that there are alternative potential sources of bentonite. The latter is motivated by the fact that Sweden alone plans to deposit at least 6,000 copper canisters which include approximately 130,000 metric tones bentonite buffer material and several times more as tunnel backfill material. Different types of sealing clay materials may also be relevant to use, since the demands on the clay will be different at the various locations in a repository. Alternative sources of bentonite would consequently be valuable in order to secure quality, supply, and price. Important aspects on buffer and tunnel backfilling materials may be summarized as: Original sealing properties. Hazardous substances in any respect. Short-term effects of ground-water chemistry. Long-term stability, i.e. effects of temperature and ground-water chemistry. Availability. Costs. The focus in this study is on the first three items. The long-term stability is indirectly considered in that mineralogical composition is determined. The availability is only considered in such a way that most of the analyzed materials represent huge clay formations, which contain much more material than needed for a repository. The cost aspects have not been included, mainly because the present day price is not relevant due to the time frame of the construction of a repository

  13. Mineralogy and sealing properties of various bentonites and smectite-rich clay materials

    Energy Technology Data Exchange (ETDEWEB)

    Karnland, Ola; Olsson, Siv; Nilsson, Ulf (Clay Technology AB (SE))

    2006-12-15

    The present work includes a coherent study of Wyoming bentonite with respect to the most relevant properties for use in a repository, and a parallel study of other potential buffer and tunnel backfilling materials. The reason for this is twofold; to quantify the effect of mineralogical variations on the various important sealing properties of bentonite, and to verify that there are alternative potential sources of bentonite. The latter is motivated by the fact that Sweden alone plans to deposit at least 6,000 copper canisters which include approximately 130,000 metric tones bentonite buffer material and several times more as tunnel backfill material. Different types of sealing clay materials may also be relevant to use, since the demands on the clay will be different at the various locations in a repository. Alternative sources of bentonite would consequently be valuable in order to secure quality, supply, and price. Important aspects on buffer and tunnel backfilling materials may be summarized as: Original sealing properties. Hazardous substances in any respect. Short-term effects of ground-water chemistry. Long-term stability, i.e. effects of temperature and ground-water chemistry. Availability. Costs. The focus in this study is on the first three items. The long-term stability is indirectly considered in that mineralogical composition is determined. The availability is only considered in such a way that most of the analyzed materials represent huge clay formations, which contain much more material than needed for a repository. The cost aspects have not been included, mainly because the present day price is not relevant due to the time frame of the construction of a repository

  14. Fe-bentonite. Experiments and modelling of the interactions of bentonites with iron

    International Nuclear Information System (INIS)

    The main objectives of this study were to enhance the understanding of the interactions of bentonites with steel containers in the near field of a repository in salt formations and to determine missing experimental thermo-hydraulical-chemical and mineralogical data needed for the THC modelling of the interactions of bentonites with iron. At the beginning of this project a literature review helped to clarify the state of the art regarding the above mentioned objectives prior to the start of the experimental work. In the following experimental programme the hydraulic changes in the pore space of compacted MX80 bentonites containing metallic iron powder and in contact with three solutions of different ionic strength containing different concentrations of Fe2+ have been investigated. The alterations of MX80 and several other bentonites have been assessed in contact with the low ionic strength Opalinus Clay Pore Water (OCPW) and the saturated salt solutions NaCl solution and IP21 solution. Under repository relevant boundary conditions we determined on compacted MX80 samples with the raw density of 1.6 g/cm3 simultaneously interdependent properties like swelling pressures, hydraulic parameters (permeabilities and porosities), mineralogical data (changes of the smectite composition and iron corrosion products), transport parameters (diffusion coefficients) and thermal data (temperature dependent reaction progresses). The information and data resulting from the experiments have been used in geochemical modelling calculations and the existing possibilities and limitations to simulate these very complex near field processes were demonstrated. The main conclusion of this study is that the alteration of bentonites in contact with iron is accentuated and accelerated. Alterations in contact with solutions of different ionic strength identified by the authors in previous studies were found be much more intensive in contact with metallic iron and at elevated temperatures. The

  15. pH buffering in compacted bentonite

    International Nuclear Information System (INIS)

    In almost all high-level waste and spent fuel repository concepts, highly compacted bentonite in one form or another is the preferred material for backfilling and sealing. During re-saturation the bentonite swells and seals against the emplacement tunnels. The very low transmissivity to water movement and good sorption characteristics make compacted bentonite an extremely effective near-field diffusion barrier to the movement of radionuclides. The ability to give a chemically well founded pore water composition is essential since such knowledge is a pre-requisite for understanding sorption and diffusion processes, assessing the influence of long term groundwater-bentonite interactions and also predicting near-field solubilities and developing sorption data bases. In this context the pH of the pore water is of central importance, particularly for sorption. Almost invariably the compositions given for highly compacted bentonite pore waters are calculated values because reliable water samples are virtually impossible to obtain, even by squeezing under very high pressures. Assumptions and simplifications are made in the geochemical models used to perform such calculations and the predictions are seldom if ever tested. One of the main hypotheses in a recently proposed model for bentonite pore water was that the initial pH is determined by the state of the amphoteric surface hydroxy groups, ≡SOH type sites, and these buffer the pH of the pore water in to a value close to 8. Surface site types, site capacities and proto-lysis constants were obtained from previous montmorillonite titration measurements and were fixed in the calculations. The aim of this work was to test the Bradbury and Baeyens (2003) model in terms of its ability to the predict one of the most important parameters for any pore water, namely the pH. Tests against the real system are not practicable for the reasons mentioned above. Hence the experiments had to be indirect but nevertheless devised to

  16. Evaluation of factors affecting diffusion in compacted bentonite

    International Nuclear Information System (INIS)

    The information available from the open literature and studies on exclusion, sorption and diffusion mechanisms of ionic and neutral species in bentonite has been compiled and re-examined in relation to the microstructure of bentonite. The emphasis is placed on a more thorough understanding of the diffusion processes taking place in compacted bentonite. Despite the scarcity of experiments performed with neutral diffusants, these imply that virtually all the pores in compacted bentonite are accessible to neutral species. Anion exclusion, induced by the overlap of electrical double layers, may render the accessible porosity for anions considerably less than the porosity obtained from the water content of the clay. On the basis of the compiled data, it is highly probable that surface diffusion plays a significant role in the transport of cations in bentonite clays. Moreover, easily soluble compounds in bentonite can affect the ionic strength of porewater and, consequently, exclusion, equilibrium between cations, and surface diffusion

  17. Greek lignites as additives for controlling filtration properties of water-bentonite suspensions at high temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Vassilios C. Kelessidis; Christina Tsamantaki; Athanasios Michalakis; George E. Christidis; Pagona Makri; Kassiani Papanicolaou; Antonios Foscolos [Technical University of Crete, Chania (Greece). Department of Mineral Resources Engineering

    2007-05-15

    The effectiveness of Greek lignites to control the filtration characteristics of water-bentonite suspensions and to minimize formation damage at high temperatures was studied. Twenty-six lignite samples from various peat/lignite deposits in Greece were used together with a commercial lignite product. The contents of humic and fulvic acids, humins, oxygen, ash and the cation exchange capacity of lignite samples were examined with respect to fluid loss of these suspensions. The results show that most samples provided very good filtration control of the water-bentonite suspensions after exposure to 177{sup o}C with some being superior to the commercial product. Better performance was observed after addition of 3% w/v lignite. Total humic and fulvic acids as percentage of dry lignite matter and the organic matter as lignite percentage showed a weak inverse correlation with the fluid loss volumes. 60 refs., 8 figs., 2 tabs.

  18. Iron content and reducing capacity of granites and bentonite

    International Nuclear Information System (INIS)

    The iron contents in various granites and in bentonite have been determined. For granites, the content is usually in the range 1-9% (weight) and 2.5-3% for bentonite. Most of the iron is divalent in the granites (70-90%); in bentonite the divalent fraction is 25-50%. A large part of the divalent iron in the granites appears to be accessible for the reduction of dissolved oxygen in an aqueous system. (author)

  19. Mechanical Properties of Plastic Concrete Containing Bentonite

    OpenAIRE

    Peng Zhang; Qiaoyan Guan; Qingfu Li

    2013-01-01

    Plastic concrete consists of aggregates, cement, water and bentonite, mixed at a high water cement ratio, to produce a ductile material. It is used for creating an impermeable barrier (cut-off wall) for containment of contaminated sites or seepage control in highly permeable dam foundations. The effects of water to binder ratio and clay dosage on mechanical properties of plastic concrete were investigated. The results indicate that the water to binder ratio and clay dosage have great influenc...

  20. Bentonites in powder detergents: softness and perfum

    OpenAIRE

    Bernal, Cristóbal; Carrión Fité, Francisco Javier

    2011-01-01

    The sodium bentonite is a mineral composed by hydrated aluminium silicates with a great capacity for absorbing several types of substrates. In cotton articles, softeners are added after the washing process. Softeners are organic products which are absorbed within the last rinse. These types of softeners can present some disadvantages as the possible lack of biodegradability, solidity and higher hydrophobicity which might reduce the sensation of comfort in the clothes as water absorption is di...

  1. Borehole sealing with highly compactd Na bentonite

    International Nuclear Information System (INIS)

    This report describes the use of highly compacted Na bentonite for borehole plugging. Bentonites have an extremely low permeability and a low diffusivity, and a swelling ability which produces a nonleaching boundary between clay and rock if the initial bulk density of the bentonite is sufficiently high. The suggested technique, which is applicable to long vertical, and inclined, as well as horizontal boreholes, is based on the use of perforated copper pipes to insert elements of compacted bentonite. Such pipe segments are connected at the rock surface and successively inserted in the hole. When the hole is equipped, the clay takes up water spontaneously and swells through the perforation, and ultimately forms an almost completely homogenous clay core. It embeds the pipe which is left in the hole. Several tests were conducted in the laboratory and one field test was run in Stripa. They all showed that a gel soon fills the slot between the pipe and the confinement which had the form of metal pipes in the laboratory investigations. Subsequently, more clay migrates through the perforation and produces a stiff clay filling in the slot. The redistribution of minerals, leading ultimately to a high degree of homogeneity, can be described as a diffusion process. The rate of redistribution depends on the joint geometry and water flow pattern in the rock. In the rock with an average joint frequence of one per meter or higher, very good homogeneity and sealing ability of the clay are expected within a few months after the application of the plug. (author)

  2. Removal of Phosphate from Aqueous Solution with Modified Bentonite

    Institute of Scientific and Technical Information of China (English)

    唐艳葵; 童张法; 魏光涛; 李仲民; 梁达文

    2006-01-01

    Bentonite combined with sawdust and other metallic compounds was used to remove phosphate from aqueous solutions in this study. The adsorption characteristics of phosphate on the modified bentonite were investigated, including the effects of temperature, adsorbent dosage, initial concentration of phosphate and pH on removal of phosphate by conducting a series of batch adsorption experiments. The results showed that 98% of phosphate removal rate was obtained since sawdust and bentonite used in this investigation were abundantly and locally available. It is concluded that modified bentonite is a relatively efficient, low cost and easily available adsorbent for the removal of phosphate from aqueous solutions.

  3. Analysis of corrosion products of carbon steel in wet bentonite

    International Nuclear Information System (INIS)

    As a part of evaluation of the long-term durability for the overpack containers for high-level radioactive waste, we have conducted corrosion tests for carbon steel in wet bentonite, a candidate buffer material. The corrosion rates were evaluated by weight difference of carbon steel and corrosion products were analyzed by Fourier transform infrared spectroscopy (FT-IR) and colorimetry. At 40degC, the corrosion rate of carbon steel in wet bentonite was smaller than that in pure water. At 95degC, however, the corrosion rate in wet bentonite was much higher than that in pure water. This high corrosion rate in wet bentonite at 95degC was considered to result from evaporation of moisture in bentonite in contact with the metal. This evaporation led to dryness and then to shrinkage of the bentonite, which generated ununiform contact of the metal with bentonite. Probably, this ununiform contact promoted the local corrosion. The locally corroded parts of specimen in wet bentonite at 95degC were analyzed by Fourier transform infrared microspectroscopy (micro-FT-IR), and lepidocrocite γ-FeO(OH) was found as well as goethite α-FeO(OH). In wet bentonite at 95degC, hematite α-Fe2O3 was identified by means of colorimetry. (author)

  4. Synthesis of PDLLA/PLLA-bentonite nanocomposite through sonication

    Science.gov (United States)

    Sitompul, Johnner; Setyawan, Daru; Kim, Daniel Young Joon; Lee, Hyung Woo

    2016-04-01

    This paper concerns the synthesis of poly(D,L-lactic acid)/poly(L-lactic acid) bentonite nanocomposites. Poly (D,L-lactic acid) (PDLLA) was synthesized using lactic acid through the ZnO-catalyzed direct polycondensation method at vacuum pressure and poly(L-lactic acid) (PLLA) was synthesized with L-lactide by ring-opening polymerization method. The PDLLA/PLLA-bentonite nanocomposite films were synthesized using the solvent casting method. The nanoclay, bentonite, was prepared using the solution-intercalation method by dissolving the nanoparticles into chloroform before sonication. In this study, PDLLA/PLLA-bentonite nanocomposite films were produced using variable amounts of nanoclay and sonication times during the mixing of PDLLA/PLLA and bentonite. The properties of the PDLLA/PLLA nanocomposites were then characterized using the X-ray Diffraction (XRD), Universal Testing Machine (UTM), Water Vapor Permeability (WVP) tests, and the enzymatic biodegradability test. The XRD test was used to measure the intercalation of nanoclay layers in the PDLLA/PLLA matrix and the PDLLA/PLLA-bentonite intercalated nanocomposite films. It was found through these various tests that adding bentonite to the PDLLA/PLLA increases tensile strength to 56.76 MP. Furthermore, the biodegradability increases as well as the barrier properties of the polymers The different sonication time used during the mixing of the polymer solution with bentonite also affected the properties of the PDLLA/PLLA-bentonite nanocomposite films.

  5. KAJIAN ADSORPSI LINEAR ALKYL BENZENE SULPHONATE (LAS DENGAN BENTONIT-KITOSAN

    Directory of Open Access Journals (Sweden)

    Miftah Rifai

    2013-11-01

    Full Text Available Deterjen pada umumnya tersusun atas surfaktan anionik seperti LAS (Linear alkyl Benzene sulphonate. pada percobaan ini LAS dapat menyerap sinar pada daerahuv dengan panjang gelombang maksimumnya adalah 223,5 nm. LAS dalam perairan dapat menimbulkan potensi masalah pencemaran.Tujuan dari penelitian ini adalah sebagai salah satu alternatif penanganan masalah pencemaran limbah domestik dengan cara menguji kinerja bentonit alam dan bentonit termodifikasi kitosan dalam mengadsorpsi LAS. Untuk mengetahui bahwa kitosan telah bereaksi dengan bentonit maka diuji dengan FTIR dan XRD pada bentonit alam dan bentonit-kitosan. Kemudian ditentukan waktu kontak optimum antara LAS dengan bentonit alam dan bentonit-kitosan. Serta penentuan isoterm adsorpsi LAS dengan bentonit alam dan bentonit-kitosan dengan cara membuat variasi konsentrasi larutan LAS. Uji kinerja bentonit alam dan bentonit-kitosan dalam mengadsorpsi LAS dilakukan dengan menggunakan sistem batch. Didapat waktu kontak optimum antara LAS berinteraksi dengan bentonit alam adalah 15 menit dengan kapasitas adsorpsi sebesar 3,265 mg/g. Sedangkan Waktu kontak optimum interaksi LAS dengan bentonit-kitosan terjadi pada waktu 15 menit dengan kapasitas adsorpsi sebesar 1,7mg/g. Dari hasil yang didapat maka dapat terlihat bahwa bentonit alam memiliki kapasitas adsorpsi yang lebih besar dibandingkan bentonit hasil modifikasi dengan kitosan. Interaksi antara bentonit alam dan bentonit–kitosan dengan LAS terjadi secara fisik dengan energi adsorpsi bentonit alam dengan LAS adalah 19,31 KJ/mol dan energi adsorpsi bentonit-kitosan dengan LAS adalah 19,60 KJ/mol.

  6. Hydrothermal alterations of Bentonites in Almeria (Spain)

    International Nuclear Information System (INIS)

    The use of bentonite as backfilling and sealing material in the high level radioactive waste disposals has been treated in previous studies accomplished by different authors. However, the use of this clayey barrier needs the resolution of different problems so that its efficiency will be enhanced. between those could be cited the study of the actual capacity of sealing the space around the canister and the accommodation to the pressure of the rocky environment; the possible variations in plasticity; the diffusion and reaction processes that can be produced through the barrier by groundwater, the capacity of radionuclides adsorption, etc. These studies, show that the bentonites with high content in smectite fulfill satisfactorily with the physical and chemical conditions to be used as sealing material, but it is known that the smectite can be unstable in diagenetic conditions similar to those are given in a deep repository of radioactive wastes, being transformed into illite. A conclusion of immediate interest is deduced from this last study. The bentonites used as sealing material in radioactive waste repositories must no contain Na as interlayer cation since it is very easily exchangeable by K. It is better to select those smectites with Ca and Mg that detain the entry of K in the interlayer and as a consequence the transformation process of smectite into illite is made more difficult. (Author)

  7. Study on bentonite-based buffer material of radioactive waste disposal facility. Influence of cement leachate on bentonite impermeability

    International Nuclear Information System (INIS)

    Cementitious materials and bentonite are planned for use as engineered barriers for the disposal of TRU waste from nuclear fuel reprocessing. When groundwater penetrates cementitious material, hyperalkaline water containing Ca ions may leach out and change bentonite physicochemically, resulting in degradation of its barrier performance. Furthermore, ion concentration of groundwater may increase due to dissolution of nitrate salt in some wastes. To investigate the hydraulic characteristics of bentonite under the disposal environment, hydraulic conductivity tests were performed using hyperalkaline solutions that imitate cement leachate and sodium nitrate solution. It was shown that ion concentration of permeant solution and exchangeable cation type of smectite had a large impact on bentonite impermeability. (author)

  8. Imaginar Cabo Verde a partir da imagem do Brasil

    Directory of Open Access Journals (Sweden)

    Víctor Barros

    2010-06-01

    Full Text Available As representações discursivas constituem sempre construções históricas das épocas e dos actores que as animam em função de determinadas funcionalidades que lhes são demandadas a cumprir. Ensaia-se a partir deste título o inquérito analítico sobre a problemática da construção de alguns dos discursos intelectuais caboverdianos que, durante o Estado Novo salazarista, puseram em destaque uma determinada representação de Cabo Verde a partir da adopção e da interiorização imaginária da imagem do Brasil como paradigma imagético de consubstanciação da obra colonial portuguesa. Assim, o exercício reflexivo orienta-se no sentido de demonstrar as correlações entre a imaginação daquilo que se pensava em Cabo Verde (a partir dos postulados lusotropicalistas sobre o Brasil e, simultaneamente, deste como exemplo de que se poderia servir para se imaginar e representar a historicidade identitária caboverdiana, com todos os efeitos hermenêuticos perversos que uma comparação estribada na importação de modelos teóricos explicativos poderá suscitar.

  9. Dual swelling mechanism model for saturated and unsaturated compacted bentonite

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. In the current concept of repository for radioactive waste disposal, compacted bentonite as well as bentonite-based material will be used as an engineered barrier mainly for inhibiting migration of radioactive nuclides. Since compacted bentonite swells when it is saturated, dry density of compacted bentonite will be redistributed and container of radioactive wastes will move during infiltration of underground water. Accurate evaluation of these events is effective in decreasing uncertainty in long term safety evaluation of radioactive waste facilities. However, sufficient evaluation is not conducted because behaviour of bentonite material during saturation process is not clarified sufficiently. Thus, stress-strain model of bentonite material during saturation process is proposed and applicability of the model is investigated. It is well known that compacted bentonite swells with large deformation by infiltration of water. Swelling behaviour of bentonite is mainly attributable to osmotic pressure caused by the difference between concentration of ions inside of montmorillonite flakes and that outside of montmorillonite flakes. Thus, swelling which is attributable to osmotic pressure is named 'swelling by osmotic pressure' here. By contrast, unsaturated ordinary clay swells or shrinks during infiltration of water without effect of osmotic pressure. Since this phenomenon is mainly attributable to reduction of suction during infiltration of water, it is reasonable to assume that unsaturated bentonite swells or shrinks during infiltration of water by reduction of suction. Thus, swelling which is attributable to reduction of suction is named 'swelling by reduction of suction' here. It is assumed in this paper that swelling by osmotic pressure occurs when bentonite is fully saturated, while swelling by reduction of suction occurs when bentonite is unsaturated. Swelling deformation under a constant vertical load is measured

  10. Modelling interaction of deep groundwaters with bentonite and radionuclide speciation

    International Nuclear Information System (INIS)

    In the safety analysis recently reported for a potential Swiss high-level waste repository, radionuclide speciation and solubility limits are calculated for expected granitic groundwater conditions. With the objective of deriving a more realistic description of radionuclide release from the near-field, an investigation has been initiated to quantitatively specify the chemistry of the near-field. In the Swiss case, the main components of the near-field are the glass waste-matrix, a thick steel canister horizontally emplaced in a drift, and a backfill of highly compacted sodium bentonite. This report describes a thermodynamic model which is used to estimate the chemical composition of the pore water in compacted sodium bentonite. Solubility limits and speciation of important actinides and the fission product technetium in the bentonite pore water are then calculated. The model is based on available experimental data on the interaction of sodium bentonite and groundwater and represents means of extrapolation from laboratory data to repository conditions. The modelled composition of the pore water of compacted sodium bentonite, as well as the various compositions resulting from the long-term extrapolation, are used to estimate radionuclide solubilities in the near-field of a deep repository. From the chemical point of view, calcium bentonite seems to be more stable than sodium bentonite in the presence of Swiss Reference Groundwater. Since the effect of calcium bentonite on the groundwater chemical composition will be considerably less marked than that of sodium bentonite, especially with respect to key parameters for the nuclide speciation like carbonate concentration and pH, the use of calcium bentonite instead of sodium bentonite will improve the reliability in the prediction of source terms for radionuclide transport in the geosphere. (author)

  11. Behaviour of bentonite/montmorillonite gel at low ionic strength

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. In the Swedish KBS-3 concept for a geological deep storage of spent nuclear fuel, bentonite of high montmorillonite content is proposed to serve as a buffer surrounding copper canisters containing the spent fuel. Montmorillonite has an exceptional affinity for water which results in the build-up of a swelling pressure when bentonite is placed in a confined volume. There may be fractures intersecting the deposition hole and at those fractures the bentonite is not restricted but can continue to swell until a steady state is reached. Under present day Swedish groundwater conditions the swelling into fractures will be limited because the montmorillonite at the swelling front will coagulate. However, at the end of a glaciation one cannot exclude that glacial meltwater of low ionic strength will permeate the bedrock. This could cause erosion of the bentonite, due to colloidal sol formation at the swelling front. A homo-ionic Ca-montmorillonite would not pose any problem because it has limited swelling due to attraction forces caused by ion correlations. In homo-ionic Na-montmorillonite, on the other hand, the correlation interactions are weak and cannot prevent the sol formation in case the montmorillonite is contacted with water of low ionic strength. Under repository conditions the montmorillonite is not homo-ionic, but contains a variety of counterions, both mono- and divalent. It was demonstrated earlier that for mixed Ca/Na-montmorillonite the sol-formation ability is much more sensitive to the ionic strength of the electrolyte than homo-ionic Na-montmorillonite. In deionized water sol formation occurs unless the equivalent charge fraction of Ca2+ is 90% or higher. However in electrolyte solution it was found that the sol is unstable if the ionic strength is above 4 mM. The investigated cases indicate that this condition holds even if the charge fraction of Ca2+ in the interlayer is as low as 20%. In this work it is

  12. Isostatic compaction of beaker shaped bentonite blocks on the scale 1:4

    Energy Technology Data Exchange (ETDEWEB)

    Johannesson, Lars-Erik [Clay Technology AB, Lund (Sweden); Nord, Sven [Ifoe Ceramics AB, Bromoella (Sweden ); Pusch, Roland [Geodevelopment AB, Lund (Sweden); Sjoeblom, Rolf [AaF-Energikonsult AB, Stockholm (Sweden)

    2000-09-01

    dimensions and relatively even surfaces. The blocks could readily be produced to desirable void ratio and density. The bentonite blocks produced had a high homogeneity. No fractures could be observed visually. Microcracks could be identified on strong magnification, as might be expected. The mechanical properties recorded were good and the spread in the values low for all blocks. No special difficulty was encountered which was related to the complex shape of the blocks (beaker-like). The complex shape influenced the design of the bag and filling system, as well as the procedure for filling. The method of machining presently used at Ifoe Ceramics AB for their ordinary production works excellently for compacted bentonite as well. A coarse estimate indicates that the machining of the blocks for one entire deposition hole may take on the order of a small number of hours. The production went very well for all the combinations of production parameters used. Variation of production parameters might be utilised to adjust some of the properties of the blocks. It should be noted that in the processes, no substances are introduced into the bentonite other than pure water. No limitations have been identified regarding the proportions of the blocks manufactured (e.g.diameter/height ratio). Although very positive conclusions are drawn on essentially all points above, further development work is necessary before a process for full scale operation can be established.

  13. Modelling the induced polarization of bentonite-sand mixtures

    OpenAIRE

    Leroy, Philippe; Ghorbani, Ahmad; Revil, André; Cosenza, P.; Okay, G.

    2014-01-01

    Spectral induced polarization (SIP) has become an increasingly popular geophysical method for hydrogeological and environmental applications. These applications include for instance the non-intrusive characterization of the textural and interfacial physicochemical properties of bentonites used as permeability barriers in landfills or to store various types of contaminants including radioactive wastes. Bentonites are mainly constituted of smectites, which have very high specific surface areas ...

  14. Filtration behavior of organic substance through a compacted bentonite

    International Nuclear Information System (INIS)

    Filtration behavior of organic substance through a compacted bentonite was investigated. Na-type bentonite containing 30wt% of quartz sand was compacted in a column and the dry density was adjusted to be 1.6 g/cm3. Polyacrylic acid solution (including three types of polyacrylic acid, average molecular weight 2,100, 15,000 and 450,000) was prepared and was passed through the compacted bentonite. Molecular weight distributions of polyacrylic acid in the effluent solution were analysed by GPC (Gel Permeation Chromatography). A batch type experiment was also carried out in order to examine a sorption behavior of these organic substances onto the surfaces of grains of the bentonite. The results indicated that the smaller size polyacrylic acid (molecular weight < 100,000) was passed through the compacted bentonite. On the other hand, the larger size polyacrylic acid (molecular weight ≥100,000) was mostly filtrated by the compacted bentonite. The batch type sorption tests clarified that the polyacrylic acid did not sorb onto the surfaces of minerals constituting the bentonite. Therefore it was suggested that the larger size molecules (≥100,000) of organic substances could be predominantly filtrated by the microstructure of the compacted bentonite. (author)

  15. Diffusion behavior for Se and Zr in sodium-bentonite

    International Nuclear Information System (INIS)

    Apparent diffusion coefficients for Se and Zr in bentonite were measured by in-diffusion method at room temperature using water-saturated sodium-bentonite, Kunigel V1 reg-sign containing 50wt% Na-smectite as a major mineral was used as the bentonite material. The experiments were carried out in the dry density range of 400--1,800 kg/m3. Bentonite samples were immersed with distilled water and saturated before the experiments. The experiments for Se were carried out under N2 atmospheric condition (O2: 2.5ppm). Those for Zr were carried out under aerobic condition. The apparent diffusion coefficients decrease with increasing density of the bentonite. Since dominant species of Se in the pore water is predicted to be SeO32-, Se may be retarded by anion-exclusion because of negative charge on the surface of the bentonite and little sorption. The dominant species of Zr in the porewater is predicted to be Zr(OH)5- or HZrO3-. Distribution coefficient measured for Zr on the bentonite was about 1.0 m3/kg from batch experiments. Therefore, the retardation may be caused by combination of the sorption and the anion-exclusion. A modeling for the diffusion mechanisms in the bentonite were discussed based on an electric double layer theory. Comparison between the apparent diffusion coefficients predicted by the model and the measured ones shows a good agreement

  16. Long-term Corrosion of Copper Container in Bentonite Buffer

    International Nuclear Information System (INIS)

    The experimental method for the evaluation of copper corrosion was discussed in this report. Especially, the corrosion behavior of a copper container in a compacted bentonite environment was reviewed in detail. Several previous studies on the copper corrosion in a bentonite environment were summarized and the applied methods were illustrated firstly. On the basis of the review, it is discussed how to execute long-term copper corrosion test as regarding korean disposal environment. The selection of bentonite medium and the composition of a medium such as bentonite-sand mixture or bentonite-sand double layer was mentioned in this report. The need for protection layer on copper surface was also discussed for reducing initial copper corrosion rate. As key aspects on the corrosion test, a measuring of corrosion rate, an observation of surface morphology, an analysis of corrosion product, and a measuring of corrosion potential were pointed out. For the purpose of a experimental consistency, the necessity of standard composition for a bentonite and a underground water might be confirmed before the test. Consequently, three experimental designs were derived for the corrosion test such as a corrosion testing design at creep condition, a simple corrosion design for the evaluation for other candidate materials, and lastly, a corrosion testing design in compacted bentonite. Through this survey and discussion for a copper corrosion in bentonite environment it would be very helpful for a high level radioactive waste disposal plan in the future

  17. LOT A2 Test, THC-modelling of bentonite buffer in a final repository of spent nuclear fuel

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. The Finnish spent nuclear fuel disposal is planned to be based on the KBS-3V repository concept. Within this concept, the role of the bentonite buffer is considered to be central. The aim of this study was to model the evolution of the buffer during the thermal phase (heat-generating period of spent fuel), when the bentonite is only partially saturated initially, and the surrounding rock matrix is assumed to be fully saturated. It is essential to study how temperature will affect saturation and also how both of these affect the chemistry of bentonite. In order to make the modeling more concrete, an example experimental case was considered: Long Term Test of Buffer Materials (LOT) A2-parcel test at the Aespoe Hard Rock Laboratory (HRL) in Sweden. In the A2-parcel the MX-80 bentonite was exposed to adverse (120-150 deg. C) temperature conditions and high temperature gradients. The test parcel diameter was smaller than in the actual KBS-3V deposition hole to speed up the saturation. The chemical behaviour of minerals causes their redistribution inside the bentonite. For example, according to the laboratory tests, gypsum dissolves and anhydrite precipitates near the heater-bentonite interface. Also, incoming groundwater affects the bentonite pore water and its properties. These changes may, in turn, influence the mechanical properties of the bentonite. A coupled Thermo-Hydro-Chemical (THC) model was applied, which means that all mechanical effects were ignored. The purpose of the model was first to achieve a satisfactory match between the model and experimental results, and, therefore, the time frame was limited to ten years (LOT A-2 parcel test lasted approximately 6 years). The system was simplified to 1-D in order to reduce the computational work, which can be very significant due to complex chemical calculations. The 1-D model results are reported in Itaelae (2009). The aim is to extend the calculations to 2-D

  18. Remediation of distilleries wastewater using chitosan immobilized Bentonite and Bentonite based organoclays.

    Science.gov (United States)

    El-Dib, F I; Tawfik, F M; Eshaq, Gh; Hefni, H H H; ElMetwally, A E

    2016-05-01

    Organic-inorganic nanocomposite, namely chitosan immobilized Bentonite (CIB) with chitosan content of 5% was synthesized in an acetic acid solution (2%). Organically modified CIB and Bentonite (mbent.) were prepared by intercalating cetyl trimethylammonium bromide (CTAB) as a cationic surfactant at doses equivalent to 1.5 and 3 times the cation exchange capacity (CEC) of clay. The prepared samples were characterized using FTIR, XRD and SEM to explore the interlayer structure and morphology of the resultant nanocomposites. The remediation of distilleries (vinasse) wastewater process was carried out using different adsorbents including CIB, modified CIB (mCIB), Bentonite (bent.), modified Bentonite (mbent.) and chitosan at different contact time. The results showed that the packing density of surfactant used in the synthesis of organoclays strongly affects the sorption capacity of the clay mineral and also showed that (mCIB)3 was found to be the most effective sorbent in the purification of distilleries wastewater with 83% chemical oxygen demand (COD) reduction and 78% color removal. PMID:26840179

  19. Effect of sulfuric acid concentration of bentonite and calcination time of pillared bentonite

    Science.gov (United States)

    Mara, Ady; Wijaya, Karna; Trisunaryati, Wega; Mudasir

    2016-04-01

    An activation of natural clay has been developed. Activation was applied by refluxing the natural bentonite in variation of the sulfuric acid concentration and calcination time of pillared bentonite (PLC). Calcination was applied using oven in microwave 2,45 GHz. Determination of acidity was applied by measuring the amount of adsorbed ammonia and pyridine. Morphological, functional groups and chrystanility characterizations were analyzed using SEM, TEM, FTIR and XRD. Porosity was analyzed using SSA. The results showed that the greater of the concentration of sulfuric acid and calcination time was, the greater the acidity of bentonite as well as the pore diameter were. FTIR spectra showed no fundamental changes in the structure of the natural bentonite, SEM, and TEM images were showing an increase in space or field due to pillarization while the XRD patterns showed a shift to a lower peak. Optimization was obtained at a concentration of 2 M of sulfuric acid and calcination time of 20 minutes, keggin ion of 2.2 and suspension of 10 mmol, respectively each amounted to 11.7490 mmol/gram of ammonia and 2.4437 mmol/gram of pyridine with 154.6391 m2/gram for surface area, 0.130470 m3/gram of pore volume and 3.37484 nm of pore diameter.

  20. Verification of substitution of bentonites by montmorillonitic clays summary report on Czech montmorillonitic clays

    International Nuclear Information System (INIS)

    Czech bentonites and smectite-rich clays were characterised in order to study if they could be used as buffer and backfill materials instead of non-Czech commercial bentonites. The characterisation work was orgnized by RAWRA (the Czech Radioactive Waste Repository Authority) and the main part of the work was performed in the Czech Republic at Charles University and at Czech Technical University. Parallel and complementary characterisation was conducted in Finland in Sweden. This report was compiled with the aim to summarise the results, and to compare the methods and results gained in different testing laboratories. The characterisation included mineralogical, chemical and geotechnical investigations and experiments on thermal stability and sorption. There were some variations between the results gained in different laboratories. This was mainly due to differences between the testing methods used but also due to heterogeneity of the samples. The Czech bentonite-clays from Rokle and Strance clay deposits contained relatively high amount of swelling minerals and thus can be considered as potential buffer and backfill materials. (orig.)

  1. Mineralogical investigations of Wyoming bentonite MX-80 and Montigel

    International Nuclear Information System (INIS)

    A project study for the final disposal of high-level radioactive wastes in deep geological formations, carried out on behalf of Nagra has shown that bentonite could serve as backfilling and sealing material for the final repository concept foreseen by Nagra. Subsequently, the Institute for Foundation and Ground Mechanics of the ETH-Zurich was charged by Nagra with the investigation of various bentonites. The investigations concentrated on the Na-bentonite MX-80 from Wyoming, which is favoured by the Swedes, and on the geographically more favourable Ca-bentonite Montigel from Bavaria. The mineral composition, surface, exchange capacity and exchangeable ions, charge distribution and density of both bentonites have been investigated

  2. Adsorption behavior of 239Pu by Gaomiaozi bentonite

    International Nuclear Information System (INIS)

    Adsorption behavior of 239Pu by Gaomiaozi bentonite as a function of the factors of aqueous phase pH value, 239Pu initial concentration and ionic species is studied by static adsorption experiments in this paper. The following results are obtained. Adsorption equilibrium time of 239Pu by Gaomiaozi bentonite samples is about 24 h, and the adsorption distribution ratio Kd value of 239Pu increases with the pH value, but decreases with increasing initial concentration of 239Pu. And adsorption of 239Pu by bentonite samples with different ionic species show that anions affect the most on adsorption of bentonite is CO32-, followed by HCO3- and SO42-, whereas Cl- and NO3- hardly have any influence on the adsorption of bentonite. (authors)

  3. Biological and oceanographic upwelling indicators at Cabo Frio (RJ

    Directory of Open Access Journals (Sweden)

    Gleyci A. O. Moser

    1997-01-01

    Full Text Available Phytoplankton biomass, chemical parameters and hydrology were studied in a transect 101.6 km long off Cabo Frio (RJ, Southeast Brazil, during summer (December 29 to 31, 1991 and winter (June 27 to 30, 1992. Wind induced upwelling events are frequently observed in the area during summer, becoming rare during winter. By the summer cruise a bloom of phytoplankton was observed in surface, close to the coast, with chlorophyll concentrations reaching 25.55 mg Chl-a m-3, uncoupled from the cold, nutrient rich waters of South Atlantic Central Water (SACW, found below 40 m depth. During the winter cruise, the SACW raised at the surface waters in front of Cabo Frio depicting an upwelling event. However, in spite of high surface nitrate concentrations (up to 7.7 f.1M chlorophyll-a were lower than 2 mg Chl-a m-3. The phytoplankton biomass, meteorological and hydrological data suggest a probable upwelling event immediately before the summer cruise, and an ongoing one during winter time. Cluster analyses and principal component analyses (PCA were applied to summer and winter data, pointing out multidimensional fronts in the area during both seasons.A biomassa fitoplanctônica, parâmetros químicos e hidrologia foram estudadas em um transecto de 101,6 Km ao largo de Cabo Frio, (RJ Brasil, durante o verão (Dezembro 29 a 31, 1991 e inverno (Junho 27 a 30, 1992. Nesta área, eventos de ressurgência induzidos pelo vento são comuns durante o verão, tornando-se mais raros durante o inverno. Durante o período de verão uma floração de fitoplâncton foi observada na superfície próximo ao continente, apresentando um máximo de clorofila-a igual a 25,55 mg Cl-a m'3 desacoplado das águas frias e ricas em nutrientes da Água Central do Atlântico Sul (ACAS, presente abaixo de 40 m. Durante o inverno, a ACAS alcançou a superflcie em frente a Cabo Frio, caracterizando um evento de ressurgência. Entretanto, apesar das altas concentrações de nitrato na superf

  4. Terminologia do direito processual civil em Cabo Verde

    OpenAIRE

    Graça, Evódia Gomes da

    2010-01-01

    O presente trabalho tem como objectivo prioritário propor, a criação de uma base de dados terminológica e textual trilingue – Português – Inglês – Francês no domínio do direito processual civil em Cabo Verde. No entanto, tencionamos no futuro introduzir o caboverdiano como uma quarta língua na base de dados. Assim, os termos e as colocações terminológicas que iremos armazenar estarão na base da preparação dos recursos linguísticos e terminológicos para o ensino do português jur...

  5. General corrosion of Ti in hot water and water saturated bentonite clay

    International Nuclear Information System (INIS)

    Titanium has been proposed as one of the candidates for canister materials for storing spent nuclear fuel in the Swedish bed-rock. The deposition milieu was simulated on a laboratory scale by embedding titanium in compacted bentonite and the general corrosion rate was investigated. More fundamental studies were also performed where titanium was exposed to water in which special attention was paid to the NaCl content and oxygen content. In reaction cells designed according to high vacuum principles it was possible to reduce the oxygen content to very low values. The exposure time ranged between 1 min. and 6 months. Analysis of the corrosion products was performed mainly with ESCA. In water at 95 degrees C the oxide growth follows a direct logarithmic law: y equals 8.7 + 3.65 ln t. Oxygen and salt do not influence the rate of the oxide growth significantly. The general corrosion rate is approximately the same as the oxide growth rate since the dissolution of Ti into the water-solution is very low. The oxide consists of an outer layer of TiO2 and a few atomic layers of suboxide close to the oxide/metal interface. Transmission electron microscopy studies of the water-formed oxides indicate that these are amorphous. The oxides formed on Ti exposed in bentonite is 70-100 Aa thick for exposure times ranging between 4 months and 2 years. It is shown, that montmorillonite - the main constituent in bentonite - is absorbed in the TiO2 formed on these samples. If it is assumed that a logarithmic growth law is valid even for long-term exposure in bentonite, the growth law which will give the highest growth rate is y equals 5.5 ln t. An oxide thickness of 160 Aa is obtained if this law is extrapolated to 100.000 years exposure. (Author)

  6. Enhanced shear strength of sodium bentonite using frictional additives

    Energy Technology Data Exchange (ETDEWEB)

    Schmitt, K.E. [GeoSyntec Consultants, Huntington Beach, CA (United States); Bowders, J.J.; Gilbert, R.B. [Univ. of Texas, Austin, TX (United States); Daniel, D.E. [Univ. of Illinois, Urbana, IL (United States)

    1997-12-31

    One of the most important obstacles to using geosynthetic clay liners (GCLs) in landfill cover systems is the low shear strength provided by the bentonitic portion of the GCL. In this study, the authors propose that granular, frictional materials might be added to the bentonite to form an admixture that would have greater shear strength than the bentonite alone while still raining low hydraulic conductivity. Bentonite was mixed with two separate granular additives, expanded shale and recycled to form mixtures consisting of 20-70% bentonite by weight. In direct shear tests at normal stresses of 34.5-103.5 kPa, effective friction angles were measured as 45{degrees} for the expanded 36{degrees} for the recycled glass, and 7{degrees} for the hydrated granular bentonite. The strength of the expanded shale mixtures increased nearly linearly as the percentage shale in the mixture increased, to 44{degrees} for a bentonite mixture with 80% shale. The addition of recycled glass showed little effect on the shear strength of the mixtures of glass and bentonite. Hydraulic conductivity measurements for both types of mixtures indicated a linear increase with log(k) as the amount of granular additive increased. For applications involving geosynthetic clay liners for cover systems, a mixture of 40% expanded shale and 60% bentonite is recommended, although further testing must be done. The 40/60 mixture satisfies the hydraulic equivalency requirement, with k = 5.1X10{sup -9} cm/sec, while increasing the shear strength parameters of the bentonitic mixture to {phi}{prime} = 17{degrees} and c{prime} = 0.

  7. Sorption of Cadmium on Na-Bentonite

    International Nuclear Information System (INIS)

    The sorption of Cd radionuclide into Na-bentonite as candidate for buffer material in the radioactive waste disposal system has been performed. Cadmium was used for this study as a model for bivalence elements. Batch experiment was adopted to study sorption isotherm, influence of carbonate and influence of EDTA. In a simple media, pure water, Cd was retained with a high affinity. Two stages Freundlich sorption isotherm was shown, with high coefficient distribution and sorption capacities. It is shown that the presence of carbonate in solution was not affect significantly to the sorption. While the presence of EDTA, decrease the distribution coefficient value. (author)

  8. Adsorption of aniline, phenol, and chlorophenols on pure and modified bentonite

    Science.gov (United States)

    Yildiz, A.; Gür, A.; Ceylan, H.

    2006-11-01

    In the present study, pure bentonite and bentonite modified by HNO3, EDTA, and HDTMA are adsorbents. The changes on the surfaces of bentonite samples are studied by IR spectroscopy. The adsorption of aniline, phenol, and phenol derivatives on these adsorbents is examined by means of gas chromatography. As the result of these examinations, it is seen that the adsorption capacities of clay-organic complexes (bentonite-EDTA and bentonite-HDTMA) are higher than those of bentonite-HNO3 and pure bentonite.

  9. Optimizing soil and water management in dryland farming systems in Cabo Verde

    OpenAIRE

    Santos Baptista Costa, Dos, I.

    2016-01-01

     “Optimizing Soil and Water Management in Dryland Farming Systems in Cabo Verde” Isaurinda Baptista Summary Soil and land degradation poses a great challenge for sustainable development worldwide and, in Cabo Verde, has strongly affected both people’s livelihood and the environment. Dryland food production in Cabo Verde faces steep slopes, inadequate practices, irregular intense rain, recurrent droughts, high runoff rates, severe soil erosion and declining soil fertilit...

  10. Impact of the changes in the chemical composition of pore water on chemical and physical stability of natural clays. A review of natural cases and related laboratory experiments and the ideas on natural analogues for bentonite erosion/non-erosion

    International Nuclear Information System (INIS)

    geological changes that have occurred in bentonites over geological time scales. The bentonite erosion project has to provide the scenarios for approximately 100,000 years, but the geological deposits have been changed and subjected to various conditions, many of those uncertain, during tens and hundreds of millions of years. The field studies of weathering of the historical K-bentonite deposits could provide interesting and new information, but the relevance related to the bentonite erosion project is questionable

  11. Impact of the changes in the chemical composition of pore water on chemical and physical stability of natural clays. A review of natural cases and related laboratory experiments and the ideas on natural analogues for bentonite erosion/non-erosion

    Energy Technology Data Exchange (ETDEWEB)

    Puura, Erik (Eridicon OUe, Tartu (Estonia)); Kirsimaee, Kalle (Univ. of Tartu, Inst. of Ecology and Earth Sciences, Tartu (Estonia))

    2010-01-15

    is the geological changes that have occurred in bentonites over geological time scales. The bentonite erosion project has to provide the scenarios for approximately 100,000 years, but the geological deposits have been changed and subjected to various conditions, many of those uncertain, during tens and hundreds of millions of years. The field studies of weathering of the historical K-bentonite deposits could provide interesting and new information, but the relevance related to the bentonite erosion project is questionable

  12. Catalytic Polymerization of Acrylonitrile by Khulays Bentonite

    Directory of Open Access Journals (Sweden)

    Matar M. Al-Esaimi

    2007-04-01

    Full Text Available The aqueous polymerization of acrylonitrile (AN catalyzed with exchanged Khulays bentonite . The influence of various polymerization parameters ( e.g., concentrations of Potassium Persulfate (K2S2O8 and monomer , various of organic solvents, and different temperature has been investigated. It was found that the rate of polymerization of AN was found to be dependent on monomer concentration, initiator and temperature. The activation energy of polymerization was calculated .Thermal properties of the polymer were studied by TGA and DSC techniques. © 2007 CREC UNDIP. All rights reserved.Received: 5 February 2007; Received in revised: 19 April 2007; Accepted: 7 May 2007[How to Cite: M. M. Al-Esaimi. (2007. Catalytic Polymerization of Acrylonitrile by Khulays Bentonite. Bulletin of Chemical Reaction Engineering and Catalysis, 2 (2-3: 32-36.  doi:10.9767/bcrec.2.1.4.6-10][How to Link/DOI: http://dx.doi.org/10.9767/bcrec.2.1.4.6-10 || or local: http://ejournal.undip.ac.id/index.php/bcrec/article/view/4] 

  13. Sorption of Uranium(VI) and Thorium(IV) by Jordanian Bentonite

    OpenAIRE

    Fawwaz I. Khalili; Salameh, Najla'a H.; Mona M. Shaybe

    2013-01-01

    Purification of raw bentonite was done to remove quartz. This includes mixing the raw bentonite with water and then centrifuge it at 750 rpm; this process is repeated until white purified bentonite is obtained. XRD, XRF, FTIR, and SEM techniques will be used for the characterization of purified bentonite. The sorption behavior of purified Jordanian bentonite towards and Th4+ metal ions in aqueous solutions was studied by batch experiment as a function of pH, contact time, temperature,...

  14. Modelling of erosion of bentonite gel by gel/sol flow

    Energy Technology Data Exchange (ETDEWEB)

    Moreno, Luis; Neretnieks, Ivars; Longcheng Liu (Chemical Engineering and Technology, School of Chemical Science and Engineering, Royal Institute of Technology, Stockholm (Sweden))

    2010-11-15

    Bentonite intrusion into a fracture intersecting the canister deposition hole is modelled. The model describes the expansion of the bentonite within the fracture. It accounts for the repulsive electrostatic double-layer forces, the attractive van der Waals forces and friction forces between the particles and the water. The model also takes into account the diffusion of the colloid particles in the smectite sol. Diffusion of a counterion, sodium, is accounted for as this strongly influences the double layer force and the viscosity of the gel/sol. The gel/sol is considered to be a fluid with a varying viscosity that is strongly dependent on the bentonite volume fraction in the gel and the sodium concentration in the water. Two different geometries were modelled; a rectangular and a cylindrical. The rectangular geometry was used to gain experience with the processes and mechanisms and how they interact since the cylindrical geometry was somewhat less stable numerically and more time consuming. In the rectangular geometry a fracture 1 metre long in the flow direction was modelled. In both geometries the fracture size was selected sufficiently large to ensure that the water velocity, near the distant border was nearly the same as the approaching water velocity and that the smectite concentration there was vanishingly small. It was found that the velocity of the fluid drops considerably where the bentonite volume fraction is larger than 1-2%. This is due to the strong increase in viscosity with increasing bentonite volume fraction. The loss of smectite by the slowly flowing fluid was found to be proportional to the square root of the seeping water velocity for the rectangular geometry. For the cylindrical geometry, the dependence is somewhat lower (exponent about 0.4) since the length of the gel/water interface decreases with increasing water flow rate. The penetration depth of the gel/water interface decreases with increasing water flow rate. For water velocity of the

  15. Modelling of erosion of bentonite gel by gel/sol flow

    International Nuclear Information System (INIS)

    Bentonite intrusion into a fracture intersecting the canister deposition hole is modelled. The model describes the expansion of the bentonite within the fracture. It accounts for the repulsive electrostatic double-layer forces, the attractive van der Waals forces and friction forces between the particles and the water. The model also takes into account the diffusion of the colloid particles in the smectite sol. Diffusion of a counterion, sodium, is accounted for as this strongly influences the double layer force and the viscosity of the gel/sol. The gel/sol is considered to be a fluid with a varying viscosity that is strongly dependent on the bentonite volume fraction in the gel and the sodium concentration in the water. Two different geometries were modelled; a rectangular and a cylindrical. The rectangular geometry was used to gain experience with the processes and mechanisms and how they interact since the cylindrical geometry was somewhat less stable numerically and more time consuming. In the rectangular geometry a fracture 1 metre long in the flow direction was modelled. In both geometries the fracture size was selected sufficiently large to ensure that the water velocity, near the distant border was nearly the same as the approaching water velocity and that the smectite concentration there was vanishingly small. It was found that the velocity of the fluid drops considerably where the bentonite volume fraction is larger than 1-2%. This is due to the strong increase in viscosity with increasing bentonite volume fraction. The loss of smectite by the slowly flowing fluid was found to be proportional to the square root of the seeping water velocity for the rectangular geometry. For the cylindrical geometry, the dependence is somewhat lower (exponent about 0.4) since the length of the gel/water interface decreases with increasing water flow rate. The penetration depth of the gel/water interface decreases with increasing water flow rate. For water velocity of the

  16. Engineering Properties of Bentonite Stabilized with Lime and Phosphogypsum

    Directory of Open Access Journals (Sweden)

    Kumar Sujeet

    2014-12-01

    Full Text Available Engineering properties such as compaction, unconfined compressive strength, consistency limits, percentage swell, free swell index, the California bearing ratio and the consolidation of bentonite stabilized with lime and phosphogypsum are presented in this paper. The content of the lime and phosphogypsum varied from 0 to 10 %. The results reveal that the dry unit weight and optimum moisture content of bentonite + 8 % lime increased with the addition of 8 % phosphogypsum. The percentage of swell increased and the free swell index decreased with the addition of 8 % phosphogypsum to the bentonite + 8 % lime mix. The unconfined compressive strength of the bentonite + 8 % lime increased with the addition of 8 % phosphogypsum as well as an increase in the curing period up to 14 days. The liquid limit and plastic limit of the bentonite + 8 % lime increased, whereas the plasticity index remained constant with the addition of 8 % phosphogypsum. The California bearing ratio, modulus of subgrade reaction, and secant modulus increased for the bentonite stabilized with lime and phosphogypsum. The coefficient of the consolidation of the bentonite increased with the addition of 8 % lime and no change with the addition of 8 % phosphogypsum.

