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Sample records for feldspar dissolution kinetics

  1. Morphological evolution of dissolving feldspar particles with anisotropic surface kinetics and implications for dissolution rate normalization and grain size dependence: A kinetic modeling study

    Zhang, Li; Lüttge, Andreas

    2009-11-01

    With previous two-dimensional (2D) simulations based on surface-specific feldspar dissolution succeeding in relating the macroscopic feldspar kinetics to the molecular-scale surface reactions of Si and Al atoms ( Zhang and Lüttge, 2008, 2009), we extended our modeling effort to three-dimensional (3D) feldspar particle dissolution simulations. Bearing on the same theoretical basis, the 3D feldspar particle dissolution simulations have verified the anisotropic surface kinetics observed in the 2D surface-specific simulations. The combined effect of saturation state, pH, and temperature on the surface kinetics anisotropy has been subsequently evaluated, found offering diverse options for morphological evolution of dissolving feldspar nanoparticles with varying grain sizes and starting shapes. Among the three primary faces on the simulated feldspar surface, the (1 0 0) face has the biggest dissolution rate across an extensively wide saturation state range and thus acquires a higher percentage of the surface area upon dissolution. The slowest dissolution occurs to either (0 0 1) or (0 1 0) faces depending on the bond energies of Si-(O)-Si ( ΦSi-O-Si/ kT) and Al-(O)-Si ( ΦAl-O-Si/ kT). When the ratio of ΦSi-O-Si/ kT to ΦAl-O-Si/ kT changes from 6:3 to 7:5, the dissolution rates of three primary faces change from the trend of (1 0 0) > (0 1 0) > (0 0 1) to the trend of (1 0 0) > (0 0 1) > (0 1 0). The rate difference between faces becomes more distinct and accordingly edge rounding becomes more significant. Feldspar nanoparticles also experience an increasing degree of edge rounding from far-from-equilibrium to close-to-equilibrium. Furthermore, we assessed the connection between the continuous morphological modification and the variation in the bulk dissolution rate during the dissolution of a single feldspar particle. Different normalization treatments equivalent to the commonly used mass, cube assumption, sphere assumption, geometric surface area, and reactive

  2. Chlorite, Biotite, Illite, Muscovite, and Feldspar Dissolution Kinetics at Variable pH and Temperatures up to 280 C

    Carroll, S. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Smith, M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Lammers, K. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2016-10-05

    Summary Sheet silicates and clays are ubiquitous in geothermal environments. Their dissolution is of interest because this process contributes to scaling reactions along fluid pathways and alteration of fracture surfaces, which could affect reservoir permeability. In order to better predict the geochemical impacts on long-term performance of engineered geothermal systems, we have measured chlorite, biotite, illite, and muscovite dissolution and developed generalized kinetic rate laws that are applicable over an expanded range of solution pH and temperature for each mineral. This report summarizes the rate equations for layered silicates where data were lacking for geothermal systems.

  3. Kinetics of infrared stimulated luminescence from feldspars

    Jain, Mayank; Sohbati, Reza; Guralnik, Benny

    2015-01-01

    thermal and optical, of the infrared stimulated luminescence signal from feldspar. Based on the application of this model, it is concluded that different infra-red stimulated luminescence emissions (UV, blue, yellow and far-red) follow the same kinetics, and, therefore, involve participation of the same...

  4. Calcite Dissolution Kinetics

    Berelson, W.; Subhas, A.; Dong, S.; Naviaux, J.; Adkins, J. F.

    2016-12-01

    A geological buffer for high atmospheric CO2 concentrations is neutralization via reaction with CaCO3. We have been studying the dissolution kinetics of carbonate minerals using labeled 13C calcite and Picarro-based measurements of 13C enrichments in solution DIC. This methodology has greatly facilitated our investigation of dissolution kinetics as a function of water carbonate chemistry, temperature and pressure. One can adjust the saturation state Omega by changing the ion activity product (e.g. adjusting carbonate ion concentration), or by changing the solubility product (e.g. adjusting temperature or pressure). The canonical formulation of dissolution rate vs. omega has been refined (Subhas et al. 2015) and shows distinct non-linear behavior near equilibrium and rates in sea water of 1-3 e-6 g/cm2day at omega = 0.8. Carbonic anhydrase (CA), an enzyme that catalyzes the hydration of dissolved CO2 to carbonic acid, was shown (in concentrations 500x. This result points to the importance of carbonic acid in enhancing dissolution at low degrees of undersaturation. CA activity and abundance in nature must be considered regarding the role it plays in catalyzing dissolution. We also have been investigating the role of temperature on dissolution kinetics. An increase of 16C yields an order of magnitude increase in dissolution rate. Temperature (and P) also change Omega critical, the saturation state where dissolution rates change substantially. Increasing pressure (achieved in a pressure reaction chamber we built) also shifts Omega critical closer to equilibrium and small pressure increases have large impact on dissolution kinetics. Dissolution rates are enhanced by an order of magnitude for a change in pressure of 1500 psi relative to the dissolution rate achieved by water chemistry effects alone for an omega of 0.8. We've shown that the thermodynamic determination of saturation state does not adequately describe the kinetics of dissolution. The interplay of mineral

  5. Feldspar dissolution rates in the Topopah Spring Tuff, Yucca Mountain, Nevada

    Bryan, C.R.; Helean, K.B.; Marshall, B.D.; Brady, P.V.

    2009-01-01

    Two different field-based methods are used here to calculate feldspar dissolution rates in the Topopah Spring Tuff, the host rock for the proposed nuclear waste repository at Yucca Mountain, Nevada. The center of the tuff is a high silica rhyolite, consisting largely of alkali feldspar (???60 wt%) and quartz polymorphs (???35 wt%) that formed by devitrification of rhyolitic glass as the tuff cooled. First, the abundance of secondary aluminosilicates is used to estimate the cumulative amount of feldspar dissolution over the history of the tuff, and an ambient dissolution rate is calculated by using the estimated thermal history. Second, the feldspar dissolution rate is calculated by using measured Sr isotope compositions for the pore water and rock. Pore waters display systematic changes in Sr isotopic composition with depth that are caused by feldspar dissolution. The range in dissolution rates determined from secondary mineral abundances varies from 10-16 to 10-17 mol s-1 kg tuff-1 with the largest uncertainty being the effect of the early thermal history of the tuff. Dissolution rates based on pore water Sr isotopic data were calculated by treating percolation flux parametrically, and vary from 10-15 to 10-16 mol s-1 kg tuff-1 for percolation fluxes of 15 mm a-1 and 1 mm a-1, respectively. Reconciling the rates from the two methods requires that percolation fluxes at the sampled locations be a few mm a-1 or less. The calculated feldspar dissolution rates are low relative to other measured field-based feldspar dissolution rates, possibly due to the age (12.8 Ma) of the unsaturated system at Yucca Mountain; because oxidizing and organic-poor conditions limit biological activity; and/or because elevated silica concentrations in the pore waters (???50 mg L-1) may inhibit feldspar dissolution. ?? 2009 Elsevier Ltd. All rights reserved.

  6. Surface studies of feldspar dissolution using surface replication combined with electron microscopic and spectroscopic techniques

    Fung, P C [Petro-Canada, Calgary, Alberta; Sanipelli, G G

    1982-04-01

    The replica of a microcline cleavage surface was examined before and at various stages of interaction with water and acid solutions at 70/sup 0/C, as part of basic geochemical research for the Canadian Nuclear Fuel Waste Management Program to investigate the feasibility of disposal of these wastes in repositories mined in crystalline rocks. The objective of the report presented was to investigate the mechanism for Al and Si removal during incongruent dissolution of feldspars and its effect on dissolution rate. It was found that phase transformation, like dissolution occured preferentially along crystal defects on the surfaces of the feldspars. Secondary minerals always occured as discrete particles occupying only a very small fraction of the total parent surface, and hence, their presence would not affect the bulk composition or, in this regard, the overall dissolution rate of the feldspars by the formation of diffusion barriers.

  7. 8 Dissolution Kinetics

    user

    Experiments measuring the dissolution rates of stilbite (NaCa [Al Si O ].14H O) in pH-buffered ... The rate law was established as R = k (a ) , where k is ... crystalline hydrated aluminosilicate minerals ..... from the crushing process, thin edges or.

  8. Kinetics of oxidic phase dissolution in acids

    Gorichev, I.G.; Kipriyanov, N.A.

    1981-01-01

    The critical analysis of the experimental data on dissolution kinetics of metal oxides (BeO, V 2 O 5 , UO 2 , Nb 2 O 5 , Ta 2 O 5 etc.) in acid media is carried out. Kinetic peculiarities of oxide dissolution are explained on the basis of the notions of electron- proton theory. It is established that the surface nonstoichiometric ccomposition of oxide phase and potential jump, appearing on the interface of the oxide-electrolyte phase are the important factors, determining the dissolution rate of a solid phase. The dissolution rate of metal oxides is limited by the transition of protons into the solid oxide phase. Morphological models of heterogeneous kinetics are used when explaining kinetic regularities of oxide dissolution process [ru

  9. A Novel Approach to Experimental Studies of Mineral Dissolution Kinetics

    Chen Zhu

    2006-08-31

    Currently, DOE is conducting pilot CO{sub 2} injection tests to evaluate the concept of geological sequestration. One strategy that potentially enhances CO{sub 2} solubility and reduces the risk of CO{sub 2} leak back to the surface is dissolution of indigenous minerals in the geological formation and precipitation of secondary carbonate phases, which increases the brine pH and immobilizes CO{sub 2}. Clearly, the rates at which these dissolution and precipitation reactions occur directly determine the efficiency of this strategy. However, one of the fundamental problems in modern geochemistry is the persistent two to five orders of magnitude discrepancy between laboratory measured and field derived feldspar dissolution rates. To date, there is no real guidance as to how to predict silicate reaction rates for use in quantitative models. Current models for assessment of geological carbon sequestration have generally opted to use laboratory rates, in spite of the dearth of such data for compositionally complex systems, and the persistent disconnect between laboratory and field applications. Therefore, a firm scientific basis for predicting silicate reaction kinetics in CO2 injected geological formations is urgently needed to assure the reliability of the geochemical models used for the assessments of carbon sequestration strategies. The funded experimental and theoretical study attempts to resolve this outstanding scientific issue by novel experimental design and theoretical interpretation to measure silicate dissolution rates and iron carbonate precipitation rates at conditions pertinent to geological carbon sequestration. In the second year of the project, we completed CO{sub 2}-Navajo sandstone interaction batch and flow-through experiments and a Navajo sandstone dissolution experiment without the presence of CO{sub 2} at 200 C and 250-300 bars, and initiated dawsonite dissolution and solubility experiments. We also performed additional 5-day experiments at the

  10. Investigation of dissolution kinetics of a Nigerian columbite in ...

    Investigation of dissolution kinetics of a Nigerian columbite in hydrofluoric acid using the shrinking core model. ... Experimental results indicate that the dissolution rate is chemical reaction controlled, with reaction order of 0.57. Dissolution of over 90 % of the columbite was achieved in 5 h, using 20 M HF at 90 oC with 100 ...

  11. Predicting the dissolution kinetics of silicate glasses using machine learning

    Anoop Krishnan, N. M.; Mangalathu, Sujith; Smedskjaer, Morten M.; Tandia, Adama; Burton, Henry; Bauchy, Mathieu

    2018-05-01

    Predicting the dissolution rates of silicate glasses in aqueous conditions is a complex task as the underlying mechanism(s) remain poorly understood and the dissolution kinetics can depend on a large number of intrinsic and extrinsic factors. Here, we assess the potential of data-driven models based on machine learning to predict the dissolution rates of various aluminosilicate glasses exposed to a wide range of solution pH values, from acidic to caustic conditions. Four classes of machine learning methods are investigated, namely, linear regression, support vector machine regression, random forest, and artificial neural network. We observe that, although linear methods all fail to describe the dissolution kinetics, the artificial neural network approach offers excellent predictions, thanks to its inherent ability to handle non-linear data. Overall, we suggest that a more extensive use of machine learning approaches could significantly accelerate the design of novel glasses with tailored properties.

  12. Kinetics of Inorganic Calcite Dissolution in Seawater under Pressure

    Dong, S.; Subhas, A.; Rollins, N.; Berelson, W.; Adkins, J. F.

    2016-02-01

    While understanding calcium carbonate dissolution is vital in constructing global carbon cycles and predicting the effect of seawater acidification as a result of increasing atmospheric CO2, there is still a major debate over the basic formulation of a dissolution rate law. The kinetics of calcium carbonate dissolution are typically described by the equation: Rate=k(1-Ω)n, while Ω=[Ca2+][CO32-]/Ksp. In this study, 13C-labeled calcite is dissolved in unlabeled seawater and the evolving d13C composition of the fluid is traced over time to establish dissolution rate. Instead of changing ion concentration to obtain varying Ω (as in our previous study; Subhas et al. 2015), we changed Ksp by conducting experiments under different pressures (described in theory as ∂lnKsp/∂P=-ΔV/RT, where ΔV is partial molal volume). This involved the construction of a pressure vessel that could hold our sample bag and provide aliquots while remaining pressurized. Pressure experiments were conducted between 0-2000PSI. Results support the conclusion in our previous study that near-equilibrium dissolution rates are highly nonlinear, but give a disparate relationship between undersaturation and dissolution rate if Ω is calculated assuming the specific ΔV embedded in CO2SYS. A revised ΔV from -37cm3 to -65cm3 would make the dissolution formulation equation agree, but clearly appears unreasonable. Our results are explained by a pressure effect on carbonate dissolution kinetics over and above the influence of pressure on Ω. If this is a phenomenon that occurs in nature, then we would predict that dissolution should be occurring shallower in the water column (as sometimes observed) than indicated by standard Ω calculations.

  13. The release of iron-bearing minerals and dissolution of feldspars by heterotrophic bacteria of Bacillus species

    Štyriaková, I.; Štyriak, I.; Galko, I.; Hradil, David; Bezdička, Petr

    2003-01-01

    Roč. 47, č. 1 (2003), s. 20-26 ISSN 0862-5468 Grant - others:AV SR(SK) 2/2107/22; GA SR(SK) 73/2000 Institutional research plan: CEZ:AV0Z4032918 Keywords : bioleaching * feldspars * Bacillus Subject RIV: CA - Inorganic Chemistry Impact factor: 0.449, year: 2003

  14. Thorium oxide dissolution kinetics for hydroxide and carbonate complexation

    Jardin, R.; Curran, V.; Czerwinski, K.R.

    2002-01-01

    The purpose of this project was to determine the kinetics and thermodynamics of thorium oxide dissolution in the environment. Solubility is important because it establishes an upper concentration limit on the concentration of a dissolved radionuclide in solution L1. While understanding the behavior of thorium fuels in the proposed repository at Yucca Mountain is most applicable, a more rigorous study of thorium solubility over a wide pH range was performed so that the data could also be used to model the behavior of thorium fuels in any environmental system. To achieve this, the kinetics and thermodynamics of thorium oxide dissolution under both pure argon and argon with P CO2 of 0. 1 were studied under the full pH range available in each atmosphere. In addition, thorium oxide powder remnants were studied after each experiment to examine structural changes that may affect kinetics

  15. Carbonate mineral dissolution kinetics in high pressure experiments

    Dethlefsen, F.; Dörr, C.; Schäfer, D.; Ebert, M.