  17. Colloid chemical aspects of the ''confined bentonite concept''

    International Nuclear Information System (INIS)

    Measurements of the amount of particles released from a bentonite gel by light scattering and visual inspection show that while particles are released in distilled water, the gel will be coagulated if in contact with ground water and consequently the release of particles is negligibly small. Studies of sedimentation volumes by ultracentrifugation also clearly indicate that the bentonite in contact with ground water under the repository pressure will form a completely stable coagulated gel. The swelling of confined bentonite was studied in an ''artificial crack'' of width 0.5 mm. The bentonite flowed readily into this crack and into the much narrower crack formed when the cell was broken. The swelling properties of the bentonite at the repository depth are discussed. It is argued that the gel, if sufficient volume is available, will swell spontaneously to a volume that is approximately 30 % larger than the initial one and then form a stable, coagulated gel containing 30-35 % water in equilibrium with the ground water. Investigations of the diffusion of colloidal matter (sodium lignosulphonate molecules of mean diameter 6 nm) and calcium ions into a dilute bentonite gel show that colloidal matter very probably will have a negligible rate of diffusion while the calcium ions diffuse rapidly. This implies that the initial bentonite gel which is partially in its sodium form will be completely exchanged to its calcium form when brought into contact with ground water which ensures that it will remain coagulated even in its swollen state

  18. Study on adsorption of 237Np on bentonite

    International Nuclear Information System (INIS)

    The performance of adsorbing 237Np for bentonite as buffer/backfill material was investigated. The adsorption coefficients of 237Np were determined for three kinds of bentonite under atmosphere and anoxic atmosphere. Further, it was studied that Kd values were affected by pH and CO32-. The results are shown as follows: (1) Distribution coefficients Kd under atmosphere: for mixed-bentonite is 47.3 mL/g, for Mg-bentonite 52.0 mL/g and for Ca-bentonite 42.4 mL/g; and the corresponding Kd under anoxic atmosphere: 89.3 mL/g, 38.8 mL/g and 29.0 mL/g, respectively. (2) When pH was lower than 9.2, Kd of the mixed-bentonite increased with the increase of pH and the maxi-mumt Kd value appeared at pH 9.2. (3) Kd of the mixed-bentonite got lower in high carbonate concentration when the total neptunium concentration was smaller than the solubility of NaNpO2CO3. (author)

  19. Modelling interaction of deep groundwaters with bentonite and radionuclide speciation

    International Nuclear Information System (INIS)

    In the safety analysis recently reported for a potential Swiss high-level waste repository, radionuclide speciation and solubility limits are calculated for expected granitic groundwater conditions. With the objective of deriving a more realistic description of radionuclide release from the near-field, an investigation has been initiated to quantitatively specify the chemistry of the near-field. In the Swiss case, the main components of the near-field are the glass waste-matrix, a thick steel canister horizontally emplaced in a drift, and a backfill of highly compacted sodium bentonite. This report describes a thermodynamic model which is used to estimate the chemical composition of the pore water in compacted sodium bentonite. Solubility limits and speciation of important actinides and the fission product technetium in the bentonite pore water are then calculated. The model is based on available experimental data on the interaction of sodium bentonite and groundwater and represents means of extrapolation from laboratory data to repository conditions. The basic reactions between sodium bentonite and groundwater are described by an ion-exchange model for sodium, potassium, magnesium, and calcium. The model assumes equilibrium with calcite as long as sufficient carbonates remain in the bentonite, as well as quartz saturation. It is calculated that the pore water of compacted sodium bentonite saturated with Swiss Reference Groundwater will have a pH value of 9.7 and a free carbonate activity of 8x10-4 M. The long-term situation is modelled by the assumption that the near-field of a deep repository behaves like a mixing tank. In this way, an attempt is made to account for the continuous water exchange between the near-field and the host rock. It is found that sodium bentonite will be slowly converted to calcium bentonite. This conversion is roughly estimated to be completed after 2 million years

  20. Effects of polyethyleneimine adsorption on rheology of bentonite suspensions

    Indian Academy of Sciences (India)

    A Alemdar; N Öztekin; F B Erim; Ö I Ece; N Güngör

    2005-06-01

    The influence of the cationic polymer, polyethyleneimine polymer (PEI) on the flow behaviour of bentonite suspensions (2%, w/w), was studied. XRD, zeta potential and adsorption studies were done together with rheological measurements. The addition of PEI at concentration ranges of 10-5–4.5 g/l and their rheological properties and stability of bentonite suspensions were studied. The adsorption rates for the bentonite suspensions are very fast. The XRD results showed that the PEG molecules did not intercalate into the layers of the clay.

  1. Diffusion of chloride and uranium in compacted sodium bentonite

    International Nuclear Information System (INIS)

    The authors discuss the measurement of sorption and diffusion of chloride (Cl-36) and uranium in compacted sodium bentonite MX-80. No sorption was observed in the sorption tests, however, in the diffusion tests slight sorption of uranium was noticed. The diffusivities of Cl-36 were found to be strongly dependent on the compaction of bentonite and on the salt concentration of the solution. Ion-exclusion can propably explain these phenomena. The diffusivities of uranium were also strongly dependent on the compaction of bentonite. Uranium shows features of both ion-exclusion and sorption

  2. Water uptake and stress development in bentonites and bentonite-sand buffer materials

    International Nuclear Information System (INIS)

    The development of swelling pressure and the transfer of pore water pressures through dense bentonite and bentonite-sand materials are examined in this report. This report focuses on the swelling pressure and total pressure developed in initially unsaturated specimens allowed access to free water on one end. The bentonite in this wetted region rapidly develops its full swelling pressure and this pressure is transferred upwards through the specimen. Hence, the bentonite plug will exert a pressure approximately equivalent to the swelling pressure even though only a small region of the plug is actually saturated. A number of specimens were tested with total pressure sensors mounted normal and parallel to the axis of compaction. Lateral pressures developed long before the wetting front reached sensor locations, suggesting stress transfer through the unsaturated portions of these specimens. On achieving saturation, specimens were found to have similar swelling pressures both normal to and parallel to the axis of compaction. This indicates that there is little or no specimen anisotropy induced by the compaction process. Tests were conducted on specimens allowed only to take on a limited quantity of water and it was found that density anisotropy was induced as the result of the swelling pressures generated by the buffer. The wetted skin of buffer developed a considerable pressure and compressed a region of buffer immediately above the wetted region. The results suggest that the buffer material placed in a disposal vault will rapidly develop and transfer swelling pressures as a result of the saturation of a limited region or 'skin' within the emplacement site. The total pressure ultimately present on the container surface should be the sum of the swelling and hydraulic components. (author). 14 refs., 4 tabs., 8 figs

  3. Comparison of the mineralogical composition, physical, swelling and hydraulic properties of untreated sodium bentonites from Canada, the United States and Japan

    International Nuclear Information System (INIS)

    A large variety of commercial grade sodium bentonite products are available from suppliers in North America and Japan. This report generally characterizes the products available for environmental engineering applications. A compilation of the swelling capacity and hydraulic properties of the available products, together with their basic mineralogical composition, physical and engineering properties is presented. This report identifies the range of materials available commercially and documents the basic physical properties of these products. The geological origins and locations of bentonite-ore deposits are discussed with reference to the availability and variability of this material. The hydraulic and swelling characteristics of 17 different bentonite products from 9 different producers were compared. Considerable variation was noted in the free-swell capacity of these clays but this was not reflected in the swelling pressure or hydraulic conductivity of densely compacted specimens. The density -hydraulic conductivity relationship was found to be independent of product for untreated sodium bentonite clays with hydraulic conductivity decreasing with increasing clay density (for materials tested at high (>500) hydraulic gradients). A large body of hydraulic conductivity data was obtained from the literature to supplement the data generated by this study. The literature values further supported the results of this study. Hydraulic conductivity and swelling pressure performance at high density are consistent when sodium bentonites of similar quality are densely compacted prior to use. (author) 27 refs., 5 tabs., 17 figs

  4. Nuevas evidencias de cazadores recolectores terrestres del Holoceno medio y tardío en Tierra del Fuego : el sitio Cabo Monmouth 20.

    OpenAIRE

    Morello, Flavia; Arroyo-Kalin, Manuel; Borrero, Luis; Torres, Jimena; Massone, Mauricio; Cárdenas, Pedro; Bahamonde, Gabriel

    2009-01-01

    The Cabo Monmouth 20 site represents new evidence of Middle and Late Holocene occupations (ca. 5.000 years BP) for the north of Isla Grande, Tierra del Fuego. In this paper we evaluate archaeo- logical evidence from a test pit excavation, synthesize stratigraphic and contextual data, and present a new radiocarbon date (5,520 + 50 years BP) on shell material of anthropic origin. The latter confrms the antiquity of the site, highlighting the presence of archaeological deposits in...

  5. Optimizing soil and water management in dryland farming systems in Cabo Verde

    NARCIS (Netherlands)

    Santos Baptista Costa, Dos I.

    2016-01-01

     “Optimizing Soil and Water Management in Dryland Farming Systems in Cabo Verde” Isaurinda Baptista Summary Soil and land degradation poses a great challenge for sustainable development worldwide and, in Cabo Verde, has strongly affected both people

  6. Study of retention mechanism of selenite on Ca/Mg bentonite

    International Nuclear Information System (INIS)

    untreated and treated bentonite B75 and its components probably responsible for selenite retention. The crushed Ca/Mg bentonite B75 originated from Rokle deposit was characterized by X-Ray Fluorescence and X-Ray Diffraction. The major mineral constituents of used bentonite are (wt %): montmorillonite (75), quartz (8), illite (4) and calcite (4). By removal of carbonates and conversion to Na and Ca ionic forms were prepared the samples of Na-B75 and Ca-B75. Montmorillonite Saz-1 (Ca-Mont), Swy-2 (Na-Mont) from the Clay Mineral Society repository and CaCO3 were used without further pre-treatment. Batch experiments were performed at m/V ratio equal to 1:10 in two liquid phases containing sodium selenite in concentration of 2 x 10-5 mol/L in 0.01 mol/L NaCl or in 0.1 mol/L NaCl. The pH was adjusted at similar pH as suspensions of untreated bentonite B75 by addition of appropriate volume of 1 mol/L NaOH solution. Suspensions were shaken for 14 days and the solid and liquid phases were subsequently separated by centrifugation. The pH and conductivity were measured in supernatant solutions. The concentration of selenium in aliquots was analyzed by inductively coupled plasma mass spectrometry. Montmorillonite contributes to the selenite retention more significantly than CaCO3. Selenite uptake by Ca montmorillonite was greater than that by Na montmorillonite and untreated bentonite, but merely in 0.01 mol/L NaCl. As can be seen, carbonates removal from the bentonite resulted in an intense increase in selenite uptake by treated bentonite samples regardless of the form. From all phases remaining after purification, clay and iron minerals seemed to be the most reactive phases for selenite retention. The results show that selenite retention is supported by the increase of ionic strength on all used solid phases. This effect can be caused by an enhancement of dissolution of some minerals containing calcium, which is then available in the liquid phase for possible selenite retention

  7. Experimental Setup to Characterize Bentonite Hydration Processes

    International Nuclear Information System (INIS)

    We present an experimental setup to follow-up the hydration process of a bentonite. Clay samples, of 2 cm x 12 cm x 12 cm, were made and introduced in a Hele-Shaw cell with two PMM windows and two steel frames. In hydration experiments, a fluid enters by an orifice in the frame, located both at the top and the bottom of the cell, to perform hydration in both senses. To get a uniform hydration we place a diffuser near the orifice. Volume influxes in hydration cells are registered in time. The evolution of the developed interface was recorded on a videotape. The video cameras was fixed to a holder so that the vertical direction in the monitor was the same as the direction of the larger extension of the cell. (Author) 6 refs

  8. Buffer construction technique using granular bentonite

    International Nuclear Information System (INIS)

    Buffer construction using bentonite pellets as filling material is a promising technology for enhancing the ease of repository operation. In this study, a test of such technology was conducted in a full-scale simulated disposal drift, using a filling system which utilizes a screw conveyor system. The simulated drift, which contained two dummy overpacks, was configured as a half-cross-section model with a height of 2.22 m and a length of 6.0 m. The average dry density of the buffer obtained in the test was 1.29 Mg/m3, with an angle of repose of 35 to 40 degrees. These test results indicate that buffer construction using a screw conveyor system for pellet emplacement in a waste disposal drift is a promising technology for repositories for high level radioactive wastes. (author)

  9. Influence of seawater on swelling characteristics of bentonite buffer material

    International Nuclear Information System (INIS)

    High-level-radioactive-waste disposal facility can be built on the coastal area. One reason is that transportation of the wastes is easy. Groundwater in the coastal zone which flows into disposal pit contains large amount of seawater salts. So, it is important to investigate the influence of seawater on bentonite buffer material which is one of the Barrier materials in the nuclear disposal facility. The purpose of this study is to investigate the influence of artificial seawater on swelling pressure and swelling deformation characteristics of five typical kinds of bentonites. Various factors, such as density, montmorillonite contents, sort of exchangeable-cation of the bentonite have been investigated. This experimental works clarified the some factors for which the influence of artificial sea water on swelling characteristics of bentonite depends. Based on experimental results, a specification for the buffer material which can overcome the influence of seawater was defined. (author)

  10. Diffusion of Fission Product Elements in Compacted Bentonite

    International Nuclear Information System (INIS)

    Study on diffusion of fission product in compacted bentonite has been conducted. The information about mobilities of these elements have been obtained from the studies resulted in many countries. It is presented that the diffusion coefficient was varied by the function of solution phase condition as well as the nature of bentonite. It is also showed that the diffusion coefficient decreased by the increasing of density, as well as the increasing of montmorillonite content in bentonite. The ratio of bentonite/silica-sand used, was related to the increasing of elements mobility. In many case variation of diffusion coefficient was related to the variation of pH, redox condition, and the presence of complex ant in solution phase. The lower diffusion coefficient could give the higher retardation factor, which is a favorable factor to retard the radionuclides release from a disposal facility to geosphere. (author)

  11. A study on the thermal conductivity of compacted bentonites

    CERN Document Server

    Tang, Anh-Minh; Le, Trung Tinh; 10.1016/j.clay.2007.11.001

    2008-01-01

    Thermal conductivity of compacted bentonite is one of the most important properties in the design of high-level radioactive waste repositories where this material is proposed for use as a buffer. In the work described here, a thermal probe based on the hot wire method was used to measure the thermal conductivity of compacted bentonite specimens. The experimental results were analyzed to observe the effects of various factors (i.e. dry density, water content, hysteresis, degree of saturation and volumetric fraction of soil constituents) on the thermal conductivity. A linear correlation was proposed to predict the thermal conductivity of compacted bentonite based on experimentally observed relationship between the volumetric fraction of air and the thermal conductivity. The relevance of this correlation was finally analyzed together with others existing methods using experimental data on several compacted bentonites.

  12. Modified Ponorogo bentonite for the removal of ampicillin from wastewater.

    Science.gov (United States)

    Rahardjo, Andi Kurniawan; Susanto, Maria Josephine Jeannette; Kurniawan, Alfin; Indraswati, Nani; Ismadji, Suryadi

    2011-06-15

    The adsorption of ampicillin onto natural and organo-bentonite was studied. Organo-bentonite was obtained by modifying the natural bentonite obtained from Ponorogo, Indonesia, using CTAB surfactant by microwave heating. The temperature dependent form of the Langmuir, Freundlich, Sips and Toth equations was employed to correlate equilibrium data. Based on the evaluation of the physical meaning of fitted isotherm parameters of each model, it is clear that Toth equation can represent the equilibrium data better than other models. The adsorption performance of natural and organo-bentonite for the removal of ampicillin from pharmaceutical company wastewater was also studied. In real wastewater, both adsorbents could not completely remove the ampicillin due to the sorption competition with other substances which also present in the wastewater. PMID:21550716

  13. Simulation of Tracer Transport in Porous Media: Application to Bentonites

    International Nuclear Information System (INIS)

    We present a formal framework to describe tracer transport in heterogeneous media, such as porous media like bentonites. In these media, mean field approximation is not valid because there exist some geometrical constraints and the transport is anomalous. (Author)

  14. Evaluation of brazilian bentonites as additive in the radwaste cementation

    International Nuclear Information System (INIS)

    The behavior of some Brazilian bentonites has been evaluated, concerning to their use as additive in the radwaste cementation. The purpose of the bentonite is to retain the radioelements in the final product in leaching process. Experiments to determine properties such as compressive strenght, viscosity, set time leaching and cesium sorption have been carried out to this evaluation. After one-year test, the results show that the bentonites greatly reduce the cesium release. A literature survey about cementation process and plants and about the cement product characteristics has been made in order to obtain a reliable final product, able to be transported and storaged. Some leaching test methods and mathematical models, that could be applied in the evaluation of cement products with bentonite have been evaluated. (author)

  15. Current status of mechanical erosion studies of bentonite buffer

    International Nuclear Information System (INIS)

    The performance of the bentonite buffer in KBS-3-type nuclear waste repository concept relies to a great extent on the buffer surrounding the canister having sufficient dry density. Loss of buffer material caused by erosion remains as the most significant process reducing the density of the buffer. The mechanical erosion, or pre-saturation erosion, is the process where flowing groundwater transports buffer material away from the deposition hole towards the deposition tunnel. This process reduces the overall buffer density and potentially creates localized regions of low density. In the worst case the process is assumed to last as long as the free volume between the pellets in the pellets filled regions is filled with groundwater. With fixed environmental and material parameters a set of experiments was performed, testing the erosive properties of different buffer and backfill materials (MX-80 and Friedland Clay) in different groundwater conditions. The method used was a pinhole erosion test using two sizescales; 100 mm and 400 mm of cell length. The purpose of the pinhole tests was to test the scenario where piping channel is formed in the buffer and water flows through a single channel. The erosion data was produced with two methods, firstly the time-related erosion rates measured in-situ during the measurement and secondly the overall mass loss in the sample cell measured after dismantling of the test. It was observed that erosion in piping channels decreases rapidly (∼24 h) and irreversibly to a level that is an order of magnitude lower than the peak values. (orig.)

  16. LABORATORY TESTING OF BENTONITE CLAYS FOR LANDFILL DESIGN AND CONSTRUCTION

    OpenAIRE

    Biljana Kovačević Zelić; Dubravko Domitrović; Želimir Veinović

    2007-01-01

    Top and bottom liners are one of the key construction elements in every landfill. They are usually made as compacted clay liners (CCLs) composed of several layers of compacted clay with strictly defined properties or by the use of alternative materials such as: GCL – geosynthetic clay liner, BES – bentonite enhanced soils or bentonite/polymer mixtures. Following the state of the art experiences in the world, GCLs are used in Croatian landfills for several years, as well. Depending upon the lo...

  17. The Effect of Bentonite on External Corrosion of Well Casings

    OpenAIRE

    Orayith, Mohammed

    2012-01-01

    ABSTRACTThe overall goal of this research is concerned with understanding the effects of bentonite on the external corrosion of bare mild steel well casing. Na-bentonite is mainly used in enormous amounts in drilling processes, so it used as the main electrochemical environment surrounding the casing at different condition. The major part of the current study was divided into 3 stages; the first stage is constant current cathodic protection (CP) with a range of 0.0 (Open Circuit Potential) to...

  18. The interaction of bentonite and glass with aqueous media

    International Nuclear Information System (INIS)

    It has been demonstrated that Si(OH)4 is an important constituent of bentonite. In bentonites natural state the Si(OH)4 in the bentonite is permeable to the diffusible components of the aqeous medium in contact with it. As a consequence, the pH of the medium is a sensitive function of its ionic strength. Permeability of the Si(OH)4 to salt is lost, however, by pretreatment of the bentonite with dilute acid to protonate fully the Si(OH)4. The pH-producing property of the Si(OH)4 then is associated with its surface properties. The glasses (ABS-39 and ABS-Y Marcoule) studied in this research program also contain hydroxylated oxide as an important constituent. These materials, however, are not observed to exhibit gel-like (three-dimensional) properties prior to or after acid pretreatment. Instead they function always as a surface (two-dimensional) and are impermeable to the diffusible components of the aqueous media that come in contact with them. As a result, the pH of the medium is depentdent on ionic strength only so far as it affects the counter-ion screening efficiency of the charged surface. In both systems, bentonite and glass, the pH of the medium is affected by the presence of CO2. The lowering of medium pH by CO2 dissolution results in the neutralization of Si(OH)4 in the untreated bentonite gel phase or in the surface of the acid pretreated bentonite or glass in contact with the medium. If glass and bentonite are in contact the action of CO2 at their interface results in both systems striving to reach different equilibria. The result is enhanced chemical reactivity at the interface. To minimize such reactivity CO2 must be excluded from the atmosphere in contact with the solid-liquid phases. (author)

  19. Unified theory for swelling deformation and swelling pressure of bentonite

    International Nuclear Information System (INIS)

    The correlation of the water volume to vertical overburden pressure (p) is obtained as Vw/ Vm=KÞDs-3 for bentonite with fractal-textured surface. The maximum swelling strain is predicted according to the correlation of the water volume to vertical overburden pressure. The predictions of the maximum swelling strain and swelling pressure are in satisfactory agreement with the experimental data of Tsukinuno and Wyoming bentonite. (authors)

  20. Effect of activation on swelling property in Ca-bentonite

    International Nuclear Information System (INIS)

    Compacted bentonite is attracting greater attention as buffer material for deep geological repository of high-level radioactive waste under current design concept. Swelling behavior is a significant property in achieving the low-permeability sealing function. The potential buffer material used is a locally available clayey material known as Zhisin clay in Taiwan. Zhisin clay is a Ca-type bentonite. Experimental data indicated that the swelling potential of Zhisin clay is much lower than that of Na-bentonite due to its exchangeable cation type and capacity. To enhance the swelling potential of Zhisin clay, a cation exchange process by addition of Na2CO3 powder is introduced in this research. Addition of Na2CO3 reagent to Zhisin clay caused precipitation of CaCO3 to occur and induced a replacement of Ca2+ ions by Na+ ions on the surface of bentonite in liquid phase. Experimental results show that Na2CO3-activated Zhisin clay is superior in swelling potential to untreated Zhisin clay. Due to the ion exchange hysteresis, activated bentonite shows different type of time-swell curve from traditional sigmoid-shaped curve. The optimal amount of Na2CO3 addition is found to be 1%, and the maximum swelling strain was found to be 3 times as much as that of untreated Zhisin clay. The Na2CO3 -activated Zhisin clay exhibited improved resistance to thermal environments and behaved similar to the Na-type bentonites under different hydrothermal temperatures. (authors)

  1. Chitosan/bentonite bionanocomposites: morphology and mechanical behavior

    International Nuclear Information System (INIS)

    This study chitosan/bentonite bionanocomposite films were prepared by solution intercalation process, seeking to investigate the effect of the chitosan/bentonite ratio (5/1 e 10/1) on the morphology and mechanical behavior of the bionanocomposites. It was used as nanophase, Argel sodium bentonite (AN), was provided by Bentonit Uniao Nordeste-BUN (Campina Grande, Brazil) and as biopolymer matrix the chitosan of low molecular weight and degree of deacetylation of 86,7% was supplied by Polymar (Fortaleza, Brazil). The bionanocomposites was investigated by X-ray diffraction and tensile properties. According to the results, the morphology and the mechanical behavior of the bionanocomposite was affected by the ratio of chitosan/bentonite. The chitosan/bentonite ratio (5/1 and 10/1) indicated the formation of an intercalated nanostructure and of the predominantly exfoliated nanostructure, respectively. And the considerable increases in the resistance to the traction were observed mainly for the bionanocomposite with predominantly exfoliated morphology. (author)

  2. Behaviour of bentonite accessory minerals during the thermal stage

    Energy Technology Data Exchange (ETDEWEB)

    Arcos, David; Bruno, Jordi [Enviros-QuantiSci, Barcelona (Spain); Benbow, Steven; Takase, Hiro [Quintessa Limited, Henley-on-Thames (United Kingdom)

    2000-03-15

    This report discusses in a quantitative manner the evolution of the accessory minerals in the bentonite as a result of the thermal event exerted by the spent fuel in the near field. Three different modelling approaches have been used and the results compared between them. The three different approaches have been calculated using two Differential Algebraic Equation (DAE) solver: DYLAN (Model-1) and the Nag DAE solver, d02ngf (Model-2) and the third approach (Model-3) using the last version of PHREEQC. The results from these calculations indicate the feasibility of the modelling approach to model the migration of bentonite accessory minerals and relevant aqueous species throughout the thermal gradient. These calculations indicate that the migration of quartz and quartz polymorphs is a lesser problem. The aqueous speciation of Ca in the bentonite pore water is fundamental in order to define the potential migration of anhydrite during the thermal stage. If CaSO{sub 4}(aq) is the predominant aqueous species, then anhydrite dissolves at the initial groundwater migration times through bentonite. However, if Ca{sup 2+} is considered to be the dominant Ca species at the bentonite pore water, then anhydrite migrates towards the clay/granite interface. This is the main difference in the chemical systems considered in the three model approaches used in this work. The main process affecting the trace mineral behaviour in bentonite is cation exchange. This process controls the concentration of calcium, which results in a direct control of the calcite precipitation-dissolution.

  3. The oolitization rate determination of bentonite moulding mixtures

    Directory of Open Access Journals (Sweden)

    F. Miksovsky

    2008-07-01

    Full Text Available Bentonite mixtures belong and will always belong among the most widespread sand mixtures for the “green sand” technology of castings production. This technology’s essential advantage is bentonite mixtures application reversibility in the closed circulation after composition modifications and circulation losses replenishment. After the casting of a mould, the surrounding sand mixture is strained by the solidifying casting heat and bentonite degradation occurs. In case of appropriate conditions the oolitization occurs. This phenomenon is specific only for bentonite-bonded mixtures. The oolitization of opening material silica grains brings a number of negative as well as positive features with it. It is not only a technological problem but economical and ecological as well because for minimization of mixture regeneration with a help of new sand it is necessary to know bentonite mixtures quality control tools even in term of the oolitization rate. This paper deals with the description of undemanding physical method of the oolitization rate evaluation with a help of powder density assessment and its examination with actual sand mixtures which were obtained from the Czech Republic foundry plants. There are foundry plants of heavier weight castings and in one case there was an operation where bentonite mixtures regeneration was applied. Moreover, the oolitization effect on metal penetration in test castings was verified.

  4. Modelling of long term geochemical evolution and study of mechanical perturbation of bentonite buffer of a KBS-3 repository

    Energy Technology Data Exchange (ETDEWEB)

    Marsal, Francois; Pellegrini, Delphine; Deleruyelle, Frederic; Serres, Christophe (French Institute for Radiological Protection and Nuclear Safety (IRSN) (FR)); Windt, Laurent de (Paris School of Mines (ENSMP) (FR))

    2008-03-15

    The Swedish Nuclear Fuel and Waste Management Co. (SKB) has recently completed a safety assessment project named SR-Can, related to the KBS-3 disposal concept. In this concept, the waste packages are surrounded by a buffer made of either MX-80 or Deponit CA-N bentonite. Interactions between the buffer and groundwater may modify the buffer composition and thus its containment properties. The Swedish Radiation Protection Authorities (SSI) requested the French Institute for Radiological Protection and Nuclear Safety (IRSN) to perform the present study in support of SSI review of the SR-Can report. The purpose is to assess the geochemical evolution of both potential buffer materials due to the intrusion of different types of groundwater, with a similar modelling layout to that reported in SR-Can. Three main categories of water inflows via a fracture intersecting a deposition hole are considered: the Forsmark reference groundwater, a high-salinity groundwater to account for up-rise of deep-seated brines and a diluted water representing ice-melting derived groundwater. In addition to this, the redox buffering capacity of Deponit CA-N bentonite and the thermal effect on MX-80 bentonite geochemistry have been assessed. This modelling work has been performed using the reactive transport modelling code HYTEC. The main outcome of the present study is that the intrusion of the considered groundwaters should not affect drastically the geochemistry of neither the Deponit CA-N nor the MX-80 bentonite on the long-term (100,000 y). Bentonite pH may reach high values (up to 10.5) in some cases but does not reach SKB criterion value related to bentonite chemical stability. Dissolution-precipitation of accessory minerals is not significant enough to induce important porosity changes (rise by maximum 2 %). Globally, the montmorillonite exchanger undergoes Na by Ca partial replacement, which may decrease the swelling pressure of the bentonite. The simulated intrusion of oxidizing waters

  5. Modelling of long term geochemical evolution and study of mechanical perturbation of bentonite buffer of a KBS-3 repository

    International Nuclear Information System (INIS)

    The Swedish Nuclear Fuel and Waste Management Co. (SKB) has recently completed a safety assessment project named SR-Can, related to the KBS-3 disposal concept. In this concept, the waste packages are surrounded by a buffer made of either MX-80 or Deponit CA-N bentonite. Interactions between the buffer and groundwater may modify the buffer composition and thus its containment properties. The Swedish Radiation Protection Authorities (SSI) requested the French Institute for Radiological Protection and Nuclear Safety (IRSN) to perform the present study in support of SSI review of the SR-Can report. The purpose is to assess the geochemical evolution of both potential buffer materials due to the intrusion of different types of groundwater, with a similar modelling layout to that reported in SR-Can. Three main categories of water inflows via a fracture intersecting a deposition hole are considered: the Forsmark reference groundwater, a high-salinity groundwater to account for up-rise of deep-seated brines and a diluted water representing ice-melting derived groundwater. In addition to this, the redox buffering capacity of Deponit CA-N bentonite and the thermal effect on MX-80 bentonite geochemistry have been assessed. This modelling work has been performed using the reactive transport modelling code HYTEC. The main outcome of the present study is that the intrusion of the considered groundwaters should not affect drastically the geochemistry of neither the Deponit CA-N nor the MX-80 bentonite on the long-term (100,000 y). Bentonite pH may reach high values (up to 10.5) in some cases but does not reach SKB criterion value related to bentonite chemical stability. Dissolution-precipitation of accessory minerals is not significant enough to induce important porosity changes (rise by maximum 2 %). Globally, the montmorillonite exchanger undergoes Na by Ca partial replacement, which may decrease the swelling pressure of the bentonite. The simulated intrusion of oxidizing waters

  6. On the presence of upper paleocene rocks in the foreland succession at Cabo Nariz, Tierra del Fuego, Chile: Geology and new palynological and U-Pb data

    International Nuclear Information System (INIS)

    On the west coast of Tierra del Fuego, south of Cabo Nariz, in Chile, Upper Cretaceous to Paleocene sedimentary successions of the Magallanes foreland basin crop out. The presence of dinoflagellate cysts, as well as radiometric U-Pb SHPJMP dating of detrital zircons, indicate that this succession ranges from the Campanian to Thanetian (Late Paleocene) in age. The base of the exposed sedimentary succession comprises siltstones of external platform facies (Cerro Cuchilla Formation), which are thrust over the Cabo Nariz Beds. The latter fonnation is divided into two members: a lower siltstone-dominated turbidite facies member and an upper member of sandstone-dominated turbidites, with sandstone and conglomerate channel facies. The presence of dinocysts in the Cerro Cuchilla Formation suggests a late Campanian to early Danian age. The fossil content in the Cabo Nariz Beds indicate a Selandian (Middle Paleocene) depositional age in accordance with the detrital zircon ages which provide a maximum possible Campanian age (76.5±0.7 Ma), and very close to the Thanetian (Late Paleocene) (57.6±1 Ma) depositional ages for the lower and upper member, respectively. The sedimentary succession of Cabo Nariz Beds, is interpreted as a north-northwest prograding submarine fan of middle to Late Paleocene age. It is considered to represent the deposition of detritus derived from an uplifting orogen located to the south. The detrital zircon age spectra suggest that there was a period of low intensity of magmatic activity in the source area around the K-T boundary

  7. Study on Preparation and Properties of Grease Based on Ultraifne Bentonite Powder

    Institute of Scientific and Technical Information of China (English)

    Wang Jing; Guo Xiaochuan; Jiang Mingjun; He Yan

    2016-01-01

    The feasibility for preparation of ultraifne bentonite powder by different milling methods was studied. And the comparison of comprehensive performance between ultraifne bentonite grease and traditional bentonite grease was also investigated. The results indicated that the statistic Z-average size of ultraifne bentonite prepared by sand milling was 250 nm with a narrow size distribution and the lattice structure of ultraifne bentonite maintained good character despite a slight distortion occasioned. The mechanical stability, colloid stability, antiwear ability and friction-reducing property of ultraifne bentonite grease were superior to the traditional one.

  8. Geochemical investigation of iron transport into bentonite as steel corrodes

    International Nuclear Information System (INIS)

    In Sweden and Finland, it is proposed that spent nuclear fuel will be encapsulated in sealed cylindrical canisters, for disposal in a geologic repository, either in vertical boreholes (KBS-3V) or in long horizontal boreholes (KBS-3H). The canisters will consist of a thick cast iron insert and a copper outer container, and each canister will be surrounded by a compacted bentonite clay buffer. It is important to investigate the possible consequences if a failure of these physical barriers was to occur. For instance, if mechanical failure of the copper outer container were to occur then groundwater could enter the annulus and reach the cast iron insert. This would result in anaerobically corroded iron from the cast iron insert interacting with the bentonite surrounding the canisters. The presence of anaerobically corroded iron in groundwater raises the question of how the bentonite will be affected by this process. In the case of the KBS-3H concept, mechanical failure of the copper outer container could lead to interaction between anaerobically corroded iron and bentonite, as above. However, direct contact between anaerobically corroding carbon steel and bentonite is also likely because of the presence of perforated carbon steel support structures in the long horizontal boreholes. As part of the NF-PRO project, an extensive experimental programme has been carried out over several years to study the interactions between anaerobically corroding carbon steel or cast iron and bentonite. The purpose of this report is to describe the modelling work that has been carried out, and the conclusions that have been reached. The experimental programme has carried out a series of long term experiments looking at anaerobic corrosion of carbon steel or cast iron in compacted MX80 bentonite at 30 deg C or 50 deg C. In the bentonite the concentration of iron decreased with increasing distance away from the iron-bentonite interface, with local iron concentrations as high as 20 wt % in

  9. Modification of bentonite with cationic surfactant for the enhanced retention of bisphenol A from landfill leachate.

    Science.gov (United States)

    Li, Yi; Jin, Fenglai; Wang, Chao; Chen, Yunxiao; Wang, Qing; Zhang, Wenlong; Wang, Dawei

    2015-06-01

    Bentonite was modified with cationic surfactant hexadecyl trimethyl ammonium bromide (HTAB) as landfill liner to retard the transportation of bisphenol A (BPA) for the first time. The modification was confirmed to form a lateral bi-layer in the interlayer space of bentonite by scanning electron microscope, X-ray diffraction, and Fourier transform infrared spectroscopy. The introduction of HTAB into the internal position of bentonite led to an increased interlayer space of bentonite from 15.0 to 20.9 Å and a higher sorption affinity for BPA (10.449 mg/g of HTAB-bentonite and 3.413 mg/g of raw bentonite). According to the Freundlich model, the maximum adsorption capacity of the HTAB-bentonite was found to be 0.410 mg/g. The sorption capacity of raw bentonite and HTAB-bentonite both decreased at alkaline conditions. Although the hydraulic conductivity of HTAB-bentonite was higher than that of raw bentonite, results of laboratory permeability and column tests indicated that HTAB-bentonite obviously extended the BPA breakthrough time by 43.4 %. The properties of the HTAB-bentonite revealed its notable advantages as components of landfill liners material to retain BPA in leachate. PMID:25874420

  10. Sobre o escândalo político em Cabo Verde

    OpenAIRE

    Anjos, José Carlos dos

    2015-01-01

    Cabo Verde será realmente um país com condições excepcionais de transparência, como é geralmente reconhecido pela comunidade internacional ? Os governantes cabo-verdeanos fizeram sempre questão de se apresentarem como uma excepção em África. Ora, podemos interrogar-nos sobre as condições sociais de sucesso das denúncias da grande corrupção em Cabo Verde e sobre o quadro moral instaurado à volta dos assuntos de Estado desde a abertura ao multipartidarismo. Uma análise dos principais escândalos...

  11. Geochemical evolution of the Fe/Febex bentonite interface under simultaneous hydration and heating

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. Carbon steel canister and compacted bentonite have been proposed as overpack and sealing materials for the engineered barrier system (EBS). This work reports the results of an experimental work designed to investigate the geochemical processes occurring in the canister/FEBEX bentonite interface during pre-saturation phase of a deep geological disposal. Corrosion behaviour of the canister depends strongly on the evolution of environmental conditions. In this way, moisture conditions at the canister surface will dictate the mechanism and extension of the corrosion process, as well as during the gradual saturation of the near-field, deliquescence of salts and other impurities could favour the initialization of localized corrosion. Therefore, saline fronts are expected to be formed during the saturation of the clay barrier and chloride and sulphate could move by advective transport towards the metallic container due to the hydraulic and thermal gradients that will be established along the bentonite barrier, compromising canister performance. In the tests bentonite was subjected simultaneously to constant hydration and heating, in opposite directions, in order to simulate the conditions of the clay barrier in the repository and better understand the coupled THMC (Thermo-Hydro-Mechanical-Chemical) processes that can affect the performance of the bentonite barrier or the metallic container. The tests were performed in cylindrical cells with an internal diameter of 70 mm and an inner length of 100 mm in which compacted FEBEX bentonite (1.65 g/cm3) and Fe powder were placed. They were made out of Teflon to prevent as much as possible lateral heat conduction. Externally, stainless steel 316 L rings avoid the deformation caused by the swelling of bentonite. The upper closing of the cells was made by means of a stainless steel plug. Inside this plug there was a deposit in which water circulated at room temperature. The bottom

  12. Effects of bentonite and yeast extract as nutrient on decrease in hydraulic conductivity of porous media due to CaCO3 precipitation induced by Sporosarcina pasteurii.

    Science.gov (United States)

    Eryürük, Kağan; Yang, Suyin; Suzuki, Daisuke; Sakaguchi, Iwao; Katayama, Arata

    2015-10-01

    The reduction mechanism of hydraulic conductivity was investigated in porous media treated with bentonite and CaCO3 precipitates induced by growing cells of Sporosarcina pasteurii (ATCC 11859). Bentonite, the bacterial cells, and a precipitation solution, composing of 0.5 M CaCl2 and 0.5 M urea with or without 2% weight/volume yeast extract allowing the bacterial growth were sequentially introduced into the continuous-flow columns containing glass beads between 0.05 and 3 mm in diameter. The treatments reduced the hydraulic conductivity of the columns from between 8.4 × 10(-1) and 4.1 × 10(-3) cm/s to between 9.9 × 10(-4) and 2.1 × 10(-6) cm/s as the lowest. With yeast extract, the conductivity continuously decreased during four days of the experiment, while became stable after two days without yeast extract. Introduction of the bacterial cells did not decrease the conductivity. The reduction in hydraulic conductivity was inversely correlated with the volume occupied by the depositions of bentonite and CaCO3 precipitates in column, showing the same efficiency but a larger effect of the CaCO3 precipitates with increasing volume by bacterial growth. The smaller glass beads resulted in larger volume of the depositions. Bentonite increased the deposition of CaCO3 precipitates. Analysis using the Kozeny-Carman equation suggested that without yeast extract, bentonite and the CaCO3 precipitates formed aggregates with glass beads, thus increasing their diameter and consequently decreasing the pore size in the column. With yeast extract, in addition to the aggregates, the individual CaCO3 precipitates formed separately from the aggregates reduced the hydraulic conductivity. PMID:25736267

  13. Diffusion in crushed rock and in bentonite clay

    International Nuclear Information System (INIS)

    Diffusion theories for porous media with sorption are reviewed to serve as a basis for considering diffusion in simple systems like sand of crushed rock. A Fickian diffusion and linear sorption model is solved both by analytical Laplance transform and Green's function methods and by numerical methods, and then applied to small-scale experiments for Finnish low- and medium-level operating waste repositories. The main properties of bentonite are reviewed. The hydraulic conductivity of compacted bentonite is so low that the major transport mechanism is diffusion. A Fickian diffusion and linear sorption model is applied to bentonite. The main component of bentonite, montmorillonite, has a high ion-exchange capacity and thus, transport in bentonite consists of interactive chemical and diffusion phenomena. A chemical equilibrium model, CHEQ, is developed for ion-exchange reactions in bentonite water systems. CHEQ is applied to some bentonite experiments with success, especially for monovalent ions. The fitted log-binding constants for sodium exchange with potassium, magnesium, and calcium were 0.27, 1.50, and 2.10, respectively. A coupled chemical and diffusion model, CHEQDIFF, is developed to take account of diffusion in pore water, surface diffusion and ion-exchange reactions. The model is applied to the same experiments as CHEQ, and validation is partly successful. In the diffusion case, the above-mentioned values for binding constants are used. The apparent diffusion (both anions and cations) and surface diffusion (only for cations) constants used are 3.0*10-11 m2/s and 6.0*10-12 m2/s, respectively, but these values are questionable, as experimental results good enough for fitting are not available. (orig.). (74 refs., 27 figs., 12 tabs.)

  14. Field test of ethanol/bentonite slurry grouting into rock fracture

    International Nuclear Information System (INIS)

    Crystalline rocks have fractures which may cause unexpected routes of groundwater seepage. Cement grouting is one of the most effective methods to minimize seepage; however, cement materials may not be suitable for the purpose of extra-long durability, because cement is neutralized or degraded by chemical and physical influence of chemical reaction. Natural clay like bentonite is one of the most promising materials for seepage barrier; however, water/bentonite grout is so viscous that enough amount of bentonite can not be grouted into rock fractures. To increase bentonite content in grout with low viscosity, the utilization of ethanol as a mixing liquid was studied. Ethanol suppresses bentonite swelling, and more bentonite can be injected more than that of water/bentonite slurry. In this paper, grouting into in-situ rock mass fracture from the ground surface was tested to investigate the barrier performance and workability of ethanol/bentonite slurry as a grouting material. (author)

  15. Performance characteristics of EZhou bentonite of Hubei province and its modification

    Institute of Scientific and Technical Information of China (English)

    Long Wei; Fan Zitian; Hu Xueting

    2009-01-01

    Both the chemical compositions and performance characteristics of the bentonite raw ores in Ezhou area of Hubei province and Honghuoshan area of Liaoning province were compared and analyzed. The properties of these two kinds of bentonites were tested before and after Na+- and Li+-modification. The results show that the Ezhou bentonite ore possesses higher montmorillonite content than the Honghuoshan bentonite ore, but the Ezhou Na-bentonite has weaker castability (e.g. Wet compression strength and hot wet tensile strength) than the Honghuoshan Na-bentonite, while the performance of Ezhou Li-bentonite, such as colloid index, swelling value, swelling volume and mould coating performance, is equivalent to that of the Honghuoshan Na-bentonite.

  16. Thermic and thermodynamic properties of desorption process of essential oil of Hyssopus seravshanicus from bentonite clays

    International Nuclear Information System (INIS)

    It shown, that desorption process of essential oil of Hyssopus seravshanicus from bentonite clays include by four parts (lines) and the nature between essential oil of Hyssopus seravshanicus from bentonite clays is physical and chemical sorption

  17. Geochemical discrimination of the Upper Ordovician Kinnekulle Bentonite in the Billegrav-2 drill core section, Bornholm, Denmark

    Directory of Open Access Journals (Sweden)

    Tarmo Kiipli

    2014-12-01

    Full Text Available The content of the trace elements Ti, Nb, Zr and Th has been analysed in 34 Upper Ordovician bentonites from the Billegrav-2 drill core, Bornholm, Denmark. The section contains two 80–90 cm thick bentonites, which potentially may represent the Kinnekulle Bentonite, as well as several rather thick but composite bentonite layers with thin terrigenous shale interbeds. Comparison of the four immobile trace elements with data from the Kinnekulle Bentonite reported from other locations in Baltoscandia indicate that the 80 cm thick bentonite between 88.30 and 89.10 m in the Billegrav-2 core represents this marker bed. The other thick (90 cm bentonite in the Billegrav-2 core, exceeding the thickness of the Kinnekulle Bentonite, belongs to the Sinsen or uppermost Grefsen Series bentonites. Bentonites in the Grefsen Series frequently contain much higher concentrations of trace elements than the Kinnekulle Bentonite.

  18. Petrology of an eclogite- and pyrigarnite-bearing polymetamorphic rock complex at Cabo Ortegal, NW Spain

    NARCIS (Netherlands)

    Vogel, D.E.

    1967-01-01

    At Cabo Ortegal, paragneisses are found in association with amphibolites, metagabbros, amphibolized eclogites, amphibolized (plagio) pyrigarnites, and serpentinized ultrabasic rocks. On the basis of petrographical and chemical evidence, their geological history was reconstructed as follows: Precambr

  19. Radioassay of vitamin B-12 employing bentonite

    International Nuclear Information System (INIS)

    Radioassay for vitamin B-12 using the unknown quantity of non-radioactive vitamin B-12 released from serum mixed with the radioactivity of a known quantity of radioactive vitamin B-12 tracer. A solution of intrinsic factor having a binding capacity less than the quantity of serum vitamin B-12 and radioactive vitamin B-12 is used to bind a portion of the vitamin B-12 mixture. The vitamin B-12 not bound to intrinsic factor is removed by addition of a bentonite-containing tablet. The quantity of radioactive vitamin B-12 bound to intrinsic factor is compared with standard values and the unknown serum vitamin B-12 obtained. In the steps of the procedure the acid assay medium is pre-combined with the radioactive tracer so that the radioactive vitamin B-12 tracer receives the same treatment as serum vitamin B-12. Certain of the other reagent solutions are pre-combined and the concentration of the components adjusted so that the volume used of each of these other reagent solutions is the same in different assay steps. Thus, fewer pipetting steps are necessary. 7 claims, 1 drawing figure

  20. Measurement of pH of the Compacted Bentonite under the Reducing Condition

    OpenAIRE

    Nessa, Syeda Afsarun; Idemitsu, Kazuya; Yamasaki, Yosuke; Inagaki, Yaohiro; Arima, Tatsumi

    2007-01-01

    Compacted bentonite and carbon steel have been considered as the good buffer and over-pack materials in the repositories of high-level radioactive waste disposal. Sodium bentonite, Kunipia-F contains approximately 95wt% of montmorillonite. It has a high cation-exchange capacity and a high specific surface area, and its properties determine the behavior of bentonite. The pH of the pore water in compacted bentonite is an extremely important parameter because of its influence on radionuclide sol...

  1. Aespoe Hard Rock Laboratory. The use of focused ion beams for structural characterisation of bentonite. A feasibility study

    Energy Technology Data Exchange (ETDEWEB)

    Wegden, Marie; Kristiansson, Per (Division of Nuclear Physics, Lund Inst. of Technology (Sweden)); Svensson, Daniel; Sjoeland, Anders (Swedish Nuclear Fuel and Waste Management Co., Stockholm (Sweden))

    2009-07-01

    Bentonite clay is planned to be used in the KBS-3 concept for future nuclear high level waste (HLW) repository in Sweden. In the concept the spent nuclear fuel is placed in an iron insert, which is encapsulated in a copper canister. The copper canister is embedded in compacted bentonite and deposited at 500 m depth in granite bedrock. The compacted bentonite will act as a buffer material, giving mechanical support for the copper canister, reducing water movements and capturing potentially escaping radionuclides. Bentonite contains high amounts of smectite minerals (most common is montmorillonite), which are swelling clay minerals. The smectite minerals are layered and have the ability to store water in its structure. This is done by intercalating water between the layers and expanding the interlayer distance. The exceptional swelling capacity makes bentonite a suitable buffer material that works as a sealant and barrier. Heterogeneity in the material, compaction and in swelling may result in porosity, both on the nano- and micrometre scale. This may affect the permeability of the clay and may mediate the transport of radionuclides, cations and corrosion products. The aim of this work is to investigate the feasibility of using common ion beam techniques for structural characterisation of bentonite, including studying the mineral composition and the coarse porosity. The analytical techniques used were scanning transmission ion microscopy (STIM), particle-induced X-ray emission (PIXE) and elastic p-p scattering, performed at the Lund Nuclear Microprobe. On-axis STIM analysis was performed in order to measure and map the areal mass density of the sample. Since it was impossible to differentiate an increase in thickness from an area of higher mass density, as well as discerning depth variations, the STIM analysis was also performed in tomographic mode, in an attempt to obtain 3D structural information. The tomographic reconstruction showed that the bentonite had an

  2. Aespoe Hard Rock Laboratory. The use of focused ion beams for structural characterisation of bentonite. A feasibility study

    International Nuclear Information System (INIS)

    Bentonite clay is planned to be used in the KBS-3 concept for future nuclear high level waste (HLW) repository in Sweden. In the concept the spent nuclear fuel is placed in an iron insert, which is encapsulated in a copper canister. The copper canister is embedded in compacted bentonite and deposited at 500 m depth in granite bedrock. The compacted bentonite will act as a buffer material, giving mechanical support for the copper canister, reducing water movements and capturing potentially escaping radionuclides. Bentonite contains high amounts of smectite minerals (most common is montmorillonite), which are swelling clay minerals. The smectite minerals are layered and have the ability to store water in its structure. This is done by intercalating water between the layers and expanding the interlayer distance. The exceptional swelling capacity makes bentonite a suitable buffer material that works as a sealant and barrier. Heterogeneity in the material, compaction and in swelling may result in porosity, both on the nano- and micrometre scale. This may affect the permeability of the clay and may mediate the transport of radionuclides, cations and corrosion products. The aim of this work is to investigate the feasibility of using common ion beam techniques for structural characterisation of bentonite, including studying the mineral composition and the coarse porosity. The analytical techniques used were scanning transmission ion microscopy (STIM), particle-induced X-ray emission (PIXE) and elastic p-p scattering, performed at the Lund Nuclear Microprobe. On-axis STIM analysis was performed in order to measure and map the areal mass density of the sample. Since it was impossible to differentiate an increase in thickness from an area of higher mass density, as well as discerning depth variations, the STIM analysis was also performed in tomographic mode, in an attempt to obtain 3D structural information. The tomographic reconstruction showed that the bentonite had an

  3. HLA polymorphisms in Cabo Verde and Guiné-Bissau inferred from sequence-based typing.

    Science.gov (United States)

    Spínola, Hélder; Bruges-Armas, Jácome; Middleton, Derek; Brehm, António

    2005-10-01

    Human leukocyte antigen (HLA)-A, -B, and -DRB1 polymorphisms were examined in the Cabo Verde and Guiné-Bissau populations. The data were obtained at high-resolution level, using sequence-based typing. The most frequent alleles in each locus was: A*020101 (16.7% in Guiné-Bissau and 13.5% in Cabo Verde), B*350101 (14.4% in Guiné-Bissau and 13.2% in Cabo Verde), DRB1*1304 (19.6% in Guiné-Bissau), and DRB1*1101 (10.1% in Cabo Verde). The predominant three loci haplotype in Guiné-Bissau was A*2301-B*1503-DRB1*1101 (4.6%) and in Cabo Verde was A*3002-B*350101-DRB1*1001 (2.8%), exclusive to northwestern islands (5.6%) and absent in Guiné-Bissau. The present study corroborates historic sources and other genetic studies that say Cabo Verde were populated not only by Africans but also by Europeans. Haplotypes and dendrogram analysis shows a Caucasian genetic influence in today's gene pool of Cabo Verdeans. Haplotypes and allele frequencies present a differential distribution between southeastern and northwestern Cabo Verde islands, which could be the result of different genetic influences, founder effect, or bottlenecks. Dendrograms and principal coordinates analysis show that Guineans are more similar to North Africans than other HLA-studied sub-Saharans, probably from ancient and recent genetic contacts with other peoples, namely East Africans. PMID:16386651

  4. Hydrothermal alkaline stability of bentonite barrier by concrete interstitial wastes

    International Nuclear Information System (INIS)

    At present, the main source of High Level radioactive Waste (HLW) is the electrical energy production during all the steps of developing. In almost all the countries with nuclear programs, the option for the final management of HLW is the Deep Geological Repository (DGR) based on the concept of multi barrier. According to this concept, the waste is isolated from biosphere by the interposition of confinement barriers. Two of the engineering barriers in the Spanish design of DGR in granitic rock are compacted bentonite and concrete. The bentonite barrier is the backfilling and sealing material for the repository gallery, because of its mechanical and physico-chemical properties. The main qualities of concrete as a component of a multi barrier system are its low permeability, mechanical resistance and chemical properties. With regard to chemical composition of concrete, the alkaline nature of cement pore water lowers the solubility of many radioactive elements. However, structural transformation in smectite, dissolution or precipitation of minerals and, consequently, changes in the bentonite properties could occurs in the alkaline conditions generated by the cement degradation. The main objective of the present work is to evaluate the effect of concrete in the stability of Spanish reference bentonite (La Serrata of Nijar, Almeria, Spain) in conditions similar to those estimated in a DGR in granitic rock. Because of the main role of bentonite barrier in the global performance of the repository, the present study is essential to guarantee its security. (Author)

  5. ADSORPTION FROM AQUEOUS SOLUTION ONTO NATURAL AND ACID ACTIVATED BENTONITE

    Directory of Open Access Journals (Sweden)

    Laila Al-Khatib

    2012-01-01

    Full Text Available Dyes have long been used in dyeing, paper and pulp, textiles, plastics, leather, paint, cosmetics and food industries. Nowadays, more than 100,000 commercial dyes are available with a total production of 700,000 tones manufactured all over the world annually. About 10-15% of dyes are being disposed off as a waste into the environment after dyeing process. This poses certain hazards and environmental problems. The objective of this study is to investigate the adsorption behavior of Methylene Blue (MB from aqueous solution onto natural and acid activated Jordanian bentonite. Both bentonites are firstly characterized using XRD, FTIR and SEM techniques. Then batch adsorption experiments were conducted to investigate the effect of initial MB concentration, contact time, pH and temperature. It was found that the percentage of dye removal was improved from 75.8% for natural bentonite to reach 99.6% for acid treated bentonite. The rate of MB removal followed the pseudo second order model with a high correlation factor. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. The Langmuir isotherm model was found more representative. The results indicate that bentonite could be employed as a low cost adsorbent in wastewater treatment for the removal of colour and dyes.

  6. Tracer diffusion in compacted, water-saturated bentonite

    International Nuclear Information System (INIS)

    Compacted Na-bentonite clay barriers, widely used in the isolation of solid-waste landfills and other contaminated sites, have been proposed for a similar use in the disposal of high-level radioactive waste. Molecular diffusion through the pore space in these barriers plays a key role in their performance, thus motivating recent measurements of the apparent diffusion coefficient tensor of water tracers in compacted, water-saturated Na-bentonites. In the present study, we introduce a conceptual model in which the pore space of water-saturated bentonite is divided into 'macropore' and 'interlayer nanopore' compartments. With this model we determine quantitatively the relative contributions of pore-network geometry (expressed as a geometric factor) and of the diffusive behavior of water molecules near montmorillonite basal surfaces(expressed as a contrastivity factor) to the apparent diffusion coefficient tensor. Our model predicts, in agreement with experiment, that the mean principal value of the apparent diffusion coefficient tensor follows a single relationship when plotted against the partial montmorillonite dry density (mass of montmorillonite per combined volume of montmorillonite and pore space). Using a single fitted parameter, the mean principal geometric factor, our model successfully describes this relationship for a broad range of bentonite-water system, from dilute gel to highly-compacted bentonite with 80 percent of its pore water in interlayer nanopores

  7. Utilization of locally available bentonites for water purification by activation

    International Nuclear Information System (INIS)

    Acid activation of commercial bentonite was conducted and tested for adsorption of impurities in water and industrial products. The properties of adsorption/absorption of bentonite are also used to remove impurities for the processing of edible oils and fats, as well as for the purification of products like honey and alcohol. The design of various experiments in order to assess and simulate the effects of acid activation of commercial bentonite on the adsorption capacity of methylene blue dye is described in this paper. The key parameters of the acid activation, namely acid concentration, contact time, temperature and type of acid, were established. The results indicated effects of these variables on the effectiveness of adsorption. The Swelling Index value of activated bentonite was 20 ml per 2 gram in deionized water as compared to 8 ml per 2 gm in unactivated samples. The acid concentration exerts a predominant individual effect as compared to other parameters. Bentonite activated by 5N HCl has more adsorption capacity than 40% HSO. Excessive 2 4 activation is discussed in terms of loss in both porosity and acid strength. (author)

  8. Electrochemical behavior of H3PW12O40/ acid-activated bentonite powders

    Directory of Open Access Journals (Sweden)

    Mojović Zorica

    2012-01-01

    Full Text Available Electrochemical behavior of 12-tungstophosphoric acid (HPW/acid-activated bentonite (AAB powders with various loadings of HPW was investigated. The physicochemical properties of the prepared powders were examined by X-ray powder diffraction, nitrogen adsorption-desorption isotherms, atomic force microscopy and cyclic voltammetry measurements. The results indicated that the prepared powders are composed mainly of oriented domains of large rock blocks, probably resulting from a preferable deposition of bentonite particles having a face-to-face interaction. The particles had a mainly disordered mesoporous structure with a pore volume that varied according to the pore size in the range of 2-50 nm. In addition, the particles had crystallite size between 4.9 and 9.0 nm. The electrocatalytic activities of prepared HPW/Aelectrodes were studied in the oxidation of NO2-ions and the results revealed that the electrodes possessed relatively higher nitrite oxidation currents than Aelectrode. The best electroactivity was observed for HPW3/Aelectrode (AAB+20 wt. % HPW and the limit of detection (3σ was determined as 8 μM.

  9. Decantation time of evaluation on bentonite clays fractionation

    International Nuclear Information System (INIS)

    Bentonite clays present a great number of industrial uses, from petroleum to pharmaceutics and cosmetic industry. The bentonite clay present particles with very fine particles that is responsible by the vast application of these materials. However, commercial clays present wide particle size distribution and a significant content of impurities, particularly quartz, in the form of silt and fine silt. So, the aim of this work is to analyze the effect of the stirring and decantation time in the deagglomeration, purification and size separation of the bentonite clay particles from Paraiba. The clays were characterized by X-ray diffraction and particle size distribution. Based on the results it was observed the decantation time give the elimination of the agglomerates formed by submicrometric particles. The uses of decantation column give separation of the fraction below 200nm. (author)

  10. Coupled behaviour of bentonite buffer results of PUSKURI project

    International Nuclear Information System (INIS)

    In the report main results form a KYT2010 programme's project Coupled behaviour of bentonite buffer (PUSKURI) are presented. In THC modelling, Aku Itaelae made and published his Master of Science Thesis. Itaelae was able to successfully model the LOT-experiment. Additionally, he also listed problems and development proposals for THC-modelling of bentonite buffer. VTT and Numerola created in collaboration a model coupling saturation, diffusion and cation exchange; the model was implemented and tested in Numerrin, COMSOL and TOUGHREACT. Petri Jussila's PhD THM-model was implemented into COMSOL to facilitate further development. At GTK, the mineralogical characterisation of bentonite was planned. The previous THM model (Jussila's model) including only small deformations was successfully generalized to finite deformations in way at least formally preserving the original formalism. It appears that the theory allows also a possibility to include finite plastic deformations in the theory. In order to measure the relevant mechanical properties of compacted bentonite, two different experiments, namely hydrostatic compression experiment and one-dimensional compression experiment were designed. In the hydrostatic compression experiment, a cylindrical sample of compacted bentonite covered with liquid rubber coating is placed in the sample chamber equipped with a piston. The same device was also used in one-dimensional compression experiment. X-ray microtomographic techniques were used in order to study the basic mechanisms of water transport in bentonite. The preliminary results indicate that in the present experimental set-up, water transport is dominated by a dispersive mechanism such as diffusion of vapour in gas phase or diffusion of water in solid phase. (orig.)

  11. El Grupo Cabo Domingo, Tierra del Fuego: bioestratigrafía, paleoambientes y acontecimientos del Eoceno-Mioceno marino The Cabo Domingo Group, Tierra del Fuego: Biostratigraphy, paleoenvironments, and events of the marine Eocene-Miocene

    Directory of Open Access Journals (Sweden)

    N. Malumián

    2006-06-01

    ón residual de Spirosigmoilinella compressa-Martinottiella spp. y por las capas del Cabo San Pablo (30- 40 m de areniscas y arcillitas, Mioceno temprano. Una generalizada regresión da lugar a una extendida discordancia en ca. 21 Ma. Finalmente, las Formaciones Carmen Silva (>50 m, fangolitas y conglomerados deltaicos y Castillo (50 m, conglomerados fluviales y capas del Cabo Viamonte (>40 m, brechas gruesas, conglomerados, areniscas y fangolitas todas con clásticos volcánicos basálticos, representan el nivel de mar alto y óptimo del Neógeno reflejado por un acontecimiento esmectítico del Mioceno medio y la existencia de un episodio basáltico en el Mioceno inferior superior.The Cabo Domingo Group, upper Eocene to middle Miocene, includes a gently deformed marine episodic sequence, mainly exposed to the north of the Punta Gruesa fault in Tierra del Fuego. Deposition of the Group started in the late Eocene with the basin deepening, resulting from global high sea level, the effects of which were amplified by regional tectonism (Incaica Phase. The Group is represented in the basin depocenter by the upper member of the Cerro Colorado Formation (140 m, mudstones and sandstones, 36-34 Ma, which records the LAD of Globigerinatheka index (34.3 Ma and the FAD of Praetenuitella insolita and Isthmolithus recurvus (36.6 Ma. Outside the depocenter this time interval is reflected by the Tchat-Chii Conglomerate (70 m, latest Eocene-earliest Oligocene, and by the Glauconítico A in the subsurface of the northern part of the island. The low smectite content and the abundance of Chiloguembelina ototara indicate active tectonism and falling temperatures during the deposition of the upper member and the Glauconítico A . Deposition of the Cabo Domingo Group was followed by that of the Estancia María Cristina beds (>75 m, claystones and sandstones, earliest Oligocene, 34-30 Ma and the Puesto Herminita beds (200 m, claystones, Oligocene, 30-26.5 Ma, which mainly contain residual

  12. Structure and forces in bentonite MX-80

    International Nuclear Information System (INIS)

    Wyoming bentonite (MX-80) and its ion exchanged forms, Na and Ca montmorillonite, have been studied experimentally and theoretically. A variety of experimental techniques have been used in order to gain insight into the structural conditions in dry clay as well as clay in equilibrium with a bulk solution of given ionic composition. The main objective has been the swelling behaviour and osmotic pressure of montmorillonite clay when the bulk solution contains a mix of monovalent sodium and divalent calcium ions. For a clay system in equilibrium with pure water, Monte Carlo simulations predict a large swelling when the clay counterions are monovalent, while in presence of divalent counterions a limited swelling is predicted with an aqueous layer between the clay lamellaes of about 1 nm. This latter result is in excellent agreement with small angle x-ray scattering data, but in disagreement with dialysis experiments, which gives a significantly larger swelling for Ca montmorillonite in pure water. Obviously, there is one lamellar swelling and a second 'extra-lamellar' swelling, which could be the result of a phase separation in the clay. Montmorillonite in contact with a salt reservoir with both Na+ and Ca2+ counterions will only show a modest swelling unless the sodium concentration in the bulk is several orders of magnitude larger than the calcium concentration. The limited swelling of clay in presence of divalent counterions is a consequence of ion-ion correlations, which reduce the entropic repulsion as well as give rise to an attractive component in the total osmotic pressure. Ion-ion correlations also favour divalent counterions in a situation where we have a competition with monovalent ones. A more fundamental result of ion-ion correlations is that the osmotic pressure as a function of clay sheet separation becomes nonmonotonic, which indicates the possibility of a phase separation into a concentrated and a dilute clay phase. This phenomenon could explain the

  13. Evaluation of phenomena affecting diffusion of cations in compacted bentonite

    International Nuclear Information System (INIS)

    In a number of diffusion studies, contradictions between the apparent diffusivities of cations and their distribution coefficients in bentonite have been found. Two principal reasons have been offered as explanations for this discrepancy; diffusion of the sorbed cations, often called surface diffusion, and the decrease of sorption in compacted clay compared to a sorption value obtained from a batch experiment. In the study the information available from the literature on sorption-diffusion mechanisms of cations in bentonite has been compiled and re-interpreted in order to improve the understanding of the diffusion process. (103 refs., 23 figs., 8 tabs.)

  14. Study on long-term performance of bentonite layer in radioactive waste repository

    International Nuclear Information System (INIS)

    It is important to appropriately evaluate the long-term performance of the bentonite layer in a radioactive waste repository because it can considerably affect the repository function for containment and delay of nuclides. Thus far, limited knowledge has been available on alkali alteration phenomena of highly compacted bentonite and their effect on its physical properties. In this study, we developed an apparatus for testing alkali alteration phenomena of highly compacted bentonite and its physical properties. Through studies conducted using the apparatus, we concluded that the alkali dissolution rate of montmorillonite in highly compacted bentonite is less than 9.7 x 10-13 mol/m2/sec and that the hydraulic conductivity of the bentonite layer is affected by the pore structure, which can be refined by the effect of dissolution and precipitation of minerals in bentonite, as well as by the density of the bentonite layer and the electrolyte concentration of pore solution. (author)

  15. Numerical simulation of alteration of sodium bentonite by diffusion of ionic groundwater components

    International Nuclear Information System (INIS)

    Experiments measuring the movement of trace amounts of radionuclides through compacted bentonite have typically used unaltered bentonite. Models based on experiments such as these may not lead to accurate predictions of the migration through altered or partially altered bentonite of radionuclides that undergo ion exchange. To address this problem, we have modified an existing transport code to include ion exchange and aqueous complexation reactions. The code is thus able to simulate the diffusion of major ionic groundwater components through bentonite and reactions between the bentonite and groundwater. Numerical simulations have been made to investigate the conversion of sodium bentonite to calcium bentonite for a reference groundwater characteristic of deep granitic formations. 20 refs., 2 figs., 2 tabs

  16. Genetic differentiation of the Cabo Verde archipelago population analysed by STR polymorphisms.

    Science.gov (United States)

    Fernandes, A T; Velosa, R; Jesus, J; Carracedo, A; Brehm, A

    2003-07-01

    Allele frequencies for 17 STR loci were analyzed in a sample of unrelated males from the Cabo Verde Archipelago. The samples were gathered in such a way that the origin of the subjects was perfectly identified, and they could be included in one of the leeward or windward groups of islands. This study reveals that there are significant differences between both groups of islands, and between Cabo Verdeans and other populations from sub-Sahara Africa including the Guineans, the most probable source population for Cabo Verdeans. This study confirms mtDNA data and, together with HLA and Y chromosome data already published, shows that the Cabo Verde population is sub-structured and atypical, diverging substantially from mainland sub-Saharan populations. Overall these differences are most probably due to admixture between sub-Saharan slaves brought into the islands and other settlers of European origin. In the absence of a clear indication of a different ethnic composition of the first sub-Saharan settlers of Cabo Verde, the differentiation exhibited in both groups of islands can be most probably be attributed to genetic drift. PMID:12914568

  17. Erosion of bentonite buffer in a KBS-3 repository

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. We have developed a Dynamic model for sodium gel expansion in fractures where the gel soaks up non-saline water as it expands. The model is based on a force balance between and on smectite particles, which move in the water. The Dynamic model of gel expansion showing the evolution in time and space of a gel was successfully tested against expansion experiments in test tubes. The expansion was measured with high resolution and in great detail over many months by Magnetic Resonance Imaging, MRI. The model also predicted the gel expansion through filters with very narrow pores well. In addition the model predicts the CCC fairly well, order to orders of magnitude better than the conventional DLVO theory. A gel viscosity model of dilute gels was derived, which accounts for ion concentration influence as well as the volume fraction of smectite in the gel. The model accounts for the presence of the DDL, which seemingly makes the particles larger so that they interact at lower particle densities. The viscosity model uses experimental data to obtain the necessary fitting parameters but is otherwise based on established theories of suspension viscosity. These models form the core of the erosion model. Both show a strong dependence on the ionic strength of the pore water. Simulations were performed for a case where the gel expands outward into the fracture that intersects the deposition hole. Fresh groundwater approaches and passes the gel/water interface. Smectite colloids move out into the water due to the repulsive forces between the particle and by Brownian motion. The dilute gel/sol is mobilised and flows downstream in a thin region where the viscosity is low enough to permit flow. Sodium diffuses from the compacted bentonite into and through the expanding gel towards the gel/water interface and further out into the seeping water. Mass transfer resistance for ions as well as smectite particles in the seeping water is

  18. Modelling of long term geochemical evolution and study of mechanical perturbation of bentonite buffer of a KBS-3 repository

    Energy Technology Data Exchange (ETDEWEB)

    Marsal, Francois; Pellegrini, Delphine; Deleruyelle, Frederic; Serres, Christophe (French Inst. for Radiological Protection and Nuclear Safety (IRSN), Fontenay-aux-Roses (FR)); Windt, Laurent de (Ecole des Mines de Paris, Paris (FR))

    2008-03-15

    PART I: The Swedish Nuclear Fuel and Waste Management Co. (SKB) has recently completed a safety assessment project named SR-Can, related to the KBS-3 disposal concept. In this concept, the waste packages are surrounded by a buffer made of either MX-80 or Deponit CA-N bentonite. Interactions between the buffer and groundwater may modify the buffer composition and thus its containment properties. The Swedish Radiation Protection Authorities (SSI) requested the French Institute for Radiological Protection and Nuclear Safety (IRSN) to perform the present study in support of SSI review of the SR-Can report. The purpose is to assess the geochemical evolution of both potential buffer materials due to the intrusion of different types of groundwater, with a similar modelling layout to that reported in SR-Can and detailed in Arcos et al. Three main categories of water inflows via a fracture intersecting a deposition hole are considered: the Forsmark reference groundwater, a high-salinity groundwater to account for up-rise of deep-seated brines and a diluted water representing ice-melting derived-groundwater. In addition to this, the redox buffering capacity of Deponit CA-N bentonite and the thermal effect on MX-80 bentonite geochemistry have been assessed. This modelling work has been performed using the reactive transport modelling code HYTEC. The main outcome of the present study is that the intrusion of the considered groundwaters should not affect drastically the geochemistry of neither the Deponit CA-N nor the MX-80 bentonite on the longterm (100,000 y). Bentonite pH may reach high values (up to 10.5) in some cases but does not reach SKB criterion value related to bentonite chemical stability. Dissolution-precipitation of accessory minerals is not significant enough to induce important porosity changes (rise by maximum 2 %). Globally, the montmorillonite exchanger undergoes Na by Ca partial replacement, which may decrease the swelling pressure of the bentonite. The

  19. Crystallite size distribution of clay minerals from selected Serbian clay deposits

    Directory of Open Access Journals (Sweden)

    Simić Vladimir

    2006-01-01

    Full Text Available The BWA (Bertaut-Warren-Averbach technique for the measurement of the mean crystallite thickness and thickness distributions of phyllosilicates was applied to a set of kaolin and bentonite minerals. Six samples of kaolinitic clays, one sample of halloysite, and five bentonite samples from selected Serbian deposits were analyzed. These clays are of sedimentary volcano-sedimentary (diagenetic, and hydrothermal origin. Two different types of shape of thickness distribution were found - lognormal, typical for bentonite and halloysite, and polymodal, typical for kaolinite. The mean crystallite thickness (T BWA seams to be influenced by the genetic type of the clay sample.

  20. Structure and forces in bentonite MX-80

    Energy Technology Data Exchange (ETDEWEB)

    Joensson, Bo; Aakesson, Torbjoern; Joensson, Bengt; Meehdi, Segad; Janiak, John; Wallenberg, Reine (Theoretical Chemistry, Chemical Center, Lund Univ., Lund (Sweden))

    2009-03-15

    Wyoming bentonite (MX-80) and its ion exchanged forms, Na and Ca montmorillonite, have been studied experimentally and theoretically. A variety of experimental techniques have been used in order to gain insight into the structural conditions in dry clay as well as clay in equilibrium with a bulk solution of given ionic composition. The main objective has been the swelling behaviour and osmotic pressure of montmorillonite clay when the bulk solution contains a mix of monovalent sodium and divalent calcium ions. For a clay system in equilibrium with pure water, Monte Carlo simulations predict a large swelling when the clay counterions are monovalent, while in presence of divalent counterions a limited swelling is predicted with an aqueous layer between the clay lamellaes of about 1 nm. This latter result is in excellent agreement with small angle x-ray scattering data, but in disagreement with dialysis experiments, which gives a significantly larger swelling for Ca montmorillonite in pure water. Obviously, there is one lamellar swelling and a second 'extra-lamellar' swelling, which could be the result of a phase separation in the clay. Montmorillonite in contact with a salt reservoir with both Na+ and Ca2+ counterions will only show a modest swelling unless the sodium concentration in the bulk is several orders of magnitude larger than the calcium concentration. The limited swelling of clay in presence of divalent counterions is a consequence of ion-ion correlations, which reduce the entropic repulsion as well as give rise to an attractive component in the total osmotic pressure. Ion-ion correlations also favour divalent counterions in a situation where we have a competition with monovalent ones. A more fundamental result of ion-ion correlations is that the osmotic pressure as a function of clay sheet separation becomes nonmonotonic, which indicates the possibility of a phase separation into a concentrated and a dilute clay phase. This phenomenon could

  1. Magnesium incorporated bentonite clay for defluoridation of drinking water

    International Nuclear Information System (INIS)

    Low cost bentonite clay was chemically modified using magnesium chloride in order to enhance its fluoride removal capacity. The magnesium incorporated bentonite (MB) was characterized by using XRD and SEM techniques. Batch adsorption experiments were conducted to study and optimize various operational parameters such as adsorbent dose, contact time, pH, effect of co-ions and initial fluoride concentration. It was observed that the MB works effectively over wide range of pH and showed a maximum fluoride removal capacity of 2.26 mg g-1 at an initial fluoride concentration of 5 mg L-1, which is much better than the unmodified bentonite. The experimental data fitted well into Langmuir adsorption isotherm and follows pseudo-first-order kinetics. Thermodynamic study suggests that fluoride adsorption on MB is reasonably spontaneous and an endothermic process. MB showed significantly high fluoride removal in synthetic water as compared to field water. Desorption study of MB suggest that almost all the loaded fluoride was desorbed (∼97%) using 1 M NaOH solution however maximum fluoride removal decreases from 95.47 to 73 (%) after regeneration. From the experimental results, it may be inferred that chemical modification enhances the fluoride removal efficiency of bentonite and it works as an effective adsorbent for defluoridation of water.

  2. A review of porosity and diffusion in bentonite

    International Nuclear Information System (INIS)

    Porosity in bentonite can be subdivided in free porewater, diffuse double layer (DDL) water, and interlayer water in montmorillonite, the most important mineral of bentonite. The proportions of these water types can be calculated from the internal and external specific surface area of montmorillonite and the width of interlayer- and DDL-water. Stacking of the TOT layers in montmorillonite in the c-direction is the master variable that determines the specific internal and external surface areas. The thickness of the water layers depends on the ionic strength and the composition of the free porewater, and on the packing density of the bentonite. When the proportions of the water types change, the diffusion of cations, anions and neutral molecules is affected in different ways since the diffusional properties vary. Diffusive fluxes are proportional with accessible porosity, chemical potential gradient, and diffusion coefficient, but not with concentration as has been proposed often in diffusion models. The equations for calculating the diffusive flux through interlayer water are derived. The potential gradient here is given by the gradient of the equivalent (or molar) fraction of the cation in the cation exchange capacity. The latter is expressed as concentration in the interlayer water. An example calculation illustrates that the flux in interlayer water can be dominant and opposite to the one in free porewater. Retardation by ion exchange is an important process in bentonite that can be modeled if the concentrations of major ions are known. Unfortunately, the analyses are almost never done in diffusion experiments.(orig.)

  3. Sodium Bentonite-Based Fire Retardant Coatings Containing Starch

    Science.gov (United States)

    Sodium bentonite (SB) gel and foam coatings were tested for their ability to suppress the rate of heat increase at the surface of commercial lap siding. Starch was added to some treatments to determine whether it stabilized the coating and prevented vertical slumping. A commercial fire protection ge...

  4. Diffusion of anions and cations in compacted sodium bentonite

    International Nuclear Information System (INIS)

    The thesis presents the results of studies on the diffusion mechanisms of anions and cations in compacted sodium bentonite, which is planned to be used as a buffer material in nuclear waste disposal in Finland. The diffusivities and sorption factors were determined by tracer experiments. The pore volume accessible to chloride, here defined as effective porosity, was determined as a function of bentonite density and electrolyte concentration in water, and the Stern-Gouy double-layer model was used to explain the observed anion exclusion. The sorption of Cs+ and Sr2+ was studied in loose and compacted bentonite samples as a function of the electrolyte concentration in solution. In order to obtain evidence of the diffusion of exchangeable cations, defined as surface diffusion, the diffusivities of Cs+ and Sr2+ in compacted bentonite were studied as a function of the sorption factor, which was varied by electrolyte concentration in solution. The measurements were performed both by a non-steady state method and by a through-diffusion method. (89 refs., 35 fig., 4 tab.)

  5. Polypropylene–clay composite prepared from Indian bentonite

    Indian Academy of Sciences (India)

    Madhuchhanda Sarkar; Kausik Dana; Sankar Ghatak; Amarnath Banerjee

    2008-02-01

    In the present work, a set of experimental polypropylene (PP) clay composites containing pristine bentonite clay of Indian origin has been prepared and then characterized. The polymer clay composites are processed by solution mixing of polypropylene with bentonite clay using a solvent xylene and high speed electric stirrer at a temperature around 130°C and then by compression molding at 170°C. The mechanical properties of PP–clay composites like tensile strength, hardness and impact resistance have been investigated. Microstructural studies were carried out using scanning electron microscope and transmission electron microscope and the thermal properties were studied using differential scanning calorimeter. Mechanical properties of the prepared composites showed highest reinforcing and toughening effects of the clay filler at a loading of only 5 mass % in PP matrix. Tensile strength was observed to be highest in case of 5 mass % of clay loading and it was more than 14% of that of the neat PP, while toughness increased by more than 80%. Bentonite clay–PP composite (5 mass %) also showed 60% increase in impact energy value. However, no significant change was observed in case of hardness and tensile modulus. Higher percentages of bentonite clay did not further improve the properties with respect to pristine polypropylene. The study of the microstructure of the prepared polymer layered silicate clay composites showed a mixed morphology with multiple stacks of clay layers and tactoids of different thicknesses.

  6. Activation of a Ca-bentonite as buffer material

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. Swelling behavior is an important criterion in achieving the low-permeability sealing function of buffer material. A potential buffer material may be used for radioactive waste repository in Taiwan is a locally available clayey material known as Zhisin clay, which has been identified as a Ca-bentonite. Due to its Ca-based origin, Zhisin was found to exhibit swelling capacity much lower than that of Na-bentonite. To enhance the swelling potential of Zhisin clay, a cation exchange process by addition of Na2CO3 powder was introduced in this paper. The addition of Na2CO3 reagent to Zhisin clay, in a liquid phase, caused the precipitation of CaCO3 and thereby induced a replacement of Ca2+ ions by Na+ ions on the surface of bentonite. Characterization test conducted on Zhisin clay includes chemical analysis, cation exchange capacity, X-ray diffraction, and thermogravimetry (TG). Free-swelling test apparatus was developed according to International Society of Rock Mechanics recommendations. A series of free-swelling tests were conducted on untreated and activated specimens to characterize the effect of activation on the swelling capacity of Zhisin clay. Efforts were made to determine an optimum dosage for the activation, and to evaluate the aging effect. Also, the activated material was evaluated for its stability in various hydrothermal conditions for potential applications as buffer material in a repository. Experimental results show that Na2CO3-activated Zhisin clay is superior in swelling potential to untreated Zhisin clay. Also, there exists an optimum amount of activator in terms of improvements in the swelling capacity. A distinct time-swell relationship was discovered for activated Zhisin clay. The corresponding mechanism refers to exchange of cations and breakdown of quasi-crystal, which results in ion exchange hysteresis of Ca-bentonite. Due to the ion exchange hysteresis, activated bentonite shows a post

  7. Activation of a Ca-bentonite as buffer material

    Science.gov (United States)

    Huang, Wei-Hsing; Chen, Wen-Chuan

    2016-04-01

    Swelling behavior is an important criterion in achieving the low-permeability sealing function of buffer material. A potential buffer material may be used for radioactive waste repository in Taiwan is a locally available clayey material known as Zhisin clay, which has been identified as a Ca-bentonite. Due to its Ca-based origin, Zhisin was found to exhibit swelling capacity much lower than that of Na-bentonite. To enhance the swelling potential of Zhisin clay, a cation exchange process by addition of Na2CO3 powder was introduced in this paper. The addition of Na2CO3 reagent to Zhisin clay, in a liquid phase, caused the precipitation of CaCO3 and thereby induced a replacement of Ca2+ ions by Na+ ions on the surface of bentonite. Characterization test conducted on Zhisin clay includes chemical analysis, cation exchange capacity, X-ray diffraction, and thermogravimetry (TG). Free-swelling test apparatus was developed according to International Society of Rock Mechanics recommendations. A series of free-swelling tests were conducted on untreated and activated specimens to characterize the effect of activation on the swelling capacity of Zhisin clay. Efforts were made to determine an optimum dosage for the activation, and to evaluate the aging effect. Also, the activated material was evaluated for its stability in various hydrothermal conditions for potential applications as buffer material in a repository. Experimental results show that Na2CO3-activated Zhisin clay is superior in swelling potential to untreated Zhisin clay. Also, there exists an optimum amount of activator in terms of improvements in the swelling capacity. A distinct time-swell relationship was discovered for activated Zhisin clay. The corresponding mechanism refers to exchange of cations and breakdown of quasi-crystal, which results in ion exchange hysteresis of Ca-bentonite. Due to the ion exchange hysteresis, activated bentonite shows a post-rise time-swell relationship different than the sigmoid

  8. Effects of the injection grout Silica sol on bentonite

    International Nuclear Information System (INIS)

    Silica sol, i.e., colloidal SiO2, may be used as a low-pH injection grout for very fine fractures in the construction of deep geological repositories for radioactive waste in Sweden and in Finland. If the bentonite barrier encounters SiO2-colloid particles under conditions favorable for aggregation, there is concern that it will modify the bentonite barrier at the bentonite/bedrock interface. In this study qualitative experiments were performed with mixed dispersions of SiO2-colloids and bentonite or homo-ionic Na/Ca-montmorillonite. Samples were prepared at different colloid concentrations and treated under various conditions such as low and high ionic strength (0.3 M NaCl), as well as dehydration and re-dispersing. Free swelling and settling experiments were performed in order to qualitatively compare the conditions in which SiO2-colloids affect the bulk/macro properties of bentonite. In order to study specific SiO2-colloid/montmorillonite interactions and preferred type of initial aggregation, dilute dispersions of homo-ionic montmorillonite dispersions mixed with varying concentrations of SiO2-colloids were prepared and selected samples were characterized by PCS, SEM/EDS, AFM and PXRD. The results from this study show that bentonite and montmorillonite particles can be modified by SiO2-colloids when mixed in comparable amounts, due to dehydration or high ionic strength. Some indications for increased colloidal stability for the SiO2-colloid modified clay particles were also found. From the AFM investigation it was found that initial attachment of the SiO2-colloids in Na+ dominated samples seemed to occur on the edges of the montmorillonite layers. In Ca2+ dominated samples not subjected to excess NaCl, SiO2-colloid sorption onto the faces of the montmorillonite layers was also found. In all, contact between the bentonite barrier and un-gelled Silica sol should preferably be avoided. (authors)

  9. Response surface optimisation for activation of bentonite with microwave irradiation

    Directory of Open Access Journals (Sweden)

    Rožić Ljiljana S.

    2011-01-01

    Full Text Available In this study, the statistical design of the experimental method was applied on the acid activation process of bentonite with microwave irradiation. The influence of activation parameters (time, acid normality and microwave heating power on the selected process response of the activated bentonite samples was studied. The specific surface area was chosen for the process response, because the chemical, surface and structural properties of the activated clay determine and limit its potential applications. The relationship of various process parameters with the specific surface area of bentonite was examined. A mathematical model was developed using a second-order response surface model (RSM with a central composite design incorporating the above mentioned process parameters. The mathematical model developed helped in predicting the variation in specific surface area of activated bentonite with time (5-21 min, acid normality (2-7 N and microwave heating power (63-172 W. The calculated regression models were found to be statistically significant at the required range and presented little variability. Furthermore, high values of R2 (0.957 and R2 (adjusted (0.914 indicate a high dependence and correlation between the observed and the predicted values of the response. These high values also indicate that about 96% of the result of the total variation can be explained by this model. In addition, the model shows that increasing the time and acid normality improves the textural properties of bentonites, resulting in increased specific surface area. This model also can be useful for setting an optimum value of the activation parameters for achieving the maximum specific surface area. An optimum specific surface area of 142 m2g-1 was achieved with an acid normality of 5.2 N, activation time of 7.38 min and microwave power of 117 W. Acid activation of bentonite was found to occur faster with microwave irradiation than with conventional heating. Microwave

  10. Evaluation of the outflow characteristic of bentonite buffer material. 2

    International Nuclear Information System (INIS)

    The outflow behaviour of bentonite buffer material was experiment to assess the physical stability in the geological disposal system, the parameters of experiment are the dry density of bentonite, mixtures ratio silica sand, fracture width, and flow velocity. The outflow phenomena were identified as extrusion and erosion, and the experimental results are as follows; 1) Extrusion: The proportional coefficient obtained from the relation between time and extrusion distance was arranged by the relation with effective clay density. The experimental equation of the proportional coefficient is as follows; A = 6.7587x10-7∼ exp(5.7261d)∼ exp((6.1598+(-0.5398d)+(-0.9272d2))∼ Pb). By model experiment, the density distribution into fracture was measured. The density distribution of an extrusion region obtained 0.8-0.2 Mgm-3. The average dry density into fracture of bentonite gel was about 0.4 Mgm-3 below. The influence of density of bentonite/sand mixtures material (30 wt%, 1.6 Mgm-3) by the extrusion phenomenon was calculated. It was assumed that the average fracture density is about eight fractures parameter. The reduction in density of the bentonite/sand mixtures material is about 4.5% (1.527 Mgm-3) of the initial value after 10,000 years. 2) Erosion: The colloid concentration and the particle size in drainage liquid were measured as parameter of flow velocity into fracture. The result of measurement, colloid concentration decreased with the increase in the flow velocity. Moreover, the particle size of colloid became large. In the case of average flow velocity 1E-5 ms-1, the colloid was generated in drainage liquid. Therefore, the flow velocity for occurrence of erosion was suggested smaller than 1E-5 ms-1. (author)

  11. Cement/bentonite interaction. Results from 16 month laboratory tests

    International Nuclear Information System (INIS)

    The work concerns possible bentonite clay mineral alteration in constructions with bentonite in close contact with cement, and the effect of such changes on bentonite buffer properties. The investigation comprises a 16 months laboratory test series with hydrothermal cell tests, percolation tests and diffusion tests. MX-80 Wyoming bentonite was used in all tests. Two types of artificial cement pore water solutions were used in the percolation and diffusion tests. The swelling pressure and the hydraulic conductivity were measured continuously in the percolation tests. After termination, the clay was analyzed with respect to changes in element distribution, mineralogy and shear strength. The water solutions were analyzed with respect to pH, cations and major anions. The results concerning chemical and mineralogical changes are in summary: Ion exchange in the montmorillonite until equilibrium with cement pore-water ions was reached; Increase in cation exchange capacity; Dissolution of original cristobalite; Increase in quartz content; Minor increase in illite content; Minor formation of chlorite; Formation of CSH(I); Wash away of CSH-gel into surrounding water. A large decrease in swelling pressure and a moderate increase in hydraulic conductivity were recorded in the samples percolated by SULFACEM pore-water solution. The mineralogical alterations only concerned a minor part of the total bentonite mass and the changes in physical properties were therefore most likely due to the replacement of the original charge balancing cation by cement pore-water cations. Comparisons between the current test result and results from 4 month tests indicate that the rates of illite and chlorite formation were reduced during the tests. The presence of zeolites in the clay could not be ensured. However, the discovery of CSH material is important since CSH is expected to precede the formation of zeolites

  12. Experimental Investigation of Near-Borehole Crack Plugging with Bentonite

    Science.gov (United States)

    Upadhyay, R. A.; Islam, M. N.; Bunger, A.

    2015-12-01

    The success of the disposal of nuclear waste in a deep borehole (DBH) is determined by the integrity of the components of the borehole plug. Bentonite clay has been proposed as a key plugging material, and its effectiveness depends upon its penetration into near-borehole cracks associated with the drilling process. Here we present research aimed at understanding and maximizing the ability of clay materials to plug near-borehole cracks. A device was constructed such that the borehole is represented by a cylindrical chamber, and a near-borehole crack is represented by a slot adjacent to the center chamber. The experiments consist of placing bentonite clay pellets into the center chamber and filling the entire cavity with distilled water so that the pellets hydrate and swell, intruding into the slot because the cell prohibits swelling in the vertical direction along the borehole. Results indicate that the bentonite clay pellets do not fully plug the slot. We propose a model where the penetration is limited by (1) the free swelling potential intrinsic to the system comprised of the bentonite pellets and the hydrating fluid and (2) resisting shear force along the walls of the slot. Narrow slots have a smaller volume for the clay to fill than wider slots, but wider slots present less resistive force to clay intrusion. These two limiting factors work against each other, leading to a non-monotonic relationship between slot width and intrusion length. Further experimental results indicate that the free swelling potential of bentonite clay pellets depends on pellet diameter, "container" geometry, and solution salinity. Smaller diameter pellets possess more relative volumetric expansion than larger diameter pellets. The relative expansion of the clay also appears to decrease with the container size, which we understand to be due to the increased resistive force provided by the container walls. Increasing the salinity of the solution leads to a dramatic decrease in the clay

  13. Genetic structure of the population of Cabo Verde (west Africa): evidence of substantial European admixture.

    Science.gov (United States)

    Parra, E J; Ribeiro, J C; Caeiro, J L; Riveiro, A

    1995-08-01

    The population of Cabo Verde was founded in the fifteenth century (1462), on the basis of slaves brought from the West African coast and a few Europeans, mainly from Portugal. The polymorphism of six red cell enzymes (ADA, AK1, ALAD, ESD, GLO1, and PGD) and ten plasma proteins (AHSG, BF, F13A, F13B, GC, HP, ORM, PLG, TBG, and TF) was studied in a sample of 268 individuals from Cabo Verde (West Africa). There is no statistical evidence of genetic heterogeneity between the two groups of islands which constitute the archipelago, Barlavento and Sotavento. The gene frequency distribution observed in Cabo Verde differs, in many markers, from that of West African populations, suggesting an important European influence. The proportion of Caucasian genes in the population of Cabo Verde has been calculated to be M = 0.3634 +/- 0.0510, and the considerable dispersion of the locus-specific admixture estimates seems to indicate random drift has also played a role in the evolution of the allele frequencies in the archipelago. Partition of the variance of the mean estimate in evolutionary and sampling variance shows the evolutionary variance is more than ten times higher than the sampling variance. When dendrograms are constructed on the basis of different genetic distances, the population of Cabo Verde clusters with Afro-Americans, forming a different group from the populations of the African continent. This is interpreted as a consequence of the importance of Caucasian admixture both in Afro-Americans and in the population of Cabo Verde. PMID:7485435

  14. Estudio de "las capas del cabo ladrillero superior" en el cabo homónimo, mioceno inferior de la cuenca austral, tierra del fuego

    Directory of Open Access Journals (Sweden)

    Estefanía P Tudisca

    2012-03-01

    Full Text Available En los acantilados del cabo Ladrillero, situado sobre la costa atlántica de la Isla Grande de Tierra del Fuego, afloran parte de los depósitos cuspidales que rellenan la cuenca de antepaís Austral o de Magallanes. Estos depósitos del Mioceno inferior son conocidos como "capas del Cabo Ladrillero" y "capas del Cabo San Pablo", siendo las "capas del Cabo Ladrillero superior" las analizadas en este trabajo. La zona de estudio, situada a una decena de kilómetros al norte del frente orogénico emergente (Punta Gruesa, permitió reconocer cuatro asociaciones de facies que registran depósitos gravitacionales resedimentados en un ambiente marino supra batial y una cuña deltaica progradante y somerizante hacia el noreste. Entre los rasgos más conspicuos observados en esta sucesión se destacan bancos deformados, intervalos macizos y abundantes diques clásticos, cuyo análisis estadístico indica un patrón transtensivo. Los microfósiles documentados en el área y utilizados previamente como herramienta para sostener un ambiente marino profundo provienen de niveles estratigráficos infrayacentes y corresponden a niveles de la Formación Desdémona y las capas del Cabo Ladrillero inferior, aflorantes hacia el sur de la zona de estudio. Las evidencias sedimentológicas no son concluyentes respecto de la batimetría, pero la ausencia de turbiditas clásicas, flujos hiperpícnicos, la abundancia de bancos deformados y resedimentados, restos vegetales y fragmentos de carbón son compatibles con un ambiente somero y deltaico con altas tasas de aporte y pendientes inestables antes que un ambiente marino profundo, y sugieren una historia compleja de la evolución del relleno sedimentario que no se explica meramente con los esquemas basados exclusivamente en el contenido de foraminíferos que domina en la literatura.

  15. Determinantes da internacionalização das empresas hoteleiras em Cabo Verde

    OpenAIRE

    Lopes, Jailson Menezes Correia.

    2012-01-01

    Esta dissertação visa identificar os determinantes da internacionalização das empresas hoteleiras em Cabo Verde, nomeadamente as de origem portuguesa. Considerando o ritmo de crescimento registado na indústria hoteleira em Cabo Verde e a crescente presença de investimento externo na actividade turística em algumas ilhas, procurou-se neste estudo verificar as principais motivações que estariam na base da decisão da realização desses investimentos. O crescimento das empresas hoteleiras na econo...

  16. Physical and chemical stability of the bentonite buffer

    International Nuclear Information System (INIS)

    A literature study was made on previous work on clay erosion and on the fundamental processes that govern the stability of clay gels. Mechanical erosion has been studied earlier and models devised to estimate the tendency to erode. We have used a different approach that we deem is fundamentally more correct. Chemical erosion processes have not been found to be studied previously and we have approached the problem by applying simple but fundamental mass balances and transport processes to the problem. The physical and chemical processes that govern the repulsive and cohesive forces in clay are well understood in principle but cannot yet be applied quantitatively to predict the gel/sol behaviour of the bentonite clay. It was necessary to rely directly on laboratory measurements for information on swelling and gel/sol properties. The backfill bentonite clay acts as a Bingham fluid over a wide range of clay density. To mobilise the clay a shear stress larger than the Bingham yield stress must be applied to the gel. The Bingham yield stress has been measured to be larger than 1 Pa (N/m2) although it cannot be ruled out that lower values can be found under different experimental conditions than those reported. Shear stresses exerted by the water flowing in the fractures that intersect the deposition holes with the clay backfill have been estimated for a wide range of fracture transmissivities, apertures and hydraulic gradients that could exist under repository conditions. This includes the extremely high gradients that could exist during some periods during an ice age. For fracture transmissivities ranging from 10-9 to 10-6 m2/s, fracture apertures from 0.1 to 2 mm and the hydraulic gradients from 0.01 to 1 mH2O/m, the largest local shear stress found in this range was about 0.1 Pa. To investigate a 'what if' situation where the shear stress exceeds the yield stress simple models were devised. They were used to assess the rate of erosion by the groundwater. In one model

  17. Transport of Iodide Ion in Compacted Bentonite Containing Ag2O - 12111

    International Nuclear Information System (INIS)

    Observations of the transport of iodide through compacted bentonite containing Ag2O as additive and that without additive were made. Compacted bentonite samples with densities of 1.41 g/cm3 and 1.60 g/cm3 were used in the experiment. The amount of Ag2O added to the compacted bentonite was in the range of 0.0064 ∼ 0.0468 wt/wt%. Two diffusion solutions were used: one in which iodide ion was dissolved in demineralized water (pure iodide solution), and one in which iodide ion was dissolved in 0.1 M NaCl solution (0.1 M NaCl-iodide solution). Experimental results confirmed that iodide ion was transported by the diffusion process in the compacted bentonite containing Ag2O as well as in the compacted bentonite without Ag2O. The time-lag of diffusion of iodide ion in the compacted bentonite containing Ag2O is larger than that in the compacted bentonite without Ag2O. The increase of the time-lag of diffusion was observed in pure iodide ion solution as well as in 0.1 M NaCl-iodide solution. The apparent diffusion coefficient of iodide ion in the compacted bentonite containing Ag2O was smaller than in the compacted bentonite without Ag2O. The effective diffusion coefficient decreased as the amount of Ag2O in the compacted bentonite increased. (authors)

  18. An Investigation of Diffusion of Iodide Ion in Compacted Bentonite Containing Ag2O

    International Nuclear Information System (INIS)

    In the compacted bentonite containing Ag2O, the transport of iodide ion was investigated by Through-diffusion method. It is confirmed that Iodide ion is transported by diffusion process in the compacted bentonite containing Ag2O as well as in the compacted bentonite without Ag2O. However, the lag-time of iodide ion in the compacted bentonite containing Ag2O is larger than that in the compacted bentonite without Ag2O. The increase of the lag-time was observed in pure iodide ion solution and also in 0.1M NaCl-iodide ion solution. The apparent diffusion coefficient of iodide ion in the compacted bentonite containing Ag2O has lower value than that in the compacted bentonite without Ag2O. The effect of Ag2O on the effective diffusion coefficient was not clearly investigated in the compacted bentonite containing Ag2O while the values of effective diffusion coefficient of iodide ion in the compacted bentonite without Ag2O obtained in this study were similar to those in the compacted bentonite reported in the literature

  19. Diffusion of strongly sorbing cations (60Co and 152Eu) in compacted Febex bentonite

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. Compacted bentonite is used as an engineered barrier in high-level radioactive waste (HLRW) repositories because is a swelling clay of very low permeability and high sorption capability for many solutes. The transport of radionuclides through compacted bentonite is a diffusion-controlled process retarded by sorption. Performance assessment calculations of a repository need diffusion coefficients data of relevant radionuclides. Several studies on diffusion behaviour of neutral, anionic and weakly sorbing elements on clay exist while very few studies are available for moderately sorbing elements, and almost no studies for Eu, a highly sorbing element are reported. In this study, diffusion experiments with strongly sorbing radionuclides, as 60Co and 152Eu, have been performed through compacted FEBEX bentonite. Diffusion essays with these strongly sorbing radionuclides are not straightforward to carry out because they are very time consuming essays, but also because sorption on the diffusion cells, tubing, filters and reservoirs, typically used in the classical through-diffusion or in-diffusion methods make hard the interpretation of the experimental results and the calculation of the diffusion coefficients. FEBEX bentonite was selected as Spanish reference buffer materials, and used in many national and international projects. The clay comes from the Cortijo de Archidona deposit (Almeria, Spain), and has a smectite content greater than 90% (93 ± 2%), with quartz (2 ± 1%), plagioclase (3 ± 1%), cristobalite (2 ± 1%), potassic feldspar, calcite, and trydimite as accessory minerals. The specific weight of the FEBEX bentonite is 2.7 g/cm3. Diffusion experiments were performed using the instantaneous plane source method. In this setup, a paper filter tagged with a tracer is introduced between two compacted tablets, avoiding contact between the tracer and the experimental vessels. The tracer can diffuse into both

  20. Coupled thermo-hydro-chemical models of swelling bentonites

    Science.gov (United States)

    Samper, Javier; Mon, Alba; Zheng, Liange; Montenegro, Luis; Naves, Acacia; Pisani, Bruno

    2014-05-01

    The disposal of radioactive waste in deep geological repositories is based on the multibarrier concept of retention of the waste by a combination of engineered and geological barriers. The engineered barrier system (EBS) includes the solid conditioned waste-form, the waste container, the buffer made of materials such as clay, grout or crushed rock that separate the waste package from the host rock and the tunnel linings and supports. The geological barrier supports the engineered system and provides stability over the long term during which time radioactive decay reduces the levels of radioactivity. The strong interplays among thermal (T), hydrodynamic (H), mechanical (M) and chemical (C) processes during the hydration, thermal and solute transport stages of the engineered barrier system (EBS) of a radioactive waste repository call for coupled THMC models for the metallic overpack, the unsaturated compacted bentonite and the concrete liner. Conceptual and numerical coupled THMC models of the EBS have been developed, which have been implemented in INVERSE-FADES-CORE. Chemical reactions are coupled to the hydrodynamic processes through chemical osmosis (C-H coupling) while bentonite swelling affects solute transport via changes in bentonite porosity changes (M-H coupling). Here we present THMC models of heating and hydration laboratory experiments performed by CIEMAT (Madrid, Spain) on compacted FEBEX bentonite and numerical models for the long-term evolution of the EBS for 1 Ma. The changes in porosity caused by swelling are more important than those produced by the chemical reactions during the early evolution of the EBS (t < 100 years). For longer times, however, the changes in porosity induced by the dissolution/precipitation reactions are more relevant due to: 1) The effect of iron mineral phases (corrosion products) released by the corrosion of the carbon steel canister; and 2) The hyper alkaline plume produced by the concrete liner. Numerical results show that

  1. Experimental indications of effects of surface deprotonation on Na-bentonite pore water chemistry in a geological repository

    International Nuclear Information System (INIS)

    Bentonite-water interaction was studied using a simple equilibrium model based on experimental measurements in order to describe bentonite porewater chemistry. Direct pH measurements for highly compacted bentonite and batch-type bentonite-water interaction experiments were performed under anaerobic conditions. In the direct pH measurements, resin particles doped with a pH indicator were sandwiched between a pair of bentonite columns immersed in a test solution. The experimental results showed that the solution compositions in equilibrium with bentonite depended on the bentonite to liquid ratio (B/L) and the initial solution composition. An equilibrium model assuming only fast equilibration processes between the bentonite minerals and the solution could be used to calculate the trends of pH and other ion concentrations with B/L. This study indicates that the surface deprotonation of smectite is a very important factor influencing the porewater chemistry in highly compacted bentonite. Copyright (2001) Material Research Society

  2. Purification of bentonitics of the city Cubati-PB to obtaining organoclays for use in oil-based drilling fluids; Purificacao de argilas bentoniticas do municipio de Cubati, PB, para obtencao de argilas organofilicas para uso em fluidos de perfuracao base oleo

    Energy Technology Data Exchange (ETDEWEB)

    Costa, J.M.R.; Vitorino, I.J.F.; Silva, I.A.; Neves, G.A.; Ferreira, H.C., E-mail: jullymrc@gmail.com [Universidade Federal de Campina Grande (UFCG/CCT/UAEMa), PB (Brazil)

    2011-07-01

    In Boa Vista, PB, are located deposits of bentonite clays commonly used in the preparation of drilling fluids. The disorderly exploitation of the deposits of Boa Vista is causing the depletion of these clays, which will cause a very serious problem for the national oil industry. This work aims to characterize new deposits of bentonite clays Cubati, PB, for the development of organoclay from its refining using a hydrocyclone for use in oil based drilling fluids. The characterization of samples of the clays was performed through the techniques: AG, XRD, EDX, TGA and DTA. The characterization is typical of bentonite for the purification process was determined the best configuration of the hydrocyclone, and the environment organic diesel fuel, the best affinity was obtained with clays organophilizated with surfactant Praepagen WB. (author)

  3. Distribution of HLA alleles in Portugal and Cabo Verde. Relationships with the slave trade route.

    Science.gov (United States)

    Spínola, H; Brehm, A; Williams, F; Jesus, J; Middleton, D

    2002-07-01

    HLA-A, -B, and -DR frequencies were analysed in populations from Portugal and the Madeira and Cabo Verde Archipelagos, aiming to characterize their genetic composition. Portuguese settlers colonized both Archipelagos in the 15th and 16th centuries. Madeira received many sub-Saharan slaves to work in the sugar plantations, and Cabo Verde served as a pivotal market in the Atlantic slave trade and was populated by individuals coming from the Senegambia region of the West African coast. The population of Madeira shows the highest genetic diversity and the presence of alleles and haplotypes usually linked to sub-Saharan populations, the haplotypes accounting for 3.5% of the total. Cabo Verde presents typical markers acknowledged to be of European or Ibero-Mediterranean origin, thus revealing the admixture of European settlers with Sub-Saharan slaves. Altogether the number of European haplotypes reaches 15% of the total. The Portuguese population shows a perceivable and significant heterogeneity both in allele and haplotype frequencies, unveiling a differential input of peoples from different origins. A PCA of the populations studied, plus other relevant ones, clearly shows gene heterogeneity in mainland Portugal as well as the differences and relationships between these populations and Madeira and Cabo Verde. PMID:12418969

  4. Improving rainwater-use in Cabo Verde drylands by reducing runoff and erosion

    NARCIS (Netherlands)

    Santos Baptista Costa, Dos I.; Ritsema, C.J.; Querido, A.; Ferreira, A.D.; Geissen, V.

    2015-01-01

    Dryland agriculture in Cabo Verde copes with steep slopes, inadequate practices, irregular intense rain, recurrent droughts, high runoff rates, severe soil erosion and declining fertility, leading to the inefficient use of rainwater. Maize and beans occupy > 80% of the arable land in low-input, l

  5. The catazonal poly-metamorphic rocks of Cabo Ortegal (NW Spain), a structural and petrofabric study

    NARCIS (Netherlands)

    Engels, J.P.

    1972-01-01

    The petrological study of the southern part of the Cabo Ortegal area is a complement of Vogel’s (1967) investigation of the northern half. The present investigations include a structural as well as a petrofabric study. The rocks belong to an eugeosynclinal sequence which during the Precambrian under

  6. Evaluation of permeability of compacted bentonite ground considering heterogeneity by geostatistics

    International Nuclear Information System (INIS)

    The permeability of the bentonite ground as an engineered barrier is possibly designed to the value which is lower than that determined in terms of required performance because of heterogeneous distribution of permeability in the ground, which might be considerable when the ground is created by the compaction method. The effect of heterogeneity in the ground on the permeability of the bentonite ground should be evaluated by overall permeability of the ground, whereas in practice, the effect is evaluated by the distribution of permeability in the ground. Thus, in this study, overall permeability of the bentonite ground is evaluated from the permeability of the bentonite ground is evaluated from the permeability distribution determined using the geostatistical method with the dry density data as well as permeability data of the undisturbed sample recovered from the bentonite ground. Consequently, it was proved through this study that possibility of overestimation of permeability of the bentonite ground can be reduced if the overall permeability is used. (author)

  7. Synthesis, characterization and antimicrobial activity of alkaline ion-exchanged ZnO/bentonite nanocomposites

    Institute of Scientific and Technical Information of China (English)

    Hamideh Pouraboulghasem; Mohammad Ghorbanpour; Razieh Shayegh; Samaneh Lotfiman

    2016-01-01

    Nanocomposites of zinc/bentonite clay were synthesized for use as an antibacterial material by a quick and simple alkaline ion exchange method. The synthesis of zinc doped bentonite nanocomposite was accomplished by placing bentonite in a melting bath of ZnSO4 for 10, 20, 40, 60 and 90 min. The complexes were characterized by XRD, SEM and DRS. XRD analyses and SEM observations confirmed the diffusion of zinc to the clay surfaces. Antibacterial activity tests againstEscherichia coli showed that bentonite did not present any antibacterial properties, but after alkaline ion exchange treatment, inhibition was noted. The highest antibacterial activity was observed with ZnO/bentonite composite alkaline ion exchange for 60 and 90 min. Interestingly, the leaching test indicated that ZnO/bentonite did not present any risk for drinking water treatment.

  8. Characteristics of thermally-enhanced bentonite grouts for geothermal heat exchanger in South Korea

    Institute of Scientific and Technical Information of China (English)

    Chulho; LEE; Kangja; LEE; Hangseok; CHOI; Hyo-Pum; CHOI

    2010-01-01

    The thermal conductivity and viscosity of bentonite grouts have been evaluated and compared each other to determine the suitability of these materials for backfilling vertical boreholes of ground heat exchangers.Seven bentonite grouts from different product sources were considered in this paper.Two additives,silica sand and graphite were added in bentonite grouts to enhance thermal performance.The bentonite grouts indicate that both the thermal conductivity and the viscosity increase with the content of silica sand and graphite.Therefore,it is recommended to select cautiously the amount of silica sand and graphite considering not only thermal conductivity but also viscosity for the optimum condition of backfilling.Finally,the effect of salinity in the pore water on the change of swelling potential of the bentonite-based grouts has been quantitatively evaluated to show the feasibility of bentonite grouts in the coastal area.

  9. Progress of research on the influence of alkaline cation and alkaline solution on bentonite properties

    International Nuclear Information System (INIS)

    Based on the previous laboratory studies and numerical simulation on bentonite in alkaline environments, the effects of alkaline cation and alkaline solution on mineral composition, microstructure, swelling capacity and hydraulic properties of bentonite are emphasized in this paper, temperature, pH values and concentration are discussed as main affecting factors. When bentonite is exposed to alkaline cation or alkaline solution, microstructure of bentonite will be changed due to the dissolution of montmorillonite and the formation of secondary minerals, which results in the decrease of swelling pressure. The amount of the reduction of swelling pressure depends on the concentration of alkaline solution. Temperature, polyvalent cation, salinity and concentration are the main factors affecting hydraulic properties of bentonite under alkaline conditions. Therefore, future research should focus on the mechanism of coupling effects of weak alkaline solutions on the mineral composition, microstructure, swelling capacity and hydraulic properties of bentonite under different temperatures and different pH values. (authors)

  10. Sorption of Lithium on Bentonite, Kaolin and Zeolite

    OpenAIRE

    Mandy Hoyer; Nicolai-Alexeji Kummer; Broder Merkel

    2015-01-01

    Li sorption was studied on natural bentonite, kaolin and zeolite in batch experiments at variable Li and Na concentrations (0, 1.5, 15, 150, 750 mM LiCl and 0.01, 0.1, 1, 3, 5 M NaCl). The solid-to-solution ratio was 1:4 and pH ranged from 2 to 10. Maximum Li sorption was determined at 0.01 M NaCl and 750 mM LiCl concentration in solution. It was 3800 ± 380 ppm, 1300 ± 130 ppm and 3900 ± 390 ppm on bentonite, kaolin and zeolite, respectively, which is in the average to upper range typical fo...