    2012-04-01

    The potential CO2 reservoirs in the North German Basin are overlain by a series of Mesozoic barrier rocks and aquifers and finally mostly by Tertiary and Quaternary close-to-surface aquifers. The unexpected rise of stored CO2 from its reservoir into close-to-surface aquifer systems, perhaps through a broken well casing, may pose a threat to groundwater quality because of the acidifying effect of CO2 dissolution in water. The consequences may be further worsening of the groundwater quality due to the mobilization of heavy metals. Buffer mechanisms counteracting the acidification are for instance the dissolution of carbonates. Carbonate dissolution kinetics is comparably fast and carbonates can be abundant in close-to-surface aquifers. The disadvantages of batch experiments compared to column experiments in order to determine rate constants are well known and have for instance been described by v. GRINSVEN and RIEMSDIJK (1992). Therefore, we have designed, developed, tested, and used a high-pressure laboratory column system to simulate aquifer conditions in a flow through setup within the CO2-MoPa project. The calcite dissolution kinetics was determined for CO2-pressures of 6, 10, and 50 bars. The results were evaluated by using the PHREEQC code with a 1-D reactive transport model, applying a LASAGA (1984) -type kinetic dissolution equation (PALANDRI and KHARAKA, 2004; eq. 7). While PALANDRI and KHARAKA (2004) gave calcite dissolution rate constants originating from batch experiments of log kacid = -0.3 and log kneutral = -5.81, the data of the column experiment were best fitted using log kacid = -2.3 and log kneutral = -7.81, so that the rate constants fitted using the lab experiment applying 50 bars pCO2 were approximately 100 times lower than according to the literature data. Rate constants of experiments performed at less CO2 pressure (pCO2 = 6 bars: log kacid = -1.78; log kneutral = -7.29) were only 30 times lower than literature data. These discrepancies in the

  16. A kinetic model for borosilicate glass dissolution based on the dissolution affinity of a surface alteration layer

    Bourcier, W.L.; Peiffer, D.W.; Knauss, K.G.; McKeegan, K.D.; Smith, D.K.

    1989-11-01

    A kinetic model for the dissolution of borosilicate glass is used to predict the dissolution rate of a nuclear waste glass. In the model, the glass dissolution rate is controlled by the rate of dissolution of an alkali-depleted amorphous surface (gel) layer. Our model predicts that all components concentrated in the surface layer, affect glass dissolution rates. The good agreement between predicted and observed elemental dissolution rates suggests that the dissolution rate of the gel layer limits the overall rate of glass dissolution. The model predicts that the long-term rate of glass dissolution will depend mainly on ion concentrations in solution, and therefore on the secondary phases which precipitate and control ion concentrations. 10 refs., 5 figs., 1 tab

  17. Kinetics of dissolution of calcium phosphate (Ca-P bioceramics

    Lukas Brazda

    2008-06-01

    Full Text Available Hydroxyapatite (HAp and β-tricalcium phosphate (β-TCP are widely used bioceramics for surgical or dental applications. This paper is dealing with dissolution kinetics of synthetically prepared β-TCP and four types of HAp granules. Two groups of HAp, treated at different temperatures, each of them with two different granule sizes, were tested. Three corrosive solutions with different pH and simulated body fluid (SBF were used for immersing of the samples. Changes in concentrations of calcium and phosphate ions, pH level and weight changes of the samples were observed. It was found that presence of TRIS buffer enhanced dissolution rate of the β-TCP approximately two times. When exposed to SBF solution, calcium phosphate (most probably hydroxyapatite precipitation predominates over β-TCP dissolution. Results from HAp samples dissolution showed some unexpected findings. Neither heat treatment nor HAp particle size made any major differences in dissolution rate of the same mass of each HAp sample.

  18. The dissolution kinetics of magnetite under regenerative conditions

    Ranganathan, S.

    2004-01-01

    Dissolution studies of magnetite were carried out under regenerative conditions in dilute chemical decontamination formulations. During regeneration of the formulation, the H + from the strong acid cation exchange resin gets released and the metal is absorbed on the resin. The efficiency of the regenerative process depends on the stability constants of the complexes involved and the selectivity on the ion exchange column. The regenerative condition helps to maintain a constant chelating agent concentration and pH during the dissolution experiment. Such a condition is ideal for obtaining data on the dissolution behaviour of the corrosion products with special application to actual reactor decontamination. The ethylenediaminetetraacetic acid (EDTA) based formulation used was found to be ineffective due to the high stability constant of Fe(III)-EDTA complex, which is not easily cleaved by the cation exchange resin. Hence, knowledge of the kinetics of magnetite dissolution under regenerative condition is of primary importance. The 2,6-pyridinedicarboxylic acid formulation is found to be better for the dissolution of Fe 3 O 4 in both static and regenerative modes in the presence of reductants than nitrilotriacetic acid and EDTA. (orig.)

  19. The dissolution kinetics of magnetite under regenerative conditions

    Ranganathan, S. [New Brunswick Univ., Frederiction (Canada). Dept. of Chemical Engineering; Raghavan, P.S.; Gopalan, R.; Srinivasan, M.P.; Narasimhan, S.V. [Water and Steam Chemistry Lab. of Bhabha Atomic Research Centre (BARC) (India)

    2004-07-01

    Dissolution studies of magnetite were carried out under regenerative conditions in dilute chemical decontamination formulations. During regeneration of the formulation, the H{sup +} from the strong acid cation exchange resin gets released and the metal is absorbed on the resin. The efficiency of the regenerative process depends on the stability constants of the complexes involved and the selectivity on the ion exchange column. The regenerative condition helps to maintain a constant chelating agent concentration and pH during the dissolution experiment. Such a condition is ideal for obtaining data on the dissolution behaviour of the corrosion products with special application to actual reactor decontamination. The ethylenediaminetetraacetic acid (EDTA) based formulation used was found to be ineffective due to the high stability constant of Fe(III)-EDTA complex, which is not easily cleaved by the cation exchange resin. Hence, knowledge of the kinetics of magnetite dissolution under regenerative condition is of primary importance. The 2,6-pyridinedicarboxylic acid formulation is found to be better for the dissolution of Fe{sub 3}O{sub 4} in both static and regenerative modes in the presence of reductants than nitrilotriacetic acid and EDTA. (orig.)

  20. Montmorillonite dissolution kinetics: Experimental and reactive transport modeling interpretation

    Cappelli, Chiara; Yokoyama, Shingo; Cama, Jordi; Huertas, F. Javier

    2018-04-01

    The dissolution kinetics of K-montmorillonite was studied at 25 °C, acidic pH (2-4) and 0.01 M ionic strength by means of well-mixed flow-through experiments. The variations of Si, Al and Mg over time resulted in high releases of Si and Mg and Al deficit, which yielded long periods of incongruent dissolution before reaching stoichiometric steady state. This behavior was caused by simultaneous dissolution of nanoparticles and cation exchange between the interlayer K and released Ca, Mg and Al and H. Since Si was only involved in the dissolution reaction, it was used to calculate steady-state dissolution rates, RSi, over a wide solution saturation state (ΔGr ranged from -5 to -40 kcal mol-1). The effects of pH and the degree of undersaturation (ΔGr) on the K-montmorillonite dissolution rate were determined using RSi. Employing dissolution rates farthest from equilibrium, the catalytic pH effect on the K-montmorillonite dissolution rate was expressed as Rdiss = k·aH0.56±0.05 whereas using all dissolution rates, the ΔGr effect was expressed as a non-linear f(ΔGr) function Rdiss = k · [1 - exp(-3.8 × 10-4 · (|ΔGr|/RT)2.13)] The functionality of this expression is similar to the equations reported for dissolution of Na-montmorillonite at pH 3 and 50 °C (Metz, 2001) and Na-K-Ca-montmorillonite at pH 9 and 80 °C (Cama et al., 2000; Marty et al., 2011), which lends support to the use of a single f(ΔGr) term to calculate the rate over the pH range 0-14. Thus, we propose a rate law that also accounts for the effect of pOH and temperature by using the pOH-rate dependence and the apparent activation energy proposed by Rozalén et al. (2008) and Amram and Ganor (2005), respectively, and normalizing the dissolution rate constant with the edge surface area of the K-montmorillonite. 1D reactive transport simulations of the experimental data were performed using the Crunchflow code (Steefel et al., 2015) to quantitatively interpret the evolution of the released cations

  1. Peroxide formation and kinetics of sodium dissolution in alcohols

    Muralidaran, P.; Chandran, K.; Ganesan, V.; Periaswami, G.