  11. LABORATORY TESTING OF BENTONITE CLAYS FOR LANDFILL DESIGN AND CONSTRUCTION

    Directory of Open Access Journals (Sweden)

    Biljana Kovačević Zelić

    2007-12-01

    Full Text Available Top and bottom liners are one of the key construction elements in every landfill. They are usually made as compacted clay liners (CCLs composed of several layers of compacted clay with strictly defined properties or by the use of alternative materials such as: GCL – geosynthetic clay liner, BES – bentonite enhanced soils or bentonite/polymer mixtures. Following the state of the art experiences in the world, GCLs are used in Croatian landfills for several years, as well. Depending upon the location and the obeying function, GCLs have to fulfill certain conditions. A legislated compatibility criterion has to be proven by various laboratory tests. In the paper are presented the results of direct shear and chemical compatibility tests of GCLs as well as the results of permeability measurement of kaolin clay (the paper is published in Croatian .

  12. Thermal stability of the thermoluminescence trap structure of bentonite

    International Nuclear Information System (INIS)

    This work reports about the thermal stability of the blue thermoluminescence (TL) of a well-characterised natural bentonite from Almeria (Spain). The main interest of this clay, mainly composed of montmorillonite, is because of its application in the field of high-level radioactive waste (HLW) repository in deep-lying rocks. As observed in other aluminosilicates, bentonite exhibits a very complex structure of the emission spectra based on a wide broad maximum peaked at ∼265 deg. C that can be associated to physico-chemical processes such as dehydroxylation processes, consecutive breaking linking of bonds, formation of hydrolysed ions and redox reactions. The thermal stability tests performed at different temperatures confirm a continuum in the distribution of traps. Hence, the glow curve analysis methods commonly used for synthetic materials based on single discrete traps cannot be applied for this material and the kinetic parameters were fitted assuming an exponential distribution of trapped electrons. (authors)

  13. Physical and chemical stability of the bentonite buffer

    Energy Technology Data Exchange (ETDEWEB)

    Jinsong Liu; Neretnieks, Ivars [Chemical Engineering and Technology, Royal I nstitute of Technology, Stockholm (Sweden)

    2007-12-15

    A literature study was made on previous work on clay erosion and on the fundamental processes that govern the stability of clay gels. Mechanical erosion has been studied earlier and models devised to estimate the tendency to erode. We have used a different approach that we deem is fundamentally more correct. Chemical erosion processes have not been found to be studied previously and we have approached the problem by applying simple but fundamental mass balances and transport processes to the problem. The physical and chemical processes that govern the repulsive and cohesive forces in clay are well understood in principle but cannot yet be applied quantitatively to predict the gel/sol behaviour of the bentonite clay. It was necessary to rely directly on laboratory measurements for information on swelling and gel/sol properties. The backfill bentonite clay acts as a Bingham fluid over a wide range of clay density. To mobilise the clay a shear stress larger than the Bingham yield stress must be applied to the gel. The Bingham yield stress has been measured to be larger than 1 Pa (N/m{sup 2}) although it cannot be ruled out that lower values can be found under different experimental conditions than those reported. Shear stresses exerted by the water flowing in the fractures that intersect the deposition holes with the clay backfill have been estimated for a wide range of fracture transmissivities, apertures and hydraulic gradients that could exist under repository conditions. This includes the extremely high gradients that could exist during some periods during an ice age. For fracture transmissivities ranging from 10{sup -9} to 10{sup -6} m{sup 2}/s, fracture apertures from 0.1 to 2 mm and the hydraulic gradients from 0.01 to 1 mH{sub 2}O/m, the largest local shear stress found in this range was about 0.1 Pa. To investigate a 'what if' situation where the shear stress exceeds the yield stress simple models were devised. They were used to assess the rate of

  14. Preparation and performance of Ecobras/bentonite biodegrading films

    International Nuclear Information System (INIS)

    Compounds based on the biodegradable polymer Ecobras and bentonite clay in its pristine, sonicated, and organically modified with a quaternary ammonium salt forms were prepared as flat films. Clays and compounds were characterized by x-ray diffraction and scanning electron microscopy. Mechanical properties of the films were determined according to pertinent ASTM standards. Reasonable properties, higher than those of the matrix, were obtained with compounds prepared with purified clays and organoclays, particularly for low clay loading. (author)

  15. Sorption of cesium on bentonite: The role of calcite

    International Nuclear Information System (INIS)

    Full text: Since bentonite is investigated for its use in Engineered Barriers Systems as backfill material, many studies of their surfaces properties have been performed in the past years to qualify and quantify adsorption on their surfaces, which can be one of the major processes limiting migration of radionuclides away from a disposal site. Nevertheless, most of these studies concerned simplified systems, such as Na-montmorillonite in mono-electrolyte solution. As ion-exchange processes are of importance in water-clays interactions, adsorption of natural major ions has also to be taken into account for natural systems. The aim of this work is (i) to quantify the sorption of the natural major cations on the montmorillonite surface; (ii) to compare the sorption of cesium, in two different systems, a simple one ( Na-montmorillonite in NaNO3 0.05 Mol.L-1) and a complex one (natural bentonite in a synthetic natural water) and then; (iii) to assess the influence of the natural major ions on this sorption, and to identify the role of the calcite phase present in bentonite. The methodology used consists in several batch experiments, first considering a very simple solution (NaNO3), then using mixtures of two different electrolytes, and lastly using a synthetic natural water. A surface complexation model, describing the surface of clays as a mixture of ion-exchange and complexation surface sites, is used to provide interpretations and quantifications of the sorption processes. Observed results indicate that affinity for the montmorillonite surface is greatest for Ca, then Mg and then K. The sorption of cesium is strongly affected by the presence in solution of Ca, witch can come from the partial dissolution of calcite. This study is one part of a work supported by ANDRA on the retention properties of bentonite materials. (author)

  16. Soil-Bentonite Cutoff Walls: Hydraulic Conductivity and Contaminant Transport

    OpenAIRE

    Britton, Jeremy Paul

    2001-01-01

    ABSTRACT Soil-bentonite cutoff walls are commonly used to contain contaminants in the subsurface. A key property in determining the effectiveness of a cutoff wall is its hydraulic conductivity. There are important difficulties and uncertainties regarding the accuracy of commonly used methods of measuring the hydraulic conductivity of cutoff walls. When predicting contaminant transport through cutoff walls, common practice is to use the average hydraulic conductivity of the wall. ...

  17. Post examination of copper ER sensors exposed to bentonite

    International Nuclear Information System (INIS)

    Highlights: • Copper sensors were used for monitoring corrosion in bentonite during 4.2-y exposure. • Corrosion rates were estimated by applying three different methods. • Average corrosion rates for copper in bentonite are several µm/year. - Abstract: Copper corrosion in saline solutions under oxic conditions is one of concerns for the early periods of disposal of spent nuclear fuel in deep geological repositories. The main aim of the study was to investigate the corrosion behaviour of copper during this oxic period. The corrosion rate of pure copper was measured by means of thin electrical resistance (ER) sensors that were placed in a test package containing an oxic bentonite/saline groundwater environment at room temperature for a period of four years. Additionally, the corrosion rate was monitored by electrochemical impedance spectroscopy (EIS) measurements that were performed on the same ER sensors. By the end of the exposure period the corrosion rate, as estimated by both methods, had dropped to approximately 1.0 μm/year. The corrosion rate was also estimated by the examination of metallographic cross sections. The post examination tests which were used to determine the type and extent of corrosion products included different spectroscopic techniques (XRD and Raman analysis). It was confirmed that the corrosion rate obtained by means of physical (ER) and electrochemical techniques (EIS) was consistent with that estimated from the metallographic cross section analysis. The corrosion products consisted of cuprous oxide and paratacamite, which was very abundant. From the types of attack it can be concluded that the investigated samples of copper in bentonite underwent uneven general corrosion

  18. Sorption of Lithium on Bentonite, Kaolin and Zeolite

    Directory of Open Access Journals (Sweden)

    Mandy Hoyer

    2015-04-01

    Full Text Available Li sorption was studied on natural bentonite, kaolin and zeolite in batch experiments at variable Li and Na concentrations (0, 1.5, 15, 150, 750 mM LiCl and 0.01, 0.1, 1, 3, 5 M NaCl. The solid-to-solution ratio was 1:4 and pH ranged from 2 to 10. Maximum Li sorption was determined at 0.01 M NaCl and 750 mM LiCl concentration in solution. It was 3800 ± 380 ppm, 1300 ± 130 ppm and 3900 ± 390 ppm on bentonite, kaolin and zeolite, respectively, which is in the average to upper range typical for clay minerals. Under these conditions, kaolin was saturated with Li, whereas Li in bentonite and zeolite occupied only about 55%–79% and 9%–26% of the typical cation exchange capacity (CEC of smectites and zeolites, respectively. This is explained by differences in the way Li is bound in the materials studied. Li sorption on bentonite was independent of pH due to strong pH buffering. Above pH 5, kaolin was transformed to gibbsite, which completely changed its Li sorption capabilities. Extremely low as well as extremely high pH destabilized the crystal lattice of zeolite. All in all it was shown that, under the studied conditions, Li sorption on the studied materials occurs in detectable quantities. So, clay minerals and zeolites can act as a sink for Li if Li concentrations in solution are sufficiently high.

  19. Bentonite-cement interaction. Preliminary results from model calculations

    International Nuclear Information System (INIS)

    The interaction between the bentonite buffer and alkaline plume from degrading cementitious material used in the construction and operation of the repository is envisaged to constitute a risk to the long-term chemical stability of bentonite. In this report, first model calculations to shed light on the possible extent of mineralogical alteration of bentonite due to the plume have been carried out. A common feature of the model outcome for every case is the clogging of the pore space at the interface between the buffer and the rock fracture carrying the plume. Depending on the pH considered in the calculations for the plume (12.17, 11.60 and 9.70), this clogging will occur after 10, 18 and 5,900 years after the onset on interaction, respectively. For each case, the heavily altered zone in bentonite is confined very close to the interface. There are uncertainties related to the present calculations, the greatest ones pertaining to the poor knowledge of mineral dissolution/precipitation kinetics and to constraining the set of secondary minerals possible to form. The effects of the latter were clearly illustrated in two model cases (pH 11.60 and 9.70), where initially supersaturated secondary mineral phases were omitted; the pore clogging did not take place at the fracture-buffer interface and the buffer was continuously exposed to the alkaline plume. According to the present model calculations, it seems that the evolution of the interfacial porosity in the model system with pH 12.17 is not very sensitive to the selection of the secondary minerals as the pore space was clogged regardless. (orig.)

  20. Post examination of copper ER sensors exposed to bentonite

    Energy Technology Data Exchange (ETDEWEB)

    Kosec, Tadeja, E-mail: tadeja.kosec@zag.si [Slovenian National Building and Civil Engineering Institute, Dimičeva 12, SI-1000 Ljubljana (Slovenia); Kranjc, Andrej [Slovenian National Building and Civil Engineering Institute, Dimičeva 12, SI-1000 Ljubljana (Slovenia); Rosborg, Bo [Royal Institute of Technology, Div. Surface and Corrosion Science, Drottning Kristinas väg 51, SE-100 44 Stockholm (Sweden); Legat, Andraž [Slovenian National Building and Civil Engineering Institute, Dimičeva 12, SI-1000 Ljubljana (Slovenia)

    2015-04-15

    Highlights: • Copper sensors were used for monitoring corrosion in bentonite during 4.2-y exposure. • Corrosion rates were estimated by applying three different methods. • Average corrosion rates for copper in bentonite are several µm/year. - Abstract: Copper corrosion in saline solutions under oxic conditions is one of concerns for the early periods of disposal of spent nuclear fuel in deep geological repositories. The main aim of the study was to investigate the corrosion behaviour of copper during this oxic period. The corrosion rate of pure copper was measured by means of thin electrical resistance (ER) sensors that were placed in a test package containing an oxic bentonite/saline groundwater environment at room temperature for a period of four years. Additionally, the corrosion rate was monitored by electrochemical impedance spectroscopy (EIS) measurements that were performed on the same ER sensors. By the end of the exposure period the corrosion rate, as estimated by both methods, had dropped to approximately 1.0 μm/year. The corrosion rate was also estimated by the examination of metallographic cross sections. The post examination tests which were used to determine the type and extent of corrosion products included different spectroscopic techniques (XRD and Raman analysis). It was confirmed that the corrosion rate obtained by means of physical (ER) and electrochemical techniques (EIS) was consistent with that estimated from the metallographic cross section analysis. The corrosion products consisted of cuprous oxide and paratacamite, which was very abundant. From the types of attack it can be concluded that the investigated samples of copper in bentonite underwent uneven general corrosion.

  1. Diffusion and sorption properties of radionuclides in compacted bentonite

    International Nuclear Information System (INIS)

    In this report, recent studies on sorption and diffusion of radionuclides in compacted bentonite have been reviewed. The sorption distribution coefficient and diffusion coefficient data obtained from experiments in the literature have been compiled. Based on these experimental data and the report SKB-TR--91-16 (Brandberg and Skagius, 1991), this report proposes a set of sorption distribution coefficient and diffusion coefficient values for modelling purpose for safety analysis of nuclear waste repositories. The variability and uncertainty of the diffusivity data span somewhat more than an order or magnitude up and down. Most of the nuclides have an effective diffusivity in around 10-10 m2/s. Ion exclusion effects are observed for C, Cl and for Tc in oxidizing waters. Effective diffusivities are nearly tow orders of magnitude lower for these elements and of the order of 10-12 m2/s. Surface diffusion effects are found for Cs, Ni, Pa, Pb, Ra, Sn, Sr and Zr. Effective diffusivities for these elements are of the order of 10-8 m2/s. The surface diffusion effect should decrease in saline waters which is seen for Cs and Sr where there are data available. It is also deemed that Ra will have this effect because of its similarity with Sr. The other nuclides should also show this decrease but no data is available. Sorption and diffusion mechanisms in compacted bentonite are discussed in the report. In highly compacted bentonite, sorption and hence its distribution coefficient is not well defined, and a pore diffusion coefficient or a surface diffusion coefficient is not well defined either. Therefore, an apparent diffusion coefficient and a total concentration gradient should be more relevant in describing the diffusion process in compacted bentonite

  2. Production of smectite organophylic clays from three commercial sodium bentonite

    International Nuclear Information System (INIS)

    Laboratory cationic exchange procedures using Brazilian's commercial quaternary ammonium salt and three samples of commercial sodium bentonites (two Brazilian's and one from Wyoming (US) are described. Swelling values in some liquid organic media are shown for the organophilic clays and for a Brazilian's commercial organophilic clay. Organophilic clays with larger swelling values than the commercial organophilic clay in kerosene, Varsol, toluene and soya bean oil were obtained. (author)

  3. The sorption of aniline on organically modified bentonites

    Czech Academy of Sciences Publication Activity Database

    Plevová, Eva; Vaculíková, Lenka; Vítámvásová, E.; Valovičová, Věra

    Ostrava: VŠB TUO, 2015. s. 47-47. ISBN 978-80-248-3745-1. [Nanomaterials and Nanotechnology Meeting, Nano Ostrava 2015 /4./. 18.05.2015-21.05.2015, Ostrava] R&D Projects: GA MŠk ED2.1.00/03.0082; GA MŠk(CZ) LO1406 Institutional support: RVO:68145535 Keywords : bentonites * alkylammonium cations * sorption * aniline Subject RIV: JI - Composite Materials

  4. Characterization of organo-modified bentonite sorbents: The effect of modification conditions on adsorption performance

    Science.gov (United States)

    Parolo, María E.; Pettinari, Gisela R.; Musso, Telma B.; Sánchez-Izquierdo, María P.; Fernández, Laura G.

    2014-11-01

    The organic modification of a natural bentonite was evaluated using two methods: exchanging the interlayer cations by hexadecyltrimethylammonium (HDTMA) and grafting with vinyltrimethoxysilane (VTMS) and γ-methacryloyloxy propyl trimethoxysilane (TMSPMA) on montmorillonite surface. The physicochemical characterization of all materials was made by X-ray diffraction (XRD), IR spectroscopy, thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) surface area techniques. HDTMA cations and organosilanes were intercalated into the interlayer space of montmorillonite, as deduced from the increase of the basal spacing. IR spectroscopy, TGA and BET area give evidence of successful organic modification. The studies show a decrease in the IR absorption band intensity at 3465 cm-1 with surfactant modification, and also a decrease of mass loss due to adsorbed water observed in two samples: the organoclay and functionalized bentonites, which are evidences of a lower interlayer hydrophilicity. The efficiency of aniline removal onto natural bentonite, organobentonite and functionalized bentonites from aqueous solutions was evaluated. Aniline sorption on natural bentonite was studied using batch experiments, XRD and IR spectroscopy. The hydrophobic surface of organobentonite and functionalized bentonites increased the retention capacity for nonionic organic substances such as aniline on bentonites. The sorption properties of modified bentonite, through different modification methods, enhanced the potential industrial applications of bentonites in water decontamination.

  5. Comparative study of bentonite properties with respect to the application as geotechnical barrier in HLRW repositories

    International Nuclear Information System (INIS)

    In concepts for the storage of high level radioactive waste (HLRW) the application of bentonite as sealing material is envisaged. Relevant properties of bentonites are cation exchange capacity (retention of pollutants), swelling (sealing of cracks), and low hydraulic conductivity. These properties significantly vary with the type of counter ion which is dominant in the smectite (commonly montmorillonite) interlayers. However, the variability of bentonites - not depending on the type of counter ion - is frequently underestimated. Bentonites vary in the mineralogical and chemical composition, and the arrangement of all components (intergrowth and micro fabric). Additionally, the main component (smectite) varies with respect to the degree of structural order, particle size, crystallite size, chemical composition, morphology, and amount and location of negative charges. This variation, of course, strongly affects bentonite properties in almost all fields of industrial application. Measurable parameters only occasionally explain the different properties. The common approach, therefore, is to perform application tests. In this study an attempt is made to identify the variation of bentonite properties with respect to the application in HLRW repositories. The study is based on the comparative investigation of 30 different bentonites from important bentonite mining areas worldwide. The bentonites were characterized intensively by mineralogical, optical, and chemical methods: XRD, IR, SEM, CEC, XRF, granulometry, layer charge density. (authors)

  6. Characteristics study of bentonite as candidate of buffer materials for radioactive waste disposal system

    International Nuclear Information System (INIS)

    Literature studies on bentonite characteristic of, as candidate for radioactive waste disposal system, have been conducted. Several information have been obtained from references, which would be contributed on performance assessment of engineered barrier. The functions bentonite includes the buffering of chemical and physical behavior, i.e. swelling property, self sealing, hydraulic conductivities and gas permeability. This paper also presented long-term stability of bentonite in natural condition related to the illitisazation, which could change its buffering capacities. These information, showed that bentonite was satisfied to be used for candidate of buffer materials in radioactive waste disposal system. (author)

  7. Compression characteristics and permeability of saturated Gaomiaozi ca-bentonite

    International Nuclear Information System (INIS)

    The compression characteristics and permeability of compacted Gaomiaozi Ca-bentonite saturated by the water uptake tests are studied by conducting a series of one-dimension compression tests. The permeability coefficient can be calculated by the Terzaghi's one-dimensional consolidation theory after the consolidation coefficient is obtained by the square root of time method. It is found that the compression curves of compacted specimens saturated by the water uptake tests tend to be consistent in the relatively high stress range. The compression indexes show a linear decrease with increasing dry density and the swelling index is a constant. The permeability coefficient decreases with increasing compression stress, and they show the linear relationship in double logarithmic coordinates. Meanwhile, the permeability coefficient shows a linear decrease with decreasing void ratio, which has no relationship with initial states, stress states and stress paths. The permeability coefficient k of GMZ Ca-bentonite at dry density Pd of 1.75 g/cm3 can be calculated as 2.0 × 10-11 cm/s by the linear relationship between Pd and log k. It is closed to the permeability coefficient of GMZ Ca-bentonite with the same dry density published in literature, which testifies that the method calculating the permeability coefficient is feasible from the consolidation coefficient obtained by the consolidation test. (authors)

  8. Segregation of bentonite components in order to achieve nano montmorillonite

    International Nuclear Information System (INIS)

    Nano technology makes the possibility to achieve specific properties for materials. In this process, by reducing the size of materials in the range of nano size, new noticeable behaviour for material can be observed. Such behaviour cannot be observed for larger particles from that material. Bentonite soils contain more than 76% montmorillonite and some other minerals. Pure montmorillonite with nano size has a vast industrial application in which its production is relatively costly and time consuming. This research is aimed to propose a method for segregation of bentonite components to reach nano montmorillonite. To achieve this objective, a mechanical method is proposed. Based on this method, a nano montmorillonite with micro and nano size is achieved. The segregation process is monitored with PSA, XRD, SSA and SEM experiments. The results of this research show that a nano montmorillonite with SSA of 522.58 m2/g and average diameter of 6.13 micron is attained. The achieved nano montmorillonite has larger purity in comparison to Cloisite Na+. In addition, it has lower average particle size than Cloisite Na+. Furthermore, according to the results of this research the extracted nano clay is free from carbonate and quartz particles. The SSA of this nano montmorillonite was 25% more than that of bentonite. The proposed method is relatively inexpensive. Moreover, since no chemical is used in its production process, it is a suitable sample for practical, research, and industrial projects.

  9. Ageing effects on swelling behaviour of compacted GMZ01 bentonite

    International Nuclear Information System (INIS)

    Highlights: • Ageing effects on compacted GMZ01 bentonite are investigated. • Swelling property decreases with ageing and influenced by initial conditions. • Ageing effects are mainly attributed to the bonding effects and the hydration of smectites. - Abstract: Ageing effects on the swelling properties of compacted GMZ01 bentonite are investigated in this paper. Samples were compacted to prescribed dry densities and water contents and kept for ageing under constant volume and K0 confined conditions for target days of 0, 1, 7, 15, 30 and 90. Then, swelling deformation and swelling pressure tests were performed on the aged samples. Results indicate that both the swelling deformation and swelling pressure decrease with ageing time, with a more significant decrease at the first few days of ageing. Ageing effects are more pronounced for samples with large dry density and high water content. At the same initial dry density and water content, samples aged under constant volume conditions show much smaller decrease of swelling pressure compared to that of samples aged under K0 confined conditions. The decrease of swelling potential of samples with ageing days is mainly attributed to the bonding effects and the internal redistribution of water within the bentonite, which was confirmed by the changes of microstructure of samples with ageing

  10. Phenol determination on HDTMA-bentonite-based electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Mojovic, Z., E-mail: zoricam@nanosys.ihtm.bg.ac.rs [University of Belgrade, Institute of Chemistry, Technology and Metallurgy, Department of Catalysis and Chemical Engineering, Njegoseva 12, 11000 Belgrade (Serbia); Jovic-Jovicic, N.; Milutinovic-Nikolic, A.; Bankovic, P.; Rabi-Stankovic, A. Abu; Jovanovic, D. [University of Belgrade, Institute of Chemistry, Technology and Metallurgy, Department of Catalysis and Chemical Engineering, Njegoseva 12, 11000 Belgrade (Serbia)

    2011-10-30

    Highlights: {yields} HDTMA-modified bentonites were tested as electrode materials in the electro-oxidation of phenol. {yields} The influences of the surfactant loading and pH of the supporting electrolyte were investigated. {yields} Rapid deactivation of electrodes occurred in an acidic environment. {yields} Good stability of the investigated electrodes was obtained in alkaline medium. {yields} The sensitivity toward phenol and stability of the electrodes was markedly improved with increasing HDTMA loading. - Abstract: The partial and complete substitution of cations in the interlayer region of clay with different amounts of hexadecyl trimethylammonium bromide (HDTMABr) was performed. The aim was to synthesize organo-bentonites to be used as constituents of porous electrodes for the electrooxidation of phenol. Domestic clay from Bogovina was subjected to a common procedure of the production of organo-bentonites. It included the following steps: grinding, sieving, Na-exchange, cation exchange and drying. The samples were characterized by X-ray diffraction (XRD) analysis, while the textural properties were evaluated by nitrogen physisorption. The multisweep cyclic voltammetry was applied to analyze the behavior of the clay modified glassy carbon electrode. The influences of the surfactant loading and pH of the support electrolyte were investigated. Rapid deactivation of electrodes occurred in an acidic environment, while good stability of the investigated electrodes was obtained in alkaline medium.

  11. Study on model for bentonite buffer intrusion. 2

    International Nuclear Information System (INIS)

    Modelling study on the extrusion phenomenon of the bentonite in a geological repository for the high-level radioactive is performed to enhance the reliability of latest model studied on fiscal year 2003 (H14), on the matter of density distribution of extruded bentonite gel. In this study, the model is reconsidered and revised based on the result of comparison between experimental and calculated results. The numerical analyses for BENTFLOW type experiments and model experiments on extrusion in a pipe are performed using the revised model. The analyses for the BENTFLOW about distribution of extrusion density reproduce the experimental results tolerably. The agreement between the calculated and experimental results of the model experiments are not good. Our model is originated in solid diffusion model of swelling clay proposed by Nakano et al. To enhance the reliability of our model, the latest model is reviewed by experts. At last, the numerical analyses for H12 type repository are performed by revised model to evaluate the long-term reduction of bentonite density for the extrusion phenomenon. The analytical results are compared with the results described in H12 report. (author)

  12. Study on model for bentonite buffer intrusion phenomenon

    International Nuclear Information System (INIS)

    Modelling study on the extrusion phenomenon in a geological repository for the high-level radioactive is performed to enhance the reliability of existing model described in H12 report. Main conclusions of this study are as follows: (1) The methods and physical interpretation of bentonite gel viscosity measurements are clarified and input data of the viscosity for the solid diffusivity are obtained. (2) The input data of the swelling pressure and hydraulic conductivity of bentonite in the low- density region necessary for the solid diffusivity are determined. (3) The consolidation-type model proposed by Ahn et al. is surveyed and compared with that used in this study. The consolidation-type model is thought to be equivalent to the solid diffusion model used in this study. (4) The numerical analyses for BENTFLOW experiments and model experiments on extrusion in a pipe are performed. The analyses for the BENTFLOW reproduce the experimental results better than the past studies. The agreement between the calculated and experimental results of the model experiments is not good. Thus further study is required for the evaluation of density distribution in extruding bentonite gel. (author)

  13. The sealing performance of bentonite/crushed basalt borehole plugs

    International Nuclear Information System (INIS)

    Mixtures of crushed rock and bentonite are considered for backfilling and sealing high-level nuclear waste repositories. Many variables affect the hydraulic conductivity of such mixtures, including the size and shape of the rock particles, method of mixing and emplacement, water content and density of the clay, and the weight ratio of rock to clay. Mixtures of crushed basalt and bentonite have been tested in two types of permeameters, 20 cm diameter stainless steel permeameters and 10 cm diameter PVC permeameters. Plugs were installed as a single lift or in many lifts; the water content of the clay ranged from air-dry to as high as 200%. Preliminary results show that a mixture of 75% crushed basalt and 25% bentonite has a hydraulic conductivity between 1 x 10-9 cm/s and 2.5 x 10-8 cm/s. In some cases, preferential flow paths have developed (possibly as a result of the montmorillonite washing out of the crushed rock matrix), giving hydraulic conductivities as high as 1 x 10-4 cm/s. Other ratios of rock to clay have similar bimodal results. The probability of failure is decreased by including a higher percentage of clay in the plug, crushing the rock finer, and evenly mixing the crushed rock and clay. 136 refs., 50 figs., 7 tabs

  14. Bentonite as a colloid source in groundwaters at Olkiluoto

    Energy Technology Data Exchange (ETDEWEB)

    Vuorinen, U. [VTT Processes, Espoo (Finland); Hirvonen, H.

    2005-02-15

    In this work bentonite was studied as a potential source of colloids in Olkiluoto groundwaters. Samples were collected at two groundwater stations, PVA1 at 37.5 m dept and PVA3 at 95.6 m depth, in the VLJ-tunnel. The deeper groundwater at PVA3 was more saline (2.6g/L of Cl-) than the shallow at PVA1 (0.8g/L of Cl-). A bentonite source had been assembled at each groundwater station so that two sample lines were available for water samples; one for collecting a sample before and the other for collecting a sample after interaction with bentonite. Before starting the actual colloid sampling groundwaters from both sample lines at both stations were analysed. Only minor alterations, mostly within the uncertainty limits of the analysis methods, were brought about in the water chemistries after interaction with the bentonite sources. The only clear changes were seen in the concentration of iron which decreased after interaction with bentonite in the groundwaters at both stations. After groundwater sampling the actual colloid sampling was performed. The water samples were collected and treated inside a movable nitrogen filled glove-box. The samples could be collected from each sampling line directly in the glove-box via two quick-couplings that had been assembled on the front face of the box. The sample lines had been assembled with 0.45 {mu}m filters before entering the glove-box, because only colloids smaller than 0.45 {mu}m were of interest, as they are not prone to sedimentation in slow groundwater flows and therefore could act as potential radionuclide carriers. Colloid samples were collected and treated similarly from both sampling lines at both groundwater stations. For estimating the colloid content the groundwater samples were filtered with centrifugal ultrafiltration tubes of different cut-off values (0.3 {mu}m, 300kD and 10kD). The ultrafiltrations produced the colloid-containing concentrate fractions and the soluble substances-containing filtrate fractions. In

  15. Preparation and thermal properties of chitosan/bentonite composite beads

    Directory of Open Access Journals (Sweden)

    Teofilović Vesna

    2014-01-01

    Full Text Available Due to their biodegradable and nontoxic nature, biopolymer composites are often used as remarkable adsorbents in treatment of wastewater. In this study chitosan/bentonite composite beads were obtained by addition of clay into the polymer using solution process. Before the composite preparation, bentonite was modified with surfactant cetyltrimethyl ammonium bromide (CTAB. The morphology of beads was examined by scanning electron microscopy (SEM. Thermal properties of the composite beads were studied by simultaneous thermogravimetry coupled with differential scanning calorimetry (SDT and differential scanning calorimetry (DSC. TG results showed that the complex decomposition mechanism of the composites depends on the preparation procedure. It was observed that the concentration of NaOH used for composites precipitation affects the final structure of beads. The influence of preparation procedure on the glass transition temperature Tg of chitosan/bentonite samples was not found (Tg values for all samples were about 144 °C. [Projekat Ministarstva nauke Republike Srbije, br. III45022 and ON172014 and Provincial Secretariat of Vojvodina for Science and Technological Development 114-451-2396/2011-01.

  16. Diffusion of radionuclides in concrete/bentonite systems

    International Nuclear Information System (INIS)

    In a repository for nuclear waste, different construction materials will be used. Two important materials among these are concrete and bentonite clay. These will act as mechanical barriers, preventing convective water flow and also retard transport due to diffusion of dissolved radionuclides by a combination of mechanical constraints and chemical interactions with the solid. An important issue is the possible change of the initial sodium bentonite into the calcium form due to ion exchange with calcium from the cement. The initial leaching of the concrete has been studied using radioactive spiked concrete in contact with compacted bentonite. The diffusion of Cs, Am and Pu into 5 different types of concrete in contact with porewater have been measured. The measured diffusivity for Cs agrees reasonable well with data found in literature. For Am and Pu no movement could be measured (less than 0.2 mm) even though the contact times were extremely long (2.5 y and 5 y, respectively). This report gives also a summary of the previously published results about sorption and diffusion of radionuclides in cement performed in Prav/KBS/SKB projects 1980-1990. 25 refs

  17. Modelling Ni diffusion in bentonite using different sorption models

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. An important component of the multi barrier disposal concept for a radioactive waste repository is the bentonite backfill surrounding the canisters containing vitrified high-level waste and spent fuel located in the tunnels deep within the chosen host rock. The effectiveness of the compacted bentonite barrier is such that calculations have indicated that many radionuclides have decayed to insignificant levels before having diffused through the thickness of bentonite. These calculations are performed using the simple Kd sorption concept in which the values are taken from batch type experiments performed on dispersed systems performed for a single metal at a time, usually at trace concentrations. However, in such complex systems many radionuclides, inactive metal contaminants/ground water components may be simultaneously present in the aqueous phase at a range of concentrations varying with time during the temporal evolution of the repository system. An important aspect influencing the sorption of any radioactive metal under a set of given geochemical conditions is its competition with other metals present, and how this may vary as a function of concentration. Competitive sorption effects are not currently included in safety assessments and are thus an issue which needs to be addressed. Here we provide some first estimates of the potential influence of competitive sorption effects on the migration of radioactive metals through compacted bentonite as a function of their concentration and the concentration of competing metals. Ni(II) and Fe(II) were chosen as possible competing cations since their concentration levels are expected to have values greater than trace levels and effects might be maximal and canister corrosion represents a permanent Fe source at the bentonite interface which could influence bivalent radionuclide diffusion. The modelling of the Ni(II) diffusion/sorption has been carried out using three

  18. Purification of Sardinella sp., Oil: Centrifugation and Bentonite Adsorbent

    Directory of Open Access Journals (Sweden)

    S.H. Suseno

    2014-01-01

    Full Text Available Centrifugation and purification using adsorbents is one example of a fish oil refining techniques applied to reduce impurities of fish oil. The study aimed to determine the sardine oil quality before treatment, to determine yield of fish oil after centrifugation treatment and to determine the influence of centrifugation speed and bentonite concentration on sardine oil quality. Factorial design with two factors was used in this study. Level of free fatty acid and peroxide value before purification was 35.53% and 170 mEq/kg. Yield of fish oil after centrifugation treatment has been ranged from 17.42±3.56 to 76.33±0.21%. The best treatment which could reduce the peroxide value and total oxidation was a treatment with centrifugation speed at 6500 rpm and bentonite concentration at 3%. Peroxide value and total oxidation of its treatment was 25.00±0.00 and 51.43±0.01 mEq/kg. The lowest value of p-anisidine was 1.29±0.05 mEq/kg and its value could be found in a treatment with centrifugation speed at 4500 rpm and bentonite concentration at 5%. The level of free fatty acid after purification process was ranged from 27.35 to 34.69%. Oil clarity tended to increase with the increase of centrifugation speed and adsorbent concentration.

  19. Hexacyanoferrates and bentonite as binders of radiocaesium for reindeer

    International Nuclear Information System (INIS)

    The effects of varying doses of caesium binders (Bentonite and several forms of iron-hexacyanoferrates) on radiocaesium accumulation in red blood cells and on radiocaesium transfer to urine and faeces were studied in feeding experiments with reindeer calves. The caesium binders were added to a ration of lichen (containing 9.5 kBq of 134Cs+137Cs originating from the Chernobyl accident) and fed together with a pelleted reindeer feed (RF-71) for 42 days. A 50% reduction in red blood cell radiocaesium concentration was obtained with a daily dose of 1 mg/kg body weigth of ammoniumironhexacyanoferrate (AFCF) and with 500 mg/kg of bentonite. Three mg/kg of AFCF or 2 g/kg of bentonite reduced both urinary excretion and RBC concentrations with more than 80%. It is concluded that iron-hexacyanoferrates, as a result of their high caesium binding capacity, are particularly useful as caesium binders for free ranging ruminants like the reindeer. (author)

  20. Reactive transport modelling of iron-bentonite interaction within the KBS-3H disposal concept

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. Posiva and SKB have developed a horizontal nuclear waste repository design (KBS-3H), in which copper canisters, each with a surrounding layer of bentonite clay, are placed in perforated metal shells prior to deposition in the drifts; the assembly is called the 'super-container'. Carbon steel is considered to be a potential super-container shell material, which however is expected to corrode under repository conditions. Interactions with dissolved Fe, hydrogen gas and other reaction products may lead to the alteration of the bentonite buffer and impair safety functions of the buffer. Thus, it is essential to get a better understanding of the long-term alteration of bentonite in contact with iron. The impact of corroding iron on clay barriers has been addressed in recent years both by experimental and modelling studies in different research programs. For example, long-term experimental studies on the interaction of zero-valent iron with MX-80 bentonite have been carried out within the KBS-3H program. In addition, a preliminary geochemical modelling study on the effect of a steel shell on the bentonite buffer in the KBS-3H concept has been conducted by Wersin et al. (2007). A general conclusion drawn from the investigations to date is that in spite of considerable experimental and theoretical efforts the understanding on iron-clay interactions is still incomplete. This is due to (i) the rather poor thermodynamic and thermodynamic data of the relevant phyllosilicates and (ii) large uncertainties in the redox reactions accompanying smectite transformation processes. The scope of this modelling exercise was to extend this preliminary simulation study by considering more recent experimental and modelling data as well as the new thermodynamic data for clays included in THERMODDEM. A specific focus was on the potential effect of high pH induced by the corrosion reaction: Fe(0) + H2O to Fe2+ + 2OH-. The increase in pH has

  1. Generation and stability of bentonite colloids at the bentonite/granite interface of a deep geological radioactive waste repository

    Science.gov (United States)

    Missana, Tiziana; Alonso, Úrsula; Turrero, Maria Jesús

    2003-03-01

    The possible mechanisms of colloid generation at the near field/far field interface of a radioactive repository have been investigated by means of novel column experiments simulating the granite/bentonite boundary, both in dynamic and in quasi-static water flow conditions. It has been shown that solid particles and colloids can be detached from the bulk and mobilised by the water flow. The higher the flow rate, the higher the concentration of particles found in the water, according to an erosion process. However, the gel formation and the intrinsic tactoid structure of the clay play an important role in the submicron particle generation even in the compacted clay and in a confined system. In fact, once a bentonite gel is formed, in the regions where the clay is contacted with water, clay colloids can be formed even in quasi-static flow conditions. The potential relevance of these colloids in radionuclide transport has been studied by evaluating their stability in different chemical environments. The coagulation kinetics of natural bentonite colloids was experimentally studied as a function of the ionic strength and pH, by means of time-resolved light scattering techniques. It has been shown that these colloids are very stable in low saline (˜1×10 -3 M) and alkaline (pH≥8) waters.

  2. Sorption and diffusion of FE(II) in bentonite

    International Nuclear Information System (INIS)

    The iron in the engineering barrier system of a nuclear waste repository interacts via the corrosion process with the swelling clay intended as the buffer material. This interaction may affect the sealing properties of the clay. In the case of iron-bentonite interaction, redox reactions, dissolution/precipitation, the diffusion and sorption are coupled together. In a combined study different processes are difficult to distinguish from each other, and more specific studies are needed for the separate processes. In particular, there is a need for well-controlled diffusion and sorption experiments where iron is kept as Fe(II). In this project, sorption and diffusion of Fe(II) in bentonite have been studied. The experiments were carried out under low-oxygen conditions in an anaerobic glove-box. The radioactive isotope (55Fe) was used as a tracer in the experiments. The sorption experiments were carried out with two batches of purified MX-80 bentonite. One was purified at Bureau de Recherches Geologiques et Minieres, French Geological Survey (BRGM) and the other one at VTT Technical Research Centre of Finland (VTT). Experiments were also carried out with synthetic smectite, which did not include iron, which was prepared at LMPC (ENSC, F 68093 Mulhouse, France). The sorption experiments were carried out in 0.3 M and 0.05 M NaCl solutions as a function of pH, and in 0.3 M NaCl solution buffered at pH 5 as a function of added Fe(II) concentration. The separation of bentonite and solution at the end of the sorption experiment was carried out in the early phase by centrifuging only. In the later phase, ultrafiltering was added in order to improve the separation. The diffusion experiments were carried out in compacted samples prepared from MX-80 purified at VTT and saturated with 0.3 M NaCl at pH 8 and 5. A non-steady-state diffusion experiment method, where the tracer was introduced as an impulse source between two bentonite plugs was used in the measurements. Qualitatively

  3. Sorption and diffusion of FE(II) in bentonite

    Energy Technology Data Exchange (ETDEWEB)

    Muurinen, A. [VTT Technical Research Centre of Finland, Espoo (Finland); Tournassat, C.; Hadi, J. [BRGM, Orleans (France); Greneche, J.-M. [LPCE, Le Mans (France)

    2014-02-15

    The iron in the engineering barrier system of a nuclear waste repository interacts via the corrosion process with the swelling clay intended as the buffer material. This interaction may affect the sealing properties of the clay. In the case of iron-bentonite interaction, redox reactions, dissolution/precipitation, the diffusion and sorption are coupled together. In a combined study different processes are difficult to distinguish from each other, and more specific studies are needed for the separate processes. In particular, there is a need for well-controlled diffusion and sorption experiments where iron is kept as Fe(II). In this project, sorption and diffusion of Fe(II) in bentonite have been studied. The experiments were carried out under low-oxygen conditions in an anaerobic glove-box. The radioactive isotope ({sup 55}Fe) was used as a tracer in the experiments. The sorption experiments were carried out with two batches of purified MX-80 bentonite. One was purified at Bureau de Recherches Geologiques et Minieres, French Geological Survey (BRGM) and the other one at VTT Technical Research Centre of Finland (VTT). Experiments were also carried out with synthetic smectite, which did not include iron, which was prepared at LMPC (ENSC, F 68093 Mulhouse, France). The sorption experiments were carried out in 0.3 M and 0.05 M NaCl solutions as a function of pH, and in 0.3 M NaCl solution buffered at pH 5 as a function of added Fe(II) concentration. The separation of bentonite and solution at the end of the sorption experiment was carried out in the early phase by centrifuging only. In the later phase, ultrafiltering was added in order to improve the separation. The diffusion experiments were carried out in compacted samples prepared from MX-80 purified at VTT and saturated with 0.3 M NaCl at pH 8 and 5. A non-steady-state diffusion experiment method, where the tracer was introduced as an impulse source between two bentonite plugs was used in the measurements

  4. Corrosion of high-level radioactive waste iron-canisters in contact with bentonite

    Energy Technology Data Exchange (ETDEWEB)

    Kaufhold, Stephan, E-mail: s.kaufhold@bgr.de [BGR, Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, D-30655 Hannover (Germany); Hassel, Achim Walter [Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße 1, D-40237 Düsseldorf (Germany); Institute for Chemical Technology of Inorganic Materials, Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz (Austria); Sanders, Daniel [Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße 1, D-40237 Düsseldorf (Germany); Dohrmann, Reiner [BGR, Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, D-30655 Hannover (Germany); LBEG, Landesamt für Bergbau, Energie und Geologie, Stilleweg 2, D-30655 Hannover (Germany)

    2015-03-21

    Graphical abstract: Corrosion at the bentonite iron interface proceeds unaerobically with formation of an 1:1 Fe silicate mineral. A series of exposure tests with different types of bentonites showed that Na–bentonites are slightly less corrosive than Ca–bentonites and highly charges smectites are less corrosive compared to low charged ones. The formation of a patina was observed in some cases and has to be investigated further. - Highlights: • At the iron bentonite interface a 1:1 Fe layer silicate forms upon corrosion. • A series of iron–bentonite corrosion products showed slightly less corrosion for Na-rich and high-charged bentonites. • In some tests the formation of a patina was observed consisting of Fe–silicate, which has to be investigated further. - Abstract: Several countries favor the encapsulation of high-level radioactive waste (HLRW) in iron or steel canisters surrounded by highly compacted bentonite. In the present study the corrosion of iron in contact with different bentonites was investigated. The corrosion product was a 1:1 Fe layer silicate already described in literature (sometimes referred to as berthierine). Seven exposition test series (60 °C, 5 months) showed slightly less corrosion for the Na–bentonites compared to the Ca–bentonites. Two independent exposition tests with iron pellets and 38 different bentonites clearly proved the role of the layer charge density of the swelling clay minerals (smectites). Bentonites with high charged smectites are less corrosive than bentonites dominated by low charged ones. The type of counterion is additionally important because it determines the density of the gel and hence the solid/liquid ratio at the contact to the canister. The present study proves that the integrity of the multibarrier-system is seriously affected by the choice of the bentonite buffer encasing the metal canisters in most of the concepts. In some tests the formation of a patina was observed consisting of Fe

  5. Corrosion of high-level radioactive waste iron-canisters in contact with bentonite

    International Nuclear Information System (INIS)

    Graphical abstract: Corrosion at the bentonite iron interface proceeds unaerobically with formation of an 1:1 Fe silicate mineral. A series of exposure tests with different types of bentonites showed that Na–bentonites are slightly less corrosive than Ca–bentonites and highly charges smectites are less corrosive compared to low charged ones. The formation of a patina was observed in some cases and has to be investigated further. - Highlights: • At the iron bentonite interface a 1:1 Fe layer silicate forms upon corrosion. • A series of iron–bentonite corrosion products showed slightly less corrosion for Na-rich and high-charged bentonites. • In some tests the formation of a patina was observed consisting of Fe–silicate, which has to be investigated further. - Abstract: Several countries favor the encapsulation of high-level radioactive waste (HLRW) in iron or steel canisters surrounded by highly compacted bentonite. In the present study the corrosion of iron in contact with different bentonites was investigated. The corrosion product was a 1:1 Fe layer silicate already described in literature (sometimes referred to as berthierine). Seven exposition test series (60 °C, 5 months) showed slightly less corrosion for the Na–bentonites compared to the Ca–bentonites. Two independent exposition tests with iron pellets and 38 different bentonites clearly proved the role of the layer charge density of the swelling clay minerals (smectites). Bentonites with high charged smectites are less corrosive than bentonites dominated by low charged ones. The type of counterion is additionally important because it determines the density of the gel and hence the solid/liquid ratio at the contact to the canister. The present study proves that the integrity of the multibarrier-system is seriously affected by the choice of the bentonite buffer encasing the metal canisters in most of the concepts. In some tests the formation of a patina was observed consisting of Fe

  6. Determinantes da inflação numa pequena economia aberta : o caso de Cabo Verde

    OpenAIRE

    Pina, João Emanuel Brito Ledo de

    2008-01-01

    Mestrado em Economia Monetária e Financeira O Acordo de Cooperação Cambial entre Cabo Verde e Portugal de Março de 1998 veio criar profundas alterações no regime de política monetária em Cabo Verde. É normalmente citado que, se um pequeno país optar por um regime de paridade fixa em relação a uma moeda dominante, esse país impõe a si próprio uma disciplina que consiste basicamente em subordinar a sua política monetária à do país da referida moeda dominante e em manter equiparadas as respec...

  7. Mitochondrial portrait of the Cabo Verde archipelago: the Senegambian outpost of Atlantic slave trade.

    Science.gov (United States)

    Brehm, A; Pereira, L; Bandelt, H-J; Prata, M J; Amorim, A

    2002-01-01

    In order to study the matrilineal genetic composition in Cabo Verde (Republic of Cape Verde), an archipelago that used to serve as a Portuguese entrepôt of the Atlantic slave trade, we have analysed a total of 292 mtDNAs sampled from the seven inhabited islands for the hypervariable segment I (HVS-I) and some characteristic RFLPs of the coding regions. The different settlement history of the northwestern group of the islands is well reflected in the mtDNA pool. The total Cabo Verde sample clearly displays the characteristic mitochondrial features of the Atlantic fringe of western Africa and testifies to almost no mitochondrial input from the Portuguese colonizers. PMID:12015000

  8. X-chromosome STR markers data in a Cabo Verde immigrant population of Lisboa.

    Science.gov (United States)

    Afonso Costa, Heloísa; Morais, Paulo; Vieira da Silva, Cláudia; Matos, Sara; Marques Santos, Rodolfo; Espinheira, Rosa; Costa Santos, Jorge; Amorim, António

    2014-01-01

    Population genetic data of 12 X chromosomal short tandem repeats markers (DXS10074, DXS10079, DXS10101, DXS10103, DXS10134, DXS10135, DXS10146, DXS10148, DXS7132, DXS7423, DXS8378 and HPRTB) were analysed in 54 females and 95 males of an immigrant population from Cabo Verde living in Lisboa. The obtained results for forensic statistical parameters such as observed heterozigosity, polymorphism information content, power of discrimination and mean exclusion chance, based on single allele frequencies, reveal that this multiplex system is highly informative and can represent an important tool for genetic identification purposes in the immigrant population of Cabo Verde. Since the studied short tandem repeats genetic markers are distributed on four linkage groups, that can provide independent genotype information, we studied those groups as haploytes. The forensic efficiency parameters for the linked groups were all higher than 0.97, with linkage group I being the most polymorphic and linkage group III the less informative. PMID:24474659

  9. Indústria solar térmica em Cabo Verde : potencialidade do mercado

    OpenAIRE

    Nascimento, Cláusia Maria Fonseca da Rocha

    2008-01-01

    O presente trabalho pretende fazer uma análise do potencial do mercado Cabo-verdiano para a utilização da energia solar, através de algumas ferramentas de análise de mercado já conhecidas, nomeadamente as cinco forças de Porter, o Diamante de Porter, a análise PESTEL e a análise SWOT. O primeiro ponto que se pretende esclarecer é a questão: Será que Cabo Verde reúne as condições para ser considerado uma potencial mercado para a produção/ venda de sistemas solares para o a...

  10. O perfil comunicativo de crianças brasileiras na escola em Cabo Verde

    OpenAIRE

    Delgado, Lígia Rêgo da Silva

    2008-01-01

    Sabe-se que existem cerca de 130 cidadãos brasileiros residindo actualmente em Cabo Verde. Integram esse total, empresários, responsáveis de missões religiosas, funcionários de embaixada e de organizações internacionais, com permanência temporária no país, além de cidadãos, na maioria do sexo feminino, que fixaram residência no Arquipélago, por razões matrimoniais. As famílias constituídas por pai cabo-verdiano e mãe brasileira (ou vice-versa) têm filhos, muitos deles nascid...

  11. Adsorption of Bezanyl Red and Nylomine Green from aqueous solutions by natural and acid-activated bentonite

    OpenAIRE

    BENGUELLA, B.; YACOUTA-NOUR, A.

    2009-01-01

    The adsorption of two acid dyes, namely, Red Bezanyl and Green Nylomine, onto natural bentonite and acid activated bentonite from aqueous solutions were studied in a batch system. The kinetic data show that at the equilibrium, the acid-activated bentonite fixes more Bezanyl Red and Nylomine Green than the natural bentonite. Adsorption equilibrium was reached within 2 h. The results also showed that the kinetics of adsorption is best descibed by a pseudo second-order expression than a first or...

  12. Silurian bentonites in Lithuania: correlations based on sanidine phenocryst composition and graptolite biozonation – interpretation of volcanic source regions

    OpenAIRE

    Tarmo Kiipli; Sigitas Radzevičius; Toivo Kallaste

    2014-01-01

    Integrated correlation of bentonites (altered volcanic ashes) and graptolite biozonation is presented. Detailed study of two Lithuanian drill core sections extended previous knowledge of the occurrence and composition of bentonites to the south. Identification of graptolite species allowed bentonites to be assigned their proper stratigraphical position. Silurian bentonites in Lithuania are mostly characterized by wide and very wide XRD 201 reflections of the main component of sanidine phenocr...

  13. Cabo Verde: Democracia, Cultura Política e Esfera Pública

    Directory of Open Access Journals (Sweden)

    Nataniel Andrade Monteiro

    2016-07-01

    Full Text Available O artigo procura contribuir para se compreender e descrever aquilo que, no meu entender, constitui a nova abordagem da discussão acerca da cultura política e da esfera pública em Cabo Verde. A pobreza, o desemprego, a justiça social e a segurança, entre outros assuntos, têm sido alvos de atenção por parte da sociedade civil cabo-verdiana, sobretudo a partir da década de noventa, com o advento da democracia. O que me incita a pensar sobre novas tendências no que se refere à cultura política dos cabo-verdianos, particularmente na afirmação e configuração de uma esfera pública que prima pela prática do debate e respeito pela opinião pública, capaz de influenciar as acções do sistema político. O ano de 2015 tem sido marcado por debates de repercussão nacional e internacional, como é o caso mediático do Estatuto de Titulares de Cargos Políticos (ETCP. Este acontecimento, ao que tudo indica, possibilita uma nova configuração da esfera pública cabo-verdiana, corroborada numa cultura política participativa, de modo que sirva, não apenas para os períodos eleitorais, mas igualmente como instrumento para a consolidação do sistema político.

  14. Daily food intake of Kajikia audax (Philippi, 1887) off Cabo San Lucas, Gulf of California, Mexico

    OpenAIRE

    Leonardo A. Abitia-Cárdenas; Felipe Galván-Magaña; Víctor H Cruz-Escalona; Peterson, Mark S.; Jesús Rodríguez-Romero

    2011-01-01

    The daily food intake rates of the striped marlin, Kajikia audax (Perciformes: Istiophoridae), were estimated using qualitative and quantitative analyses of their trophic spectrum. We analyzed the stomach contents of 505 striped marlin caught by the sport fishing fleet off Cabo San Lucas, Baja California Sur, Mexico, sampled from October 1987 through December 1989. The most important preys were chub mackerel (Scomber japonicus), California pilchard (Sardinops caeruleus), and jumbo squid (Dosi...

  15. Daily food intake of Kajikia audax (Philippi, 1887) off Cabo San Lucas, Gulf of California, Mexico

    OpenAIRE

    Abitia Cárdenas, Leonardo Andrés; Galván Magaña, Felipe; Cruz Escalona, Víctor Hugo; Peterson, Mark S.; Rodriguez Romero, Jesús

    2011-01-01

    The daily food intake rates of the striped marlin, Kajikia audax (Perciformes: Istiophoridae), were estimated using qualitative and quantitative analyses of their trophic spectrum. We analyzed the stomach contents of 505 striped marlin caught by the sport fishing fleet off Cabo San Lucas, Baja California Sur, Mexico, sampled from October 1987 through December 1989. The most important preys were chub Mackerel (Scomber japonicus), California pilchard (Sardinops caeruleus), and jumbo squid (Dosi...

  16. Effects of Maghnian bentonite on physical properties of sandy soils under semi-arid Mediterranean climate.

    Science.gov (United States)

    Benkhelifa, M; Belkhodja, M; Daoud, Y; Tessier, D

    2008-01-01

    This research has for object to study the influence of clay addition, i.e., Maghnian bentonite, like deposit clay, in the physical properties of sandy materials from Mostaganem plateau (North-West Algeria) submitted to salinity and sodicity. The first result was to show that the clay content changes drastically the physical properties of clay-sand mixtures. Important differences were observed as a function of the sand particle size distribution. At given clay content, the saturated Hydraulic Conductivity (HCs) was lower when the sand size was small and spread. For the coarse sand the salinity was maintained, even for high clay contents, a significant hydraulic conductivity. One of the main characteristics of Maghnia clay is the presence of calcium carbonates in the natural material. In comparison to that of Mostaganem clay of other deposit, it appears less sensitive to sodicity. An important aspect is the initial state of the clay when used in addition to sands, i.e., disturbance, conditions of preparation of sand clay mixtures and presence of associated components such as carbonates. Maghnia clay appeared to be adapted to the improvement of sandy soils, not because its mineralogical characteristics, but for its natural cationic form and obviously the presence of calcite in it. PMID:18819588

  17. Cellular uptake and cytotoxic potential of respirable bentonite particles with different quartz contents and chemical modifications in human lung fibroblasts.

    Science.gov (United States)

    Geh, Stefan; Yücel, Raif; Duffin, Rodger; Albrecht, Catrin; Borm, Paul J A; Armbruster, Lorenz; Raulf-Heimsoth, Monika; Brüning, Thomas; Hoffmann, Eik; Rettenmeier, Albert W; Dopp, Elke

    2006-02-01

    Considering the biological reactivity of pure quartz in lung cells, there is a strong interest to clarify the cellular effects of respirable siliceous dusts, like bentonites. In the present study, we investigated the cellular uptake and the cytotoxic potential of bentonite particles (Øbentonite samples were tested for endotoxins with the in vitro-Pyrogen test and were found to be negative. Cellular uptake of particles by IMR90-cells was studied by transmission electron microscopy (TEM). Cytotoxicity was analyzed in IMR90-cells by determination of viable cells using flow cytometry and by measuring of the cell respiratory activity. Induced apoptotic cells were detected by AnnexinV/Propidiumiodide-staining and gel electrophoresis. Our results demonstrate that activated bentonite particles are better taken up by IMR90-cells than untreated (native) bentonite particles. Also, activated bentonite particles with a quartz content of 5-6% were more cytotoxic than untreated bentonites or bentonites with a quartz content lower than 4%. The bentonite samples induced necrotic as well as apoptotic cell death. In general, bentonites showed a high membrane-damaging potential shown as hemolytic activity in human erythrocytes. We conclude that cellular effects of bentonite particles in human lung cells are enhanced after chemical treatment of the particles. The cytotoxic potential of the different bentonites is primarily characterized by a strong lysis of the cell membrane. PMID:16059726

  18. Freezing of bentonite. Experimental studies and theoretical considerations

    Energy Technology Data Exchange (ETDEWEB)

    Birgersson, Martin; Karnland, Ola; Nilsson, Ulf (Clay Technology AB, Lund (Sweden))

    2010-01-15

    During its lifetime, a KBS-3 repository will be subject to various ambient temperatures. Backfilled tunnels, shafts and investigation bore holes closest to ground level will experience periods of temperature below 0 deg C. From a safety assessment perspective, it is therefore essential to understand the behavior of compacted bentonite below 0 deg C. A theoretical framework for predicting the pressure response in compacted water saturated bentonite due to temperature changes has been developed based on thermodynamics and a single pore-type. This model predicts an approximately linear temperature dependence of swelling pressure P{sub s}(w,DELTAT) = P{sub s}(w,0 deg C) + DELTAs(w)DELTAT/nu{sub clay}(w) where DELTAT denotes a temperature difference from 0 deg C, DELTAs(w) is the difference in partial molar entropy between clay water and bulk water, nu{sub clay} (w) is the partial molar volume of the clay water and w denotes the water/solid mass ratio of the clay. As bulk water changes phase at 0 deg C, DELTAs(w) has a different value dependent on whether DELTAT is negative or positive. Above 0 deg C DELTAs(w) is a small value for all relevant densities which means that the pressure response due to temperature changes is small. A further consequence of this fact is that DELTAs(w) is a large positive number below 0 deg C when the external water phase is transformed to ice. Consequently, the model predicts a large drop of swelling pressure with temperature below 0 deg C, in the order of 1.2 MPa/deg C. Specifically, the swelling pressure is zero at a certain (negative) temperature T{sub C}. T{sub C} also quantifies the freezing point of the bentonite sample under consideration, as ice formation in the bentonite does not occur until swelling pressure is lost. A large set of laboratory tests have been performed where fully water saturated samples of bentonites have been exposed to temperatures in the range -10 deg C to +25 deg C. The swelling pressure response has been

  19. Freezing of bentonite. Experimental studies and theoretical considerations

    International Nuclear Information System (INIS)

    During its lifetime, a KBS-3 repository will be subject to various ambient temperatures. Backfilled tunnels, shafts and investigation bore holes closest to ground level will experience periods of temperature below 0 deg C. From a safety assessment perspective, it is therefore essential to understand the behavior of compacted bentonite below 0 deg C. A theoretical framework for predicting the pressure response in compacted water saturated bentonite due to temperature changes has been developed based on thermodynamics and a single pore-type. This model predicts an approximately linear temperature dependence of swelling pressure Ps(w,ΔT) = Ps(w,0 deg C) + Δs(w)*ΔT/νclay(w) where ΔT denotes a temperature difference from 0 deg C, Δs(w) is the difference in partial molar entropy between clay water and bulk water, νclay (w) is the partial molar volume of the clay water and w denotes the water/solid mass ratio of the clay. As bulk water changes phase at 0 deg C, Δs(w) has a different value dependent on whether ΔT is negative or positive. Above 0 deg C Δs(w) is a small value for all relevant densities which means that the pressure response due to temperature changes is small. A further consequence of this fact is that Δs(w) is a large positive number below 0 deg C when the external water phase is transformed to ice. Consequently, the model predicts a large drop of swelling pressure with temperature below 0 deg C, in the order of 1.2 MPa/deg C. Specifically, the swelling pressure is zero at a certain (negative) temperature TC. TC also quantifies the freezing point of the bentonite sample under consideration, as ice formation in the bentonite does not occur until swelling pressure is lost. A large set of laboratory tests have been performed where fully water saturated samples of bentonites have been exposed to temperatures in the range -10 deg C to +25 deg C. The swelling pressure response has been recorded continuously. The samples have been varied with respect to

  20. Corrosion of high-level radioactive waste iron-canisters in contact with bentonite.

    Science.gov (United States)

    Kaufhold, Stephan; Hassel, Achim Walter; Sanders, Daniel; Dohrmann, Reiner

    2015-03-21

    Several countries favor the encapsulation of high-level radioactive waste (HLRW) in iron or steel canisters surrounded by highly compacted bentonite. In the present study the corrosion of iron in contact with different bentonites was investigated. The corrosion product was a 1:1 Fe layer silicate already described in literature (sometimes referred to as berthierine). Seven exposition test series (60 °C, 5 months) showed slightly less corrosion for the Na-bentonites compared to the Ca-bentonites. Two independent exposition tests with iron pellets and 38 different bentonites clearly proved the role of the layer charge density of the swelling clay minerals (smectites). Bentonites with high charged smectites are less corrosive than bentonites dominated by low charged ones. The type of counterion is additionally important because it determines the density of the gel and hence the solid/liquid ratio at the contact to the canister. The present study proves that the integrity of the multibarrier-system is seriously affected by the choice of the bentonite buffer encasing the metal canisters in most of the concepts. In some tests the formation of a patina was observed consisting of Fe-silicate. Up to now it is not clear why and how the patina formed. It, however, may be relevant as a corrosion inhibitor. PMID:25536393

  1. Microcapillary flow behavior of magnetic nanofluids in the presence of plate shaped bentonite particles

    International Nuclear Information System (INIS)

    Plate shaped bentonite particles of size ∼600 nm and thickness ∼2 nm are dispersed in a magnetic nanofluid. Magnetic field dependent flow behavior of this composite suspension is studied using a horizontal microcapillary placed between the poles of an electromagnet. The plate shaped bentonite particle produces extra hindrance to the flow under the application of moderate magnetic field and produces an enhanced magnetoviscous effect. 75% volume concentration of bentonite produces eight times larger change in magnetic field dependent viscosity than does the pure magnetic nanofluid. Hindrance to the flow is due to the chain like structure of magnetic nanoparticles, tumbling and rotational motion of bentonite particles and interaction between magnetic and bentonite particles. The field-induced structures are also observed using an optical microscope. Results offer several advantages over the inverse MR effect as well as to study the motion of biological cells and tissues under the effect of magnetic field. -- Highlights: ► Dispersed plate shaped bentonite particles in magnetic fluids to study capillary viscosity. ► Increased viscosity is due to the hindrance to the rotation of the bentonite particles. ► Increase in viscosity is five times larger for bentonite particles than the pure magnetic fluids. ► This is a new kind of magnetoviscous effect, dispersing anisotropic particles in magnetic fluids

  2. Synthesis and characterization of poly(sodium acrylate)/ bentonite superabsorbent composite

    International Nuclear Information System (INIS)

    Poly(sodium acrylate)/bentonite superabsorbent composite with water absorbency 1562 g·g−1 was synthesized by inverse suspension polymerization. The introduction of bentonite improves the water absorbency and facilitates the particle size even distribution of the composite. The network structure in the superabsorbent hydrogel is confirmed.

  3. Facile synthesis of carbon nanotube/natural bentonite composites as a stable catalyst for styrene synthesis.

    Science.gov (United States)

    Rinaldi, Ali; Zhang, Jian; Mizera, Jan; Girgsdies, Frank; Wang, Ning; Hamid, Sharifah Bee Abd; Schlögl, Robert; Su, Dang Sheng

    2008-12-28

    Natural bentonite mineral, without any wet chemical treatment, was used directly to catalyze the growth of multi-wall CNTs and the produced CNTs/bentonite as an integrated composite stably catalyzed the oxidative dehydrogenation reaction over a long period of time; this concept provides a highly economical way for large-scale synthesis of nanocarbons and manufacture of styrene synthesis catalysts. PMID:19057768

  4. Characterization of Cr/Bentonite and HZSM-5 Zeolite as Catalysts for Ethanol Conversion to Biogasoline

    Directory of Open Access Journals (Sweden)

    Robert Ronal Widjaya

    2012-04-01

    Full Text Available In this research it has been done characterization on Cr/Bentonit and Zeolit HZSM-5 catalysts for ethanol catalytic process to biogasoline (equal to gasoline. Cr/Bentonit has high acidity and resistant to a lot of moisture, so in addition to being able to processing feed which a lot of moisture (>15% from ethanol-water mixture, also it is not easy deactivated. Cr/Bentonit which is then used as the catalyst material on the process of ethanol conversion to be biogasoline and the result was compared with catalyst HZSM-5 zeolite. Several characterization methods: X-ray diffraction, Brunauer Emmett Teller (BET, thermogravimetry analysis (TGA, and catalyst activity tests using catalytic Muffler instrument and gas chromatography-mass spectrometry (GC-MS for product analysis were performed on both catalysts. From acidity measurement, it is known that acidity level of Cr/Bentonit is the highest and also from XRD result, it is known there is shift for 2theta in Cr/Bentonit, which indicates that Cr-pillar in the Bentonite can have interaction. It is also supported by BET data that shows the addition of specific surface are in Cr/Bentonite compared with natural Bentonite before pillarization. Futhermore catalyst activity test produced the results, analyzed by GC-MS, identified as butanol and also possibly formed hexanol, decane, dodecane, undecane, which are all included in gasoline range (C4 until C12.

  5. Physico-chemical characterization of bentonite and its application for Mn2+ removal from water

    Directory of Open Access Journals (Sweden)

    Ranđelović Marjan S.

    2011-01-01

    Full Text Available Bentonite is mainly composed of clay minerals from smectite group, therefore it has a well developed and chemically active surface area and high cation exchange capacity. Moreover, an interlayer space of smectite has unusual hydration properties, which manifest as swelling of bentonite in water. These properties make bentonite as a commonly used raw material in chemistry and industry, and it is very important in environmental protection and water treatment as an effective sorbent of heavy metals. The results of X-ray diffraction, a cationic exchange capacity, specific surface area, acid-base properties of the surface and the swelling index showed that the bentonite sample contains mostly montmorillonite. The aim of this study was to test the efficacy of bentonite in the removal of Mn2+ from aqueous systems. The experimental results of Mn2+ adsorption on the bentonite were interpreted by Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherms. The adsorption isotherm studies indicate that the adsorption of Mn2+ follows Langmuir isotherm very well. Theoretical monolayer saturation capacity according to Langmuir model was 12.41 mg/g. The removal of Mn2+ is achieved by ion exchange mechanism with naturally occurring cations in bentonite, as well as by forming the inner- and outer-sphere complexes with bentonite surface.

  6. Literature study on the microstructure of bentonite and its effect on diffusion

    International Nuclear Information System (INIS)

    In the study the available information from the literature on the microstructural properties of bentonite and its main component montmorillonite have been compiled, together with different phenomena which have been found to participate in the diffusion process in bentonite. (167 refs., 36 figs., 6 tabs.)

  7. Iron and organo-bentonite for the reduction and sorption of trichloroethylene.

    Science.gov (United States)

    Cho, Hyun-Hee; Lee, Taeyoon; Hwang, Sun-Jin; Park, Jae-Woo

    2005-01-01

    Hybrid barriers using dechlorination and immobilization were studied to remove trichloroethylene (TCE) in this study. Hybrid barriers of iron filings and organo (hexadecyltrimethylammonium, HDTMA)-bentonite were simulated in columns to assess the performance of the hybrid barriers. TCE reduction rate for the mixture of zero valent iron (ZVI) and HDTMA-bentonite was approximately seven times higher than that for ZVI, suggesting the reduction of TCE was accelerated when HDTMA-bentonite was mixed with ZVI. For the column of two separate layers of iron and HDTMA-bentonite, TCE reduction rate was nearly similar to that for ZVI alone, but the partition coefficient (Kd) was 4.5 times higher than that for ZVI only. TCE was immobilized in the first layer with HDTMA-bentonite due to sorption, and then dechlorinated in the second layer with iron filings due to reduction. The HDTMA-bentonite and minimally-desorbed HDTMA from the organo-bentonite are believed to contribute the increase in TCE concentration on iron surface so that more TCE could be available for reduction. Therefore, the incorporation of HDTMA-bentonite into ZVI not only can effectively retard the transport of chlorinated organic contaminants from landfill leachate or oil shock in subsurface environment, also can expedite the reduction rate of TCE. PMID:15522338

  8. Bentonite barriers. New experiments and state of the art. Bentonite as barrier material for the sealing of underground disposal sites. Final report

    International Nuclear Information System (INIS)

    Bentonite is intensively investigated from many institutes for its properties and feasibility as engineering barrier material for many environmental facilities like landfill, underground landfill for chemotoxic waste and also HLW repositories. A summary of the current state of knowledge regarding the origin of bentonites and different processes through bentonite is provided together with the potential further research and development needs. Diffusion experiments with gas (CO2, H2, CH4 and SF6) and heavy metals Pb, Cd and Cs in highly saline solution (50 % and 90 % NaCl solutions, 90 % IP21 solution) at room temperature and atmosphere pressure conditions through compacted MX-80 bentonite with three different bulk dry densities (1,400 kg/m3,1,600 kg/m3 and/or 1,800 kg/m3) were performed. Numerical simulations of some experiments were undertaken.

  9. Preparation, characterization and thermal stability of bentonite modified with bis-imidazolium salts

    Energy Technology Data Exchange (ETDEWEB)

    Makhoukhi, B., E-mail: benamarmakh@yahoo.fr [Laboratory of Separation and Purification Technologies, Department of Chemistry, Tlemcen University, Box 119, Tlemcen (Algeria); Villemin, D. [Laboratoire de Chimie Moléculaire et Thio-organique, UMR CNRS 6507, INC3M, FR 3038, ENSICAEN and Université de Caen, 14050 Caen (France); Didi, M.A. [Laboratory of Separation and Purification Technologies, Department of Chemistry, Tlemcen University, Box 119, Tlemcen (Algeria)

    2013-02-15

    Sodium bentonite was modified with several organic bis-imidazolium salts. Organoclays with water soluble surfactants were prepared by the traditional cation exchange reaction. The bis-imidazolium-bentonites were characterized by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction analysis (PXRD) and thermogravimetric analysis (TGA). The effect of chemical composition and molecular weight of the salts on the thermal stability and basal spacing were evaluated. The bis-imidazolium-bentonites showed enhanced thermal stability (300–400 °C) and may be potentially useful materials for melt processing of polymer/layered silicates nanocomposites. - Highlights: ► Geometry and volume of the molecule influence on interlayer spacing of modified bentonites. ► The intercalation increases with molecule length. ► The modified bentonites have an appreciably higher thermal stability.

  10. Corrosion behavior of carbon steel in wet Na-bentonite medium

    International Nuclear Information System (INIS)

    Corrosion behaviors of carbon steel in wet Na-bentonite medium were studied. Corrosion rate of carbon steel in wet bentonite was measured to be 20 μm/yr at 25 deg C using the AC impedance technique. This value is agreed with that obtained by weight loss at 40 deg C for 1 year. The effect of bicarbonate ion on the corrosion of carbon steel in wet bentonite was also evaluated. The carbon steels in wet bentonite having 0.001, 0.01, and 0.1 M concentration of bicarbonate ion gave corrosion rates of 20, 8, and 0.2 μm/yr, respectively. Corrosion potentials of specimens were also measured and compared with the AC impedance results. Both results indicated that bicarbonate ion could effectively reduce the corrosion rate of carbon steels in bentonite due to the formation of protective layer on the carbon steel. (author)

  11. Cytotoxicity and mechanical behavior of chitin-bentonite clay based polyurethane bio-nanocomposites.

    Science.gov (United States)

    Zia, Khalid Mahmood; Zuber, Mohammad; Barikani, Mehdi; Hussain, Rizwan; Jamil, Tahir; Anjum, Sohail

    2011-12-01

    Chitin based polyurethane bio-nanocomposites (PUBNC) were prepared using chitin, Delite HPS bentonite nanoclay enriched in montmorillonite (MMT), 4,4'-diphenylmethane diisocyanate (MDI) and polycaprolactone polyol CAPA 231 (3000 g/mol(-1)). The prepolymers having different concentration of Delite HPS bentonite nanoclay were extended with 2 moles of chitin. The structures of the resulted polymers were determined by FT-IR technique. The effect of nanoclay contents on mechanical properties and in vitro biocompatibility was investigated. The mechanical properties of the synthesized materials were improved with increase in the Delite HPS bentonite nanoclay contents. Optimum mechanical properties were obtained from the PU bio-nanocomposite samples having 4% Delite HPS bentonite nanoclay. The results revealed that the final PU bio-nanocomposite having 2% Delite HPS bentonite nanoclay contents is ideal contenders for surgical threads with on going investigations into their in vitro biocompatibility, non-toxicity, and mechanical properties. PMID:21945787

  12. The Bentonite Barrier: Microstructural properties and the influence of γ-radiation

    International Nuclear Information System (INIS)

    The main objectives of this work were to investigate three different topics relevant for the bentonite barrier, namely: - The microstructural properties of compacted bentonite, by i) testing the possibility of colloid transport and ii) by determining the interparticle and interlayer porosity, i.e. the free porosity in the saturated compacted bentonite by a basal spacing analysis (Paper I and II, respectively). - Potential γ-radiation-induced effects on i) montmorillonite colloid stability and changes in sol/gel properties, ii) the structural Fe(II)/Fe(III) ratio in montmorillonite and its effect on the montmorillonites reactivity towards one of the major oxidants formed upon water radiolysis, H2O2, and iii) radionuclide retention in compacted bentonite (Paper III-V, respectively). - Potential interactions of bentonite particles with Silica sol, i.e. the SiO2-colloids that are planned to be used as an injection grout during construction of the repository (Paper VI)

  13. Sorption of cesium on bentonite: The role of calcite

    International Nuclear Information System (INIS)

    Full text: Since bentonite is investigated for its use in Engineered Barriers Systems as backfill material, many studies of their surfaces properties have been performed in the past years to qualify and quantify adsorption on their surfaces, which can be one of the major processes limiting migration of radionuclides away from a disposal site. Nevertheless, most of these studies concerned simplified systems, such as Na-montmorillonite in mono-electrolyte solution. As ion-exchange processes are of importance in water-clays interactions, adsorption of natural major ions has also to be taken into account for natural systems. The aim of this work is (i) to quantify the sorption of the natural major cations on the montmorillonite surface, (ii) to compare the sorption of cesium, in two different systems, a simple one (Na-montmorillonite in NaNO3 0.05 Mol.L-1) and a complex one (natural bentonite in a synthetic natural water) and then (iii) to assess the influence of the natural major ions on this sorption, and to identify the role of the calcite phase present in bentonite. The methodology used consists in several batch experiments, first considering a very simple solution (NaNO3), then using mixtures of two different electrolytes, and lastly using a synthetic natural water. A surface complexation model, describing the surface of clays as a mixture of ion-exchange and complexation surface sites, is used to provide interpretations and quantifications of the sorption processes. Observed results indicate that affinity for the montmorillonite surface is greatest for Ca, then Mg and then K. The sorption of cesium is strongly affected by the presence in solution of Ca, witch can come from the partial dissolution of calcite. (author)

  14. Interactions between copper corrosion products and MX-80 bentonite

    International Nuclear Information System (INIS)

    The report presents results from a study of the possible interaction between copper corrosion products and MX-80 bentonite under conditions that might occur in a final repository for spent nuclear fuel in Finland. The first part of the report describes the results from a literature survey, the objective of which was to identify some relevant corrosion products that might form when copper corrodes in wet MX-80 bentonite. On the basis of the literature survey, atacamite and a green copper corrosion product produced in-house were used for experimental studies. Experiments were performed with both soft and compacted MX-80. The soft samples consisted of water-saturated MX-80 mixed with CuCl2 solutions of various concentrations. The samples were kept under anaerobic conditions at ambient room temperature or at 75 deg C for 330 days. Porewater samples were then squeezed from the samples and analysed. Compacted MX-80 samples were stored under anaerobic conditions and kept in contact with an NaCl solution. The samples were kept at room temperature and 75 deg C for 2.9 years and then analysed. The presence of either atacamite or the green copper corrosion product on the plates did not have any notable effects on the porewater chemistry. However, the Cu concentration profiles indicated that the corrosion products did dissolve, and then diffused into the surrounding bentonite. Concentration profiles were found to be roughly the same, irrespective of whether the samples had been stored at room temperature or at 75 deg C. (orig.)

  15. Influence of dry density on HTO diffusion in GMZ bentonite

    International Nuclear Information System (INIS)

    With the low permeability and high swelling property, Gaomiaozi (GMZ) bentonite is regarded as the favorable candidate backfilling material for a potential repository. The diffusion behaviors of HTO in GMZ bentonite were studied to obtain effective diffusion coefficient (De) and accessible porosity (ε) by through- and out-diffusion experiments. A computer code named Fitting for diffusion coefficient (FDP) was used for the experimental data processing and theoretical modeling. The De and ε values were (5.2-11.2) x 10-11 m2/s and 0.35-0.50 at dry density from 1,800 to 2,000 kg/m3, respectively. The De values at 1,800 kg/m3 was a little higher than that of at 2,000 kg/m3, whereas the D e value at 1,600 kg/m3 was significantly higher (approximately twice) than that of at 1,800 and 2,000 kg/m3. It may be explained that the diffusion of HTO mainly occurred in the interlayer space for the highly compacted clay (dry density exceeding 1,300 kg/m3). 1,800 and 2,000 kg/m3 probably had similar interlayer space, whereas 1,600 kg/m3 had more. Both De and ε values decreased with increasing dry density. For compacted bentonite, the relationship of De and ε could be described by Archie's law with exponent n = 4.5 ± 1.0. (author)

  16. Performance of bentonite/crushed tuff seals for nuclear waste repositories

    International Nuclear Information System (INIS)

    Mixtures of bentonite and crushed rock are potential sealing materials for high level nuclear waste repositories. To allow for overall repository performance assessments, evaluations of the sealing performance under diverse conditions are needed. American Colloid c/s granular bentonite and Apache Leap tuff have been mixed to prepare samples for laboratory flow testing. Bentonite weight percent and crushed tuff gradation are the major variables studied. The sealing performance assessments include high injection pressure flow tests, polyaxial flow tests, high temperature flow tests, and piping tests. The results indicate that an appropriate composition would have at least 25% bentonite by weight mixed with well-graded crushed rock. The sealing performance of bentonite/crushed rock mixtures can be enhanced by increasing the amount of bentonite to 35%. The piping damage to the sealing performance is small if the maximum hydraulic gradient does not exceed 120 and 280 for 25 and 35% bentonite content, respectively. The hydraulic gradients above which flow of bentonite takes place are deemed critical. The pressure required to generate a critical gradient probably is related to the yield stress of the bentonite in the mixture. A difference up to one or two orders of magnitude has been observed between the vertical and horizontal permeabilities. The high horizontal permeability results from the uneven bentonite distribution in the pores between the crushed rock particles due to particle segregation. Temperature seems to have no negative effects on the sealing performance within the test range from room temperature to 60. Recommendations for future research are included. 15 refs., 5 figs., 1 tab

  17. Effective diffusivities of iodine, chlorine, and carbon in bentonite buffer material

    International Nuclear Information System (INIS)

    Effective diffusivities of iodine, chlorine, and carbon in mixtures of bentonite and sand were determined by measuring the effective diffusivities of common chemical compounds labeled with radioactive isotopes of these elements. For carbon, both inorganic and organic carbon compounds were used in order to consider the variety of chemical forms of carbon possible in a radioactive waste repository. The bentonite content and dry density of the bentonite-sand mixture were varied. Two chemically different aqueous solutions, representing concrete pore water and bentonite pore water, were used to represent different conditions that could affect diffusivity in bentonite buffer material in a hypothetical radioactive waste disposal situation. The effective diffusivities of iodine, chlorine, and carbon tended to decrease with increasing bentonite content and dry density of the mixture. In the presence of simulated concrete pore water, the effective diffusivities for iodine, chlorine, and carbon in the bentonite mixtures were not higher than those obtained when simulated bentonite pore water was used. Except for some organic compounds, the measured effective diffusivities were lower than that of tritiated water under the same experimental conditions. This was attributed primarily to exclusion of anions from the bentonite pores. The effective diffusivity of carbon depended on its chemical form. The effective diffusivity of the anionic forms of organic carbon tested (carboxylic acids) was as low as that of inorganic anionic carbon. Measured effective diffusivities were compared with those calculated using a model based on electrical double layer theory. The theory was applied to calculate distributions of electrolyte ions and diffusion ions in the bentonite pores. The calculated effective diffusivities showed good agreement with the measured values

  18. Study of aggregation in a micellar solution within bentonite clay by SANS

    International Nuclear Information System (INIS)

    Aggregation studies of surfactant solutions exposed to different surfaces are relevant to their applications as detergents, oil recovery agents etc. The infusion of SDS micellar solutions into the pores of compacted normal bentonite clay and the clay saturated with sodium at different concentrations viz. 1, 2 and 5 molar percentages, has been studied here by small angle neutron scattering and X-ray diffraction. In the sodium saturated bentonite, the Na+ ion (having a positive scattering length) is held in the interlayer of the clay and on account of this, the scattering length density difference (i.e. contrast) between the bentonite matrix and the inter-layer pores is lower than the bentonite which has less sodium. The average pore size in normal bentonite clay is 13 Å while in the clay saturated with 1M Na+ ions it is 20 Å . For a 10% SDS solution, the micelles are prolate ellipsoids having average semi major and minor axes of 22.5 Å and 16.7 Å, respectively with an effective charge of 30 e.u. and an aggregation number of 75. Both aggregation number and effective charge increase with concentration of SDS solution. Sodium is present in normal bentonite but is enhanced in concentration in the case of sodium saturated bentonite. Aggregation number and micellar separation are reduced for SDS loaded into raw bentonite clay and then into Na saturated clay. Likewise, there is a reduction of fractional charge on the micelle in going from raw to sodium bentonite caused by the Na+ ions present on the surface of the clay pores which would be attracted to the negative surface of each micelle thereby reducing its net charge. The effective attraction between micelles and Na+ ion concentration control the growth of aggregates, their volumes and aggregation numbers. Hence the sodium ion in the bentonite plays a vital role in the change of these parameters by effectively reducing charge on the micellar aggregates.

  19. Adsorption of La(III) onto GMZ bentonite. Effect of contact time, bentonite content, pH value and ionic strength

    International Nuclear Information System (INIS)

    Bentonite has been studied extensively because of its strong adsorption capacity. A local Na-bentonite named GMZ bentonite, collected from Gaomiaozi County (Inner Mongolia, China), was selected as the first choice of buffer/backfill material for the high-level radioactive waste repository in China. In this research, the adsorption of La (III) onto GMZ bentonite was performed as a function of contact time, pH, solid content and metal ion concentrations by using the batch experiments. The results indicate that the adsorption of La (III) on GMZ bentonite achieves equilibration quickly and the kinetic adsorption follows the pseudo-second-order model; the adsorption of La (III) on the adsorbent is strongly dependent on pH and solid content, the adsorption process follows Langmuir isotherm. The equilibrium batch experiment data demonstrate that GMZ bentonite is effective adsorbent for the removal of La (III) from aqueous solution with the maximum adsorption capacity of 26.8 mg g-1 under the given experimental conditions. (author)

  20. ADSORPTION STUDY OF RHODAMIN B DYE ON IRAQI BENTONITE AND MODIFIED BENTONITE BY NANOCOMPOUNDS TIO2, ZNO, AL2O3 AND SODIUM DODECYL SULFATE

    Directory of Open Access Journals (Sweden)

    Iqbal Salman AL-Jobouri

    2013-01-01

    Full Text Available The adsorption of Rhodamin B on Iraqi bentonite at the concentration range from 50 to 250 μg mL-1 was studied, Nano compounds; ZnO, TiO2, Al2O3 m and SDS in different amounts 0.01-0.1 g 10-1 g of Bentonite were used to modified the adsorption capacity of bentonite to remove the Rhodamin B from aqueous solutions. The study indicated that using 0.05 g and 0.1 of Sodium Dodecyl Sulfate (SDS lead to increase the percentage removal (%R from 79.3% for pure bentonite to 99.3%. While using 0.05 g TiO2 lead to increase the %R to 98.9%, 0.05 of ZnO to 98.6%. The other amount additives and Al2O3 using was not success to increase the %R for the Rhodamin B on bentonite surface. SEM measurement was achieved to discover the Nanoparticl exists in the bentonite surfaces.

  1. Eutrophication management in surface waters using lanthanum modified bentonite

    DEFF Research Database (Denmark)

    Copetti, Diego; Finsterle, Karin; Marziali, Laura;

    2016-01-01

    This paper reviews the scientific knowledge on the use of a lanthanum modified bentonite (LMB) to manage eutrophication in surface water. The LMB has been applied in around 200 environments worldwide and it has undergone extensive testing at laboratory, mesocosm, and whole lake scales. The...... alkalinity waters. To date there are no indications for long-term negative effects on LMB treated ecosystems, but issues related to La accumulation, increase of suspended solids and drastic resources depletion still need to be explored, in particular for sediment dwelling organisms. Application of LMB in...... saline waters need a careful risk evaluation due to potential lanthanum release....

  2. Swelling characteristics of immersed sand-bentonite mixtures

    Institute of Scientific and Technical Information of China (English)

    丰土根; 崔红斌; 孙德安; 杜冰

    2008-01-01

    A laboratory one-dimensional consolidation apparatus was employed to research the swelling stress and volume of the sand-bentonite mixture under immersed conditions. The stress-strain characteristics of mixtures under varied mixing ratios and loading statuses were analyzed. Based on the results of tests, the mechanism of mixture swelling and collapsing was further discussed. The results show that mixtures with low sand ratios are suitable as hydraulic barrier or containment barriers of general landfills, geological repository and other hydraulic infrastructure works.

  3. Efficient removal of Eu(III) from aqueous solutions using super-adsorbent of bentonite-polyacrylamide composites

    International Nuclear Information System (INIS)

    The bentonite has been studied extensively to preconcentrate radionuclides from aqueous solutions, however, the low sorption capacity limits it application in real work. Herein, bentonite embedded in the polyacrylamide (PAAm) gels is synthesized and used as a novel adsorbent for the removal of Eu(III) from aqueous solutions. The bentonite-PAAm composites show much higher sorption capacity for Eu(III) preconcentration than bare bentonite. The bentonite-PAAm composites can be used as super-adsorbent for the removal of Eu(III) from aqueous solution in radioactive pollution cleanup. (author)

  4. Retention of chromium by modified Al-Bentonite Retenção de cromo por Al-bentonita modificada

    OpenAIRE

    C. Volzone; L.B. Garrido

    2002-01-01

    Retention of chromium (III) from a tanning wastewater by modified Al-bentonites was studied. One bentonite from San Juan province, Argentina, was used. Al-bentonite was prepared by contact of bentonite with hydrolyzed OH-Al solutions (0.10 M in Al) for 24 hours. The modified Al-bentonites were obtained by: a) treatment with 0.5 M sodium chloride; b) with 0.5 M sodium chloride adjusted at pH 8; and c) treatment with an hexametaphosphate solution after sodium addition. Then, the samples were dr...

  5. National Wildlife Refuge Visitor Survey 2010/2011 : Individual refuge results for Cabo Rojo National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report summarizes the National Wildlife Refuge Visitor Survey for Cabo Rojo NWR and is part of the USGS Data Series 643. The survey was conducted to better...

  6. Characterization of natural organic matter in bentonite clays for potential use in deep geological repositories for used nuclear fuel

    International Nuclear Information System (INIS)

    extracts from contemporary soils and sediments as well as the lack of amino acids suggests that the material corresponding to the aromatic signal is not composed of lignin or proteins but may be derived from another source such as black carbon or some other non-extractable aromatic-rich NOM. The aliphatic signal appears to correspond to long-chain compounds with little side branching based on the results of the one-dimensional (1D) and two-dimensional (2D) solution-state 1H NMR analyses. Overall, the organic geochemical analyses suggest that the NOM is composed mainly of plant-derived waxes and highly aromatic carbon with low contributions from small molecules. The compounds identified by the molecular-level analysis of NOM in the clay samples are hypothesized to be recalcitrant but future studies should examine if these compounds may serve as a microbial substrate to further test the observations of this study. Furthermore, our study suggests that the NOM has undergone diagenesis and that marine NOM signatures are no longer recognizable or detectable. As such, future work may also examine the diagenesis of these deposits to further understand the NOM geochemistry and paleoenvironmental conditions in bentonite deposits

  7. Numerical analysis for heating and infiltration test at model deposition hole in underground hard rock laboratory

    International Nuclear Information System (INIS)

    Various insitu tests for the safety disposal of radioactive waste are conducted in the Swedish underground hard rock laboratory. Canister Retrieval Test (CRT) is a heating and infiltration test at a full-scale deposition hole. In this paper, we conducted thermo-hydro-mechanical coupled analysis for CRT and compared the results with measured data. The evolution of temperature and relative humidity and the profiles of bentonite's dry density were well reproduced by numerical analysis. Sensitivity analysis was also conducted in order to investigate the influence of hydraulic properties of surrounding rock mass on re-saturation behavior of bentonite in a deposition hole. (author)

  8. Stress/strain/time properties of highly compacted bentonite

    International Nuclear Information System (INIS)

    In this paper, a recently developed creep theory based on statistical mechanics has been used to analyze a number of experimental creep curves, the conclusion being that the creep behavior of dense MX-80 bentonite is in agreement with the physical model, and that the average bond strength is within the hydrogen bond region. The latter conclusion thus indicates that interparticle displacements leading to macroscopic creep takes place in interparticle and intraparticle water lattices. These findings were taken as a justification to apply the creep theory to a prediction of the settlement over a one million year period. It gave an estimated settlement of 1 cm at maximum, which is of no practical significance. The thixotropic and viscous properties of highly compacted bentonite present certain difficulties in the determination and evaluation of the stress/strain/time parameters that are required for ordinary elastic and elasto-plastic analyses. Still, these parameters could be sufficiently well identified to allow for a preliminary estimation of the stresses induced in the metal canisters by slight rock displacements. The analysis, suggests that a 1 cm rapid shear perpendicular to the axes of the canisters can take place without harming them. (author)

  9. Adsorption behaviour of bivalent ions onto Febex bentonite

    Energy Technology Data Exchange (ETDEWEB)

    Missana, T.; Garcia-Gutierrez, M. [Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas (CIEMAT), Dpt. de Impacto Ambiental de la Energia Madrid (Spain)

    2005-07-01

    The sorption and transport properties of radionuclides in the near and far field barriers of a deep geological radioactive waste repository are amongst the principal aspects to be evaluated for the performance assessment (PA) of such a kind of disposal. The study of the clayey materials is crucial because the backfill material is constituted by compacted clay in most countries design; in addition, argillaceous formations are particularly suitable as host rock formations. It is widely recognised that, to acquire predictive modelling capability, a theoretical effort is needed for a mechanistic understanding of sorption processes, as they greatly influence the transport of radionuclides in clay porous structures. In this work, an exhaustive experimental study of the Co(II), Sr (II) and Ca(II) sorption behaviour on a Spanish bentonite was carried out. The clay used for these experiments is the FEBEX bentonite, which is basically formed by smectite (93 {+-} 2%) with small percentages of quartz (2 {+-} 1 %), plagioclase (3 {+-} 1 %), cristobalite (2 {+-} 1 %) and traces of minerals such as K-feldspar and calcite. (authors)

  10. Buffer construction technique by means of granular bentonite

    International Nuclear Information System (INIS)

    Buffer construction technology using bentonite pellets as filling material is one of the promising technologies for enhancing the ease of buffer construction. In this study, a bentonite pellet filling test was conducted, using a filling system equipped with a screw conveyor system, in a full-scale simulated disposal drift. A simulated waste disposal drift configured as a half-cross-section model with a height of 2.22 m and a length of 6.0 m was constructed for the test, and two dummy overpacks were placed in the drift. The filling test was conducted in two phases. The average dry density of the buffer fill was 1.29 Mg/m3, which was close to the target value. The angle of repose was approximately 40 degrees. The test results indicate that the buffer construction technology using screw conveyor system for pellet conveyance in a waste disposal drift is a promising technology of the disposal of high level radioactive wastes. (author)

  11. Electrophysical characteristics of polyurethane/organo-bentonite nano composites

    International Nuclear Information System (INIS)

    Modification of the Egyptian Bentonite (EB) was carried out using organo-modifier namely; octadecylamine ODA. Before the modification, the cation exchange capacity (CEC) of the EB was measured, also it was purified from different impurities using HCl and distilled water. The Organo-bentonite OB was characterized using IR, XRD, and TEM. PU/ODA-B nano composites were prepared by in situ polymerization then characterized by XRD and TEM. An amount of ODA-B ranging from 0.25% up to 5% by weight was added to the polyol component of the resin before mixing with toluene diisocynate TDI. TEM showed that the nano composites achieved good dispersion in the polyurethane matrix. The mechanical, swelling and electrical properties of the nano composites were measured. The results indicate that the tensile strength of all the nano composites enhanced with the addition of OB compared with the pure PU. The crosslink density of the nano composites increases with increasing the content of OB. The Pool-Frenckel conduction mechanism predominates for all the nano composite samples and the blank one

  12. O Desenvolvimento de Cabo Verde: abordagem ao mercado de tradução

    OpenAIRE

    De Oliveira, Bruno,

    2010-01-01

    Orientador: Mestre Alberto Couto O Presente Trabalho de Projecto contextualiza o arquipélago de Cabo Verde nos aspectos histórico, geográfico, político e económico e aborda as parcerias internacionais para o seu desenvolvimento ancoradas, nomeadamente, na União Europeia, CEDEAO, Millennium Challenge Corporation e a Organização Mundial do Comércio, etc. No capítulo do desenvolvimento e internacionalização analisa-se o mercado de tradução, e de como estas novas parcerias estão...

  13. Guiné-Bissau e Cabo Verde : da unidade à separação

    OpenAIRE

    Fernandes, Antero da Conceição Monteiro

    2007-01-01

    Depois da Segunda Guerra Mundial, a conjuntura política internacional tornou-se favorável para os países que se encontravam sob a dominação estrangeira no que concerne à descolonização. É neste contexto que nas colónias portuguesa surgiram movimentos independentistas, entre os quais o PAIGC, fundado por Amílcar Cabral a 19 de Setembro de 1956. Esse partido tinha dois objectivos: primeiro libertar a Guiné e Cabo Verde e depois fazer a união desses dois Estados. Depois da independência desses d...

  14. Arquitetura, património e turismo: o caso da Cidade Velha Cabo Verde

    OpenAIRE

    Vilas Boas, Carlos Manuel Rodrigues

    2013-01-01

    A presente dissertação de Mestrado foca-se na análise da primeira Capital do Arquipélago de Cabo verde, a Ribeira Brava ou atualmente designada Cidade Velha, esta foi colónia Portuguesa até 1975. O objetivo da análise passa por apresentar formas adequadas de intervenção urbana tendo em conta o facto da Cidade Velha ter sido distinguida em Junho de 2009 Património Mundial da Humanidade, e estar ainda numa fase de consolidação e desenvolvimento do seu edificado e da sua economia. Com a disti...

  15. Reposicionamiento para destinos turísticos consolidados: el caso de los Cabos, México

    OpenAIRE

    Montaño Armendáriz, Angélica; Pérez Concha, Juan Carlos; O Burrola, Veronica De La

    2014-01-01

    Los Cabos es un destino internacional, en fase de madurez, sustentado en tres ventajas: localización, naturaleza e infraestructura turística. En este documento se revisan los conceptos y estudios relacionados con los destinos de sol y playa; se contextualiza la problemática y se esbozan las perspectivas de esta actividad, ya que de continuar el actual modelo la competitividad del destino se ve amenazada. La aplicación de la teoría del «Ciclo de vida de los destinos turísticos»,...

  16. Imagens de um destino turístico: o caso de Cabo Verde

    OpenAIRE

    Santos, Maria do Carmo Lorena

    2012-01-01

    Partindo do contributo teórico e empírico de alguns autores, este artigo pretende estimular uma reflexão sobre os mecanismos subjacentes à construção da imagem turística de um destino que pressupõem um processo complexo de construção de representações sociais sobre determinados lugares e culturas. Com base numa análise do discurso promocional de Cabo Verde, procurámos desvendar a forma como este arquipélago é descrito enquanto destino turístico, revelando a diversidade de elementos presentes ...

  17. Deep repository - engineered barrier systems. Assessment of backfill materials and methods for deposition tunnels

    International Nuclear Information System (INIS)

    The main objectives of this report are to: (1) present density criteria considering deposition tunnels for the investigated backfill materials, (2) evaluate what densities can be achieved with the suggested backfill methods, (3) compare the density criteria to achievable densities, (4) based on this comparison evaluate the safety margin for the combinations of backfill materials and methods and, (5) make recommendations for further investigations and development work. The backfilling methods considered in this report are compaction of backfill material in situ in the tunnel and placement of pre-compacted blocks and pellets. The materials investigated in the second phase of the SKB-Posiva backfilling programme can be divided into three main categories: (1) Bentonite clays: two high-grade Na-bentonites from Wyoming (MX-80 and SPV200), one low-grade bentonite from Kutch (India Asha 2 0), and one high- and one low-grade Ca-bentonite from Milos (Deponite CA-N and Milos backfill). The highgrade bentonites are used in different bentonite-ballast mixtures. (2) Smectite-rich mixed-layer clays: one from Dnesice-Plzensko Jih (DPJ) located in the Czech Republic and one from Northern Germany (Friedland clay). (3) Mixtures of bentonite and ballast: Mixtures consisting of high-grade bentonite (30, 40 and 50 w-%) and crushed rock with different type of grain size distribution or sand. The general conclusion from the comparison between estimated achievable densities and the density criteria is that placing pre-compacted blocks of swelling clay or 50/50 mixture and pellets in the tunnel results in the highest safety margin. (orig.)

  18. Evaluation of hydraulic conductivities of bentonite and rock under hyper alkaline and nitrate conditions

    International Nuclear Information System (INIS)

    The chemical conditions of TRU waste repository were estimated as alkaline conditions effected by cementitious materials. And, some TRU wastes include soluble nitrate salt, we have to consider the repository conditions might be high ionic strength condition leaching of nitrate salt. In this study, experimental studies were carried out to evaluate hydraulic conductivities of bentonite and rock under hyper alkaline and nitrate conditions. The followings results were obtained for bentonite. 1) In the immersion experiments of bentonite in hyper alkaline fluids with and without nitrate, the disappearance of montmorillonite of bentonite was observed and CSH formation was found after 30 days. In hyper alkaline fluid with nitrate, minerals at θ=37 nm by XRD was identified. 2) Significant effects of hyper alkaline on hydraulic conductivity of compacted bentonite were not observed. However, hydraulic conductivities of hyper alkaline fluid with nitrate and ion exchanged bentonite increased. In hyper alkaline with nitrate, more higher hydraulic conductivities of exchanged bentonite were measured. The followings results were obtained for rock. 1) In the immersion experiments of crushed tuff in hyper alkaline fluids with and without nitrate, CSH and CASH phases were observed. 2) The hydraulic conductivity of tuff in hyper alkaline fluids decreased gradually. Finally, hyper alkaline flow in tuff stopped after 2 months and hyper alkaline flow with nitrate stopped shorter than without nitrate. In the results of analysis of tuff after experiment, we could identified secondary minerals, but we couldn't find the clogging evidence of pores in tuff by secondary minerals. (author)

  19. Applicability of low alkaline cement for construction and alteration of bentonite in the cement. 2

    International Nuclear Information System (INIS)

    This study consists of accelerating corrosion test of rebar in saline, automogeneous shrinkage test of HFSC, accelerating test for bentonite and rock, and summarizing rock and bentonite alteration. Corrosion of rebars in HFSC: Since sorption capacity of HFSC for Cl ion is slow due to low alkalinity, rate of corrosion of rebar in HFSC is very large. Cracking due to corrosion is generating in 4 years or 20 years, although service period is deferent in OPC amount. Automogenous shrinkage: Automogenous shrinkage of HFSC is larger than OPC in cement paste. It decreases corresponding to rise of fly ash content. The shrinkage in HFSC 226 is quite similar to OPC. The shrinkage in HFSC concrete is smaller than OPC concrete. 720 days alteration test of bentonite by solution of low alkaline cement: Ion exchange to Ca bentonite and calcite are observed in the solid phase. Thin plate of bentonite is disappeared and round shaped secondary mineral is generated. Dissolution of bentonite and generation of secondary minerals are limited in pH 11.0 or less, since pH of bentonite is about 10.0. 720 days alteration test of rock by solution of low alkaline cement: Calcite is generated in very test. Very small evidence is observed as generation of secondary minerals. Etched pits are observed in tuff A due to corrosion. (author)

  20. Composition and diagenetic processes of sandstone and tuff deposits of the Cenomanian Cardiel Formation, Cardiel Lake area, province of Santa Cruz

    OpenAIRE

    R.R. Andreis; P.E. Zalba; M.E. Morosi

    2007-01-01

    The Cardiel Formation (Cenomanian), around 200 m in thickness in the studied area, includes different types of volcaniclastic deposits, mainly represented by fine tuffs and massive bentonites, and subordinated epiclastics such as lithic sandstones of yellowish-brown, dusky yellow, or light olive hues, siltstones and claystones. Reddened paleosols with some small axial roots and weak prismatic structures appear on top of siltstones, tuffs and bentonites. Tufites and tuffs contain the same neov...

  1. Project Caesium - An ion exchange model for the prediction of distribution coefficients of caesium in bentonite

    International Nuclear Information System (INIS)

    A surface chemical model is established to thermodynamically describe caesium sorption on bentonite. Caesium sorption is studied on Wyoming bentonite MX-80 in solutions of NaCl, KCl, MgCl2, CaCl2, NaNO3 and Ca(NO3)2 of concentrations varying between 0.025M and 1M, as well as in the weakly saline Allard groundwater and the strongly saline Aespoe groundwater. Based on these experiments it is shown that the sorption behaviour of caesium on bentonite can be described, within the experimental and model uncertainties, in terms of a one-site ion exchange model. The ion exchange constant for the replacement of Na+ on montmorillonite by Cs+ is logKex degrees = 1.6. The model predictions compare well with sorption data published in the open literature on both Wyoming bentonite MX-80 and other types of bentonite. For the analysis of diffusion experiments in compacted bentonite, the apparent diffusivity of tritiated water, HTO, is used as an analogue to estimate the pore diffusivity of Cs+. Since insufficient information is available at present to estimate the porosity actually available for diffusion in compacted bentonite, it is assumed that the diffusion porosity can be approximated by using the value of the bulk porosity. Under these circumstances, the cation ex change capacity (CEC) found to be available for the diffusing species in compacted bentonite corresponds to about 12% of the total CEC of bentonite. It is recognised that the errors made in the estimation of the pore diffusivity and of the diffusion porosity are contained in the reduction factor of the CEC. A discussion of the factors affecting the diffusivities of radionuclides and the problem of establishing consistent sets of diffusivity data is given in the Appendix. 33 refs, 7 figs, 12 tabs

  2. Characterization of organo-modified bentonite sorbents: The effect of modification conditions on adsorption performance

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Modification of clay was evaluated by two methods for removing an organic substance. • Surfactant cations and organosilanes were intercalated into the interlayer space. • The hydrophobic surface of adsorbents increased the retention of organic substances. • Clay grafted with vinyltrimethoxysilane showed the highest adsorption for aniline. - Abstract: The organic modification of a natural bentonite was evaluated using two methods: exchanging the interlayer cations by hexadecyltrimethylammonium (HDTMA) and grafting with vinyltrimethoxysilane (VTMS) and γ-methacryloyloxy propyl trimethoxysilane (TMSPMA) on montmorillonite surface. The physicochemical characterization of all materials was made by X-ray diffraction (XRD), IR spectroscopy, thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) surface area techniques. HDTMA cations and organosilanes were intercalated into the interlayer space of montmorillonite, as deduced from the increase of the basal spacing. IR spectroscopy, TGA and BET area give evidence of successful organic modification. The studies show a decrease in the IR absorption band intensity at 3465 cm−1 with surfactant modification, and also a decrease of mass loss due to adsorbed water observed in two samples: the organoclay and functionalized bentonites, which are evidences of a lower interlayer hydrophilicity. The efficiency of aniline removal onto natural bentonite, organobentonite and functionalized bentonites from aqueous solutions was evaluated. Aniline sorption on natural bentonite was studied using batch experiments, XRD and IR spectroscopy. The hydrophobic surface of organobentonite and functionalized bentonites increased the retention capacity for nonionic organic substances such as aniline on bentonites. The sorption properties of modified bentonite, through different modification methods, enhanced the potential industrial applications of bentonites in water decontamination

  3. Characterization of organo-modified bentonite sorbents: The effect of modification conditions on adsorption performance

    Energy Technology Data Exchange (ETDEWEB)

    Parolo, María E., E-mail: maria.parolo@fain.uncoma.edu.ar [Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas (PROBIEN), Facultad de Ingeniería, Universidad Nacional del Comahue, Neuquén 8300 (Argentina); Pettinari, Gisela R. [Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas (PROBIEN), Facultad de Ingeniería, Universidad Nacional del Comahue, Neuquén 8300 (Argentina); Musso, Telma B. [Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas (PROBIEN), Facultad de Ingeniería, Universidad Nacional del Comahue, Neuquén 8300 (Argentina); CONICET, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires (Argentina); Sánchez-Izquierdo, María P.; Fernández, Laura G. [Facultad de Ingeniería, Universidad Nacional del Comahue, Neuquén 8300 (Argentina)

    2014-11-30

    Graphical abstract: - Highlights: • Modification of clay was evaluated by two methods for removing an organic substance. • Surfactant cations and organosilanes were intercalated into the interlayer space. • The hydrophobic surface of adsorbents increased the retention of organic substances. • Clay grafted with vinyltrimethoxysilane showed the highest adsorption for aniline. - Abstract: The organic modification of a natural bentonite was evaluated using two methods: exchanging the interlayer cations by hexadecyltrimethylammonium (HDTMA) and grafting with vinyltrimethoxysilane (VTMS) and γ-methacryloyloxy propyl trimethoxysilane (TMSPMA) on montmorillonite surface. The physicochemical characterization of all materials was made by X-ray diffraction (XRD), IR spectroscopy, thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) surface area techniques. HDTMA cations and organosilanes were intercalated into the interlayer space of montmorillonite, as deduced from the increase of the basal spacing. IR spectroscopy, TGA and BET area give evidence of successful organic modification. The studies show a decrease in the IR absorption band intensity at 3465 cm{sup −1} with surfactant modification, and also a decrease of mass loss due to adsorbed water observed in two samples: the organoclay and functionalized bentonites, which are evidences of a lower interlayer hydrophilicity. The efficiency of aniline removal onto natural bentonite, organobentonite and functionalized bentonites from aqueous solutions was evaluated. Aniline sorption on natural bentonite was studied using batch experiments, XRD and IR spectroscopy. The hydrophobic surface of organobentonite and functionalized bentonites increased the retention capacity for nonionic organic substances such as aniline on bentonites. The sorption properties of modified bentonite, through different modification methods, enhanced the potential industrial applications of bentonites in water decontamination.