    1997-01-01

    Suitable techniques for sodium removal and decontamination of sodium wetted components of Liquid Metal Fast Reactors (LMFRs) are necessary both for repair, reuse and decommissioning of such components. Among the methods followed for sodium removal, alcohol dissolution is usually employed for small components like bellow sealed valves, gripping tools to handle core components and sodium sampling devices (primary and secondary). One of the concerns in the alcohol dissolution method is the possible role of peroxide formation in the ethoxy group during storage and handling leading to explosion. This paper describes the study of peroxide formation in ethyl carbitol and butyl cellosolve as well as some of the results of dissolution kinetic studies carried out in our laboratory using different alcohols. The peroxide formation of ethyl carbitol and butyl cellosolve were studied by iodometric technique. It has been found that the peroxide formation is less in sodium containing alcohol than in pure one. Ethyl carbitol, butyl cellosolve and Jaysol-SS (mixture of ethyl alcohol, methyl alcohol, isopropyl alcohol and methyl isobutyl ketone) were used in dissolution kinetics studies. The effects due to area and orientation of the fresh sodium surface have also been investigated. The reaction rates were studied in the temperature range of 303-343 K. The rate of dissolution was estimated by measuring the sodium content of alcohol at periodic intervals. It is found that the reaction rate varies in the order of ethyl alcohol-water mixture > Jaysol-SS > butyl cellosolve > ethyl carbitol. While cleaning sodium using alcohol, the concentration of alcohol is held essentially constant throughout the process. The rate of reaction depends only on the amount of sodium and follows pseudo-first order kinetics. Increase in surface area has a marked impact on the dissolution rate at lower temperatures while at higher temperatures, the temperature factor overrides the effect due to surface area

  2. Differential rates of feldspar weathering in granitic regoliths

    White, A.F.; Bullen, T.D.; Schulz, M.S.; Blum, A.E.; Huntington, T.G.; Peters, N.E.

    2001-01-01

    Differential rates of plagioclase and K-feldspar weathering commonly observed in bedrock and soil environments are examined in terms of chemical kinetic and solubility controls and hydrologic permeability. For the Panola regolith, in the Georgia Piedmont Province of southeastern United States, petrographic observations, coupled with elemental balances and 87Sr/86Sr ratios, indicate that plagioclase is being converted to kaolinite at depths > 6 m in the granitic bedrock. K-feldspar remains pristine in the bedrock but subsequently weathers to kaolinite at the overlying saprolite. In contrast, both plagioclase and K-feldspar remain stable in granitic bedrocks elsewhere in Piedmont Province, such as Davis Run, Virginia, where feldspars weather concurrently in an overlying thick saprolite sequence. Kinetic rate constants, mineral surface areas, and secondary hydraulic conductivities are fitted to feldspar losses with depth in the Panola and Davis Run regoliths using a time-depth computer spreadsheet model. The primary hydraulic conductivities, describing the rates of meteoric water penetration into the pristine granites, are assumed to be equal to the propagation rates of weathering fronts, which, based on cosmogenic isotope dating, are 7 m/106 yr for the Panola regolith and 4 m/106 yr for the Davis Run regolith. Best fits in the calculations indicate that the kinetic rate constants for plagioclase in both regoliths are factors of two to three times faster than K-feldspar, which is in agreement with experimental findings. However, the range for plagioclase and K-feldspar rates (kr = 1.5 x 10-17 to 2.8 x 10-16 mol m-2 s-1) is three to four orders of magnitude lower than for that for experimental feldspar dissolution rates and are among the slowest yet recorded for natural feldspar weathering. Such slow rates are attributed to the relatively old geomorphic ages of the Panola and Davis Run regoliths, implying that mineral surface reactivity decreases significantly with

  3. Surface controlled dissolution rates of gypsum in aqueous solutions exhibit nonlinear dissolution kinetics

    Jeschke, Alexander A.; Vosbeck, Katrin; Dreybrodt, Wolfgang

    2001-01-01

    The effective dissolution rates of gypsum are determined by mixed kinetics, where the rate constants of dissolution at the surface and the transport constant of molecular diffusion of dissolved material are similar. To obtain the surface reaction rate law it is necessary to know the transport constant. We have determined the surface rate law for monocrystalline selenite by using a rotating disc set-up, where the transport coefficients are well known. As a result, up to a calcium concentration of 0.6 · ceq, we find a nearly linear rate law Rs = ksl (1- cs/ ceq) n1, where cs is the total calcium concentration at the surface and ceq the equilibrium concentration with respect to gypsum, n1 = 1.2 ± 0.2, and ksl = 1.1 · 10 -4 mmol cm -2 s -1 ± 15%. We also employed batch-experiments for selenite, alabaster and gypsum rock samples. The result of these experiments were interpreted by using a transport constant determined by NaCl dissolution experiments under similar physical conditions. The batch experiments reveal a dissolution rate law Rs = ksl (1- cs/ ceq) n1, ksl = 1.3 · 10 -4 mmol · cm -2 s -1, n1 = 1.2 ± 0.2 for c ≤ 0.94 · ceq. Close to equilibrium a nonlinear rate law, Rs = ks2 (1- cs/ ceq) n2, is observed, where ks2 is in the order of 10 mmol · cm -2 s -1 and n2 ≈ 4.5. The experimentally observed gypsum dissolution rates from the batch experiments could be accurately fitted, with only minor variations of the surface reaction constant obtained from the rotating disk experiment and the transport coefficient from the NaCl dissolution batch experiment. Batch experiments on pure synthetic gypsum, reveal a linear rate law up to equilibrium. This indicates inhibition of dissolution in natural samples close to equilibrium, as is known also for calcite minerals.

  4. The kinetics of Dissolution of Biologically Formed Calcific Deposits.

    Rokidi, Stamatia; Koutsoukos, Petros

    2015-04-01

    The calcification of aortic valves results in the formation of non stoichiometric apatitic deposits which may have serious health implications because of the fact that these minerals adhere tenaciously on tissues like heart valves and arteries causing permanent damage which is partly due to their low solubility. In the present work, calcium phosphate biominerals were extracted from clinically removed tissues and were characterized with respect to their mineralogical constituents and other properties including morphology, specific surface area analyses and thermogravimetric analysis. In all cases, the biominerals may be described as non stoichiometric apatitic materials, although traces of the precursor phase of octacalcium phosphate (Ca8H2(PO4)6•5H2O, OCP) were identified on the basis of their morphological examination. The kinetics of dissolution of the biomineral deposits was investigated in solutions undersaturated with respect to hydroxyapatite (Ca5(PO4)3OH, HAP) at conditions of constant undersaturation at pH 7.40, 37°C, 0.15M NaCl. Synthetic stoichiometric HAP was used as the control mineral. The experiments in the present work used solutions prepared from calcium chloride and sodium hydrogen phosphate and the relative undersaturation, σ, was in the range 0.38-0.74 with respect to HAP and 0.49-0.85 with respect to OCP (σ=1 in water). The dissolution process started immediately upon the introduction of an accurately weighted amount of powdered biomineral in the undersaturated solutions homogenized by magnetic stirring. Inert atmosphere was ensured with the bubbling of water vapor saturated nitrogen through the demineralizing solutions. A glass/Ag/AgCl combination electrode was used as a probe to monitor the process and to control the addition of diluent solutions with the stoichiometry of the dissolving mineral. The measurements of the rates of crystal dissolution, showed a parabolic dependence on the relative solution undersaturation for HAP and higher

  5. Influence of oxalic acid on the dissolution kinetics of manganese oxide

    Godunov, E. B.; Artamonova, I. V.; Gorichev, I. G.; Lainer, Yu. A.

    2012-11-01

    The kinetics and electrochemical processes of the dissolution of manganese oxides with various oxidation states in sulfuric acid solutions containing oxalate ion additives is studied under variable conditions (concentration, pH, temperature). The parameters favoring a higher degree of the dissolution of manganese oxides in acidic media are determined. The optimal conditions are found for the dissolution of manganese oxides in acidic media in the presence of oxalate ions. The mechanism proposed for the dissolution of manganese oxides in sulfuric acid solutions containing oxalic acid is based on the results of kinetic and electrochemical studies. The steps of the dissolution mechanism are discussed.

  6. Structure-dependent interactions between alkali feldspars and organic compounds: implications for reactions in geologic carbon sequestration.

    Yang, Yi; Min, Yujia; Jun, Young-Shin

    2013-01-02

    Organic compounds in deep saline aquifers may change supercritical CO(2) (scCO(2))-induced geochemical processes by attacking specific components in a mineral's crystal structure. Here we investigate effects of acetate and oxalate on alkali feldspar-brine interactions in a simulated geologic carbon sequestration (GCS) environment at 100 atm of CO(2) and 90 °C. We show that both organics enhance the net extent of feldspar's dissolution, with oxalate showing a more prominent effect than acetate. Further, we demonstrate that the increased reactivity of Al-O-Si linkages due to the presence of oxalate results in the promotion of both Al and Si release from feldspars. As a consequence, the degree of Al-Si order may affect the effect of oxalate on feldspar dissolution: a promotion of ~500% in terms of cumulative Si concentration was observed after 75 h of dissolution for sanidine (a highly disordered feldspar) owing to oxalate, while the corresponding increase for albite (a highly ordered feldspar) was ~90%. These results provide new insights into the dependence of feldspar dissolution kinetics on the crystallographic properties of the mineral under GCS conditions.