  4. Bacterial and Archaeal Communities Variability Associated with Upwelling and Anthropogenic Pressures in the Protection Area of Arraial do Cabo (Cabo Frio region - RJ).

    Science.gov (United States)

    Coelho-Souza, Sergio A; Araújo, Fábio V; Cury, Juliano C; Jesus, Hugo E; Pereira, Gilberto C; Guimarães, Jean R D; Peixoto, Raquel S; Dávila, Alberto M R; Rosado, Alexandre S

    2015-09-01

    Upwelling systems contain a high diversity of pelagic microorganisms and their composition and activity are defined by factors like temperature and nutrient concentration. Denaturing gradient gel electrophoresis (DGGE) technique was used to verify the spatial and temporal genetic variability of Bacteria and Archaea in two stations of the Arraial do Cabo coastal region, one under upwelling pressure and another under anthropogenic pressure. In addition, biotic and abiotic variables were measured in surface and deep waters from three other stations between these stations. Six samplings were done during a year and adequately represented the degrees of upwelling and anthropogenic pressures to the system. Principal Component Analysis (PCA) showed negative correlations between the concentrations of ammonia and phosphorous with prokaryotic secondary production and the total heterotrophic bacteria. PCA also showed negative correlation between temperature and the abundance of prokaryotic cells. Bacterial and archaeal compositions were changeable as were the oceanographic conditions, and upwelling had a regional pressure while anthropogenic pressure was punctual. We suggest that the measurement of prokaryotic secondary production was associated with both Bacteria and Archaea activities, and that substrate availability and temperature determine nutrients cycling. PMID:26375020

  5. Concrete/Febex Bentonite Interaction: Results On Short-Term Column Experiments

    Energy Technology Data Exchange (ETDEWEB)

    Escribano, A.; Turrero, M.J.; Torres, E.; Martin, P.L. [CIEMAT, Environmental Department, Avda. Complutense, 22, 28040 Madrid (Spain)

    2008-07-01

    Interaction between the alkaline pore fluids from the concrete engineered barriers and the bentonite at the repository conditions may generate products that can diffuse through the porous structure of the bentonite affecting their properties. A comprehensive study based on series of short term experiments is being performed to provide experimental evidences on the physical, chemical and mineralogical changes during the concrete-compacted bentonite interaction. Samples were analyzed by XRD, SEM-EDS and FTIR. Measurements of swelling capacity, specific surface area and chemical analysis for cation exchange capacity and soluble salts analyses were also performed. (authors)

  6. Long-term dissolution behavior of spent fuel in compacted bentonite and synthetic granitic groundwater

    International Nuclear Information System (INIS)

    This contribution describes experimental work which aims to get the information on corrosion behaviour of Spent Fuel, and to obtain the release rate of radionuclides from the fuel within domestic bentonite and synthetic granitic ground water. Specimens of fuel with burn-up up to 39 GWd/tU, with and without bentonite, have been subjected to leaching. The effects of bentonite on the dissolution rate, and of structural materials, copper and stainless steel on caesium release have been identified and are reported. (author)

  7. The study on bentonite slurry grout with ethanol for fractured rock masses

    International Nuclear Information System (INIS)

    The purpose of this paper is to propose the grouting material and method for fractured rock masses. So experimental study is executed in order to grasp that the properties of grouting material is stable and impermeable. In this study, experiments of hydraulic test and grouting injection test are performed on bentonite slurry mixes in the laboratory. From the results of the tests, a mixer of ethanol and bentonite is found to be very suitable for a grouting material. Also, dynamic grouting method is able to inject the concentrated bentonite slurry in the fractured aperture. (author)

  8. NBR/ORGANOMODIFIED BENTONITE INTERCALATED HYBRIDS AND THEIR EFFECTS ON THE TOUGHNESS OF PVC

    Institute of Scientific and Technical Information of China (English)

    Chang-jiang You; De-min Jia; Zeng-yong Zhen; Kui Ding; Song Xi; Hai-lin Mo; Yong-hua Zhang

    2003-01-01

    Hybrids of intercalative nitrile-butadiene rubber/organomodified bentonite (NBR/OMB) were prepared by the latex intercalation technique. Investigation of their mechanical properties and the microstructure of NBR/OMB showed that the organomodified bentonite is an effective toughener for NBR. Transmission electronic microscopy (TEM) and X-ray diffraction (XRD) tests showed that the NBR macromolecule could be intercalated into the galleries of bentonite.Incorporation of NBR/OMB hybrids as tougheners into poly(vinyl chloride) (PVC) results in a substantial increase in the impact strength of PVC, but little decrease in its tensile strength and flexural strength, compared to the unmodified PVC.

  9. Concrete/Febex Bentonite Interaction: Results On Short-Term Column Experiments

    International Nuclear Information System (INIS)

    Interaction between the alkaline pore fluids from the concrete engineered barriers and the bentonite at the repository conditions may generate products that can diffuse through the porous structure of the bentonite affecting their properties. A comprehensive study based on series of short term experiments is being performed to provide experimental evidences on the physical, chemical and mineralogical changes during the concrete-compacted bentonite interaction. Samples were analyzed by XRD, SEM-EDS and FTIR. Measurements of swelling capacity, specific surface area and chemical analysis for cation exchange capacity and soluble salts analyses were also performed. (authors)

  10. Study of Interaction between Fly Ash-cement and Bentonite Matrices

    Directory of Open Access Journals (Sweden)

    Daněk Tomáš

    2015-01-01

    Full Text Available Among the important factors characterizing the quality of sealing mixtures is strength, durability, compatibility and permeability. Experimental work was therefore conducted to assess the use of cement, fly ash, gravel and bentonite in the form of artificial self-hardening sealing mixture. The results of the work show a good compatibility between the bentonite and cement during its fly ash replacement. Compactness of the structure was confirmed by studying of permeability and SEM microscopy, which in the system of ash-cement-bentonite matrix allowed assessing successive microstructure development of hydrating gel.

  11. Modified bentonite as adsorbent and catalyst for purification of wastewaters containing dyes

    Directory of Open Access Journals (Sweden)

    Žunić Marija J.

    2010-01-01

    Full Text Available Modification and characterization of bentonite from location Bogovina, Serbia was performed in order to obtain material applicable in wastewater purification. The <75μm bentonite fraction was used in organobentonite synthesis while the <2μm bentonite fraction, obtained by hydroseparation was used in pillaring procedure. Organo-modification of bentonite was performed with (1-hexadecyltrimethylammonium bromide (HDTMA-Br. Pillared bentonite was obtained using standard procedure. Al3+ and Fe3+ ions were incorporated in pillars in 4:1 ratio and applied as catalyst in catalytic wet peroxide oxidation. Differences in structure of starting and modified bentonites were established by XRD analysis and nitrogen physisorption on -196 °C. The (001 smectite peak around 2θ = 6° shifts during the modification process. The Na-exchange process lowered d001 from 1.53 nm (2θ = 5.78° for starting clay to 1.28 nm (2θ = 6.92°, but the clay retained its swelling properties. The pillaring process increased and fixed the basal spacing to 1.74 nm. Intercalation of HDTMA ions into smectite structure increased d001 to 2.00 nm for organobentonite. Specific surface area, SBET, was affected by particle size and type of modification. The samples with finer bentonite fraction had higher SBET due to increased smectite content. Na-exchanged bentonite samples had higher SBET value than starting clay samples of same granulation. Organomodification caused dramatic decrease in SBET value, while the pillaring process lead to an increase of SBET value. Adsorptive and catalytic purification of wastewaters containing dyes was tested using Acid Yellow 99 as a model dye. Na-exchanged bentonite had greater adsorption affinity for dye adsorption than raw bentonite owing to higher SBET. By organomodification this affinity was enhanced more than 70 times due to transition of bentonite surface from hydrophilic to organophilic. Al,Fe pillared bentonite was proven to be efficient in

  12. Removal of natural uranium from water produced in the oil industry using Algerian bentonite

    International Nuclear Information System (INIS)

    Batch sorption experiments have been carried out to remove natural uranium (NORM) from water obtained together with crude oil and natural gas, using Algerian bentonites. The effect of some important factors such as S/L ratio, pH, initial concentration, particle size was evaluated and a kinetic study performed. The value of the distribution coefficient (Kd) at equilibrium for natural uranium varied from 30 to 600 cm3 x g-1 and 50 to 1100 cm3 x g-1 (∼ 10% margin error) using natural bentonite and drilling bentonite, respectively. The isotherms showed that the data are consistent with both Freundlich and Langmuir models. (author)

  13. Experimental study on self-healing of bentonite/sand mixtures in hydraulic permeability

    International Nuclear Information System (INIS)

    Effects of gas permeation on the impervious characteristics of bentonite/sand mixtures were studied experimentally by conducting permeability tests with various fluids and microscopic observations. In this test, hydraulic permeabilities were measured before/after helium gas was applied to permeate through the mixtures. It was found that gas formed preferential paths to migrate through the mixtures, and that the bentonite/sand mixtures never deteriorated in impervious capacity because the paths were-filled with swelling bentonite in re-saturation. (author)

  14. Bentonite-stabilized CDA/CTA membranes for seawater desalination. Pt. 2

    International Nuclear Information System (INIS)

    The bentonite-stabilized seawater desalination membranes developed at GKSS were characterized by two transport coefficients. Both the hydrodynamic permeability as well as the electro-mechanical coefficient were significantly changed after 2000 hours RO rest runs. Their alterations were interpreted - applying the fively-porous membrane model - as an increase of the diffusion potential and a decrease of the streaming potential. The salt diffusion coefficient was analysed to be diminished by about 10%. The lowest performance changes of the membranes with 1000 ppm bentonite dope, support the experimental findings of flux-stabilization of bentonite-containing CDA/CTA membranes, published previously. (orig.)

  15. The Presence and Origin of Enterococcus faecalis in Cabo Rojo, Puerto Rico

    Science.gov (United States)

    Zachman, A. J.; Sturm, P.; Viqueira Ríos, R.

    2015-12-01

    Currently, a watershed management plan is being developed for Cabo Rojo region in Southwest Puerto Rico. This project fills in major gaps for water quality data on the Rio Viejo, a tributary on the Guanajibio River. The Rio Viejo flows through the town of Cabo Rojo, a town of 51,245 people. The project has identified 5 sites along the river to track bacterial loads. In the tropics, Enterococcus faecalis is an important indicator for fecal contamination in surface waters as it does not reproduce as quickly soils as E. coli. A combination of EPA 1600 and 9230B from Standard Methods for the Examination of Water and Wastewater for identification of E. faecalis were utilized. The assay is a four step procedure that identifies the four criteria of bacteria in the group D Streptococcus system. The criteria require that the bacteria are Gram-positive cocci and Esculin-positive. There also must be growth in Brain Heart Infusion Broth at 35C and 45C as well as growth in Brain Heart Infusion broth + 6.5% NaCl. Further research will be conducted at North Carolina State University to ascertain the vertebrate species that is the source of the contamination through the use of qPCR.

  16. An observational study of the evolution of the atmospheric boundary-layer over Cabo Frio, Brazil

    Directory of Open Access Journals (Sweden)

    S. H. Franchito

    2007-08-01

    Full Text Available The effect of coastal upwelling on the evolution of the atmospheric boundary layer (ABL in Cabo Frio (Brazil is investigated. For this purpose, radiosounding data collected in two experiments made during the austral summer (upwelling case and austral winter (no upwelling case are analysed. The results show that during the austral summer, cold waters that crop up near the Cabo Frio coast favour the formation of an atmospheric stable layer, which persists during the upwelling episode. Due to the low SSTs, the descending branch of the sea-breeze circulation is located close to the coast, inhibiting the development of a mixed layer mainly during the day. At night, with the reduction of the land-sea thermal contrast the descending motion is weaker, allowing a vertical mixing. The stable ABL favours the formation of a low level jet, which may also contribute to the development of a nocturnal atmospheric mixed layer. During the austral winter, due to the higher SSTs observed near the coast, the ABL is less stable compared with that in the austral summer. Due to warming, a mixed layer is observed during the day. The observed vertical profiles of the zonal winds show that the easterlies at low levels are stronger in the austral summer, indicating that the upwelling modulates the sea-breeze signal, thus confirming model simulations.

  17. Thermo-hydro-geochemical modelling of the bentonite buffer. LOT A2 experiment

    Energy Technology Data Exchange (ETDEWEB)

    Sena, Clara; Salas, Joaquin; Arcos, David (Amphos 21 Consulting S.L., Barcelona (Spain))

    2010-12-15

    The Swedish Nuclear Fuel and waste management company (SKB) is conducting a series of long term buffer material (LOT) tests at the Aespoe Hard Rock Laboratory (HRL) to test the behaviour of the bentonite buffer under conditions similar to those expected in a KBS-3 deep geological repository for high level nuclear waste (HLNW). In the present work a numerical model is developed to simulate (i) the thermo-hydraulic, (ii) transport and (iii) geochemical processes that have been observed in the LOT A2 test parcel. The LOT A2 test lasted approximately 6 years, and consists of a 4 m long vertical borehole drilled in diorite rock, from the ground of the Aespoe HRL tunnel. The borehole is composed of a central heater, maintained at 130 deg C in the lower 2 m of the borehole, a copper tube surrounding the heater and a 100 mm thick ring of pre-compacted Wyoming MX-80 bentonite around the copper tube /Karnland et al. 2009/. The numerical model developed here is a 1D axis-symmetric model that simulates the water saturation of the bentonite under a constant thermal gradient; the transport of solutes; and, the geochemical reactions observed in the bentonite blocks. Two cases have been modelled, one considering the highest temperature reached by the bentonite (at 3 m depth in the borehole, where temperatures of 130 and 85 deg C have been recorded near the copper tube and near the granitic host rock, respectively) and the other case assuming a constant temperature of 25 deg C, representing the upper part of borehole, where the bentonite has not been heated. In the LOT A2 test, the initial partially saturated bentonite becomes progressively water saturated, due to the injection of Aespoe granitic groundwater at granite - bentonite interface. The transport of solutes during the bentonite water saturation stage is believed to be controlled by water uptake from the surrounding groundwater to the wetting front and, additionally, in the case of heated bentonite, by a cyclic evaporation

  18. Thermo-hydro-geochemical modelling of the bentonite buffer. LOT A2 experiment

    International Nuclear Information System (INIS)

    The Swedish Nuclear Fuel and waste management company (SKB) is conducting a series of long term buffer material (LOT) tests at the Aespoe Hard Rock Laboratory (HRL) to test the behaviour of the bentonite buffer under conditions similar to those expected in a KBS-3 deep geological repository for high level nuclear waste (HLNW). In the present work a numerical model is developed to simulate (i) the thermo-hydraulic, (ii) transport and (iii) geochemical processes that have been observed in the LOT A2 test parcel. The LOT A2 test lasted approximately 6 years, and consists of a 4 m long vertical borehole drilled in diorite rock, from the ground of the Aespoe HRL tunnel. The borehole is composed of a central heater, maintained at 130 deg C in the lower 2 m of the borehole, a copper tube surrounding the heater and a 100 mm thick ring of pre-compacted Wyoming MX-80 bentonite around the copper tube /Karnland et al. 2009/. The numerical model developed here is a 1D axis-symmetric model that simulates the water saturation of the bentonite under a constant thermal gradient; the transport of solutes; and, the geochemical reactions observed in the bentonite blocks. Two cases have been modelled, one considering the highest temperature reached by the bentonite (at 3 m depth in the borehole, where temperatures of 130 and 85 deg C have been recorded near the copper tube and near the granitic host rock, respectively) and the other case assuming a constant temperature of 25 deg C, representing the upper part of borehole, where the bentonite has not been heated. In the LOT A2 test, the initial partially saturated bentonite becomes progressively water saturated, due to the injection of Aespoe granitic groundwater at granite - bentonite interface. The transport of solutes during the bentonite water saturation stage is believed to be controlled by water uptake from the surrounding groundwater to the wetting front and, additionally, in the case of heated bentonite, by a cyclic evaporation

  19. Experimental study of the transport of HTO, {sup 3}6Cl and {sup 1}37Cs through barriers of bentonite and granite; Estudio experimental del transporte de HTO, {sup 3}6Cl y {sup 1}37Cs a traves de barreras de bentonita y granito

    Energy Technology Data Exchange (ETDEWEB)

    Mingarro, M.; Garcia-Gutierrez, M.; Morejon, J.; Missana, T.; Gil, P.

    2013-07-01

    The evaluation of the behavior of the engineered (bentonite) and natural (granite) barrier of a deep geological repository of high level radioactive waste, needs the knowledge of radionuclide migration and retention processes under conditions as similar as possible to the real ones. In CIEMAT a large-scale experiment has been designed with the objective of studying diffusive transport at the bentonite/granite interface of a geological repository in crystalline rock. The diffusion of three tracers has been analyzed: HTO (as conservative and neural element); Cl (as conservative anionic element) and Cs (as conservative cationic element). It was observed that cesium disappeared very fast from the water deposit, due to its strong retention on bentonite. On the other hand, HTO and Cl, disappeared much slower and could be finally detected in the granite at several centimeters from the original source.

  20. A study on long term stability of bentonite. The preliminary study on the bentonite stability in the groundwater influenced by cementitious material

    International Nuclear Information System (INIS)

    In the geological disposal concept of radioactive wastes, a kind of clay with sorption ability and low permeability, called bentonite, is envisaged as an engineered barrier system in the geological repository. Also, the cementitious material is envisaged as the backfill material in the vaults and the structure material of the vaults. The groundwater in contact with the cementitious material will promote hyperalkaline conditions in the repository environment and these conditions will affect the performance of the bentonite. Therefore, it is necessary to investigate the interaction between the cementitious material and the bentonite for the evaluation of long term stability of the disposal system. In this study, for the identification and the investigation of the secondary minerals, the batch immersion experiments of the powder bentonite were carried out using synthetic cement leachates (pH=7, 12.5, 14) at 200degC. As the results, it was confirmed that Na as exchangeable cations in the bentonite can exchange relatively easily with Ca in the solution from the experiment results. And the ratio of cation exchange was estimated to be about 25% based on the amount of exchangeable cations Ca2+ between layers. Furthermore, it was concretely shown that the generation of analcime might be affected by the Na concentration from results of the solution analyses and a stability analysis of analcime using the chemical equilibrium model, in addition to the pH in the solution. (author)

  1. A global sensitivity analysis of two-phase flow between fractured crystalline rock and bentonite with application to spent nuclear fuel disposal

    Science.gov (United States)

    Dessirier, Benoît; Frampton, Andrew; Jarsjö, Jerker

    2015-11-01

    Geological disposal of spent nuclear fuel in deep crystalline rock is investigated as a possible long term solution in Sweden and Finland. The fuel rods would be cased in copper canisters and deposited in vertical holes in the floor of deep underground tunnels, embedded within an engineered bentonite buffer. Recent experiments at the Äspö Hard Rock Laboratory (Sweden) showed that the high suction of unsaturated bentonite causes a de-saturation of the adjacent rock at the time of installation, which was also independently predicted in model experiments. Remaining air can affect the flow patterns and alter bio-geochemical conditions, influencing for instance the transport of radionuclides in the case of canister failure. However, thus far, observations and model realizations are limited in number and do not capture the conceivable range and combination of parameter values and boundary conditions that are relevant for the thousands of deposition holes envisioned in an operational final repository. In order to decrease this knowledge gap, we introduce here a formalized, systematic and fully integrated approach to study the combined impact of multiple factors on air saturation and dissolution predictions, investigating the impact of variability in parameter values, geometry and boundary conditions on bentonite buffer saturation times and on occurrences of rock de-saturation. Results showed that four parameters consistently appear in the top six influential factors for all considered output (target) variables: the position of the fracture intersecting the deposition hole, the background rock permeability, the suction representing the relative humidity in the open tunnel and the far field pressure value. The combined influence of these compared to the other parameters increases as one targets a larger fraction of the buffer reaching near-saturation. Strong interaction effects were found, which means that some parameter combinations yielded results (e.g., time to

  2. Nanocomposites of PP and bentonite clay modified with different surfactants

    International Nuclear Information System (INIS)

    The aim of this work was the development of nano composites of polypropylene (PP) and national bentonite clay modified with different surfactants. The results of X-Ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) showed that the organophilization process was effective. The surfactants led to a significant increase in the basal spacing of Brasgel PA clay. XRD results of the mixture PP/Brasgel PA clay modified with Praepagem WB surfactant indicated that a nanocomposite with intercalated structure was formed. When the Brasgel PA clay was modified with Praepagem HY surfactant, DRX results indicated that a micro composite was formed. Screw speed, clay content and PP viscosity had no influence on the XRD pattern of the obtained materials. (author)

  3. Sorption behaviour of caesium on a bentonite sample

    International Nuclear Information System (INIS)

    Sorption of elements like Cs on clay is one of the principal processes delaying their release from deep repositories of nuclear wastes into the environment. The sorption processes taking place between non-purified natural clay material (bentonite) and synthetic groundwater (containing Ca, Mg, Na, K and carbonates) were therefore studied experimentally and modelled for Cs to determine whether thermodynamic computer codes capable of predicting the behaviour of this element in natural systems might be developed. The model used, based on the properties of a pure montmorillonite phase, incorporates the surface reactions for natural major ions and sorbing cations but does not have any adjustable parameters. The weight of each parameters used in the model is assessed. Surface reactions are classified as either major or minor, and a simplified model of Cs sorption that considers only the major processes is proposed. This simplified model might correspond to the less sophisticated thermodynamic model included in coupled geochemistry-transport models. (orig.)

  4. Sorption behaviour of caesium on a bentonite sample

    Energy Technology Data Exchange (ETDEWEB)

    Hurel, C. [Lab. de Chimie Analytique Bio-Inorganique et Environnement, UMR CNRS 5034, Univ. de Pau et des Pays de l' Adour, Helioparc Pau Pyrenees, Pau (France); GRECI, Univ. de Reims Champagne-Ardenne, Moulin de la Housse, Reims (France); Marmier, N.; Fromage, F. [GRECI, Univ. de Reims Champagne-Ardenne, Moulin de la Housse, Reims (France); Seby, F.; Bourg, A.C.M. [Lab. de Chimie Analytique Bio-Inorganique et Environnement, UMR CNRS 5034, Univ. de Pau et des Pays de l' Adour, Helioparc Pau Pyrenees, Pau (France); Giffaut, E. [ANDRA, Agence Nationale pour la Gestion des Dechets Radioactifs, Chatenay-Malabry (France)

    2002-07-01

    Sorption of elements like Cs on clay is one of the principal processes delaying their release from deep repositories of nuclear wastes into the environment. The sorption processes taking place between non-purified natural clay material (bentonite) and synthetic groundwater (containing Ca, Mg, Na, K and carbonates) were therefore studied experimentally and modelled for Cs to determine whether thermodynamic computer codes capable of predicting the behaviour of this element in natural systems might be developed. The model used, based on the properties of a pure montmorillonite phase, incorporates the surface reactions for natural major ions and sorbing cations but does not have any adjustable parameters. The weight of each parameters used in the model is assessed. Surface reactions are classified as either major or minor, and a simplified model of Cs sorption that considers only the major processes is proposed. This simplified model might correspond to the less sophisticated thermodynamic model included in coupled geochemistry-transport models. (orig.)

  5. Effect of freezing and thawing on compacted bentonite buffer performance

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. Over the time scale of the lifecycle of the spent nuclear fuel repository at Olkiluoto, local conditions involving both permafrost and glacial climactic phases, possibly repeatedly, cannot be excluded. Permafrost typically occurs when cold and dry climate conditions prevail with no ice-sheet formation or during glaciation as sub-glacial permafrost. Permafrost is generally defined as ground (soil or rock) that remains at or below 0 deg. C for at least two consecutive years. The growth and development of permafrost to some depth of the geologic subsurface depends on a complex heat exchange process across the atmosphere/ground interface and on the geothermal heat flow. Due to the potential impact on hydraulic, mechanical, and chemical subsurface properties and conditions, permafrost penetration is of interest for the performance and safety assessment of a deep, geologic repository. Deleterious effects on porous soil material, resulting from freezing and thawing, are generally ascribed to the occurrence of ice formation. Of course exposure to permafrost does not necessarily imply the presence of ice in the affected material. Indeed the primary consequence of the confinement of water in small pores is a depression to lower temperature of the melting transition. However, when ice forms in porous material, there is a corresponding increase in volume and/or pressure depending on the particular confining stresses at hand and the permeability to water migration. If ice is not formed in the fully saturated buffer system, no increase in volume and/or pressure need be considered. If, on the other hand, ice does form, increased stress from the buffer on the canister and host rock will need to be taken into account. In order to evaluate the effect of freezing and thawing on compacted bentonite buffer performance a series of experiments were conducted using constant-volume swelling pressure cells as follows: - Pre- and post

  6. Hydrothermal stability of bentonite-based buffer materials

    International Nuclear Information System (INIS)

    The reactions expected in bentonite-based buffer materials under conditions typical of a nuclear fuel waste disposal include mineral transformations (e.g. smectite to illite; smectite to zeolite) and a range of low-temperature cementation reactions. The probable extent and significance of these reactions are reviewed, and other reactions involving proposed filler sands are also examined briefly. The effects of mineral transformations on buffer performance will be insignificant if disposal vault temperatures do not exceed 100-120 degrees C and pH remains in the range 4 to 8. At pH > 9, zeolitization and silica dissolution may occur and buffer stability cannot be assured. The effects of cementation reactions may be significant, but are difficult to predict and require further investigation

  7. Properties of zeolite a synthesized by natural bentonite

    International Nuclear Information System (INIS)

    Synthetic zeolite was prepared by using of natural bentonite from Kampo area and the application of detergent builder was investigated. The optimum synthetic condition was SiO2/Al2O3 = 2, Na2O/Al2O3 = 1, H2O/Al2O3 30 at 90 deg C for 3 hr and it was found by XRD analysis that the zeolite synthesized under this condition was type A. When the zeolite A synthesized under the optimum condition was contacted with 40 deg Dh CaCl2 solution at 30 deg C for 15 min, the cation exchange capacity was 264.9 mg CaO/g-zeolite. And the whiteness of the sample was 89% and the mean particle size was 9.95μm. (author)

  8. Characterization of Unye bentonite after treatment with sulfuric acid

    Directory of Open Access Journals (Sweden)

    Bulent Caglar

    2013-01-01

    Full Text Available Unye bentonite was found to consist predominantly of a dioctahedral smectite along with quartz, tridymite, cristobalite, and minor fractions of feldspar and anatase. A considerable amount of Al was retained as a constituent in acid-resistant impurities following the decomposition of the montmorillonite via acid treatment at an acid/clay ratio of 0.4. These impurities were mesoporous with a maximum surface area of 303.9±0.4 m² g-1. A sharp decrease in the d001 lattice spacing of the montmorillonite to 15.33 Å reflected the reduction of the crystallinity in the activated products. In addition, the increase in the ease with which newly formed hydroxyl groups were lost paralleled the severity of the acid treatment.

  9. Evaluation of impact strength of polyamide 6/bentonite clay nanocomposites

    International Nuclear Information System (INIS)

    Nanocomposites of polymer/clay have had much attention in recent years, particularly those developed with layered silicates due to the need of engineering materials more efficient than pure polymers for certain applications. The level of exfoliation of layered silicates in crystalline structure of polymer matrices has been studied and has been observed that they affect the crystalline behavior and the physical and mechanical properties. In this study, nanocomposites of polyamide 6 were obtained by the melt intercalation method, using a regional bentonite modified with a quaternary ammonium salt in an amount of 3% by weight. XRD results showed that incorporation of salt among the layers of clay, making it organophilic and obtaining exfoliated and/or partially exfoliated structures. The impact properties of the nanocomposites showed inferior in relation to pure polyamide, in other words, lost of toughness. (author)

  10. Decontamination effectiveness of bentonite in pigs and sheep repeatedly contaminated with radiocesium

    International Nuclear Information System (INIS)

    The investigations were conducted on 10 pigs and 10 sheep contaminated daily for 21 days with 137CsCl and fed twice a day a normal diet or the same diet supplemented with 10% of bentonite. The animals were killed at days 7, 14 and 21 of radiocesium administration and after cessation of the administration. The abomasum, liver, kidneys, lung, spleen, brain, heart, muscles, tongue and skin were sampled for radiometric determinations. The animals fed a bentonite-supplemented diet revealed substantially lower contents of Cs-137 as compared to the controls. The radioactivities of pig and sheep organs after 21 d Cs-137 administration were lower by about 67.5 and 81.3%, respectively, compared to the controls. The cessation of Cs-137 administration decreased organ radioactivities in bentonite-fed sheep and pigs by about 74.5 and 64.1%, respectively, compared to those in animals without bentonite. (author). 12 refs, 2 tabs

  11. EVALUATION OF THE BENTONITE CONTENT IN SPENT FOUNDRY SANDS AS A FUNCTION OF HYDRAULIC CONDUCTIVITY COEFFICIENT

    Directory of Open Access Journals (Sweden)

    Schirlene Chegatti

    2013-06-01

    Full Text Available This study evaluates the relationship of the bentonite content and hydraulic conductivity coefficient (k of waste foundry sands in tests of hydraulic conductivity in a flexible wall permeameter. The test samples had concentrations of activated sodium bentonite and natural sodium bentonite between 4% and 15%. It was also analyzed chemically the liquid leachate (aluminum, barium, chromium, cadmium, lead, phenols, iron, fluoride, and manganese, following de standard tests of Standard Methods 3111 B e D for the determination of this components in liquid samples. The experiments were supplemented with cation exchange capacity analysis. The results indicate that the values of are is related to the content of bentonite in waste foundry sand and the percolation from this waste disposal.

  12. Swelling and hydraulic properties of Ca-bentonite for the buffer of a waste repository

    International Nuclear Information System (INIS)

    Swelling and hydraulic tests were carried out to provide the information for the selection of buffer material in a radioactive waste repository. Ca-bentonite and de-ionized water were used for the tests. The swelling pressures of compacted bentonite were in the wide range of 0.7 Kg/cm2 to 190.2 Kg/cm2, and they largely increased with an increase in the dry density and bentonite content. However, the swelling pressures decreased with increasing the initial water content and beyond about 12 wt.% of the initial water content, leveled off to a nearly constant value. The hydraulic conductivities were lower than 10-11 m/s for the compacted bentonite with the dry density higher than 1.4 Mg/m3. They increased with increasing temperature in the range of 20 deg. C to 150 deg. C. (author)

  13. Practical and theoretical basis for performing redox-measurements in compacted bentonite. A literature survey

    International Nuclear Information System (INIS)

    This report reviews the state-of-the-art with regard to redox measurements, especially in compacted water saturated bentonite, but also in natural systems like sediments and ground waters. Both theoretical and practical aspects of redox measurements are discussed, as well as some basic concepts like terminal electron-accepting processes (TEAPs) and oxidative capacity (OXC). The problems associated with the interpretation of measured electrode potentials are treated. Despite many practical and theoretical difficulties, redox measurements continue to be carried out by researchers all over the world. The over-all conclusion from the literature survey is that fruitful redox-measurements can be performed in compacted bentonite. Irrespective of whether the measured redox potentials are absolute or not, the use of electrodes provide a valuable tool for studying, e.g., long-term changes in the pore water of compacted bentonite and/or the diffusion of oxygen into a bentonite. (orig.)

  14. Temperature effects on geotechnical and hydraulic properties of bentonite hydrated with inorganic salt solutions

    DEFF Research Database (Denmark)

    Rashid, H. M. A.; Kawamoto, K.; Saito, T.;

    2015-01-01

    © 2015, International Journal of GEOMATE. This study investigated the combined effect of temperature and single-species salt solutions on geotechnical properties (swell index and liquid limit) and hydraulic conductivity of bentonite applying different cation types, concentrations, and temperatures...

  15. RECEIVING FUNCTIONAL FEED ADDITIVE ON THE BASIS OF BENTONITE CLAYS AND CAROTENE CONTAINING RAW MATERIALS

    Directory of Open Access Journals (Sweden)

    Zholobova I. S.

    2014-02-01

    Full Text Available In this article we have shown the results of studying of biologically active connections in bentonite clays, carotene containing raw materials for the purpose of receiving functional feed additive for agricultural birds

  16. Hydraulic permeability of bentonite-polymer composites for application in landfill technology

    Science.gov (United States)

    Dehn, Hanna; Haase, Hanna; Schanz, Tom

    2015-04-01

    Bentonites are often used as barrier materials in landfill technology to prevent infiltration of leachates to the natural environment. Since decades, geoenvironmental engineering aims at improving the hydro-mechanical performance of landfill liners. Various studies on the permeability performance of geosynthetic clay liners (GCLs) show effects of non-standard liquids on behaviour of Na+-bentonite regarding its sealing capacity. With increasing concentration of chemical aggressive solutions the sealing capacity decreases (Shackelford et al. 2000). An opportunity to improve the hydraulic permeability of the bentonites is the addition of polymers. The changes in hydraulic permeability performance of polymer treated and untreated bentonites while adding chemical aggressive solutions were studied by several authors. Results obtained by Scalia et al. (2014) illustrate that an increase in permeability can be prevented by adding polymer to Na+-bentonite. On the other hand, Ashmawy et al. (2002) presented results on the incapability of several commercial bentonite-polymer-products. The objective of this study is to characterize the influence of polymer addition on hydraulic performance of Na+-bentonite systematically. Therefore, the influence of 1% polymer addition of cationic and anionic polyacrylamide on the swelling pressure and hydraulic permeability of MX 80 bentonite was investigated. Preparation of bentonite-polymer composites was conducted (1) in dry conditions and (2) using solution-intercalation method. Experiments on hydraulic permeability were carried out using distilled water as well as CaCl2-solution. References Ashmawy, A. K., El-Hajji, D., Sotelo, N. & Muhammad, N. (2002), `Hydraulic Performance of Untreated and Polymer-treated Bentonite in Inorganic Landfill Leachates', Clays and Clay Minerals 50(5), 546-552. Scalia, J., Benson, C., Bohnhoff, G., Edil, T. & Shackelford, C. (2014), 'Long-Term Hydraulic Conductivity of a Bentonite-Polymer Composite Permeated

  17. An Evaluation of Models of Bentonite Pore Water Evolution

    International Nuclear Information System (INIS)

    The determination of a bentonite pore water composition and understanding its evolution of with time underpins many radioactive waste disposal issues, such as buffer erosion, canister corrosion, and radionuclide solubility, sorption, and diffusion, inter alia. The usual approach to modelling clay pore fluids is based primarily around assumed chemical equilibrium between Na+, K+, Ca2+, and Mg2+ aqueous species and ion exchange sites on montmorillonite, but also includes protonation- deprotonation of clay edge surface sites, and dissolution-precipitation of the trace mineral constituents, calcite and gypsum. An essential feature of this modelling approach is that clay hydrolysis reactions (i.e. dissolution of the aluminosilicate octahedral and tetrahedral sheets of montmorillonite) are ignored. A consequence of the omission of clay hydrolysis reactions from bentonite pore fluid models is that montmorillonite is preserved indefinitely in the near-field system, even over million-year timescales. Here, we investigate the applicability of an alternative clay pore fluid model, one that incorporates clay hydrolysis reactions as an integral component and test it against well-characterised laboratory experimental data, where key geochemical parameters, Eh and pH, have been measured directly in compacted bentonite. Simulations have been conducted using a range of computer codes to test the applicability of this alternative model. Thermodynamic data for MX-80 smectite used in the calculations were estimated using two different methods. Simulations of 'end-point' pH measurements in batch bentonite-water slurry experiments showed different pH values according to the complexity of the system studied. The most complete system investigated revealed pH values were a strong function of partial pressure of carbon dioxide, with pH increasing with decreasing PCO2 (log PCO2 values ranging from -3.5 to -7.5 bars produced pH values ranging from 7.9 to 9.6). A second set of calculations

  18. Highly compacted bentonite: a self-healing substance for nuclear waste isolation

    International Nuclear Information System (INIS)

    Granular Na bentonite acquires considerable microstructural homogeneity through water and particle redistribution processes. This yields a very low permeability and thus excellent barrier functions in repositories. This self-healing property also means that large bentonite volumes tend to reach a homogeneous condition. Thus, local voids or inhomogeneities produced, for instance, by minor displacement of the surrounding rock will be healed. The swelling potential also means that a perfect contact is established between the clay barrier and the rock

  19. Removal of formaldehyde from aqueous solution by adsorption on kaolin and bentonite: a comparative study

    OpenAIRE

    Salman, Muhammad; Athar, Makshoof; SHAFIQUE, Umer; Rehman, Rabia

    2012-01-01

    The adsorption of formaldehyde on bentonite and kaolin was studied in batch mode. Parameters like adsorbent dose, pH, contact time and agitation speed were investigated. Langmuir, Freundlich and Temkin isotherms were employed for describing adsorption equilibrium. The maximum amounts of formaldehyde adsorbed (qmax), as evaluated by Langmuir isotherm, were 3.41 and 5.03 milligrams per gram of ground kaolin and bentonite, respectively. The study results led to the conclusion that kaol...

  20. An investigation on physical properties of polyethylene composite with bentonite, kaolin and calcium carbonate additives

    OpenAIRE

    Karabeyoğlu, Sencer S.; , Nurşen Öntürk

    2014-01-01

    Bentonite, Kaolin, Calcium carbonate easily obtained in nature as mineral products are widely used in plastics industry for additive materials. In this study, Bentonite, Kaolin, and Calcium carbonate minerals were compounded with polyethylene matrix used in specific rates. Prepared compounds melted in sheet metal molds and cooled down under appropriate conditions. Thus, production of composite material was achieved. Hardness, water absorption, and physical properties of manufactured composite...

  1. Surface Modification of Bentonites. II. Modification of Montmorillonite with Cationic Poly(ethylene oxides)

    OpenAIRE

    Dau, Jörn; Lagaly, Gerhard

    1998-01-01

    Surface modification of clay minerals has become increasingly important for optimizing the practical application of bentonites, kaolins, and clays. We describe the reaction of montmorillonite, an important mineral in bentonites, with cationic poly(ethylene oxides). Poly(ethylene oxides), PEOs, with molecular masses between 1550 and 35000, were modified by substituting the OH end groups by bromine, then replacing Br by trimethylammonium (TMA) groups. Mono-endcapped PEOs were prepared from poly...

  2. Adsorption of and acidic dye from aqueous solution by surfactant modified bentonite

    International Nuclear Information System (INIS)

    The aim of this paper is to study the adsorption of an acidic dye S. Y. 4 GL (i.e: Supranol yellow 4GL) from aqueous solution on inorgano-organo clay. Bentonite is a kind of natural clay with good exchanging ability. By exchanging its inter lamellar cations with Cetyltrimethylammonium bromide (CTAB) and hydroxy aluminic or chromium poly cations, the properties of natural bentonite can be greatly improved. (Author)

  3. Research program to study the gamma radiation effects in Spanish bentonites

    International Nuclear Information System (INIS)

    The engineering barrier of a radioactive waste underground disposal facility, placed in a granitic host rock, will consist of a backfill of compacted bentonite blocks. At first, this material will be subjected to a gamma radiation field, from the waste canister, and heat from the spent fuel inside the canister. Moreover, any groundwater that reaches the repository will saturate the bentonite. For these reasons the performance of the engineered barrier must be carefully assessed in laboratory experiments. (Author)

  4. The effect of pore structural factors on diffusion in compacted sodium bentonite

    International Nuclear Information System (INIS)

    Four kinds of diffusion experiments; (1) through-diffusion (T-D) experiments for diffusion direction dependency to compacted direction, (2) in-diffusion (I-D) experiments for composition dependency of silica sand in bentonite, (3) I-D experiments for initial bentonite grain size dependency, and (4) I-D experiments for the effect of a single fracture developed in bentonite, were carried out using tritiated water (HTO) to evaluate the effect of pore structural factors on diffusion. For (1), effective diffusivities (De) in Na-bentonites, Kunigel-V1 and Kunipia-F, were measured for densities of 1.0 and 1.5 Mg.m-3 in the axial and perpendicular directions to compacted one. Although De values in Kunigel-V1 for both directions were similar over the density, De values for perpendicular direction to compacted one in Kunipia-F were higher than those for the same direction as compacted one. For (2), apparent diffusivities (Da) in Kunigel-V1 with silica sand were measured for densities of 0.8 to 1.8 Mg.m-3. No significant effect of the mixture of silica sand was found. For (3), Da values for densities of 0.8 to 1.8 Mg.m-3 were measured for a granulated Na-bentonite, OT-9607. However, no effect of initial bentonite grain size was found. For (4), Da values in Kunigel-V1, in which a single fracture was artificially reproduced and immersed in distilled water, were measured. No effect of the fracture on Da was found. Based on this, it may be said that the composition of smectite in bentonite affects the orientation property of clay particle and also affects diffusion. Furthermore, a penetrated fracture formed in bentonite is restored for a short while and does not affect diffusion. Copyright (2001) Material Research Society

  5. Chitosan/bentonite bionanocomposites: morphology and mechanical behavior; Bionanocompositos quitosana/bentonita: morfologia e comportamento mecanico

    Energy Technology Data Exchange (ETDEWEB)

    Braga, C.R.C.; Melo, F.M.A. de [Universidade Federal de Campina Grande (UFCG), PB (Brazil). Programa de Pos-graduacao em Ciencia e Engenharia de Materiais; Vitorino, I.F. [Universidade Federal de Campina Grande (UFCG), PB (Brazil). Dept. de Ciencia e Engenharia de Materiais; Fook, M.V.L.; Silva, S.M.L., E-mail: suedina@dema.ufcg.edu.b [Universidade Federal de Campina Grande (UFCG), PB (Brazil). Unidade Academica de Engenharia de Materiais

    2010-07-01

    This study chitosan/bentonite bionanocomposite films were prepared by solution intercalation process, seeking to investigate the effect of the chitosan/bentonite ratio (5/1 e 10/1) on the morphology and mechanical behavior of the bionanocomposites. It was used as nanophase, Argel sodium bentonite (AN), was provided by Bentonit Uniao Nordeste-BUN (Campina Grande, Brazil) and as biopolymer matrix the chitosan of low molecular weight and degree of deacetylation of 86,7% was supplied by Polymar (Fortaleza, Brazil). The bionanocomposites was investigated by X-ray diffraction and tensile properties. According to the results, the morphology and the mechanical behavior of the bionanocomposite was affected by the ratio of chitosan/bentonite. The chitosan/bentonite ratio (5/1 and 10/1) indicated the formation of an intercalated nanostructure and of the predominantly exfoliated nanostructure, respectively. And the considerable increases in the resistance to the traction were observed mainly for the bionanocomposite with predominantly exfoliated morphology. (author)

  6. Investigation of Co(II) sorption on GMZ bentonite from aqueous solutions by batch experiments

    International Nuclear Information System (INIS)

    In this study, a local bentonite from Gaomiaozi county (Inner Mongolia, China) was converted to Na-bentonite and was characterized by FTIR and XRD to determine its chemical constituents and micro-structure. The removal of cobalt from aqueous solutions by Na-bentonite was investigated as a function of contact time, pH, ionic strength, foreign ions and temperature by batch technique under ambient conditions. The results indicated that the sorption of Co(II) was strongly dependent on pH. At low pH, the sorption of Co(II) was dominated by outer-sphere surface complexation or ion exchange whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The Langmuir, Freundlich, and D-R models were used to simulate the sorption isotherms of Co(II) at the temperatures of 293.15, 313.15 and 333.15 K, respectively. The thermodynamic parameters (ΔG0, ΔS0, ΔH0) of Co(II) sorption on GMZ bentonite calculated from the temperature-dependent sorption isotherms indicated that the sorption of Co(II) on GMZ bentonite was an exothermic and spontaneous process. The Na-bentonite is a suitable material for the preconcentration and solidification of Co(II) from aqueous solutions. (author)

  7. Study of combined effect of proteins and bentonite fining on the wine aroma loss.

    Science.gov (United States)

    Vincenzi, Simone; Panighel, Annarita; Gazzola, Diana; Flamini, Riccardo; Curioni, Andrea

    2015-03-01

    The wine aroma loss as a consequence of treatments with bentonite is due to the occurrence of multiple interaction mechanisms. In addition to a direct effect of bentonite, the removal of aroma compounds bound to protein components adsorbed by the clay has been hypothesized but never demonstrated. We studied the effect of bentonite addition on total wine aroma compounds (extracted from Moscato wine) in a model solution in the absence and presence of total and purified (thaumatin-like proteins and chitinase) wine proteins. The results showed that in general bentonite alone has a low effect on the loss of terpenes but removed ethyl esters and fatty acids. The presence of wine proteins in the solution treated with bentonite tended to increase the loss of esters with the longest carbon chains (from ethyl octanoate to ethyl decanoate), and this was significant when the purified proteins were used. The results here reported suggest that hydrophobicity can be one of the driving forces involved in the interaction of aromas with both bentonite and proteins. PMID:25665100

  8. Adsorption of dye from wastewater using chitosan-CTAB modified bentonites.

    Science.gov (United States)

    Guo, Jianzhong; Chen, Shunwei; Liu, Li; Li, Bing; Yang, Ping; Zhang, Lijun; Feng, Yanlong

    2012-09-15

    Dyeing wastewater removal is important for the water treatment, and adsorption is an efficient treatment process. In this study, three modified bentonites, chitosan modified bentonite (CTS-Bent), hexadecyl trimethyl ammonium bromide (CTAB) modified bentonite (CTAB-Bent), and both chitosan and hexadecyl trimethyl ammonium bromide modified bentonite (CTS-CTAB-Bent) were prepared and characterized by FTIR and XRD analysis. Batch experiments were conducted to evaluate the adsorptive removal of weak acid scarlet from aqueous phase using modified bentonites under different conditions. The results show that the adsorption capacity of weak acid scarlet onto natural bentonite was low (4.9%), but higher for 1CTS-Bent and 1CTS-10CTAB-Bent. The optimal conditions for weak acid scarlet adsorption were 1% chitosan, 10% CTAB, at 80°C and reaction time 2.5h. The best removal efficiency was ∼85%, and the adsorption capacity of weak acid scarlet was around 102.0mg g(-1), much higher than that of commercial activated carbon (27.2mg g(-1)). These results suggest that 1CTS-10CTAB-Bent is an excellent adsorbent for effective weak acid scarlet removal from water. The adsorption isotherms of weak acid scarlet were investigated. It was found that Langmuir and Temkin models fitted the data very well (R(2)>0.99). PMID:22738850

  9. Monitoring of bentonite pore water with a probe based on solid-state microsensors

    International Nuclear Information System (INIS)

    Repositories for the disposal of radioactive waste generally rely on a multi-barrier system to isolate the waste from the biosphere. This multi-barrier system typically comprises Natural geological barrier provided by the repository host rock and its surroundings and an engineered barrier system (EBS). Bentonite is being studied as an appropriated porous material for an EBS to prevent or delay the release and transport of radionuclides towards biosphere. The study of pore water chemistry within bentonite barriers will permit to understand the transport phenomena of radionuclides and obtain a database of the bentonite-water interaction processes. In this work, the measurement of some chemical parameters in bentonite pore water using solid-state microsensors is proposed. Those sensors are well suited for this application since in situ measurements are feasible and they are robust enough for the long periods of time that monitoring is needed in an EBS. A probe containing an ISFET (ion sensitive field effect transistor) for measuring pH, and platinum microelectrodes for measuring conductivity and redox potential was developed, together with the required instrumentation, to study the chemical changes in a test cell with compacted bentonite. Response features of the sensors' probe and instrumentation performance in synthetic samples with compositions similar to those present in bentonite barriers are reported. Measurements of sensors stability in a test cell are also presented

  10. EFFECT OF BENTONITE ON SKIN WOUND HEALING: EXPERIMENTAL STUDY IN THE RAT MODEL

    Directory of Open Access Journals (Sweden)

    S. H. Emami-Razavi

    2006-08-01

    Full Text Available Wound healing in the skin depends upon the availability of appropriate trace metals as enzyme cofactors and structural components in tissue repair. The present study is a part of a series of experimental investigations to examine the influence of Bentonite on skin wound healing. Surgically induced skin wounds in 48 young adult male rats were exposed topically to Bentonite (12 round wound and 12 incisional wound and control wounds (12 round wound and 12 incisional wound received de-ionized water only. Skin wounds (round and incisional treated with Bentonite exhibited no significant difference in margins with erythema and edematous changes. Scab and wound debris was more extensive and persisted for at least 7 days after surgery in control group (P < 0.05. Skin wounds exposed to Bentonite exhibited a mild retarded re-epithelialization, the treatment wounds were characterized by a prominent central mass of inflammatory cells, cell debris and wound exudate. The intense infiltrate of lymphocytes, macrophages, monocytes and fibroblasts extended from the wound margin into the region of the panniculus carnosus muscle and hypodermis. Vascular dilatation and dermal oedema were prominent features of these wounds. External utilization of Bentonite for wound healing is safe and feasible, and we finalized that macroscopic healing of wound that treated by Bentonite was superior versus control group.

  11. The influence of the addition of polymers on the physico-chemical properties of bentonite suspensions

    Directory of Open Access Journals (Sweden)

    Stojiljkovic S.

    2014-01-01

    Full Text Available Bentonite clays have many applications in industries ranging from construction to cosmetics. Addition of polymers can profoundly influence the properties of bentonite suspensions and we now describe the influence of a range of different polymers. Whereas polyvinyl pyrolidone and soy isolate only slightly influenced the pH and the electrical conductivity of bentonite polymers in suspension, Carbopol solution caused decreases in both pH and electrical conductivity. As expected, strong electrolytes like sodium chloride caused big changes in the electrical conductivity of the suspensions. When the temperature of the bentonite suspensions was increased, the pH was almost unchanged, but the electrical conductivity increased. Bentonite treated with polymer suspensions can be used in purifying polluted water; for example, our results suggest that high pH caused by phosphorous salts can be addressed using bentonite modified with Carbopol. [Projekat Ministarstva nauke Republike Srbije: Stanisa Stojiljkovic, Vojkan Miljkovic, Goran Nikolic, Ivana Savic and Ivan Savic, TR 34020, Danijela Kostic 172047 and Biljana Arsic 174007

  12. Fundamental study on anisotropy of diffusion and migration pathway in compacted bentonite

    International Nuclear Information System (INIS)

    SEM observations for micropore structure in compacted bentonite and through-diffusion experiments for non-sorptive tritiated water (HTO) were conducted to evaluate the anisotropy of diffusive pathway in compacted bentonite used as a buffer material in the geological disposal of high-level radioactive waste. The SEM observations and thorough-diffusion experiments were conducted for axial and perpendicular directions to the compacted direction of bentonite as a function of bentonite's dry density. Two types of Na-bentonites, Kunigel-V1 and Kunipia-F with different smectite contents were used in both experiments. No orientation of clay particles was found for low-smectite content Kunigel-V1, while layers of clay particles orientated in the perpendicular direction to compacted direction were observed for Kunipia-F with approximately 100 wt% smectite content. This tendency is in good agreement with that for HTO's effective diffusivities obtained from diffusion experiments, indicating that smectite content in bentonite affects the orientation properties of clay particles and diffusive pathway. (author)

  13. [Study on performance of double mineral base liner using modified bentonite as active material].

    Science.gov (United States)

    Qu, Zhi-Hui; Zhao, Yong-Sheng; Wang, Tie-Jun; Ren, He-Jun; Zhou, Rui; Hua, Fei; Wang, Bing; Hou, Yin-Ting; Dai, Yun

    2009-06-15

    The absorbing capacity of clay,roasting bentonites by 450 degrees C and dual-cation organobentonites of the pollutions in landfill leachate was compared through static experiment, and investigations were conducted into availability of controlling the permeating of landfill leachate and feasibility of removing the main pollutants in leachate on the double mineral base liners of clay/roasting bentonites by 450 degrees C and clay/dual-cation organobentonites by using nice landfill leachate as the filter fluid. Experiment indicated that the adsorption equilibrium time of landfill leachate in clay, roasting bentonites by 450 degrees C and dual-cation organobentonites was 24 h; the absorbing capacity of roasting bentonites by 450 degrees C and dual-cation organobentonites was larger than that of clay. Simultaneous the penetration coefficients of the two liners were respective 1.31 x 10(-8) cm x s(-1) and 2.80 x 10(-8) cm x s(-1); Double mineral base liners of clay/roasting bentonites by 450 degrees C owned larger absorbing capacity of NH4+, however, double mineral base liners of clay/dual-cation organobentonites had strong absorbing capacity of organic pollutants and the attenuation rate of COD was 33.82% higher than the other. Conclusion was drawn that different types of modified bentonite should be chosen as "the active layer" according to different styles of landfill pollutants. PMID:19662882

  14. Salt content impact on the unsaturated property of bentonite-sand buffer backfilling materials

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Ming [Key Laboratory of Mechanics on Disaster and Environment in Western China, Lanzhou University, Lanzhou 730000 (China); Zhang Huyuan, E-mail: p1314lvp@yahoo.com.cn [Key Laboratory of Mechanics on Disaster and Environment in Western China, Lanzhou University, Lanzhou 730000 (China); Jia Lingyan; Cui Suli [Key Laboratory of Mechanics on Disaster and Environment in Western China, Lanzhou University, Lanzhou 730000 (China)

    2012-09-15

    Highlights: Black-Right-Pointing-Pointer SWCC and infiltration process of bentonite-sand mixtures is researched. Black-Right-Pointing-Pointer The k{sub u} of bentonite-sand mixtures was evaluated as the buffer backfilling materials. Black-Right-Pointing-Pointer Salt content impacting on the unsaturated property of bentonite-sand materials is small. - Abstract: Bentonite mixed with sand is often considered as possible engineered barrier in deep high-level radioactive waste disposal in China. In the present work, the vapor transfer technique and water infiltration apparatus were used to measure the soil water characteristic curve (SWCC) and unsaturated hydraulic conductivity (k{sub u}) of bentonite-sand mixtures (B/S) effected by salt content. Results show, the water-holding capacity and k{sub u} increase slightly with the concentration of Na{sup +} in pore liquid increasing from 0 g/L to 12 g/L, similar with the solution concentration of Beishan groundwater in China. Salt content in the laboratory produced only one order of magnitude increase in k{sub u}, which is the 'safe' value. The different pore liquid concentrations used in this study led to small differences in thickness of diffuse double layer of bentonite in mixtures, this might explain why some differences have been found in final values of k{sub u}.

  15. Influence of Water Salinity on the Hydraulic Conductivity of Compacted Bentonite

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Won Jin; Kim, Jin Seop; Choi, Jong Won [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2011-12-15

    The influence of water salinity on the hydraulic conductivities of compacted bentonite with several dry densities were studied. The hydraulic conductivity increases with increasing salinity only when the dry density of bentonite is relatively low. The degree of increase becomes more remarkable at a lower dry density of bentonite. For bentonite with the density of 1.0 Mg/m{sup 3} and 1.2 Mg/m{sup 3}, the hydraulic conductivity of the 0.4 M NaCl solution increases up to about 7 times and 3 times, respectively higher than that of freshwater. However, for the bentonite with a dry density higher than 1.4 Mg/m{sup 3}, the salinity has an insignificant effect on the hydraulic conductivity, and the hydraulic conductivity is nearly constant within the salinity range of 0.04 to 0.4 M NaCl. The pre-saturation of the bentonite specimen with freshwater has no significant influence on the hydraulic conductivity.

  16. Study of Japanese and Serbia bentonite on the fraction of 137Cs from cement-ion exchange resins-bentonite clay mixture

    International Nuclear Information System (INIS)

    Leaching tests in cement-ion exchange resins-bentonite matrix, were carried out in accordance with a method recommended by IAEA. The cement specimens were prepared from construction cement which is basically a standard Portland cement. The cement was mixed with saturated wet cation exchange resins, (100 g. of dry resins +100 g. of water containing 137Cs) and two bentonite clay, from Serbia, and another from Japan. After each leaching period the radioactivity in the leachant was measured. All results exhibit practically the same general characteristics. An enhanced initial period of leaching occurs during the first 25-30 days or so, followed by a distinct reduction in the leach rate which is broadly maintained up to the long period of leaching. The leach behaviour of cement-mortar materials can be explained as a combination of two processes: surface wash-off, which is not diffusion controlled, followed by a static diffusion stage. Enhanced initial period of leaching can be explained in terms of a rapid equilibrium being established between spaces present in the surface pores of the Portland cement and ions in solution in the leachant; hence the term wash-off. It is the second stage which is controlled by diffusion that dominates the long-term leaching behaviour of the material. We also prove that increasing amount of bentonite causes a significant reduction in the leaching rate, because of bentonite good sorption characteristics and ion selectivity. We showed that the bentonite from Serbia can successfully be used for the immobilisation of radioactive waste with same quality as Japanese bentonite

  17. Assessment of groundwater salinization mechanisms in Santiago Island - Cabo Verde: An environmental isotopic approach

    International Nuclear Information System (INIS)

    Two sampling campaigns were carried out at Santiago Island - Cabo Verde under the scope of an isotopic and geochemical research study. An evaluation of the groundwater systems was carried out through the application of environmental isotopes and geochemical data in order to answer questions such as: origin and mechanisms of groundwater recharge; relation between the hydrochemical evolution of the groundwater systems with the geological matrix (minerals dissolution) or mixture with seawater and aerosol marine influence; identification of seawater intrusion mechanisms and, determination of the apparent groundwater 'age'. The results obtained so far are not conclusive on the identification of the process responsible for the increase of salinity. In general, all the data obtained seems to indicate that the waters have the same isotopic history but different geochemical evolution, which depends on the weathering and permeability of the rocks. (author)

  18. Multi-stage supra-subduction metasomatism in the Cabo Ortegal Complex, Spain

    Science.gov (United States)

    Tilhac, Romain; O'Reilly, Suzanne; Griffin, William; Pearson, Norman; Ceuleneer, Georges; Grégoire, Michel

    2015-04-01

    Three harzburgitic massifs are exposed in the Cabo Ortegal Complex as part of the Variscan suture in Spain. Among these, the Herbeira massif has an unusually high volume of massive and layered pyroxenites whose formation has never comprehensively understood due to a particularly complex tectonothermal history (Ábalos et al., 2003). We use a detailed structural and geochemical approach to reveal a multi-stage metasomatic scenario unraveling the intricacy of magmatic and metamorphic features. Our new mapping of the Herbeira massif suggests that it consists of a single exposure of heterogeneous mantle cross-cut by different generations of mafic veins, outlining a potential metasomatic conduit developed in a subduction zone. The recognition of an overprinting sheath-fold deformation confirms that the whole massif has been deformed in a deep-subduction setting. However, thickness variations in pyroxenites may not only result from various degrees of shear deformation as previously suggested (Girardeau and Gil Ibarguchi, 1991), thus more than a single magmatic event potentially occurred. Structural and textural observations are consistent with the massive pyroxenites intruding the package of harzburgite and layered pyroxenites prior to its intrusion into the subduction zone. The massive pyroxenites display homogeneous enrichments of light rare earth elements (LREE) whereas layered pyroxenites are variously enriched, resulting in spoon-shaped to strongly LREE-fractionated patterns, characteristic of varying degrees of chromatographic re-equilibration. We suggest that an initial metasomatic episode occurred when the parental melt of the massive pyroxenites percolated through the massif, forming dunitic aureoles via additional melt extraction from harzburgites. After intrusion into the subduction zone, shear deformation was accompanied by fluid percolation controlled by inherited lithological heterogeneities and specifically the existence of dunitic channels, as evidenced

  19. Effect of pH, ionic strength and fulvic acid on the sorption and desorption of cobalt to bentonite

    International Nuclear Information System (INIS)

    Humic substances and bentonite have attracted great interest in radioactive waste management. Here the sorption of cobalt on bentonite in the presence and absence of fulvic acid (FA) under ambient conditions was studied. The effects of pH, ionic strength, FA and solution concentrations on cobalt sorption to bentonite were also investigated using batch techniques. The results indicate that the sorption of cobalt is strongly dependent on pH and is independent of ionic strength under our experimental conditions. Surface complexation is considered the main mechanism of cobalt sorption to bentonite. In the presence of FA, little effect of FA on cobalt sorption was found at pH8. The addition sequences of FA/Co2+ to the bentonite suspension on the sorption of cobalt to FA-coated bentonite were also studied. The results indicated that the sorption is not influenced by the addition sequences. Some possible mechanisms are discussed

  20. Process and machinery description of equipment for deposition of canisters in medium-long deposition holes

    International Nuclear Information System (INIS)

    In this report twelve methods are presented to deposit a canister with spent nuclear fuel in a horizontal hole, several canisters per hole (MLH). These methods are part of the KBS-3 system. They have been developed successively, after an analysis of weak points and strong points in previously described methods. In conformance with the guidelines for Project JADE, a choices of system has been considered during the development work. This is whether canister and bentonite buffer should be deposited 'in parts', i.e. at different occasions, but shortly after each other or 'in a package', i.e. together in a single package. The other choice in the guidelines for the JADE project, whether the canister should be placed in a radiation shield or not during transport in the secondary tunnels, was not relevant to MLR. The basic technical problem is depositing heavy objects, the canister and the buffer components, in an horizontal hole which is approximately 200 m deep. Two methods for depositing of the bentonite barrier and the canisters in separate processes have been studied. For depositing of the bentonite barrier and the canister 'in a package', four alternative techniques have been studied: a metallic sleeve around the package, a loading scoop that is rotated, a fork carriage and rails. The repeated transports in a hole, a consequence of depositing several canisters in the same hole, could lead to the rock being crushed. The mutual impact of machines, load and rock wall has therefore been particularly considered. In several methods, the use of a gangway has been proposed (steel plates or layer of ice). A failure mode and effect analysis has been performed for one of the twelve methods. When comparing with a method to deposit one canister per hole using the same technique, the need for equipment and resources is far larger for this MLH method if incidents should occur during depositing. The development work reported here has not yet yielded a definitive method for placing

  1. Cabo Verde, "Pousada" nos Caminhos do Atlântico. Interinluências culturais num arquipélago miscigenado

    OpenAIRE

    Évora, José Silva

    2014-01-01

    [POR] Descoberto entre 1460 e 1462, o Arquipélago de Cabo Verde, situado no Oceano Atlântico, constituiu ao longo de vários séculos, escala obrigatória dos navios que faziam as ligações atlânticas entre os portos das Américas, da Europa e da África Graças a sua situação privilegiada, o espaço cabo-verdiano não foi um mero ponto de reabastecimento, mas também um importante ponto de cruzamento de culturas e de raças. Pretende-se, neste texto, abordar o papel que Cabo Verde teve no Atlântico inc...

  2. The Optimization of Aniline Adsorption from Aqueous Solutions by Raw Bentonite and Bentonite Modified with Cationic Surfactants Using the Taguchi Model

    Directory of Open Access Journals (Sweden)

    F. Taherkhani

    2015-04-01

    Full Text Available Introduction & Objectives: Aniline is an organic compound widely used in various industries. The release of this compound has had various environmental impacts. Thus, the assessment of efficient and practical methods for the removal of aniline from wastewater of these industries is remarkable. Taguchi model is a model for the analysis of experiments, that predicts both the effects of each factors and the optimum level of them using a certain number of experiment. The purpose of this study was the optimization of aniline adsorption on the raw and modified bentonite with a cationic surfactant using Taguchi model. Materials & Methods: In this experimental study, the raw bentonite and modified bentonite was prepared in a few steps. Then, 4 main factors (i.e. pollutant concentration, contact time, pH, and adsorbent dosage on 4 levels were selected by Matrix L16 trials and the experiments were conducted in this matrix. The factors were also ranked based on the R-value. Then , the data were analyzed with Minitab 17 software. Finally, the adsorption of aniline on raw and modified bentonite was determined in optimal conditions. Results: The optimization of adsorption process using Taguchi model showed that the factors of importance for optimizing respectively were: contact time of 360 minutes, pH =10 pH, ani-line initial concentration of 300 mg/L and adsorbent dosages of 40 g/L. The maximum ad-sorption of aniline onto raw bentonite and modified bentonite with cationic surfactant in op-timal conditions were determined 81.86 and 8.75, respectively. The results revealed that Freundlich isotherm and pseudo-second-order kinetic model provided a better ?t to the ex-perimental data. Conclusion: The results showed that the bentonite modified with cationic surfactant is efficient in the removal of aniline. At the same time, since bentonite is cheap and easily accessible ,it is considered a desirable adsorbant. (Sci J Hamadan Univ Med Sci 2015; 22 (1:55-64

  3. Reciclagem de fios e cabos elétricos - cabo paralelo Recycling of parallel wires using unit operations of mineral processing

    Directory of Open Access Journals (Sweden)

    Mishene Christie Pinheiro Bezerra de Araújo

    2008-09-01

    Full Text Available O descarte de produtos eletro-eletrônicos vem crescendo anualmente. Por esse motivo, necessita-se de reciclagem para que se evite o desperdício de recursos naturais não-renováveis. O objetivo desse trabalho é estudar a reciclagem dos cabos tipo cordão paralelo através de operações unitárias de tratamento de minérios. As seguintes operações unitárias foram testadas: moagem, separação granulométrica, separação em meio denso, separação eletrostática, atrição, bateamento e elutriação. Ao final desses processos, observou-se que as operações utilizadas obtiveram concentrados de cobre com baixo grau de contaminação. Observou-se que todas as técnicas precisam de uma outra técnica para complementá-las. Concluiu-se, ainda, que a moagem em moinho de facas com grelha de 3mm é necessária para se conseguir a total liberação dos materiais.The composition and discharge of eletro-electronic products is increasing year after year. To avoid the loss of non-renewable mineral resources and energy, the establishment of a recycling loop for such products is necessary. The goal of this work is to study the recycling of parallel wires using unit operations of mineral processing. The following unit operations were used: grinding, size separation, sink-and-float, electrostatic separation, scrubbing, panning and elutriation. One can observe a low contamination grade in the obtained copper. However, in all cases, a two step flow sheet must be used to completely separate plastics from copper. One can conclude that the total liberation of materials during grinding was reached when the final particle sizes were inferior to 3mm.

  4. Experimental study on self-healing of bentonite/sand mixtures and its impact on hydraulic permeability

    International Nuclear Information System (INIS)

    The effects of gas permeation on the hydraulic permeability of bentonite/sand mixtures were studied experimentally by conducting permeability tests with various fluids and by microscopic observations. In these tests, hydraulic permeabilities were measured before and after helium gas was applied to permeate the mixtures. Although gas formed preferential migration paths through the mixtures, the imperviousness of the bentonite/sand mixtures to the tested fluids never deteriorated because the paths became filled by swelling bentonite on re-saturation

  5. A meta-analysis of water quality and aquatic macrophyte responses in 18 lakes treated with lanthanum modified bentonite (PHOSLOCK®)

    OpenAIRE

    Spears, Bryan M.; Mackay, Eleanor B.; Yasseri, Said; Gunn, Iain D.M.; Waters, Kate E.; Andrews, Christopher; Cole, Stephanie; de Ville, Mitzi; Kelly, Andrea; Meis, Sebastian; Moore, Alanna L.; Nurnberg, Gertrud K.; van Oosterhout, Frank; Pitt, Jo-Anne; Madgwick, Genevieve

    2015-01-01

    Lanthanum (La) modified bentonite is being increasingly used as a geo-engineering tool for the control of phosphorus (P) release from lake bed sediments to overlying waters. However, little is known about its effectiveness in controlling P across a wide range of lake conditions or of its potential to promote rapid ecological recovery. We combined data from 18 treated lakes to examine the lake population responses in the 24 months following La-bentonite application (range of La-bentonite loads...

  6. Mineral alteration in a 4.5 years concrete-bentonite interface

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. Chemical processes occurring in the concrete-bentonite interface can affect the feasibility of the clay barriers implemented for the isolation of nuclear wastes. During the concrete degradation, highly alkaline waters from the concrete will diffuse through the clay barrier. This may produce geochemical and microstructural transformations in the bentonite. Particularly, the studies carried out with the FEBEX bentonite in contact with concrete showed montmorillonite dissolution, precipitation of zeolites, Mg-smectite, CSH gels and brucite. These studies focused mainly in a highly reactive alteration environment (pH>13). During the NF-PRO integrated project the concrete-compacted bentonite interaction was also studied containing the materials and conditions as close as possible to real ones, with simultaneous heating and hydration. Several experimental cells were designed and mounted at a time in CIEMAT, starting in 2006. Presently, in the context of the PEBS project a long-term cell has been dismounted after 4.5 years. The tests were performed in cells especially designed in CIEMAT for the experiments. Blocks of FEBEX bentonite were compacted with its hygroscopic water content at a dry density of 1.65 g/cm3. At the bottom of the cell, the bentonite block was inserted just in contact with the heater. On top of this, a 30-mm thick concrete block was placed. The hydration occurred through the concrete block. In a few days after the beginning of the test the sensor placed at the concrete/bentonite interface recorded stable relative humidities of 100% and temperatures of 45 deg. C. The 4.5 years cell was dismantled with the aim to preserve the concrete/bentonite interface. Then, a detailed sampling of the concrete/bentonite interface and the cement matrix of the concrete was performed for mineralogical, microscopy, and geochemical characterization. The water injected to hydrate the concrete/bentonite cells is synthetic

  7. Modelo de formação a distância para a Universidade Pública de Cabo Verde

    OpenAIRE

    Santos, João Moreira Lopes dos

    2008-01-01

    O presente trabalho propõe apresentar o perfil de e-formadores que, no momento, são docentes de Instituições de Ensino Superior de Cabo Verde. Nele são apresentadas as características desses docentes a nível da literacia informática e de competências de e-formador. Com base nesse perfil e nas especificidades do ensino em Cabo Verde são apresentadas pistas para superação das dificuldades identificadas. ABSTRACT: This work aims to present an e-tutor profile for higher educat...

  8. Abordagem da compreensão na leitura no ensino básico em Cabo Verde

    OpenAIRE

    Cunha, João Bernardino Ramos

    2008-01-01

    O presente estudo procura analisar questões teórico-práticometodológicas suscitadas pelo desenvolvimento de competências em compreensão na leitura em alunos do 4º Ano do Ensino Básico, no âmbito do ensino do Português como Língua Segunda na República de Cabo Verde. Para tanto, procedeu-se à análise de planificações dos professores de Português de uma Escola do Ensino Básico em Cabo Verde. ABSTRACT: This study was aimed to discuss theoretical, practical and methodo...

  9. Título da página electrónica: CIDLOT/Universidade de Cabo Verde

    OpenAIRE

    Andréia Moassab; Patrícia Anahory

    2013-01-01

    O Centro de Investigação em Desenvolvimento Local e Ordenamento de Território (CIDLOT) da Universidade de Cabo Verde representa um laboratório de ponta da primeira universidade pública do país, fundada apenas há quatro anos, que tem o objectivo de fazer dialogar o mundo académico com as maiores dinâmicas de desenvolvimento do arquipélago. Desde a sua fundação em 2009, o CIDLOT tem trabalhado com vista a preencher uma série de lacunas de conhecimento existentes em Cabo Verde, por exemplo, real...

  10. Evaluation of long-term interaction between cement and bentonite for geological disposal (2) XAFS analysis of calcium silicate hydrate precipitates at cementitious and bentonite material interface

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. Numerical analyses of the long-term alteration of the engineered barriers used for the disposal of TRU waste predicted precipitation of C-S-H minerals at the interface between the cementitious materials and the bentonite-based buffer. When the C-S-H precipitates at this interface, the diffusion coefficient in the engineered barriers will decrease, resulting in reduced mass transport, which feeds back to reduce the rate of subsequent alteration. The C-S-H predicted to form at the cement-bentonite interface could not be identified directly using conventional analytical tools, including XRD, due to its low crystallinity. The authors propose that XAFS analysis, which provides spectra sensitive to the valency and coordination of the element of interest regardless of its crystallinity, would be capable of characterizing the C-S-H. The presence of the C-S-H precipitated as a secondary mineral has already been confirmed by applying chemical and XAFS analyses to bentonite specimens collected from the compacted bentonite-cement interface. However, because of the limitations on the width of specimens that can be collected by cutting from block samples, i.e. approximately 1 mm, detailed concentration profiles could not be obtained for this secondary C-S-H. In this study, XAFS spectra of thin specimens were measured using an X-ray detector in order to obtain detailed concentration profiles for the C-S-H formed at the interface between the cementitious material and the bentonite-based buffer. The X-ray detector used in the XAFS analysis consists of 1024 photodiodes arranged in line with a 0.025 mm pitch (photodiode array; PDA). Ca-K-edge XAFS measurements were conducted at the Photon Factory of the KEK. The synchrotron was operated in top-up mode with 450 mA during the measurements. Specimens were taken from a contact sample of compacted bentonite (Kunigel V1; dry density of 1.6 g/cm3) and hardened OPC (w/c = 0.6) immersed in

  11. Evaluation of Chlorophyll Fluorescence and Biochemical Traits of Lettuce under Drought Stress and Super Absorbent or Bentonite Application

    Directory of Open Access Journals (Sweden)

    Akram Valizadeh Ghale Beig

    2014-03-01

    Full Text Available The effects of two superabsorbents (natural-bentonite and (synthetic-A 200 on the chlorophyll fluorescence index, proline accumulation, phenolic compounds, antioxidant activity and total carbohydrate in lettuce (Lactuca sativa L. was evaluated. For this purpose, a factorial experiment using completely randomized design with superabsorbents at 3 levels (0, 0.15, 0.30 w/w%, drought stress at 2 levels (60 and 100% of field capacity and 4 replicates was conducted. Results showed that photosystem photochemical efficiency (Fv/Fm II under drought stress (60% FC as well as lower levels of bentonite superabsorbent polymer reduced. The minimum and maximum proline content were obtained in 0.3% bentonite, 100% FC and 0 benetonite, 60% FC, respectively. The lowest and highest phenolic compounds was corresponded to the highest levels in both super absorbents and control respectively, so that the super absorbent and bentonite, reduced phenolic compounds by 62.65 and 66.21% compared to control. 0 and 0.15 wt % bentonite in high drought stress (60% FC showed the highest and 0.3 wt % bentonite and 100% FC attained the lowest level of antioxidant activity. Control bentonite treatment beds at 60% FC and beds containing 0.3 wt. % bentonite in 100% FC, showed the lowest and the highest total carbohydrate content respectively. Results of this study indicate that bentonite can reduce the negative effects of drought stress similar to artificial super absorbent.

  12. The adsorption characteristics and porous structure of bentonite adsorbents as determined from the adsorption isotherms of benzene vapor

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    LEPA STOJANOVSKA

    2004-02-01

    Full Text Available The adsorption of benzene vapor on natural and acid activated bentonites was treated by the theory of volume filling of micropores. The micropore volume and characteristic values of the free energy of adsorption were determined from the adsorption isotherms. The Dubinin–Radushkevish–Stoeckli and Dubinin–Astakhov equations were used for this purpose. The results showed that natural bentonite has a more homogeneous micropore structure than the acid activated ones. The characteristic values of the free energy of adsorption for the natural bentonite were higher than those of the acid activated bentonite. This is due to differences in its structure and the pore size.

  13. Silurian bentonites in Lithuania: correlations based on sanidine phenocryst composition and graptolite biozonation – interpretation of volcanic source regions

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    Tarmo Kiipli

    2014-02-01

    Full Text Available Integrated correlation of bentonites (altered volcanic ashes and graptolite biozonation is presented. Detailed study of two Lithuanian drill core sections extended previous knowledge of the occurrence and composition of bentonites to the south. Identification of graptolite species allowed bentonites to be assigned their proper stratigraphical position. Silurian bentonites in Lithuania are mostly characterized by wide and very wide XRD 201 reflections of the main component of sanidine phenocrysts. Only fourteen of the 69 samples studied contained sanidine with a sharp reflection, which gave the best correlation potential. In the Lithuanian sections one bentonite was found in the Rhuddanian, five bentonites were recognized in the Aeronian, 17 bentonites in the Telychian, 26 in the Sheinwoodian, 10 in the Homerian and six in the Ludlow. All bentonites found in Lithuania are characterized by the main component of sanidine. A large number of Lithuanian bentonites are not known in Latvia and Estonia, indicating that volcanic ashes reached the East Baltic area from two source regions – the Central European and Norwegian Caledonides.

  14. Studies on dynamic compaction and hydraulic properties of Bentonite-based materials for geological disposal of radioactive wastes

    International Nuclear Information System (INIS)

    As the safe disposal method of high-level radioactive waste from nuclear power plants, there is the 'geological disposal' that buries the waste in the stable soil. For cushioning materials to be used for geological disposal, performances such as low permeability. self-sealing ability, and nuclide sorption ability are required, and bentonite has been picked up as a candidate for its main base material. This paper takes up granular bentonite and bentonite - silica sand mixed material as the bentonite-based materials used as cushioning materials for site application, and explains their dynamic compaction test and easy-to-use evaluation method. As for the granular bentonite, it was found that its compaction properties can be predicted from the plastic limit of pulverized sample of the original ore as a raw material for granular bentonite. As for bentonite - silica sand mixed material, the relationship between maximum dry density, optimum moisture content, and plastic limit showed a very good match between the measured results and calculated results. The permeability coefficient of granular bentonite can be predicted from the wet volume strain of montmorillonite, or the partial density of montmorillonite. As for the bentonite - silica sand mixed material, the permeability of Fe(III) type montmorillonite became significantly larger. (A.O.)

  15. Modified swelling pressure apparatus using vapor pressure technique for compacted bentonite

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. bentonite. The compacted bentonite is found in unsaturated conditions before applying of swelling due to absorption. The behaviour of compacted bentonite is not consistent with the principle and concepts of classical, saturated soil mechanics. An unsaturated soil theoretical framework using soil water characteristic curve has been fairly established over the past several decades. The soil-water characteristic curve is a relationship between soil moisture and soil suction obtained by the axis translation technique, vapor pressure technique or osmotic suction control which is a key feature in unsaturated soil mechanics. The soil-water characteristic curve can be used for prediction of the shear strength, volume change and hydraulic conductivity. Cui et al. 2002 indicated soil-water characteristic curve of expansive clay soil in high soil suction ranges using osmotic suction technique. Tripathy et al. 2010 described the soil-water characteristic curve both using the axis translation technique and vapor pressure technique in the entire soil suction ranges. Nishimura and Koseki 2011 measured suction of bentonite applied high soil suction due vapor pressure using a chilled mirror dew point potentiometer (WP4-T of DECAGON Device). The bentonite with gravimetric water content of 18 % indicated soil suction of 2.8 MPa at least. It is predicted that suction efforts to swelling pressure and shear strength of unsaturated compacted bentonite. This study focuses on the influence of suction on both swelling pressure and shear strength of compacted bentonite. The soil-water characteristic curve (SWCC) tests were conducted for compacted bentonite using both axis-translation technique and vapor pressure technique. The SWCC had a range from 0 kPa to 296 MPa in suction. The compacted bentonite having two different soil suctions were prepared for swelling pressure tests. Newly swelling pressure testing apparatus was developed in order

  16. Modelling bentonite pore waters for the Swiss high-level radioactive waste repository

    International Nuclear Information System (INIS)

    The main objective of this investigation is to contribute to definition of representative compositions of bentonite pore waters in the near-field of the Swiss repository for high-level radioactive waste. Such compositions are necessary for determining the solubility limits of radionuclides for the safety analysis KRISTALLIN I. The model developed here is based on the premise, supported by experimental data, that the composition of bentonite pore waters is largely controlled by the dissolution or precipitation of reactive trace solids in bentonite. Selectivity constants for the exchange equilibria among Na-K, Na-Ca, and Ca-Mg were derived from water-bentonite interaction experiments performed for NAGRA by the British Geological Survey (BGS). An important parameter for the prediction of radionuclide solubilities is the oxidation potential of the bentonite water. Since the BGS experiments yielded no information on this, the oxidation potential had to be estimated from model assumptions. Bentonite pore waters were defined by computer simulation with the geochemical code MINEQL. They have been modelled in a closed system, i.e. assuming the bentonite, once it has reacted with a fixed volume of groundwater, does not exchange further chemical species with an external reservoir. No attempt was made to model the evolution of the pore water by simulating diffusive exchange processes. It can be anticipated that uncertainties in the concentrations of some major elements (e.g. Al, Si) will not significantly affect the calculated radionuclide solubilities. The latter will depend primarily on the concentrations of a few major ligands (OH-, Cl- and CO3-2) and, for multivalent elements, also on the oxidation potential of the solution. (author) 10 figs., 22 tabs., 40 refs

  17. Adsorption properties and porous structure of sulfuric acid treated bentonites determined - SHORT COMMUNICATION

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    SNEZANA BREZOVSKA

    2005-02-01

    Full Text Available In a previous paper adsorption isotherms of benzene vapor on natural bentonite from Ginovci, Macedonia, and forms acid activated with 10 % and 15 % solutions of hydrochloric were interpreted by means of the Dubinin–Radushkevich–Stoeckli and Dubinin–Astakhov equations; the investigation has been continued with bentonites acid activated with 10 % and 15 % solutions of sulfuric acid where X-ray analysis indicates smaller structural changes. Using the above equations, the heterogeneity of the micropores and the energetic heterogeneity of the bentonites were determined from the differential distribution of the micropore volume with respect to the structural parameter of the equations characterizing the microporous structure and to the molar free energy of adsorption. Activated bentonites obtain bigger pores but also a certain quantity of new small pores appear during acid activation with the higher concentration of acid. The micropore volumes, determined from the adsorption of benzene vapor, of bentonites activated with 10 % and 15 % solution of hydrochloric acid (144.60 cm3 kg-1 and 110.06 cm3 kg-1, respectively, decrease in comparison with that of natural bentonite (162.55 cm3 kgv.1 In contrast, the values of the micropore volume for bentonities treated with 10 % and 15 % solutions of sulfuric acids increase (169.19 cm3 kg-1 and 227.74 cm3 kg-1. That is due to the difference in the structural changes occurring during activation with hydrochloric and sulfuric acids. The values of the free energy of adsorption of benzene vapor for natural bentonite are higher than those of the acid acitivated bentonities, what is in accordance with the structural and porosity changes.

  18. Na + and HTO diffusion in compacted bentonite: Effect of surface chemistry and related texture

    Science.gov (United States)

    Melkior, T.; Gaucher, E. C.; Brouard, C.; Yahiaoui, S.; Thoby, D.; Clinard, Ch.; Ferrage, E.; Guyonnet, D.; Tournassat, C.; Coelho, D.

    2009-05-01

    SummaryIn underground repository concepts for radioactive waste, bentonite is studied as a reference swelling material to be used as an engineered barrier. Under the changing geochemical conditions prevailing within the barrier (saturation with the fluid coming from the host formation, diffusion of various chemical plumes caused by the degradation of some constituents of the barrier-system, etc.), the surface chemistry of the clay particles could evolve. This work aims to characterize the effects of these changes on (i) the microstructure of compacted bentonite samples and (ii) the diffusion properties of HTO and Na in these samples. For this purpose, bentonite sets were equilibrated with different solutions: NaCl, CaCl 2, CsCl solutions as well as an artificial clayey porewater solution. The microstructure of the different samples was characterized by HRTEM and XRD, in a water saturated state. In parallel, effective diffusion coefficients of both HTO and 22Na were measured for the different samples. The density of the bentonite in the diffusion tests and in the HRTEM observations was set at 1.6 Mg m -3. From the microstructural observations and the results of diffusion tests, it is deduced that one key parameter is the occurrence of a gel phase in the material, which is found to depend strongly on the bentonite set: the gel phase dominates in Na-bentonite, while it is lacking in Cs-bentonite. The HTO diffusion coefficients are found to be lower in the samples with high gel phase content. Sodium diffusion does not follow the same trend: when compared with HTO, Na diffuses faster when the gel phase content is high. The latter result could indicate that the "accelerated diffusion mechanism" of cations, already mentioned in the literature, is enhanced in clayey materials that contain a gel phase.

  19. Engineered barrier experiments and analytical studies on coupled thermal - hydraulic - chemical processes in bentonite buffer material

    International Nuclear Information System (INIS)

    It is anticipated that thermal - hydraulic - mechanical - chemical (THMC) processes will be coupled in the bentonite buffer material of a high-level radioactive waste repository. The main contributors to these processes are heat arising from the radioactive decay of the vitrified waste, infiltration of groundwater from the host rock and/or leachate from the cementitious component of the repository, and the consequent increase in swelling pressure and chemical reactions. In order to evaluate these coupled processes in the bentonite buffer material, it is necessary to take steps towards the development of a credible and robust THMC model. The current paper describes the measured data of an engineering-scale coupled THC process experiment and the calculated results of a THC model undergoing development. The coupled experiment used an electric heater, bentonite blocks and a mortar block, subjected to infiltrating water to simulate a high-alkaline porewater derived from the concrete tunnel support seeping into the bentonite buffer material under a thermal gradient provided by the vitrified waste. Temperature and water content of the bentonite buffer material were measured by several sensors continuously for several months. After this time, the buffer material was sampled. The results of mineral analysis of the samples suggested that the precipitate of amorphous hydrate with silica was found in the buffer material in contact with the mortar. The developing THC model simulated C-S-H gel precipitation as a secondary mineral in the exact same locality because of the solution being saturated with respect to portlandite and chalcedony, thereby providing some confidence in the chemical feature of the developing THC model. Some important issues in the future development of the model were also identified, including the concentration of porewater being influenced by vapor movement in the bentonite buffer material due to heating from the vitrified waste and geochemical reactions

  20. Sorption of Uranium(VI and Thorium(IV by Jordanian Bentonite

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    Fawwaz I. Khalili

    2013-01-01

    Full Text Available Purification of raw bentonite was done to remove quartz. This includes mixing the raw bentonite with water and then centrifuge it at 750 rpm; this process is repeated until white purified bentonite is obtained. XRD, XRF, FTIR, and SEM techniques will be used for the characterization of purified bentonite. The sorption behavior of purified Jordanian bentonite towards and Th4+ metal ions in aqueous solutions was studied by batch experiment as a function of pH, contact time, temperature, and column techniques at 25.0∘C and . The highest rate of metal ions uptake was observed after 18 h of shaking, and the uptake has increased with increasing pH and reached a maximum at . Bentonite has shown high metal ion uptake capacity toward uranium(VI than thorium(IV. Sorption data were evaluated according to the pseudo- second-order reaction kinetic. Sorption isotherms were studied at temperatures 25.0∘C, 35.0∘C, and 45.0∘C. The Langmuir, Freundlich, and Dubinin-Radushkevich (D-R sorption models equations were applied and the proper constants were derived. It was found that the sorption process is enthalpy driven for uranium(VI and thorium(IV. Recovery of uranium(VI and thorium(IV ions after sorption was carried out by treatment of the loaded bentonite with different concentrations of HNO3 1.0 M, 0.5 M, 0.1 M, and 0.01 M. The best percent recovery for uranium(VI and thorium(IV was obtained when 1.0 M HNO3 was used.

  1. Decontamination of cesium, strontium, and cobalt from aqueous solutions by bentonite

    Energy Technology Data Exchange (ETDEWEB)

    Khan, M.A. [Univ. of the Punjab, Lahore (Pakistan); Khan, S.A. [Government F.C. College, Lahore (Pakistan)

    1996-12-31

    Sorption studies of cesium, strontium, and cobalt (Cs, Sr, and Co) on bentonite under various experimental conditions, such as contact time, pH, sorbent and sorbate concentration, and temperature, have been performed. The sorption data for all these metals have been interpreted in terms of Freundlich, Langmuir, and Dubinin-Radushkevich equations. Thermodynamics parameters, such as heat of sorption {Delta}H{degrees}, free energy change {Delta}G{degrees}, and entropy change {Delta}S{degrees}, for the sorption of these metals on bentonite have been calculated. The value of {Delta}H{degrees} shows that the sorption of Cs was exothermic, while the sorption of Sr and Co on bentonite were endothermic in nature. The value of {Delta}G{degrees} for their sorption was negative, showing the spontaneity of the process. The maximum loading capacity of Cs, Sr, and Co were 75.5, 22, and 27.5 meq, respectively, for 100 g of bentonite. The mean free energy E of Cs, Sr, and Co sorption on bentonite was 14.5, 9, and 7.7 kJ/mol, respectively. The value of E indicates that ion exchange may be the predominant mode of sorption for these radionuclides. The desorption studies with 0.01 M CaCl{sub 2} and groundwater at low-metal loading on bentonite showed that about 95% of Cs, 85-90% of Sr, and 97% of Co were irreversibly sorbed. Bentonite could be effectively used for the decontamination of wastewater effluent containing low concentrations of radioactive nuclides of Cs, Sr, and Co. 16 refs., 7 figs., 3 tabs.

  2. Force interactions between magnetite, silica, and bentonite studied with atomic force microscopy

    Science.gov (United States)

    Dobryden, I.; Potapova, E.; Holmgren, A.; Weber, H.; Hedlund, J.; Almqvist, N.

    2015-04-01

    Iron ore pellets consist of variety of mineral particles and are an important refined product used in steel manufacturing. Production of high-quality pellets requires good understanding of interactions between different constituents, such as magnetite, gangue residues, bentonite, and additives. Much research has been reported on magnetite, silica, and bentonite surface properties and their effect on pellet strength but more scant with a focus on a fundamental particle-particle interaction. To probe such particle interaction, atomic force microscopy (AFM) using colloidal probe technique has proven to be a suitable tool. In this work, the measurements were performed between magnetite-magnetite, bentonite-magnetite, silica-bentonite, and silica-magnetite particles in 1 mM CaCl2 solution at various pH values. The interaction character, i.e., repulsion or attraction, was determined by measuring and analyzing AFM force curves. The observed quantitative changes in interaction forces were in good agreement with the measured zeta-potentials for the particles at the same experimental conditions. Particle aggregation was studied by measuring the adhesion force. Absolute values of adhesion forces for different systems could not be compared due to the difference in particle size and contact geometry. Therefore, the relative change of adhesion force between pH 6 and 10 was used for comparison. The adhesion force decreased for the magnetite-magnetite and bentonite-silica systems and slightly increased for the magnetite-bentonite system at pH 10 as compared to pH 6, whereas a pronounced decrease in adhesion force was observed in the magnetite-silica system. Thus, the presence of silica particles on the magnetite surface could have a negative impact on the interaction between magnetite and bentonite in balling due to the reduction of the adhesion force.

  3. Effect of Different Levels of Kaolin, Bentonite and Zeolite on Broilers Performance

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    M. Safaei Katouli

    2010-01-01

    Full Text Available An experiment was conducted to study the effects of different levels of kaolin, bentonite and zeolite on broiler performance in 6 weeks. Four hundred and forty eight day-old broilers of male Ross 308 strain were allocated to 7 treatments with four replications and 16 broilers in each. The experiment was carried out in a completely randomized design. Treatments were control and 1.5, 3% of kaolin, bentonite and zeolite. Treatments with 3% zeolite and bentonite was significantly (p<0.05 increased weight gain during the 1st and 6th weeks, 1.5% kaolin and zeolite, significantly (p<0.05 increased weight gain in 5th and 6th weeks compared to the control, respectively. Treatments 1.5% bentonite in 4th and 5th weeks and 1.5% zeolite and 3% bentonite in 5th week was significantly (p<0.05 increased feed intake compared to the control. Feed conversion ratio in diets with 3% kaolin in the 1st and 2nd weeks and 3% zeolite in the 1st week was significantly (p<0.05 improved compared to the control. There was no significant (p>0.05 differences in internal organs and fecal pH between trial groups and control. Fecal moisture in treatments with 1.5% kaolin, 3% bentonite and zeolite was significantly (p<0.05 different from control. Growth rate in treats containing 3% kaolin at 0-3 week and 1.5% zeolite, 1.5% kaolin and 3% kaolin, bentonite and zeolite at 0-6 week was more than control (p<0.05. The results demonstrated that adding silicate minerals in diet, improve performance of broiler chickens.

  4. La zaratita de Cabo Ortegal (A Coruña: historia de su descubrimiento y caracterización actual

    Directory of Open Access Journals (Sweden)

    La Iglesia, A.

    2014-06-01

    Full Text Available Zaratite, Ni3CO3(OH4.4H2O is one of the few minerals discovered in Spain. Taking into account that it is an amorphous compound with variable chemical composition depending on the ore deposits, the International Mineralogical Association (IMA currently considers zaratita in the Q status (Questionable. In this article we analyze first the nearly simultaneous discoveries of the Spanish zaratite and other material called “Emerald of Nickel” from Texas, Lancaster County, Pennsylvania (USA, of similar chemical composition. Both led to the current zaratite, where the Spanish mineral provides the name and the American one, the chemical composition anc physical properties. In addition, here we also include an experimental characterization of the zaratite historical specimen from Ortegal Cape, by electron microprobe, scanning electron microscopy, X-ray diffraction, differential thermal and thermo-gravimetric analyses, micro-Raman, infrared transmission spectroscopy and spectral cathodoluminescence together with a discussion of the analytical results.La zaratita, Ni3CO3(OH4.4H2O es uno de los pocos minerales descubiertos en España. Por ser una fase de baja cristalinidad y presentar una composición química variable según los diferentes yacimientos, la International Mineralogical Association (IMA actualmente la considera con status Q (questioned. En este artículo se analizan en primer lugar los descubrimientos, casi simultáneos, del mineral español y del llamado “Emerald of Nickel” de Texas, Lancaster County, Pennsilvania (USA, de similar composición química, que dieron lugar a la actual zaratita, donde el mineral español aportó el nombre y el americano la composición química y la descripción de las propiedades físicas. En segundo lugar, se presenta una nueva caracterización de la muestra histórica de zaratita de Cabo Ortegal, por microsonda electrónica, microscopia electrónica de barrido, difracción de rayos-X, análisis termo

  5. Susceptibility profile of Aedes aegypti from Santiago Island, Cabo Verde, to insecticides.

    Science.gov (United States)

    Rocha, Hélio Daniel Ribeiro; Paiva, Marcelo Henrique Santos; Silva, Norma Machado; de Araújo, Ana Paula; Camacho, Denise dos Reis da Rosa de Azevedo; Moura, Aires Januário Fernandes da; Gómez, Lara Ferrero; Ayres, Constância Flávia Junqueira; Santos, Maria Alice Varjal de Melo

    2015-12-01

    In 2009, Cabo Verde diagnosed the first dengue cases, with 21,137 cases reported and Aedes aegypti was identified as the vector. Since the outbreak, chemical insecticides and source reduction were used to control the mosquito population. This study aimed to assess the susceptibility of A. aegypti populations from Santiago, Cabo Verde to insecticides and identify the mechanisms of resistance. Samples of A. aegypti eggs were obtained at two different time periods (2012 and 2014), using ovitraps in different locations in Santiago Island to establish the parental population. F1 larvae were exposed to different concentrations of insecticides (Bacillus thuringiensis var israelensis (Bti), diflubenzuron and temephos) to estimate the lethal concentrations (LC90) and calculate the respective rate of resistance (RR90). Semi-field tests using temephos-ABATE(®) were performed to evaluate the persistence of the product. Bottle tests using female mosquitoes were carried out to determine the susceptibility to the adulticides malathion, cypermethrin and deltamethrin. Biochemical and molecular tests were performed to investigate the presence of metabolic resistance mechanisms, associated with the enzymes glutathione S-transferases (GSTs), esterases and mixed-function oxidases (MFO) and to detect mutations or alterations in the sodium channel and acetylcholinesterase genes. A. aegypti mosquitoes from Santiago exhibited resistance to deltamethrin, cypermethrin (mortality<80%) and temephos (RR90=4.4) but susceptibility to malathion (mortality≥98%), Bti and diflubenzuron. The low level of resistance to temephos did not affect the effectiveness of Abate(®). The enzymatic analysis conducted in 2012 revealed slight changes in the activities of GST (25%), MFO (18%), α-esterase (19%) and β-esterase (17%), but no significant changes in 2014. Target site resistance mutations were not detected. Our results suggest that the A. aegypti population from Santiago is resistant to two major

  6. Internal stratification of two thick Ordovician bentonites of Estonia: deciphering primary magmatic, sedimentary, environmental and diagenetic signatures

    Directory of Open Access Journals (Sweden)

    Sven Siir

    2015-05-01

    Full Text Available Twenty-six samples from two major altered volcanic ash beds, Kinnekulle and BII Bentonite of the Kuressaare core section (K-3, Saaremaa Island, were explored to record the geochemical and mineralogical heterogeneity of beds. Signs of ash transport fractionation, redeposition of volcanic ash and diagenetic redistribution of material are described and interpreted. In authigenic mineralogy of the Kinnekulle Bentonite illite–smectite dominates with addition of K-feldspar at the margins. The BII Bentonite is composed of chlorite–smectite and illite–smectite. The stability of phenocryst compositions, including that of sanidine and biotite, indicates that both bentonites originate from a single eruption. The observed rather stable pyroclastic sanidine compositions in the cross section of bentonites confirm the reliability of sanidine-based fingerprinting of altered volcanic ash beds. Trace element distribution in bentonites and host rocks indicates that Zr, Ga, Rb, Nb, Ti and Th stayed largely immobile during volcanic ash alteration and reflect primary ash composition. However, some redistribution of Nb and Ti as well as Y has probably occurred near the contacts of bentonite with the host rock. More scattered grain size distribution and immobile element patterns of the Kinnekulle Bentonite support the idea that the primary ash bed had a heterogeneous composition and it was one of the biggest bentonites of the Phanerozoic and most likely records an extended volcanic event. Significant geochemical variations, including a high S content, near the upper and lower contacts of the Kinnekulle Bentonite and elevated Ca and P in host rocks of both bentonites suggest that the studied large ash-falls caused notable perturbations in shallow marine and early post-sedimentary environment.

  7. Review of the properties and uses of bentonite as a buffer and backfill material

    International Nuclear Information System (INIS)

    Research carried out by SKB on the use and behaviour of bentonite as a buffer and backfill material in a radioactive waste repository has been reviewed. The following research areas have been evaluated: mechanical properties; hydraulic and other transport properties; geochemical properties; thermal properties and resaturation; gas migration; manufacturing and emplacement procedures. This review has shown that SKB has carried out much pioneering and world-leading research on bentonite, particularly with regard to analogue studies, microtextural work and practical manufacturing and emplacement procedures. However, there are a number of subject areas which appear less well addressed than others which require further attention: The extrapolation of experimental results of the mechanical properties of bentonite to repository timescales and repository conditions should be investigated further. There is a need for detailed microstructural analysis of materials as part of experimental programmes. This would enable SKB to build confidence in the interpretations of results and reveal whether the mechanical processes occurring during experimentation truly reflect expectations of the performance of the repository. The large amount of experimental, theoretical, empirical datasets and computer models of the mechanical properties of bentonite need to be collated to form a database which is assessable and relevant to those involved in performance assessment calculations. At present, the valuable results of many excellent research projects on mechanical properties of bentonite buffer are not readily available. There seems to be a relatively poor understanding of the mechanisms of radionuclide diffusion through compacted bentonite. Other international work suggests that diffusion coefficients are much lower than those applied by SKB in its PA work. The importance of surface diffusion to describe diffusion in bentonite for certain chemical species ascribed by SKB is not reflected in

  8. Review of the properties and uses of bentonite as a buffer and backfill material

    Energy Technology Data Exchange (ETDEWEB)

    Savage, D.; Lind, A. [QuantiSci Ltd., Melton Mowbray (United Kingdom); Arthur, R.C. [QuantiSci lnc., Denver, CO (United States)

    1999-05-01

    Research carried out by SKB on the use and behaviour of bentonite as a buffer and backfill material in a radioactive waste repository has been reviewed. The following research areas have been evaluated: mechanical properties; hydraulic and other transport properties; geochemical properties; thermal properties and resaturation; gas migration; manufacturing and emplacement procedures. This review has shown that SKB has carried out much pioneering and world-leading research on bentonite, particularly with regard to analogue studies, microtextural work and practical manufacturing and emplacement procedures. However, there are a number of subject areas which appear less well addressed than others which require further attention: The extrapolation of experimental results of the mechanical properties of bentonite to repository timescales and repository conditions should be investigated further. There is a need for detailed microstructural analysis of materials as part of experimental programmes. This would enable SKB to build confidence in the interpretations of results and reveal whether the mechanical processes occurring during experimentation truly reflect expectations of the performance of the repository. The large amount of experimental, theoretical, empirical datasets and computer models of the mechanical properties of bentonite need to be collated to form a database which is assessable and relevant to those involved in performance assessment calculations. At present, the valuable results of many excellent research projects on mechanical properties of bentonite buffer are not readily available. There seems to be a relatively poor understanding of the mechanisms of radionuclide diffusion through compacted bentonite. Other international work suggests that diffusion coefficients are much lower than those applied by SKB in its PA work. The importance of surface diffusion to describe diffusion in bentonite for certain chemical species ascribed by SKB is not reflected in

  9. Evaluation of impact strength of polyamide 6/bentonite clay nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Paz, Rene Anisio; Araujo, Edcleide Maria; Tomas Jeferson Alves; Amanda Damiao; Medeiros, Vanessa da Nobrega [Federal University of Campina Grande (CCT/UFCG), Campina Grande, PB (Brazil). Centro de Ciencias e Tecnologia; Pessan, Luiz Antonio [Federal University of Sao Carlos (DEMa/UFSCar), SP (Brazil). Materials Engineering Department

    2012-07-15

    Nanocomposites of polymer/clay have had much attention in recent years, particularly those developed with layered silicates due to the need of engineering materials more efficient than pure polymers for certain applications. The level of exfoliation of layered silicates in crystalline structure of polymer matrices has been studied and has been observed that it affects the crystalline behavior and the physical and mechanical properties. In this study, nanocomposites of polyamide 6 were obtained by the melt intercalation method, using a Brazilian bentonite modified with a quaternary ammonium salt. X-Ray Diffraction (XRD) results showed the incorporation of salt among the layers of clay, making it organophilic and that the nanocomposites presented exfoliated and/or partially exfoliated structures and confirmed by transmission electron microscopy (TEM). By thermogravimetry (TG), the results indicated that the presence of clay increased the thermal stability of polyamide 6. The impact properties of the nanocomposites showed inferior values in relation to the pure polyamide, in other words, decrease the toughness. (author)

  10. Evaluation of impact strength of polyamide 6/bentonite clay nanocomposites

    Directory of Open Access Journals (Sweden)

    Rene Anisio Paz

    2012-08-01

    Full Text Available Nanocomposites of polymer/clay have had much attention in recent years, particularly those developed with layered silicates due to the need of engineering materials more efficient than pure polymers for certain applications. The level of exfoliation of layered silicates in crystalline structure of polymer matrices has been studied and has been observed that it affects the crystalline behavior and the physical and mechanical properties. In this study, nanocomposites of polyamide 6 were obtained by the melt intercalation method, using a Brazilian bentonite modified with a quaternary ammonium salt. X-Ray Diffraction (XRD results showed the incorporation of salt among the layers of clay, making it organophilic and that the nanocomposites presented exfoliated and/or partially exfoliated structures and confirmed by transmission electron microscopy (TEM. By thermogravimetry (TG, the results indicated that the presence of clay increased the thermal stability of polyamide 6. The impact properties of the nanocomposites showed inferior values in relation to the pure polyamide, in other words, decrease the toughness.

  11. Experimental Study on Volume Change Indices of Bentonite Soils

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    This paper reports experimental results regarding statically compacted clay specimens to study the volume change behavior of bentonites. The volume change indices such as the coefficients of compressibility, volume compressibility, and consolidation ( i. e.av , mv and cv respectively) and the saturated coefficient of permeability k at different surcharge pressures were determined with the commonly adopted procedures. The swell potentials, swelling pressures, different phases of the swollen specimens were analyzed for the volume change behavior during compression. Experimental results revealed that the swell potential is dependent on the initial dry density, the initial water content and the vertical pressure at which the clay specimens were allowed to swell. The swelling pressure was found to be similar for the specimens with varying water content, showing strong dependency on the initial void ratio. The compression indices ( viz. mv and av) of saturated specimens decreased with an increase in the vertical pressure. About 80% to 90% of the volume change occurred in the primary compression phase under any given vertical pressure. The coefficient of consolidation cv and the saturated coefficient of permeability k decreased with an increase in the vertical pressure.

  12. Thermal detoxification and bloating of chromium(VI) with bentonite

    International Nuclear Information System (INIS)

    This study stabilizes and bloats Cr(VI)-sorbed bentonite by heating at high temperature. Cr leaching decreases with increasing temperatures. Heating the sample at 1100 oC results in a non-detectable Cr concentration in the leachate, equivalent to a Cr leaching percent less than 0.001% (i.e., Cr TCLP concentration -1 of leachate). Morphology observed with a scanning electron microscopy indicates the occurrence of sintering of the sample heated at 1100 oC. The heated samples also show the occurrence of a vesicant process at 1100 oC. X-ray absorption spectroscopy results indicate that heating at 500 oC for 4 h can convert approximately 87% Cr(VI) into Cr(III) that is negligibly toxic; Cr2O3 was detected to be the most abundant Cr species. After heating at higher temperatures, namely 900-1100 oC, almost all doped Cr(VI) is reduced to Cr(III) as inferred from the height of the pre-edge peak of XANES spectra and/or from XANES simulation.

  13. Modelling the in situ performance of bentonite-sand buffer

    International Nuclear Information System (INIS)

    In the Canadian nuclear fuel waste management concept, a number of engineered barriers, such as the bentonite-sand buffer which surrounds the waste container in the emplacement boreholes, are used to inhibit the transport of radionuclides. The buffer material is also required to effectively conduct heat from the fuel-waste containers to the surrounding rock. To a large extent, in situ buffer performance will depend on the degree of moisture within the buffer. The moisture content will in turn depend on temperature, temperature gradients, and buffer initial and moisture flux boundary conditions. Modelling of coupled heat and moisture transport in the buffer before resaturation is necessary to assess in situ buffer performance. This paper describes the results of a parametric study using the Philip and de Vries coupled heat and moisture transport model to assess the effects of variations in the moisture diffusivity parameters and the boundary conditions on buffer performance. The results show that the thermal performance of the buffer is affected by heat-induced moisture movement. In particular, the thermal vapor diffusivity, DTvap, has the most significant effect on thermal drying in a closed system. Work is currently underway to improve capability to model coupled heat and moisture transport in buffer. Laboratory experiments are in progress to more accurately define the moisture diffusivity parameters and the model is being modified to include the effects of boundary moisture fluxes and pressure potentials so that the resaturation process may be modelled

  14. Y-chromosome lineages in Cabo Verde Islands witness the diverse geographic origin of its first male settlers.

    Science.gov (United States)

    Gonçalves, Rita; Rosa, Alexandra; Freitas, Ana; Fernandes, Ana; Kivisild, Toomas; Villems, Richard; Brehm, António

    2003-11-01

    The Y-chromosome haplogroup composition of the population of the Cabo Verde Archipelago was profiled by using 32 single-nucleotide polymorphism markers and compared with potential source populations from Iberia, west Africa, and the Middle East. According to the traditional view, the major proportion of the founding population of Cabo Verde was of west African ancestry with the addition of a minor fraction of male colonizers from Europe. Unexpectedly, more than half of the paternal lineages (53.5%) of Cabo Verdeans clustered in haplogroups I, J, K, and R1, which are characteristic of populations of Europe and the Middle East, while being absent in the probable west African source population of Guiné-Bissau. Moreover, a high frequency of J* lineages in Cabo Verdeans relates them more closely to populations of the Middle East and probably provides the first genetic evidence of the legacy of the Jews. In addition, the considerable proportion (20.5%) of E3b(xM81) lineages indicates a possible gene flow from the Middle East or northeast Africa, which, at least partly, could be ascribed to the Sephardic Jews. In contrast to the predominance of west African mitochondrial DNA haplotypes in their maternal gene pool, the major west African Y-chromosome lineage E3a was observed only at a frequency of 15.9%. Overall, these results indicate that gene flow from multiple sources and various sex-specific patterns have been important in the formation of the genomic diversity in the Cabo Verde islands. PMID:12942365

  15. Adsorption Properties of Bentonite with In Situ Immobilized Polyaniline Towards Anionic Forms of Cr(VI), Mo(VI), W(VI), V(V)

    OpenAIRE

    Kateryna RYABCHENKO; Elina YANOVSKA; Mariya MELNYK; Dariusz STERNIK; Olga KYCHKIRUK; Valentun TERTYKH

    2016-01-01

    A new composite material bentonite-PANI was synthesized by in situ immobilization of polyaniline (PANI) on the surface of natural mineral bentonite. It was established as a result of the modification of bentonite a surface area and an interlayer distance of mineral decrease and particles of bentonite transformed of irregular shape with different porosity on irregularly shaped particles of smaller size. It has been found that the total Cr(VI) ions extraction took place under the acid condition...