  7. Formalization of the kinetics for autocatalytic dissolutions. Focus on the dissolution of uranium dioxide in nitric medium

    Charlier, F.; Canion, D.; Gravinese, A.; Magnaldo, A.; Lalleman, S.; Borda, G.; Schaer, E.

    2017-01-01

    Uranium dioxide dissolution in nitric acid is a complex reaction. On the one hand, the dissolution produces nitrous oxides (NOX), which makes it a triphasic reaction. On the other hand, one of the products accelerates the kinetic rate; the reaction is hence called autocatalytic.The kinetics for these kinds of reactions need to be formalized in order to optimize and design innovative dissolution reactors. In this work, the kinetics rates have been measured by optical microscopy using a single particle approach. The advantages of this analytical technique are an easier management of species transport in solution and a precise following of the dissolution rate. The global rate is well described by a mechanism considering two steps: a non-catalyzed reaction, where the catalyst concentration has no influence on the dissolution rate, and a catalyzed reaction. The mass transfer rate of the catalyst was quantified in order to discriminate when the reaction was influenced by catalyst accumulated in the boundary layer or uncatalyzed. This first approximation described well the sigmoid dissolution curve profile. Moreover, experiments showed that solutions filled with catalyst proved to lose reactivity over time. Results pointed out that the higher the liquid-gas exchanges, the faster the kinetic rate decreases with time. Thus, it was demonstrated, for the first time, that there is a link between catalyst and nitrous oxides. The outcome of this study leads to new ways for improving the design of dissolvers. Gas-liquid exchanges are indeed a lever to impact dissolution rates. Temperature and catalyst concentration can be optimized to reduce residence times in dissolvers. (authors)

  8. Crystallization Kinetics of Barium and Strontium Aluminosilicate Glasses of Feldspar Composition

    Hyatt, Mark J.; Bansal, Narottam P.

    1994-01-01

    Crystallization kinetics of BaO.Al2O3.2SiO2 (BAS) and SrO.Al2O3.2SiO2 (SAS) glasses in bulk and powder forms have been studied by non-isothermal differential scanning calorimetry (DSC). The crystal growth activation energies were evaluated to be 473 and 451 kJ/mol for bulk samples and 560 and 534 kJ/mol for powder specimens in BAS and SAS glasses, respectively. Development of crystalline phases on thermal treatments of glasses at various temperatures has been followed by powder x-ray diffraction. Powder samples crystallized at lower temperatures than the bulk and the crystallization temperature was lower for SAS glass than BAS. Crystallization in both glasses appeared to be surface nucleated. The high temperature phase hexacelsian, MAl2Si2O8 (M = Ba or Sr), crystallized first by nucleating preferentially on the glass surface. Also, monoclinic celsian does not nucleate directly in the glass, but is formed at higher temperatures from the transformation of the metastable hexagonal phase. In SAS the transformation to monoclinic celsian occurred rapidly after 1 h at 1100 C. In contrast, in BAS this transformation is sluggish and difficult and did not go to completion even after 10 h heat treatment at 1400 C. The crystal growth morphologies in the glasses have been observed by optical microscopy. Some of the physical properties of the two glasses are also reported.

  9. Dissolution kinetics of lead telluride in alkali solutions of hydrogen peroxide

    Danilova, M.G.; Sveshnikova, L.L.; Stavitskaya, T.A.; Repinskij, S.M.

    1991-01-01

    Dissolution kinetics of lead telluride in alkali solutions of hydrogen peroxide was investigated. Dependences of change of PbTe dissolution rate on concentration of hydrogen peroxide and alkali in the solution were obtained. It is shown that dissolution rate of lead telluride is affected by dissolution rate of lead oxide, representing the product of ReTe dissolution. The obtained regularities can be explained by change of solution structure with increase of KOH concentration and by the state of hydrogen peroxide in the solution

  10. Coupled multiphase reactive flow and mineral dissolution-precipitation kinetics: Examples of long-term CO2 sequestration in Utsira Sand, Norway and Mt. Simon Formation, Midwest USA

    Zhang, Y.; Zhang, G.; Lu, P.; Hu, B.; Zhu, C.

    2017-12-01

    The extent of CO2 mineralization after CO2 injection into deep saline aquifers is a result of the complex coupling of multiphase fluid flow, mass transport, and brine-mineral reactions. The effects of dissolution rate laws and groundwater flow on the long-term fate of CO2 have been seriously overlooked. To investigate these effects, we conducted multiphase (CO2 and brine) coupled reactive transport modeling of CO2 storage in two sandy formations (Utsira Sand, Norway1,2 and Mt. Simon formation, USA 3) using ToughReact and simulated a series of scenarios. The results indicated that: (1) Different dissolution rate laws for feldspars can significantly affect the amount of CO2 mineralization. Increased feldspar dissolution will promote CO2 mineral trapping through the coupling between feldspar dissolution and carbonate mineral precipitation at raised pH. The predicted amount of CO2 mineral trapping when using the principle of detailed balancing-based rate law for feldspar dissolution is about twice as much as that when using sigmoidal rate laws in the literature. (2) Mineral trapping is twice as much when regional groundwater flow is taken into consideration in long-term simulations (e.g., 10,000 years) whereas most modeling studies neglected the regional groundwater flow back and effectively simulated a batch reactor process. Under the influence of regional groundwater flow, the fresh brine from upstream continuously dissolves CO2 at the tail of CO2 plume, generating a large acidified area where large amount of CO2 mineralization takes place. The upstream replenishment of groundwater results in ˜22% mineral trapping at year 10,000, compared to ˜4% when this effect is ignored. Refs: 1Zhang, G., Lu, P., Wei, X., Zhu, C. (2016). Impacts of Mineral Reaction Kinetics and Regional Groundwater Flow on Long-Term CO2 Fate at Sleipner. Energy & Fuels, 30(5), 4159-4180. 2Zhu, C., Zhang, G., Lu, P., Meng, L., Ji, X. (2015). Benchmark modeling of the Sleipner CO2 plume

  11. Mechanism and kinetics of mineral weathering under acid conditions

    Anbeek, C.

    1994-01-01

    This study deals with the relationships between crystal structure, grain diameter, surface morphology and dissolution kinetics for feldspar and quartz under acid conditions.

    Intensively ground samples from large, naturally weathered mineral fragments are frequently used in

  12. Dissolution of kinetics of nanoscale liquid Pb/Bi inclusions at a grain boundary in aluminium

    Prokofjev, Sergei I.; Johnson, Erik; Zhilin, Victor M.

    2008-01-01

    of the inclusions was observed until their complete disappearance. Digitized video recordings of the process of dissolution were used to obtain the dependence of the inclusion size with time. The kinetics of the dissolution of the grain boundary inclusions can be described with a model where it is assumed...

  13. Effect of dissolution kinetics on flotation response of calcite with oleate

    D. G. Horta

    Full Text Available Abstract Phosphate flotation performance can be influenced by the dissolution kinetics of the minerals that compose the ore. The purpose of this work was to investigate the effect of dissolution kinetics on flotation response with oleate (collector of calcites from different origins and genesis. The calcite samples were first purified and characterized by x-ray Fluorescence (XRF and the Rietveld method applied to x-ray Diffractometry data (RXD. Experiments of calcite dissolution and microflotationwere performed at pH 8 and pH 10.The pH effect on the calcite dissolution and flotation indicates the possible influence of the carbonate/bicarbonate ions provided by the CO2 present in the air. In addition, the flotation response is greater as the dissolution increases, making more Ca2+ ions available to interact with collector molecules. This result corroborates the surface precipitation mechanism proposed foroleate adsorption on the calcite surface.

  14. investigation of dissolution kinetics of a nigerian columbite

    user

    1,2 DEPARTMENT OF CHEMICAL ENGINEERING, OBAFEMI AWOLOWO UNIVERSITY, ILE-IFE, OSUN STATE NIGERIA. E-mail addresses: ... Experimental results indicate that the dissolution rate is chemical reaction ..... Nuclear Instruments.

  15. Kinetics of dissolution of magnetite in PDCA based formulations

    Ranganathan, S.; Prince, A.A.M.; Raghavan, P.S.; Gopalan, R.; Srinivasan, M.P.; Narasimhan, S.V.

    1997-01-01

    Magnetite is one of the important corrosion products of pressurized heavy water reactors (PHWRs) where carbon steel is the dominant surface in the primary heat transport system. Designing of formulations capable of dissolving magnetite is important for effective decontamination of such surfaces. The rate of dissolution of synthetically prepared magnetite was studied in low concentrations of PDCA containing acidic formulations. The effect of addition of ascorbic acid, citric acid, Fe 2+ -PDCA complex on the rate was also studied. The effects of pH and the temperature on the dissolution rate were determined. The PDCA as a complexant has some positive factors like low protonation constant and enhanced stability to radiation. (author)

  16. Organic ligand-induced dissolution kinetics of antimony trioxide

    Xingyun Hu; Mengchang He

    2017-01-01

    The influence of low-molecular-weight dissolved organic matter (LMWDOM) on the dissolution rate of Sb2O3 was investigated.Some representative LMWDOMs with carboxyl,hydroxyl,hydrosulfuryl and amidogen groups occurring naturally in the solution were chosen,namely oxalic acid,citric acid,tartaric acid,EDTA,salicylic acid,phthalandione,glycine,thiolactic acid,xylitol,glucose and catechol.These LMWDOMs were dissolved in inert buffers at pH =3.7,6.6 and 8.6 and added to powdered Sb2O3 in a stirred,thermostatted reactor (25℃).The addition of EDTA,tartaric acid,thiolactic acid,citric acid and oxalic acid solutions at pH 3.7 and catechol at pH 8.6 increased the rate of release of antimony.In the 10 mmol/L thiolactic acid solution,up to 97% by mass of the antimony was released after 120 min reaction.There was no effect on the dissolution of Sb2O3 for the other ligands.A weak correlation between dissolution rate with the dissociation constant of ligands and the stability of the dissolved complex was also found.All the results showed that the extent of the promoting effect of ligands on the dissolution of Sb2O3 was not determined by the stability of the dissolved complex,but by the dissociation constant of ligands and detachment rate of surface chelates from the mineral surface.This study can not only help in further understanding the effect of individual low-molecular-weight organic ligands,but also provides a reference to deduce the effect of natural organic matters with oxygen-bearing functional groups on the dissolution of antimony oxide minerals.

  17. Organic ligand-induced dissolution kinetics of antimony trioxide.

    Hu, Xingyun; He, Mengchang

    2017-06-01

    The influence of low-molecular-weight dissolved organic matter (LMWDOM) on the dissolution rate of Sb 2 O 3 was investigated. Some representative LMWDOMs with carboxyl, hydroxyl, hydrosulfuryl and amidogen groups occurring naturally in the solution were chosen, namely oxalic acid, citric acid, tartaric acid, EDTA, salicylic acid, phthalandione, glycine, thiolactic acid, xylitol, glucose and catechol. These LMWDOMs were dissolved in inert buffers at pH=3.7, 6.6 and 8.6 and added to powdered Sb 2 O 3 in a stirred, thermostatted reactor (25°C). The addition of EDTA, tartaric acid, thiolactic acid, citric acid and oxalic acid solutions at pH3.7 and catechol at pH8.6 increased the rate of release of antimony. In the 10mmol/L thiolactic acid solution, up to 97% by mass of the antimony was released after 120min reaction. There was no effect on the dissolution of Sb 2 O 3 for the other ligands. A weak correlation between dissolution rate with the dissociation constant of ligands and the stability of the dissolved complex was also found. All the results showed that the extent of the promoting effect of ligands on the dissolution of Sb 2 O 3 was not determined by the stability of the dissolved complex, but by the dissociation constant of ligands and detachment rate of surface chelates from the mineral surface. This study can not only help in further understanding the effect of individual low-molecular-weight organic ligands, but also provides a reference to deduce the effect of natural organic matters with oxygen-bearing functional groups on the dissolution of antimony oxide minerals. Copyright © 2016. Published by Elsevier B.V.

  18. The kinetics of anodic dissolution of rhenium in aqueous electrolyte solutions

    Atanasyants, A.G.; Kornienko, V.A.

    1986-01-01

    The kinetics of anodic rhenium dissolution was investigated by means of potentiodynamic and potentiostatic polarization curves recorded at temperature from 293 to 333 K in different media (NaOH, KOH, NaCl, NaBr, HCl, H 2 SO 4 ) using the rotating disc technique. It is shown that the kinetics of anodic rhenium dissolution and effective activation energy depend not only on the composition and pH value of the solutions but also on the structure of the dissolving rhenium surface. The investigation of the anodic behaviour of the rhenium monocrystal revealed the existence of anisotropy of the monocrystal electrochemical properties. The experimental results point to an important role of adsorption processes in anodic rhenium dissolution. Rhenium dissolution proceeds with formation of intermediate surface adsorption complexes between the metal and the components of the solution

  19. The Use of Artificial Neural Network for Prediction of Dissolution Kinetics

    H. Elçiçek

    2014-01-01

    Full Text Available Colemanite is a preferred boron mineral in industry, such as boric acid production, fabrication of heat resistant glass, and cleaning agents. Dissolution of the mineral is one of the most important processes for these industries. In this study, dissolution of colemanite was examined in water saturated with carbon dioxide solutions. Also, prediction of dissolution rate was determined using artificial neural networks (ANNs which are based on the multilayered perceptron. Reaction temperature, total pressure, stirring speed, solid/liquid ratio, particle size, and reaction time were selected as input parameters to predict the dissolution rate. Experimental dataset was used to train multilayer perceptron (MLP networks to allow for prediction of dissolution kinetics. Developing ANNs has provided highly accurate predictions in comparison with an obtained mathematical model used through regression method. We conclude that ANNs may be a preferred alternative approach instead of conventional statistical methods for prediction of boron minerals.

  20. Surface properties, solubility and dissolution kinetics of bamboo phytoliths

    Fraysse, Fabrice; Pokrovsky, Oleg S.; Schott, Jacques; Meunier, Jean-Dominique

    2006-04-01

    Although phytoliths, constituted mainly by micrometric opal, exhibit an important control on silicon cycle in superficial continental environments, their thermodynamic properties and reactivity in aqueous solution are still poorly known. In this work, we determined the solubility and dissolution rates of bamboo phytoliths collected in the Réunion Island and characterized their surface properties via electrophoretic measurements and potentiometric titrations in a wide range of pH. The solubility product of "soil" phytoliths ( pKsp0=2.74 at 25 °C) is equal to that of vitreous silica and is 17 times higher than that of quartz. Similarly, the enthalpy of phytoliths dissolution reaction (ΔHr25-80°C=10.85kJ/mol) is close to that of amorphous silica but is significantly lower than the enthalpy of quartz dissolution. Electrophoretic measurements yield isoelectric point pH IEP = 1.2 ± 0.1 and 2.5 ± 0.2 for "soil" (native) and "heated" (450 °C heating to remove organic matter) phytoliths, respectively. Surface acid-base titrations allowed generation of a 2-p K surface complexation model. Phytoliths dissolution rates, measured in mixed-flow reactors at far from equilibrium conditions at 2 ⩽ pH ⩽ 12, were found to be intermediate between those of quartz and vitreous silica. The dissolution rate dependence on pH was modeled within the concept of surface coordination theory using the equation: R=k1·{>SiOH2+}n+k2·{>SiOH0}+k3·{>SiO-}m, where {> i} stands for the concentration of the surface species present at the SiO 2-H 2O interface, ki are the rate constants of the three parallel reactions and n and m represent the order of the proton- and hydroxy-promoted reactions, respectively. It follows from the results of this study that phytoliths dissolution rates exhibit a minimum at pH ˜ 3. This can explain their good preservation in the acidic soil horizons of Réunion Island. In terms of silicon biogeochemical cycle, phytoliths represent a large buffering reservoir

  1. Kinetics of dissolution of magnetite in PDCA based formulations

    Ranganathan, S.; Prince, A.A.M.; Raghavan, P.S.; Gopalan, R. [Madras Christian Coll., Tambaram (India); Srinivasan, M.P.; Narasimhan, S.V.