  16. Adsorption behavior of a textile dye of Reactive Blue 19 from aqueous solutions onto modified bentonite

    International Nuclear Information System (INIS)

    The aim of this study is to evaluate adsorption kinetics, isotherms and thermodynamic parameters of Reactive Blue 19 (RB19) onto modified bentonite from aqueous solutions. The effects of pH, contact time, initial dye concentration and temperature were investigated in the experimentally. Natural bentonite was modified by using 1,6-diamino hexane (DAH) as a modifying agent. The characterization of modified bentonite (DAH-bentonite) was accomplished by using FTIR, TGA, BET and elemental analysis techniques. The optimum pH value for the adsorption experiments was found to be 1.5 and all the experiments were carried out at this pH value. The pseudo-second-order kinetic model agrees very well with the experimental results. Equilibrium data were also fitted well to the Langmuir isotherm model in the studied concentration range of RB19 at 20 deg. C. The results indicate that DAH-modified bentonite is a suitable adsorbent for the adsorption of textile dyes.

  17. Effect of bentonite on muscle radioactivity in pigs and sheep contaminated repeatedly with radiocesium

    International Nuclear Information System (INIS)

    Twelve pigs and twelve sheep were contaminated daily with Cs-137 for 21 days. The animal feed was fortified with a 10% supplement of bentonite. Control and bentonite-fed animals were slaughtered 7, 14 and 21 days after contamination and 7 and 14 days after contamination ceased. Samples (1 g) collected from 6 various parts of muscles (joint, jam, sirloin, chuck, heart and tongue) were measured radiometrically. Pigs fed bentonite showed muscle Cs-137 levels reduced by 70.3, 70.9 and 71.6% after 7, 14 and 21 days, respectively, as compared to those in the controls. Sheep fed bentonite showed Cs-137 radioactivity decreased by 83.7, 88.9% after 7 and 14 days, respectively. When the contamination ceased the Cs-137 levels were reduced by about 80.4% and 83.7% after 7 and 14 days, respectively, compared to those in the controls. The marked reduction of radiocesium from pig and sheep tissues emphasized, from an economic point of view, the importance of bentonite use. (author)

  18. FACTORS AFFECTING THE HYDRAULIC BARRIER PERFORMANCE OF SOIL-BENTONITE MIXTURE CUT-OFF WALL

    Science.gov (United States)

    Takai, Atsushi; Inui, Toru; Katsumi, Takeshi; Kamon, Masashi; Araki, Susumu

    Containment technique using cut-off walls is a valid method against contaminants in subsurface soil and/or groundwater. This paper states laboratory testing results on hydraulic barrier performance of Soil-Bentonite (SB), which is made by mixing bentonite with in-situ soil. Since the bentonite swelling is sensitive to chemicals, chemical compatibility is important for the hydraulic barrier performance of SB. Hydraulic conductivity tests using flexible-wall permeameter were conducted on SB specimens with various types and concentrations of chemicals in the pore water and/or in the permeant and with various bentonite powder contents. As a result, hydraulic barrier performance of SB was influenced by the chemical concentration in the pore water of original soil and bentonite powder content. In the case that SB specimens have damage parallel to the permeating direction, no significant leakage in the SB occurs by the self-sealing property of SB. In addition, the hydraulic conductivity values of SB have excellent correlation with their plastic indexes and swelling pr essures, thus these properties of SB have some possibility to be indicators for estimation of the hydraulic barrier performance of SB.

  19. Photodegradation of Methylene Blue by TiO2-Fe3O4-Bentonite Magnetic Nanocomposite

    Directory of Open Access Journals (Sweden)

    Wei Chen

    2015-01-01

    Full Text Available Fe3O4-bentonite nanoparticles have been prepared by a coprecipitation technique under a nitrogen atmosphere. An aqueous suspension of bentonite was first modified with FeCl2 and FeCl3. TiO2 was then loaded onto the surface of the Fe3O4-bentonite by a sol-gel method. After sufficient drying, the colloidal solution was placed in a muffle furnace at 773 K to obtain the TiO2-Fe3O4-bentonite composite. The material has been characterized by scanning electron microscopy (SEM, X-ray diffraction (XRD analysis, and vibrating sample magnetometry (VSM. Morphological observation showed that Fe3O4 and TiO2 nanoparticles had been adsorbed on the surface of bentonite nanoneedles. The material was then applied for the photodegradation of the azo dye methylene blue (MB. It was found that the removal efficiency of MB exceeded 90% under UV illumination, and that only a 20% mass loss was incurred after six cycles. The composite material thus showed good photocatalytic performance and recycling properties.

  20. Modeling cation diffusion in compacted water-saturated Na-bentonite at low ionic strength

    International Nuclear Information System (INIS)

    Sodium bentonites are used as barrier materials for the isolation of landfills and are under consideration for a similar use in the subsurface storage of high-level radioactive waste. The performance of these barriers is determined in large part by molecular diffusion in the bentonite pore space. We tested two current models of cation diffusion in bentonite against experimental data on the relative apparent diffusion coefficients of two representative cations, sodium and strontium. On the 'macropore/nanopore' model, solute molecules are divided into two categories, with unequal pore-scale diffusion coefficients, based on location: in macropores or in interlayer nanopores. On the 'surface diffusion' model, solute molecules are divided into categories based on chemical speciation: dissolved or adsorbed. The macropore/nanopore model agrees with all experimental data at partial montmorillonite dry densities ranging from 0.2 (a dilute bentonite gel) to 1.7 kg dm-3 (a highly compacted bentonite with most of its pore space located in interlayer nanopores), whereas the surface diffusion model fails at partial montmorillonite dry densities greater than about 1.2 kg dm-3

  1. Microbial incidence on copper and titanium embedded in compacted bentonite clay

    Energy Technology Data Exchange (ETDEWEB)

    Persson, Joergen; Lydmark, Sara; Edlund, Johanna; Paeaejaervi, Anna; Pedersen, Karsten (Microbial Analytics Sweden AB (Sweden))

    2011-10-15

    The incidence of bacteria on metal surfaces was examined in an experimental setting simulating conditions of the proposed Swedish concept for disposal of spent nuclear fuel. Titanium and copper rods were embedded in compacted bentonite clay saturated with groundwater collected at a depth of 450 m. Bentonite blocks were exposed to an external flux of groundwater with or without added lactate or H{sub 2} for up to 203 days. Bacterial accumulation on metal rods and in the surrounding bentonite was analyzed using real-time quantitative PCR (qPCR), with genetic markers for overall bacterial presence (16S rDNA) as well as specific for sulfate-reducing bacteria (apsA). Clay species composition was analyzed by cloning and sequencing 16S rDNA extracted from the clay. Results suggest limited bacterial accumulation on metal surfaces, amounting to a maximum of approximately 106 apsA copies cm-2, corresponding to a 3.7% coverage of metal surfaces. Bacterial species composition appeared to be a mix of species originating from the bentonite clay and from the added groundwater, including an apparently high proportion of sulfate-reducing bacteria. While titanium surfaces exhibited higher bacterial presence than did copper surfaces, neither the degree of bentonite compaction nor the addition of lactate or H{sub 2} appeared to have any effect on the bacterial incidence on metal surfaces

  2. Heat and Radiation Effects on Iodide Sorption by Surfactant Modified Bentonite (SMB)

    International Nuclear Information System (INIS)

    Radioactive waste repository is designed using multiple barriers to prevent the release of radionuclides to environments. Bentonite has been used as engineering barrier in many countries. Although the bentonite is an effective sorbent for cationic radionuclides, it is not good for anions such as 129-I and 99-Tc because of negative surface charges over the pH. Radioactive iodine exists usually as anions such as iodate (IO3-) and iodide (I-) as stable iodine species in groundwater environments. Therefore, the iodine is one of the most difficult elements for its transport through engineering barrier (i. e., bentonite) to be controlled by sorption processes in the geological repository. We modified the bentonite using a cationic surfactant to enhance iodine sorption capability. The goal of this study is addressed to evaluate the effects of sorption of high heat and radiation on iodide sorption to surfactant modified bentonite (SMB) which can be used as engineering barrier in the repository. The iodide sorption on the SMBs was significantly affected by temperature conditions rather than radiation. As temperature increases, the iodide sorption decreases. Considering the similar sorption abilities between 100 and 200% SMBs, the 100% SMB is economical sorbent to apply for engineering barrier in a geological repository

  3. Polypropylene Fiber Amendments to Alleviate Initiation and Evolution of Desiccation Cracks in Bentonite Liners

    Science.gov (United States)

    Tuller, M.; Gebrenegus, T. B.

    2009-12-01

    Sodium saturated bentonite is a major constituent of compacted and geosynthetic liners and covers for hydraulic isolation of hazardous waste, playing a crucial role in protecting groundwater and other environmental resources from harmful landfill leachates. Due to favorable hydraulic properties (i.e., low permeability), large surface area and associated adsorption capacity for particular contaminants, and relative abundance and low cost, bentonite is the material of choice in many modern waste containment systems. However, long-term interactions between bentonite and waste leachate and exposure of bentonite to desiccative conditions may significantly deteriorate liner or cover performance and ultimately lead to failure of containment systems. In the presented study, the potential usefulness of polypropylene fiber amendments for preventing initiation and evolution of desiccation cracks, while maintaining acceptably low permeability under saturated conditions was investigated. Well-controlled desiccation experiments were conducted using initially saturated bentonite-sand mixtures that contained varying amounts of polypropylene fibers. Initiation and evolution of surface cracks were observed by means of X-Ray Computed Tomography (CT). Advanced image analysis techniques were employed to characterize and quantify 2-D and 3-D features of the evolving crack networks. Potential negative effects of employed additives on saturated hydraulic conductivity were determined with fully-automated Flexible Wall Permeametry (FWP).

  4. Modeling cation diffusion in compacted water-saturated sodium bentonite at low ionic strength.

    Science.gov (United States)

    Bourg, Ian C; Sposito, Garrison; Bourg, Alain C M

    2007-12-01

    Sodium bentonites are used as barrier materials for the isolation of landfills and are under consideration for a similar use in the subsurface storage of high-level radioactive waste. The performance of these barriers is determined in large part by molecular diffusion in the bentonite pore space. We tested two current models of cation diffusion in bentonite against experimental data on the relative apparent diffusion coefficients of two representative cations, sodium and strontium. On the "macropore/nanopore" model, solute molecules are divided into two categories, with unequal pore-scale diffusion coefficients, based on location: in macropores or in interlayer nanopores. On the "surface diffusion" model, solute molecules are divided into categories based on chemical speciation: dissolved or adsorbed. The macropore/nanopore model agrees with all experimental data at partial montmorillonite dry densities ranging from 0.2 (a dilute bentonite gel) to 1.7 kg dm(-3) (a highly compacted bentonite with most of its pore space located in interlayer nanopores), whereas the surface diffusion model fails at partial montmorillonite dry densities greater than about 1.3 kg dm(-3). PMID:18186346

  5. Role of bentonite colloids on europium and plutonium migration in a granite fracture

    International Nuclear Information System (INIS)

    To establish when the presence of colloids can favour contaminant migration is a critical task for the performance assessment of a high level radioactive waste repository. In this study, the effects of the presence of bentonite colloids on the migration of highly sorbing elements, such as Eu and Pu, in a granite environment were investigated. Special efforts were made to quantify the filtration of bentonite colloids in this medium and to determine the experimental uncertainties that could bias the interpretation of the results. The migration of bentonite colloids in a granite fracture was studied in the laboratory by dynamic column experiments under low water flow rates (4-11 mL/h). The breakthrough curves of bentonite colloids always showed a peak in a similar position to conservative tracers, but the colloids recovery critically depended on their initial concentration and on the water flow rate. In the presence of colloids, the breakthrough curves of Eu and Pu always showed a peak in the same position as conservative tracers, thus indicating the migration of these radionuclides to be mostly colloid-driven. The recovery of Pu adsorbed onto the colloids was approximately that expected when the experimentally determined bentonite colloid filtration in the column was accounting for but the Eu recovery was always significantly lower

  6. Swelling deformation characteristics of Gaomiaozi bentonite-sand mixture inundated in water

    International Nuclear Information System (INIS)

    A bentonite from Gaomiaozi, Xinghe County, Inner Mongolia, has been regarded as the first choice for using as buffer/backfill materials in the high-level waste geological disposal in China. In this paper, one-dimensional swelling deformation tests, collapse tests and swelling pressure tests due to wetting were carried out on Gaomiaozi sodium bentonite by using oedometer, for analyzing the swelling and collapse deformation characteristics of mixtures of bentonite and quartz sand in different sand additions. Based on the concept of the montmorillonite void ratio, the de- formation characteristics of bentonite-sand mixtures at saturation were consistently identified. Test results indicated that when the content of sand in the mixture is small, the relationship between the montmorillonite void ratio and vertical pressure at saturation is a straight line in the log scales. For different kinds of bentonites, the relationship is different; Test results of the mixture with high sand fractions were analyzed by using the sand skeleton void ratio, which can predict whether the sand skeleton forms and the vertical pressure when the sand skeleton begins to form. (authors)

  7. IMPLEMENTAÇÃO DO OEE EM UMA FÁBRICA DE CABOS ÓPTICOS

    Directory of Open Access Journals (Sweden)

    KODA, Carlos Alberto

    2013-10-01

    Full Text Available This project proposes action research in a company of telecommunications cables. The research is to raise the awareness of employees, diagnose and meet the influence of losses in the index of overall efficiency, identify intervention alternatives, devise a plan of actions aiming at the increase of this index and the improvement of the working environment in the daily lives of employees. Process data were collected through the use of a tool called OEE (Overall Equipment Effectiveness. The information from this tool will be the basis for making decisions and proposals for solutions at the operational level, the Organization's strategic and tactical. Este projeto propõe a pesquisa-ação em uma empresa de cabos de telecomunicações. A pesquisa consiste em conscientizar os colaboradores, diagnosticar e conhecer a influência das perdas no índice de eficiência global, identificar alternativas de intervenção, elaborar um plano de ações visando o aumento deste índice e a melhoria do ambiente de trabalho no cotidiano dos colaboradores. Os dados referentes ao processo foram coletados através do uso de uma ferramenta chamada OEE (Overall Equipment Effectiveness. As informações provenientes desta ferramenta serão a base para a tomada de decisões e propostas de soluções no nível operacional, tático e estratégico da organização

  8. [Vector-borne parasites of dogs on the Islands of Cabo Verde].

    Science.gov (United States)

    Kirchner, Marlene; Brunner, Adrian; Edelhofer, Renate; Joachim, Anja

    2008-01-01

    During an animal welfare campaign on the Islands of Cape Verde (in the capital Praia on the island of Santiago) a total of 57 dogs were examined for ectoparasites and blood parasites. 84% of the animals were infested with arthropods, mostly ticks. Haemotropic parasites were examined via blood smear, polymerase chain reaction (PCR) and/or serology. 23 dogs had single infections, five multiple infections with haemoparasites. In eight dogs Ehrlichia canis and in one Amaplasma phagocytophilum were detected by PCR, while 43.1% and 36.2% respectively were serologically positive. In 23 blood smears Babesia gibsoni, but no Babesia canis could be detected. In four cases Hepatozoon canis was found in the smears. All animals were negative for Dirofilaria larvae or antibodies against Leishmania. Arthropod-infested animals more frequently harboured babesiae (44%), ehrlichiae (19%) or H. canis (8%) compared to non-infested animals (20%, 0%, 0%). In bitches and dogs aged one year or less babesiae were more frequently detected (48% of the bitches and 13% of the male dogs; 45% of animals less than one year and 26% of the older ones). Due to the high infection rates the import of animals from Cabo Verde to Central Europe must be seen as critical, since an endemisation of (sub-)tropical infectious agents cannot be excluded. PMID:19066773

  9. Hydrogeological investigation in Santiago Island (Cabo Verde) using magnetotellurics and VLF methods

    Science.gov (United States)

    Monteiro Santos, Fernando A.; Almeida, Eugénio P.; Gomes, Mota; Pina, António

    2006-08-01

    A geoelectromagnetic research was carried out in the Santa Cruz region (Santiago Island, Cabo Verde) during June 2004. The survey comprised MT soundings and VLF profiles. The main purpose of the MT profile, carried out across three important valleys associated with freshwater aquifers, was to study the tectonic structures correlated to seawater infiltration. The VLF method was used inside of the valleys for investigating shallow structures related to the aquifer contamination by seawater. Numerical modelling shows that the ocean effect is not important for MT data collected at periods shorter than 1 s. The MT data were inverted using a two-dimensional approach, to obtain the sub-superficial electrical conductivity distribution. The VLF data were processed applying the Karous-Hjelt filters to obtain the equivalent current distribution and inverted using 2-D approach. The results obtained in one of the most important valleys show anomalous current concentration/low resistivity (<20 Ω m) areas at depths greater than 40 m that may correspond to an increase in seawater content. The MT data modelling show that the deep zones beneath the valley are strongly fractured representing good pathways for seawater circulation. The depth of the conductive zones increases from south to north, suggesting a northward decreasing of the seawater infiltration effect. This observation correlates very well with in situ geochemical observations.

  10. INDICADORES BIOFÍSICOS DE DESERTIFICAÇÃO, CABO VERDE/ÁFRICA

    Directory of Open Access Journals (Sweden)

    Vládia Pinto Vidal de Oliveira

    2011-01-01

    Full Text Available El trabajo discute el diagnostico geoambiental de la Isla de Santiago de Cabo Verde. Tiene como objetivo evaluar la dinámica ambiental y el estado de evolución de los sistemas naturales, estableciendo las categorías de los medios ecodinámicos. Cada categoría del medio está asociada al comportamiento y a la vulnerabilidad de las condiciones geoambientales en función de los procesos de degradación. Sobre el punto de vista teórico- -metodológico, se adoptaron criterios integrativos capaces de atender a las relaciones de interdependencia entre componentes físico-bióticos y socioeconómicos. Se seleccionaron siete (7 indicadores biofísicos: geología, geomorfología, cobertura vegetal (estratifi cación, cobertura vegetal (porcentual de ocupación, suelos (espesura y suelos (erosión. Resultaron diez (10 sistemas ambientales, que, en el análisis de los Indicadores Biofísicos de Desertifi cación (IBFD, apuntaron a la ocurrencia de dos grupos distintos: índice muy alto de desertifi cación y de muy bajo a bajo índice biofísico de desertifi cación.

  11. ¿Cómo llevar a cabo un turismo sostenible en Monserrate?

    Directory of Open Access Journals (Sweden)

    Ana Milena Hamón Ruíz

    2008-11-01

    Full Text Available El Cerro de Monserrate es uno de los más importantes y reconocidos atractivos turísticos a nivel ambiental y cultural de la ciudad de Bogotá. Sin embargo, en él existen varias problemáticas a nivel ambiental, cultural, social y económico desconocidas para muchos, las cuales inciden en el desarrollo de un turismo sostenible en este atractivo de la ciudad. Por este motivo se propuso un estudio, como trabajo de tesis, en donde se realizó un análisis de cado uno de los siguientes ámbitos: ambiental, social, económico y cultural, determinando las necesidades y problemáticas que han impedido que este lugar turístico cumpla con los principios del turismo sostenible. De acuerdo con lo anterior, al final de la investigación, se plantean algunas estrategias e indicadores para lo cual se toma como base un estudio dofa. Este es un primer aporte que brinda elementos para la planificación de proyectos que se quieran llevar a cabo en este atractivo de la ciudad, respetando y valorando los principios de sostenibilidad.

  12. Report on Thermo-Hydro-Mechanical Laboratory Tests Performed by CIEMAT on Febex Bentonite 2004-2008

    International Nuclear Information System (INIS)

    The results of the laboratory studies performed by CIEMAT with the FEBEX bentonite in the context of WP3.2 of the NF-PRO Project and of the Agreement ENRESA-CIEMAT Anexo V are presented and analysed in this report. They refer to the effect of the hydraulic gradient on the permeability of bentonite, the effect of the thermal gradient on the hydration kinetics of bentonite, and the repercussion of temperature on the hydro-mechanical properties of bentonite (swelling, permeability and water retention capacity). In all the cases the bentonite has been used compacted to densities expected in the engineered barrier of a high-level radioactive waste repository. The existence of threshold and critical hydraulic gradients has been observed, both of them dependent on bentonite density and water pressures. After more than seven years of hydration, the 40-cm high bentonite columns are far from full saturation, the thermal gradient additionally delaying the process, which is very slow. Temperatures below 100 degree centigrade slightly decrease the swelling and the water retention capacity of the bentonite and increase its permeability. The information obtained improves the knowledge on the behaviour of expansive clay and will help the development of constitutive models and the interpretation of the results obtained in the mock-up and the in situ tests. (Author) 35 refs

  13. Transport of heavy metals and chemical compatibility of hydraulic conductivity of a compacted sand-bentonite mixture

    Directory of Open Access Journals (Sweden)

    Nanthanit Charoenthaisong

    2008-03-01

    Full Text Available Clayey soils are usually used as barrier material in landfill liners because of its low hydraulic conductivity and high sorption capacity. Bentonite, which consists mainly of montmorillonite, has a high cation exchange capacity resulting in a high retention capacity of heavy metals. Sand is a permeable material but its hydraulic conductivity decreases significantly when mixed with bentonite. However, using a sand-bentonite mixture as landfill liners is questionable, because the hydraulic conductivity of the sand-bentonite mixture may increase when permeated with heavy metal solutions, which are normally found in landfill leachates. In this paper, transport of heavy metals through a compacted sand-bentonite mixture and its chemical compatibility were studied through the batch adsorption test, the column test, and the hydraulic conductivity test.Experimental results indicate that the sorption capacity of the bentonite, ranked in descending order, was Cr3+, Pb2+, Cd2+, Zn2+, and Ni2+, respectively. The diffusion coefficients of the sand-bentonite mixture were in the order of 10-5 cm2/s and the retardation factors were 130, 115, 111, and 90 for Pb2+, Ni2+, Zn2+, and Cd2+, respectively. The hydraulic conductivity of thesand-bentonite mixture was only compatible with a chromium solution having a concentration not greater than 0.001 M.

  14. Modelling the induced polarization of bentonite-sand mixtures. In : Proceedings of the 3rd International Workshop on Induced Polarization

    OpenAIRE

    Leroy, Philippe; Ghorbani, Ahmad; Revil, André; Cosenza, P.; Okay, G.

    2014-01-01

    Spectral induced polarization (SIP) has become an increasingly popular geophysical method for hydrogeological and environmental applications. These applications include for instance the non-intrusive characterization of the textural and interfacial physicochemical properties of bentonites used as permeability barriers in landfills or to store various types of contaminants including radioactive wastes. Bentonites are mainly constituted of smectites, which have very high specific surface areas ...

  15. Model for diffusion and porewater chemistry in compacted bentonite. Experimental arrangements and preliminary results of the porewater chemistry studies

    International Nuclear Information System (INIS)

    This report describes the progress of the experimental research on the porewater chemistry in bentonite. The research is part of the project Microstructural and chemical parameters of bentonite as determinants of waste isolation efficiency within the Nuclear Fission Safety Program organized by The Commission of the European Communities. The study was started by a literature overview on the properties of bentonite, porewater-sampling methods and obtained results. On the basis of the literature study, porewater extraction by squeezing seemed the most promising method for further development. The apparatus developed in this study consists of a pressing apparatus, which is used to create the necessary long-term compression, and of the compaction cell where porewater is separated from bentonite and collected in a syringe. The constant log-term force is maintained by a strong spring. An experimental study of solution-bentonite interactions was initiated. The parameters varied are the bentonite density, bentonite-water ratio, composition of the solutions, and the composition of bentonite. The report presents the experimental arrangements, the preliminary results for studying the evolution of water chemistry and the results of pre-modelling. (orig.) (27 refs.)

  16. CRIEPI's research results (2006-2011) and clarified future issues on alteration behavior of bentonite barrier by alkaline solutions

    International Nuclear Information System (INIS)

    In radioactive waste disposal facilities, bentonite barrier would be altered by alkaline solutions which arise by leaching of cementitious materials. Consequently suitable properties of the bentonite barrier would be degraded for a long time period. In CRIEPI, the investigation on the alteration of the bentonite under alkaline conditions was started in 2006, and several CRIEPI reports have been published. Specifically, we have investigated the kinetics of montmorillonite dissolution, the mineralogical alteration of compacted bentonite (with high- and low-dry density) and the change of permeability of the compacted bentonite (with high- and low-dry density) during alteration under the alkaline conditions. Furthermore, stability of saponite, which has similar physical properties to the bentonite, under the alkaline conditions was also examined. In this report, we show the outline of those research results, and lay out the clarified future issues extracted from our results. Ten clarified future issues were divided three categories as follows: 1) the estimation of the alteration behavior of the bentonite by alkaline solutions, 2) the elucidation of the mechanism of physical properties (e.g., permeability, swelling properties and mechanistic properties) change of the compacted bentonites during alteration, and 3) the development of the model building and simulation technology concerning the change in physical properties during alteration under alkaline conditions. (author)

  17. A coupled THC model of the FEBEX in situ test with bentonite swelling and chemical and thermal osmosis

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, L.; Samper, J.; Montenegro, L.

    2011-04-01

    The performance assessment of a geological repository for radioactive waste requires quantifying the geochemical evolution of the bentonite engineered barrier. This barrier will be exposed to coupled thermal (T), hydrodynamic (H), mechanical (M) and chemical (C) processes. This paper presents a coupled THC model of the FEBEX (Full-scale Engineered Barrier EXperiment) in situ test which accounts for bentonite swelling and chemical and thermal osmosis. Model results attest the relevance of thermal osmosis and bentonite swelling for the geochemical evolution of the bentonite barrier while chemical osmosis is found to be almost irrelevant. The model has been tested with data collected after the dismantling of heater 1 of the in situ test. The model reproduces reasonably well the measured temperature, relative humidity, water content and inferred geochemical data. However, it fails to mimic the solute concentrations at the heater-bentonite and bentonite-granite interfaces because the model does not account for the volume change of bentonite, the CO{sub 2}(g) degassing and the transport of vapor from the bentonite into the granite. The inferred HCO{sub 3}{sup -} and pH data cannot be explained solely by solute transport, calcite dissolution and protonation/deprotonation by surface complexation, suggesting that such data may be affected also by other reactions.

  18. Thermodynamic modelling of bentonite-groundwater interaction and implications for near field chemistry in a repository for spent fuel

    International Nuclear Information System (INIS)

    Predictions of near field geochemistry are made using a thermodynamic model for bentonite/ground interaction. This model is a refinement and extension of the model developed by the senior author. It is based on recent experiments performed at high solid/water ratio and adapted to the Swedish type of HLW repository design. Thus, from the obtained experimental results on solution composition, the model includes chemical reactions resulting from both the impurities and the main clay fraction within the bentonite. Ion exchange reactions are treated both with and without the contribution of edge sites. Due to its thermodynamic basis, the model exhibits prediction capability over a wide range of conditions in terms of solid/water ratio. The modelling of repository conditions implies, due to the lack of experimental information, simplifications with regard to thermodynamic properties of the bentonite. This mainly involves the non-consideration of the temperature effects and of the acid/base properties of the solid. Nevertheless, our results yield insight into important processes affecting porewater chemistry. Thus, the model suggests that proton exchange reactions may exert a strong control on calcite dissolution within highly compacted bentonite. Estimations of chemical changes over time in the bentonite were done in the basis of a mixing tank model. These results indicate transformation of Na-bentonite to Ca-bentonite over time. The extent of this process, however, critically depends on the amount of carbonate present in the bentonite. (authors) (34 refs.)

  19. Report on Thermo-Hydro-Mechanical Laboratory Tests Performed by CIEMAT on Febex Bentonite 2004-2008

    Energy Technology Data Exchange (ETDEWEB)

    Villar, M. V.; Gomez-Espina, R.

    2009-11-25

    The results of the laboratory studies performed by CIEMAT with the FEBEX bentonite in the context of WP3.2 of the NF-PRO Project and of the Agreement ENRESA-CIEMAT Anexo V are presented and analysed in this report. They refer to the effect of the hydraulic gradient on the permeability of bentonite, the effect of the thermal gradient on the hydration kinetics of bentonite, and the repercussion of temperature on the hydro-mechanical properties of bentonite (swelling, permeability and water retention capacity). In all the cases the bentonite has been used compacted to densities expected in the engineered barrier of a high-level radioactive waste repository. The existence of threshold and critical hydraulic gradients has been observed, both of them dependent on bentonite density and water pressures. After more than seven years of hydration, the 40-cm high bentonite columns are far from full saturation, the thermal gradient additionally delaying the process, which is very slow. Temperatures below 100 degree centigrade slightly decrease the swelling and the water retention capacity of the bentonite and increase its permeability. The information obtained improves the knowledge on the behaviour of expansive clay and will help the development of constitutive models and the interpretation of the results obtained in the mock-up and the in situ tests. (Author) 35 refs.

  20. Time evolution of the general characteristics and Cu retention capacity in an acid soil amended with a bentonite winery waste

    DEFF Research Database (Denmark)

    Fernandez Calviño, David; Rodríguez-Salgado, Isabel; Pérez-Rodríguez, Paula;

    2015-01-01

    The effect of bentonite waste added to a "poor" soil on its general characteristic and copper adsorption capacity was assessed. The soil was amended with different bentonite waste concentrations (0, 10, 20, 40 and 80Mgha-1) in laboratory pots, and different times of incubation of samples were...

  1. MX-80 Bentonite. Thermal-Hydro-Mechanical Characterisation Performed at CIEMAT in the Context of the Prototype Project

    International Nuclear Information System (INIS)

    This document details the results of the thermo-hydro-mechanical (THM) characterisation of the commercial MX-80 bentonite performed by CIEMAT from 2001 to 2004 in the context of a project carried out at the AEspoe Hard Rock Laboratory (Sweden), the Prototype Repository. The swelling pressure and the permeability of the bentonite compacted to different dry densities has been determined, as well as the influence of the permeant salinity on hydraulic conductivity. The influence of salinity on the retention capacity of the compacted bentonite has been studied. For that, a new methodology has been designed. Water retention curves have been determined at temperatures of 20 and 600C. Suction controlled odometer tests have been performed at 20oC. Finally, the behaviour of the MX-80 bentonite has been compared to that of the Spanish FEBEX bentonite. (Author) 13 refs

  2. Leachability of bentonite/cement for medium-level waste immobilisation

    Energy Technology Data Exchange (ETDEWEB)

    Hamlat, M.S.; Rabia, N. [Centre de Radioprotection et de Surete, Alger-Gare (Algeria)

    1998-12-31

    The release of radionuclides from Algerian bentonite/cement matrix has been measured experimentally using static and dynamic testing procedures. The waste forms were cement/sand and bentonite/cement matrices contaminated with Cs-137. To characterise radionuclide/waste form combination, two parameters, diffusion (D) and distribution coefficients ({alpha}) were used. (D) is an effective diffusion coefficient that describes the kinetic behaviour and is most easily determined using Soxhlet test, whereas, ({alpha}) describes the distribution of radionuclide between aqueous and solid phases at equilibrium and is best measured in static test. Leach rates obtained being very low. Distribution coefficient values have showed that the bentonite has relatively a high degree of fixation. It was concluded that the matrix under study seems play a role for the immobilisation. (orig.)

  3. Diffusion of Radionuclides in Bentonite Clay - Laboratory and in situ Studies

    International Nuclear Information System (INIS)

    This thesis deals with the diffusion of ions in compacted bentonite clay. Laboratory experiments were performed to examine in detail different processes that affect the diffusion. To demonstrate that the results obtained from the laboratory investigations are valid under in situ conditions, two different kinds of in situ experiments were performed. Laboratory experiments were performed to better understand the impact of ionic strength on the diffusion of S2+ and Cs+ ions, which sorb to mineral surfaces primarily by ion exchange. Furthermore, surface related diffusion was examined and demonstrated to take place for Sr2+ and Cs+ but not for Co2+, which sorbs on mineral surfaces by complexation. The diffusion of anions in bentonite clay compacted to different dry densities was also investigated. The results indicate that anion diffusion in bentonite clay consists of two processes, one fast and another slower. We ascribe the fast diffusive process to intralayer diffusion and the slow process to diffusion in interparticle water, where anions are to some extent sorbed to edge sites of the montmorillonite. Two different types of in situ experiments were performed, CHEMLAB and LOT. CHEMLAB is a borehole laboratory, where cation (Cs+, Sr2+ and Co2+) and anion (I- and TcO4-) diffusion experiments were performed using groundwater from a fracture in the borehole. In the LOT experiments cylindrical bentonite blocks surrounding a central copper rod were placed in a 4 m deep vertical borehole. The borehole was then sealed and the blocks are left for 1, 5 or >> 5 years. When the bentonite was water saturated the central copper rod is heated to simulate the temperature increase due to radioactive decay of the spent fuel. Bentonite doped with radioactive Cs and Co was placed in one of the lower blocks. Interestingly, the redox-sensitive pertechnetate ion (TcO4-) which thermodynamically should be reduced and precipitate as TcO2 n H2O, travelled unreduced through the bentonite

  4. CHARACTERIZATION OF BENTONITE FOR ENGINEERED BARRIER SYSTEMS IN RADIOACTIVE WASTE DISPOSAL SITES

    Directory of Open Access Journals (Sweden)

    Dubravko Domitrović

    2012-07-01

    Full Text Available Engineered barrier systems are used in radioactive waste disposal sites in order to provide better protection of humans and the environment from the potential hazards associated with the radioactive waste disposal. The engineered barrier systems usually contain cement or clay (bentonite because of their isolation properties and long term performance. Quality control tests of clays are the same for all engineering barrier systems. Differences may arise in the required criteria to be met due for different application. Prescribed clay properties depend also on the type of host rocks. This article presents radioactive waste management based on best international practice. Standard quality control procedures for bentonite used as a sealing barrier in radioactive waste disposal sites are described as some personal experiences and results of the index tests (free swelling index, water adsorption capacity, plasticity limits and hydraulic permeability of bentonite (the paper is published in Croatian.

  5. Rebounding process of moulding sands-thermal degradation of bentonite binding qualities

    Directory of Open Access Journals (Sweden)

    R. Dańko

    2010-01-01

    Full Text Available Problems related to a gradual degradation of binding qualities of montmorillonite, the main component of foundry bentonites, are presented in the paper. This degradation is caused by high temperatures originated from liquid metal influencing moulding sands. Laboratory measurements of an active binding agent content in classic moulding sands prepared with two types of bentonite and subjected to a controlled heating to high temperatures – were performed. These laboratory examinations were compared to industrial tests, in which a temperature distribution was being determined in several places in the thickness of the casting ingot mould for 24 hours from the moment of pouring liquid metal. On the basis of the performed examinations, the method allowing to determine optimal additions in the rebounding process of the tested bentonites was developed.

  6. Effect of sodium dodecyl sulfate on flow and electrokinetic properties of Na-activated bentonite dispersions

    Indian Academy of Sciences (India)

    E Günıster; S İşçı; A Alemdar; N Güngör

    2004-06-01

    The present study reports the effect of anionic surfactant sodium dodecyl sulfate (SDS, C12H25 OSO3Na) upon the electrokinetic (electrophoretic mobility, zeta potential) and rheological (viscosity, yield value) properties of the Ca-bentonitic clay found in Turkey and its Na-activated form. The SDS dispersant was added in different concentrations in the range of 1 × 10-5-5 × 10-2 mol/l. The results show that the viscosity and zeta potential values of bentonite dispersion are affected by the addition of anionic surfactant. The obtained data are analysed by considering the kind of exchangeable cations. Thixotropic property effect was observed in bentonite dispersions.

  7. Effect of bentonite on radiation induced dissolution of UO{sub 2} in an aqueous system

    Energy Technology Data Exchange (ETDEWEB)

    Barreiro Fidalgo, Alexandre, E-mail: alebf@kth.se; Sundin, Sara, E-mail: saramara@kth.se; Jonsson, Mats, E-mail: matsj@kth.se

    2014-04-01

    In order to elucidate the impact of bentonite on the process of radiation induced oxidative dissolution of UO{sub 2} in an aqueous system, the dissolution of U(VI) and consumption of H{sub 2}O{sub 2} over time has been studied. In addition, γ-irradiation experiments were performed to study a more relevant and complex system, serving as a comparison with the previously stated system. In both cases, the experiments revealed that the presence of bentonite in water could either delay or prevent in part the release of uranium to the environment. The cause is mainly attributed to the scavenging of radiolytic oxidants rather than to the adsorption of uranium onto bentonite.

  8. Influence of ionic strength on the viscosities and water loss of bentonite suspensions containing polymers

    Directory of Open Access Journals (Sweden)

    Luciana Viana Amorim

    2007-03-01

    Full Text Available A study was made of the influence of ionic strength (S on the apparent (AV and plastic (PV viscosities and water loss (WL of sodium bentonite suspension with polymers. Na-bentonite was dispersed in water (4.86% w/w of different ionic strengths (S = 0.0, 0.015, 0.030 and 0.045 M followed by the addition of polymer. Three polymer samples were studied, i.e., low viscosity carboxymethyl cellulose (CMC BV, polyanionic cellulose (PAC, and partially hydrolyzed polyacrylamide (HPAM. The results indicated that the presence of salts and increased salinity greatly influence the apparent and plastic viscosities and water loss of bentonite suspensions with polymer.

  9. Removal of radioactive cesium, strontium, and iodine from natural waters using bentonite, zeolite, and activated carbon

    International Nuclear Information System (INIS)

    Cs-134, Sr-85, and I-131 were produced by neutron irradiation of CsCl, SrCl2, and K2TeO3, respectively, using the Kyoto University Reactor. These radioactive nuclides were added to river water and seawater to prepare artificially contaminated samples, and the removal of these nuclides using bentonite, zeolite, and activated carbon was then investigated. In the river water samples, Cs-134 and Sr-85 were successfully removed using bentonite and zeolite, and I-131 was removed using activated carbon. In the seawater samples, Cs-134 was removed using bentonite and zeolite, whereas Sr-85 and I-131 were hardly removed at all by these adsorbents. (author)

  10. Analysis of X-ray micro-CT images observed with compacted bentonite

    International Nuclear Information System (INIS)

    In this study, a method of statistical analyses was developed and applied to the data sets of images observed with a micro focus X-ray computed tomograph for compacted bentonite, which is a candidate of buffer material for geological disposal of high-level radioactive waste. The bentonite sample used in this study has the grain size around 100 microns under dry state, but less than the size under water-saturated state due to the gel formation of the sample. Statistical information of bentonite grains (i.e. the sizes and the shapes of the grains) before and after water-saturation was analyzed with a boundary determination algorithm developed in this study. Since the images obtained with micro CT apparatus contain ring-shaped artifacts and noise with higher intensity than that of signal, a radial averaging technique and a Gaussian filter were applied to the images before the analysis. (author)

  11. Diffusion of Am, Pu, U, Np, Cs, I and Tc in compacted sand-bentonite mixture

    International Nuclear Information System (INIS)

    In order to predict the diffusion of actinides and fission products through a backfill mixture of sand and clay from a high-level waste repository, the diffusion of the actinides 241Am, 239Pu, 237Np and 233U and the fission products 134Cs, 131I and 99mTc have been measured in a mixture of 90% silica sand-10% bentonite (MX-80, Wyoming bentonite). The sand-bentonite mixture was compacted to a density of 2000 kg/m3. The water phase used was an artificial groundwater representative of Swedish deep granitic groundwater (pH∼8, I∼0.01). The apparent diffusivity is in all cases slightly higher than in pure clay. (author)

  12. Thermodynamic and fully-coupled reactive transport models of a steel–bentonite interface

    International Nuclear Information System (INIS)

    Highlights: • Radioactive waste disposal systems often include steel and bentonite. • Thermodynamic models suggest potential iron–bentonite reaction pathways. • Dissolved silica activity is an important control on Fe-rich clay mineral stability. • Reactive-transport models demonstrate complex process couplings. • Steel corrosion rates may vary as bentonite undergoes alteration. - Abstract: Engineered barrier system (EBS) designs for the geological disposal of high-level radioactive waste often include a bentonite buffer, the primary function of which is to protect metal waste containers or overpacks from mechanical shearing. The buffer also acts as a barrier to solute transport. One potentially deleterious process that may occur in the buffer is the alteration of swelling clay to iron-rich minerals, some of which have a limited capacity to swell. There is a dearth of relevant natural analogues of iron–bentonite interactions, and experimental data do not provide an unequivocal indication of the conditions that will promote non-swelling clay minerals (such as berthierine) to form rather than swelling clays (such as iron-rich saponite). In addition, many of the previously-published reactive transport models of iron–bentonite or iron–claystone interfaces have not considered how evolution of mineral–fluid equilibria in the bentonite buffer could affect the nature and rate of steel corrosion. In this study, new thermodynamic models of iron-rich clay minerals are presented which suggest that the activities of major ions, especially Fe2+, Fe3+, Al3+, H+ and SiO2(aq), act as key controls on the relative stabilities of iron-rich clay minerals. In particular, they suggest that Fe-saponite is stabilised under low f O2(g) conditions when SiO2(aq) activities are buffered by quartz or more soluble silica polymorphs (e.g. chalcedony). Iron-rich 1:1 clay minerals, such as berthierine, tend to be stabilised in fluids that are quartz under-saturated. The

  13. Preparation of Bentonite Supported Nano Titanium Dioxide Photocatalysts by Electrostatic Self-assembly Method

    Institute of Scientific and Technical Information of China (English)

    WANG Cheng; SHI Huisheng; LI Yan

    2012-01-01

    Electrostatic self-assembly method (ESAM) was used to prepare bentonite supported-nano titanium dioxide photocatalysts.The materials were characterized by X-ray diffraction (XRD),fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM).Methyl orange was used to estimate the photocatalytic activity of the materials.The effects of the calcination temperature and silane dosage on the photocatalytic activity of the samples were investigated.The experimental results show that the bentonite facilitates the formation of anatase and restrains the transformation of anatase to rutile.Part of nano-size TiO2 particles insert into the galleries of bentonite.The photocatalysts exhibit a synergistic effect of adsorption and photocatalysis on methyl orange.Photocatalysts prepared by ESAM method exhibit higher photocatalytic activity and better recycle ability than those of the traditional method.

  14. Techniques for freeing deposited canisters. Final report

    International Nuclear Information System (INIS)

    Four different techniques for removal of the bentonite buffer around a deposited canister have been identified, studied and evaluated: mechanical, hydrodynamical, thermal, and electrical techniques. Different techniques to determine the position of the canister in the buffer have also been studied: mechanical, electromagnetic, thermal and acoustic techniques. The mechanical techniques studied are full-face boring, milling and core-drilling. It is expected that the bentonite can be machined relatively easily. It is assessed that cooling by means of flushing water over the outer surfaces of the tools is not feasible in view of the tendency of bentonite to form a gel. The mechanical techniques are characterized by the potential of damaging the canister, a high degree of complexity, and high requirements of energy/power input. The generated byproduct is solid and cannot be removed by means of flushing. Removal is assessed to be simplest in conjunction with full-face boring and most difficult when coredrilling is applied. The hydrodynamical techniques comprise high-pressure hydrodynamic techniques, where pressures above and below 100 bar, and low pressure hydrodynamical techniques (< 10 bar) are separated. At pressures above 100 bar, a water jet with a diameter of approximately a millimetre cuts through the material. If desired, sand can be added to the jet. At pressures below 100 bar the jet has a diameter of one or a few centimetres. The liquid contains a few percent of salt, which is essential for the efficiency of the process. The flushing is important not only because it removes the modified bentonite but also because it frees previously unaffected bentonite and thereby makes it accessible to chemical modification. All of the hydrodynamical techniques are applicable for freeing the end surface as well as the mantle surface. The degree of complexity and the requirement on energy/power decrease with a decrease in pressure. A significant potential for damaging the

  15. Heat conductivity of bentonite MX80 and Montigel using the hot wire method

    International Nuclear Information System (INIS)

    A project study on behalf of Nagra for high radioactive waste disposal in deep geological formations as well as literature studies have shown that bentonite could be a suitable filling and sealing material. The Institute for Foundation and Soil Mechanics of the Swiss Institute of Technology is under contract by Nagra to investigate different bentonites. The investigations concentrate on the Na-bentonite MX-80 from Wyoming, which is foreseen by the Swedes, and on the geographically more favorable Ca-bentonite Montigel from Bavaria. Montigel powder and granulate, which show certain manufacturing advantages, were investigated. The heat conductivity of dense bentonite was investigated using the hot wire method. Heat conductivities of MX-80 and Montigel were similar. It amounted at room temperature from 0.451 W/degree C m with a water content of 0 % and a density of 1.7 Mg/m3 up to 1.336 W/degree C m with a water content of 14 % and a density of 2.21 Mg/m3. At higher temperatures the heat conductivity was determined only on dry samples. The value at 40 degrees C and a density of 1.63 Mg/m3 was 0.457 W/degree C m and 0.778 W/degree C m at 120 degrees C and a density of 2.09 Mg/m3. The heat conductivity of condensed bentonites can be calculated as a function of water content, density and temperature by the following approximative formula: K = -0.60 + 0.60D + 0.004WD3 + 0.01T1/2 K heat conductivity (W/degree C m) D density wet (Mg/m3) W water content (%) T temperature (degrees C) 3 refs., 8 figs., 4 tabs

  16. Evaluation of gas migration characteristics of compacted bentonite considering in-situ conditions of disposal facility

    International Nuclear Information System (INIS)

    In the current concept of repository for radioactive waste disposal, compacted bentonite will be used as an engineered barrier mainly for inhibiting migration of radioactive nuclides. Hydrogen gas can be generated inside the engineered barrier by anaerobic corrosion of metals used for containers, etc. If the gas generation rate exceeds the diffusion rate of gas molecules inside of the engineered barrier, gas will accumulate in the void space inside of the engineered barrier until its pressure becomes large enough for it to enter the bentonite as a discrete gaseous phase. It is expected to be not easy for gas to entering into the bentonite as a discrete gaseous phase because the pore of compacted bentonite is so minute. Therefore it is necessary to investigate the effect of gas pressure generation and gas migration on the engineered barrier, peripheral facilities and ground. CRIEPI already proposed an analytical method for simulating gas migration through the compacted bentonite using the model of two phase flow through deformable porous media. Though validity of the analytical code of CRIEPI was examined by comparing existing gas migration test results with the calculated results, further validation is needed because in situ conditions, such as stress conditions and boundary condition, are different from conventional laboratory gas migration tent. In this study, gas migration tests whose initial axial stress is larger than initial radial stress and gas migration tests whose gas inlet is small. Simulation of the test results is also conducted. Comparing the test results with the calculated results, it is revealed that the analytical code of CRIEPI can simulate gas migration behavior through compacted bentonite with accuracy. (author)

  17. Approval condition in application of bentonite grouting to the radioactive waste disposal

    International Nuclear Information System (INIS)

    The purpose of this study is to understand the flow properties and the permeability of bentonite grout added NaCl by the laboratory tests, and to clarify the approval condition of bentonite as materials. The viscosity of the bentonite suspension was measured under the weight ratio of water and bentonite (W/B) is 6 to 20. The suspension of which W/B is smaller than 10 is difficult to inject into the rock joints, because the viscosity is higher than the thickest cement milk on dam grouting. When the necessary permeability of the clay grout is assumed to be 10-7 (cm/sec), the W/B becomes 10 or less. Then, when we add NaCl to the suspension of which W/B is 6, the viscosity decreases as the amount of NaCl increases. The injectable viscosity is achieved by adding NaCl as the proportion of water to NaCl is 1 to 40. Next, the permeability of the bentonite suspension that added NaCl was examined by the falling head permeability test. It was found that the initial permeability 10-6 (cm/sec) decreased to 10-8∼10-9 (cm/sec) by the test of the sample of 'B:W:NaCl=20:20:1' for 10 days. From these results, the suspension to inject into the rock joints can be made by adding NaCl. And it was clarified that the groundwater permeation to the suspension causes the decrease of the permeability. In addition, the bentonite is swelling according to the infiltration of underground water, the persistence in the suppression effect of diffusion and stability to erosion can be expected. (author)

  18. Radionuclide transport coupled with bentonite extrusion in a saturated fracture system

    Science.gov (United States)

    Borrelli, Robert Angelo

    The study in this dissertation focuses on the characterization of radionuclide migration in a water saturated fracture. The near field of a high level radioactive waste repository contains the engineered barrier system, which provides manufactured components designed to limit radionuclide releases to the environment. A major component in this system involves the utilization of bentonite as a buffer to protect the degraded waste package and limit release of radionuclides into intersecting fractures that pose possible pathways for transport to the environment. A model is derived for radionuclide migration through this fracture. The model incorporates the features of bentonite: extrusion into the fracture, sorption, and the effect of bentonite swelling on groundwater flow. The resulting derivation of this model is a coupled system of differential equations. The differential equation describing the mass conservation of radionuclides is coupled to the equation system for bentonite extrusion. The models are coupled through the parameters in the radionuclide transport model, which are dependent on the spatial distribution of solid material in the domain. Numerical evaluations of the solution to this radionuclide transport model were conducted for neptunium, a weakly sorbing radionuclide and americium, a strongly sorbing radionuclide. Results were presented in terms normalized spatial distribution of radionuclide concentration in the fluid phase and normalized radionuclide release rate in the fluid phase. Major findings of the study conducted for this dissertation are provided. (1) Bentonite extrusion affects fluid phase advection resulting in groundwater flow countercurrent to the direction of extrusion to the direction of radionuclide migration. (2) The sorption distribution coefficient is the most important parameter affecting radionuclide behavior in this system for this model. (3) Simulations of the model for americium, a highly sorbing radionuclide, indicate that

  19. Coupled behaviour of bentonite buffer results of PUSKURI project; Bentoniittipuskurin kytketty kaeyttaeytyminen PUSKURI-hankkeen tuloksia

    Energy Technology Data Exchange (ETDEWEB)

    Olin, M.; Rasilainen, K.; Itaelae, A. [and others

    2011-08-15

    In the report main results form a KYT2010 programme's project Coupled behaviour of bentonite buffer (PUSKURI) are presented. In THC modelling, Aku Itaelae made and published his Master of Science Thesis. Itaelae was able to successfully model the LOT-experiment. Additionally, he also listed problems and development proposals for THC-modelling of bentonite buffer. VTT and Numerola created in collaboration a model coupling saturation, diffusion and cation exchange; the model was implemented and tested in Numerrin, COMSOL and TOUGHREACT. Petri Jussila's PhD THM-model was implemented into COMSOL to facilitate further development. At GTK, the mineralogical characterisation of bentonite was planned. The previous THM model (Jussila's model) including only small deformations was successfully generalized to finite deformations in way at least formally preserving the original formalism. It appears that the theory allows also a possibility to include finite plastic deformations in the theory. In order to measure the relevant mechanical properties of compacted bentonite, two different experiments, namely hydrostatic compression experiment and one-dimensional compression experiment were designed. In the hydrostatic compression experiment, a cylindrical sample of compacted bentonite covered with liquid rubber coating is placed in the sample chamber equipped with a piston. The same device was also used in one-dimensional compression experiment. X-ray microtomographic techniques were used in order to study the basic mechanisms of water transport in bentonite. The preliminary results indicate that in the present experimental set-up, water transport is dominated by a dispersive mechanism such as diffusion of vapour in gas phase or diffusion of water in solid phase. (orig.)

  20. Comparative tests for evaluating permeability changes of a compacted bentonite/sand mixture during shear

    International Nuclear Information System (INIS)

    A compacted mixture of Kunigeru VI bentonite and D-sand is being considered for use as an engineered barrier in low-level radioactive waste disposal facilities in Japan. An important issue is the maintenance of the retardation property of the mixture during shear that might be induced in such barriers by earthquakes and/or gradual tectonic deformations occurring over the design life of the facility. Comparative tests on a bentonite-sand mixture and kaolin-sand mixture were conducted by means of a recently-developed coupled shear and permeability testing apparatus under temperature controlled condition. The specific storage of bentonite-sand specimen during shear is also systematically evaluated with the new analytical theory for the constant flow permeability test. The present study reveals that (1) temperature control is preferred for measuring the permeability of extremely-low permeability materials with the constant-flow pump method; (2) both the permeability and specific storage of the mixture of Kunigeru VI bentonite and D-sand were not significantly influenced by shear strains up to 3% whereas the permeability of the kaolin-sand mixture increased almost linearly with the increment of shear strain; (3) the swelling of bentonite in the mixture under low confining stress decreases both the permeability and specific storage of bentonite-sand mixture; and (4) the constant flow permeability test method, with the newly derived theoretical analysis, promises to become a very effective means of investigating, rapidly and systematically, the permeability and specific storage of extremely-low permeability materials with relatively-low hydraulic gradients