    1997-08-01

    Magnetite is one of the important corrosion products of pressurized heavy water reactors (PHWRs) where carbon steel is the dominant surface in the primary heat transport system. Designing of formulations capable of dissolving magnetite is important for effective decontamination of such surfaces. The rate of dissolution of synthetically prepared magnetite was studied in low concentrations of PDCA containing acidic formulations. The effect of addition of ascorbic acid, citric acid, Fe{sup 2+}-PDCA complex on the rate was also studied. The effects of pH and the temperature on the dissolution rate were determined. The PDCA as a complexant has some positive factors like low protonation constant and enhanced stability to radiation. (author)

  2. Kinetics of dissolution of thorium and uranium doped britholite ceramics

    Dacheux, N., E-mail: nicolas.dacheux@univ-montp2.f [Groupe de Radiochimie, Institut de Physique Nucleaire d' Orsay, Bat. 100, Universite Paris-Sud-11, 91406 Orsay (France); Institut de Chimie Separative de Marcoule, UMR 5257 (Universite Montpellier 2/CNRS/CEA/ENSCM), Bat. 426, Centre de Marcoule, BP 17171, 30207 Bagnols sur ceze cedex (France); Du Fou de Kerdaniel, E. [Groupe de Radiochimie, Institut de Physique Nucleaire d' Orsay, Bat. 100, Universite Paris-Sud-11, 91406 Orsay (France); Clavier, N. [Groupe de Radiochimie, Institut de Physique Nucleaire d' Orsay, Bat. 100, Universite Paris-Sud-11, 91406 Orsay (France); Institut de Chimie Separative de Marcoule, UMR 5257 (Universite Montpellier 2/CNRS/CEA/ENSCM), Bat. 426, Centre de Marcoule, BP 17171, 30207 Bagnols sur ceze cedex (France); Podor, R. [Institut de Chimie Separative de Marcoule, UMR 5257 (Universite Montpellier 2/CNRS/CEA/ENSCM), Bat. 426, Centre de Marcoule, BP 17171, 30207 Bagnols sur ceze cedex (France); Institut Jean Lamour - Departement CP2S - Equipe 206, Faculte des Sciences et Techniques - Nancy Universite, BP 70239, 54506 Vandoeuvre les Nancy cedex (France); Aupiais, J. [CEA DAM DIF, 91297 Arpajon (France); Szenknect, S. [Institut de Chimie Separative de Marcoule, UMR 5257 (Universite Montpellier 2/CNRS/CEA/ENSCM), Bat. 426, Centre de Marcoule, BP 17171, 30207 Bagnols sur ceze cedex (France)

    2010-09-01

    In the field of immobilization of actinides in phosphate-based ceramics, several thorium and uranium doped britholite samples were submitted to leaching tests. The normalized dissolution rates determined for several pH values, temperatures and acidic media from the calcium release range from 4.7 x 10{sup -2} g m{sup -2} d{sup -1} to 21.6 g m{sup -2} d{sup -1}. Their comparison with that determined for phosphorus, thorium and uranium revealed that the dissolution is clearly incongruent for all the conditions examined. Whatever the leaching solution considered, calcium and phosphorus elements were always released with higher R{sub L} values than the other elements (Nd, Th, U). Simultaneously, thorium was found to quickly precipitate as alteration product, leading to diffusion phenomena for uranium. For all the media considered, the uranium release is higher than that of thorium, probably due to its oxidation from tetravalent oxidation state to uranyl. Moreover, the evaluation of the partial order related to proton concentration and the apparent energy of activation suggest that the reaction of dissolution is probably controlled by surface chemical reactions occurring at the solid/liquid interface. Finally, comparative leaching tests performed in sulphuric acid solutions revealed a significant influence of such media on the chemical durability of the leached pellets, leading to higher normalized dissolution rates for all the elements considered. On the basis of the results of chemical speciation, this difference was mainly explained in the light of higher complexion constants by sulfate ions compared to nitrate, chloride and phosphate.

  3. Kinetics of reductive bulk dissolution of lepidocrocite, ferrihydrite, and geothite

    Larsen, O.; Postma, Diederik Jan

    2001-01-01

    of the reduction experiments, lepidocrocite crystals were subsampled and the change in crystal habit and size distribution was studied by transmission electron microscopy. The rate of complete dissolution was described by the function J/m0 5 k9(m/m0)g where J is the overall rate of dissolution (mol/s), m0...... for lepidocrocite showed strong etch-pitting of the crystals parallel to the c-axis resulting ultimately in disintegration of the crystals. For the different iron oxides, the initial rate was independent of the specific surface area, emphasizing the importance of the crystal structure for the dissolution rate....... However, among the lepidocrocites the initial rate was proportional to the specific surface area. The exponent, g was found to vary from a value near 1.0 for one of the 2-line ferrihydrites, two of the lepidocrocites and the goethite, to values close to 2.3 for the other 2-line ferrihydrite and the 6-line...

  4. Dissolution kinetics of B clusters in crystalline Si

    De Salvador, D.; Napolitani, E.; Bisognin, G.; Carnera, A.; Bruno, E.; Mirabella, S.; Impellizzeri, G.; Priolo, F.

    2005-01-01

    Boron (B) clustering in crystalline Si induced by interaction with Si self-interstitials is a widely studied phenomenon of fundamental importance for Si micro- and nano-electronic technology. The requested B activation increase brings the B concentration to a very high level and a detailed understanding of B clustering at high concentration is demanded. In the present work we present some recent results regarding the B clustering process starting from B concentration both below and above the B solubility limit. We show that B clusters, produced by self-interstitial interaction with substitutional B in crystalline Si, dissolve under annealing according to two distinct paths with very different characteristic times. The two regimes generally coexist, but while the faster dissolution path is predominant for clusters formed at low B concentration (1 x 10 19 B/cm 3 ), the slower one is characteristic of clusters formed above the solubility limit and dominates the dissolution process at high B concentration (2 x 10 2 B/cm 3 ). The activation energies of both processes are characterized and discussed. It is shown that the faster path can be connected to a direct emission of mobile B from small clusters, while the slower path is demonstrated not to be self-interstitial limited and it is probably related to a more complex cluster dissolution process

  5. Kinetics of carbonate mineral dissolution in CO2-acidified brines at storage reservoir conditions.

    Peng, Cheng; Anabaraonye, Benaiah U; Crawshaw, John P; Maitland, Geoffrey C; Trusler, J P Martin

    2016-10-20

    We report experimental measurements of the dissolution rate of several carbonate minerals in CO 2 -saturated water or brine at temperatures between 323 K and 373 K and at pressures up to 15 MPa. The dissolution kinetics of pure calcite were studied in CO 2 -saturated NaCl brines with molalities of up to 5 mol kg -1 . The results of these experiments were found to depend only weakly on the brine molality and to conform reasonably well with a kinetic model involving two parallel first-order reactions: one involving reactions with protons and the other involving reaction with carbonic acid. The dissolution rates of dolomite and magnesite were studied in both aqueous HCl solution and in CO 2 -saturated water. For these minerals, the dissolution rates could be explained by a simpler kinetic model involving only direct reaction between protons and the mineral surface. Finally, the rates of dissolution of two carbonate-reservoir analogue minerals (Ketton limestone and North-Sea chalk) in CO 2 -saturated water were found to follow the same kinetics as found for pure calcite. Vertical scanning interferometry was used to study the surface morphology of unreacted and reacted samples. The results of the present study may find application in reactive-flow simulations of CO 2 -injection into carbonate-mineral saline aquifers.

  6. Effects of natural organic matter properties on the dissolution kinetics of zinc oxide nanoparticles

    Jiang, Chuanjia; Aiken, George R.; Hsu-Kim, Heileen

    2015-01-01

    The dissolution of zinc oxide (ZnO) nanoparticles (NPs) is a key step of controlling their environmental fate, bioavailability, and toxicity. Rates of dissolution often depend upon factors such as interactions of NPs with natural organic matter (NOM). We examined the effects of 16 different NOM isolates on the dissolution kinetics of ZnO NPs in buffered potassium chloride solution using anodic stripping voltammetry to directly measure dissolved zinc concentrations. The observed dissolution rate constants (kobs) and dissolved zinc concentrations at equilibrium increased linearly with NOM concentration (from 0 to 40 mg C L–1) for Suwannee River humic and fulvic acids and Pony Lake fulvic acid. When dissolution rates were compared for the 16 NOM isolates, kobs was positively correlated with certain properties of NOM, including specific ultraviolet absorbance (SUVA), aromatic and carbonyl carbon contents, and molecular weight. Dissolution rate constants were negatively correlated to hydrogen/carbon ratio and aliphatic carbon content. The observed correlations indicate that aromatic carbon content is a key factor in determining the rate of NOM-promoted dissolution of ZnO NPs. The findings of this study facilitate a better understanding of the fate of ZnO NPs in organic-rich aquatic environments and highlight SUVA as a facile and useful indicator of NOM interactions with metal-based nanoparticles.

  7. Mechanism and Kinetics for the Dissolution of Apatitic Materials in Acid Solutions

    Calmanovici C.E.

    1997-01-01

    Full Text Available Abstract - This work concerns the study of the digestion step in the production process of phosphoric acid. Some qualitative experiments indicate that the difference between the pH at the surface of the phosphate and that in the bulk of the solution is negligible and that the dissolution is controlled by diffusion of products away from the phosphate particle. In further experiments, to isolate the dissolution phenomenon from the formation of calcium sulfate, the sulfuric acid normally used industrially is replaced by hydrochloric acid. The phosphate material used in our experiments is a model apatitic material: synthetic hydroxyapatite (HAP. The dissolution of calcium hydroxyapatite was studied with increasing amounts of calcium and phosphate at different temperatures. A simple method was developed for this observation based on the time required for complete dissolution of the HAP powder. The results confirm that the dissolution is controlled by a diffusional process through an interface of calcium and phosphate ions released from the solid surface. A kinetic model for the dissolution of apatitic materials is proposed which assumes a shrinking particle behaviour controlled by diffusion of calcium ions. The experimental results are fitted to this model to determine the mass transfer constant for HAP dissolution in acid solutions. The activation energy of the reaction is about 14kJ/mol. This study was carried on in conditions similar to the industrial ones for the production of phosphoric acid by the dihydrate-process

  8. Dissolution kinetics of volatile organic compound vapors in water : An integrated experimental and computational study

    G. Mahmoodlu, Mojtaba; Pontedeiro, Elizabeth M.; Pérez Guerrero, Jesús S.; Raoof, Amir; Hassanizadeh, S. Majid; van Genuchten, Martinus Th

    In this study we performed batch experiments to investigate the dissolution kinetics of trichloroethylene (TCE) and toluene vapors in water at room temperature and atmospheric pressure. The batch systems consisted of a water reservoir and a connected headspace, the latter containing a small glass

  9. Kinetic study of the thorium phosphate - diphosphate dissolution

    Dacheux, N.; Thomas, A.C.; Brandel, V.; Genet, M.

    2000-01-01

    The thorium phosphate-diphosphate Th 4 (PO 4 ) 4 P 2 O 7 (TPD) structure allows the replacement of large amounts of thorium by tetravalent actinides leading to the formation of solid solutions. This compound was obtained in powdered or sintered form after pressing at room temperature at 300-800 MPa then heating at 1250 deg. C for 10-30 hours. The resistance of this material to aqueous corrosion was determined by varying several parameters such as surface, leaching flow, acidity or temperature. It was thus possible to independently determine the influence of each parameter on the leaching rate provided that the saturation of the solution was not obtained. In acidic media, the partial order related to [H 3 O + ] was found to be in the 0.31-0.35 range while, in basic media, the partial order related to [OH - ] was almost the same (0.45). The activation energy (42 kJ/mol) was determined between 4 deg. C and 120 deg. C. Moreover, the addition of phosphate in the leachate slightly increased the TPD dissolution rate. When the saturation of the solution is reached, a gelatinous precipitate controls the thorium and phosphate concentrations. The complete characterization of this solid led to the proposed general formula Th 2 (PO 4 ) 2 (HPO 4 ). n H 2 O which conventional solubility product (at I = 0 M) is very low: K * S,0 10 -66.6±1.2 even in very acidic media. (authors)

  10. Dissolution kinetics of purified and synthetic smectites at 25°C and PH∼9

    Marty, Nicolas C.M.; Tournassat, Christophe; Gaucher, Eric C.; Chino, Daisuke; Sato, Tsutomu; Villieras, Frederic; Giffaut, Eric; Cama, Jordi; Soler, J.M.

    2010-01-01

    Document available in extended abstract form only. Mineral rate laws that account for the kinetics of dissolution/precipitation of clays and other minerals are used in reactive transport codes to simulate and evaluate the evolution of geochemical conditions in the near-field of high level radioactive waste (HLW) in deep geological repositories. Smectite is the main component in the compacted bentonite used in the Multi-barrier system to lower permeability. As a consequence, molecular diffusion becomes the main mechanism of mass transport, and dissolution and precipitation reactions take place in close-to-equilibrium conditions. Nonetheless, in the reactive transport codes, databases utilized mainly incorporate rate laws derived at far-from- equilibrium conditions, which are not representative of near-field and far-field conditions of concrete-clay or iron-clay interfaces. Hence, there is an important need to derive kinetic rate laws that allow extrapolation of mineral dissolution/precipitation as a function of the solution saturation state (i.e., Gibbs free energy, ΔG r ). Once the effect of the environmental variables, such as pH, T and ΔG r , etc. exert on smectite dissolution is discerned, evaluation of the evolution of geochemical conditions in the HLW repository is carried out using reactive transport codes that couple the rate laws with transport equations. Several studies related dissolution of natural smectites with pH, and just a few dealt with the rate dependency on Gibbs free energy. The present study aims at estimating dissolution rates of montmorillonite in conditions as close as possible to those expected in the Callovo-Oxfordian formation, i.e. pH∼7.2 and 25 deg. C. Dissolution kinetics of two montmorillonites (natural Na-montmorillonite purified from MX80 and synthetic smectite) were investigated by means of flow-through experiments and solution-chemistry data obtained. The calculated rates were based on release of Si, Al and Mg and normalized

  11. Thermodynamic stability and kinetic dissolution of perovskite in natural waters

    Nesbitt, H.W.; Bancroft, G.M.; Fyfe, W.S.; Karkhanis, S.; Melling, P.; Nishijima, A.

    1981-01-01

    Ringwood and coworkers have recently proposed using titanates and zirconates as hosts for nuclear waste in the Synroc B process. Three minerals are used as hosts: perovskite (CaTiO 3 ), Ba-hollandite (BaAl 2 Ti 6 O 16 ), and zirconolite (CaZrTi 2 O 7 ). The Synroc philosophy relies heavily on geological and geochemical observations in selecting stable host minerals. Although it has been recognized that the Synroc minerals are not thermodynamically compatible with siliceous rocks, the minerals are considered to be thermodynamically stable in the presence of water, and it has been reported that these minerals are kinetically stable under high-temperature (up to 900 0 C) hydrothermal conditions. Detailed thermodynamic calculations and leach tests have been performed which demonstrate: first, that perovskite is thermodynamically unstable in all known natural waters; and second, that pervoskite leaches at a significant rate even at 100 0 C. Hydrothermal leach tests have been made on natural and synthetic perovskite and perovskite analogues between 100 0 C and 300 0 C. Weight losses and solution concentrations were monitored. The results reported previously in the literature also show that perovskite is kinetically unstable in the presence of common silicates. Our results show that perovskite may be no more stable than siliceous glasses, such as rhyolite, which have been studied previously. Geologic evidence from common alkaline rocks also indicates that hollandite and zirconolite probably will not survive in common rock matrices

  12. Kinetic study of the thorium phosphate - diphosphate dissolution

    Dacheux, N.; Thomas, A.C.; Brandel, V.; Genet, M. [Paris-11 Univ., 91 - Orsay (France). Inst. de Physique Nucleaire; Aupiais, J. [CEA/DAM-Ile de France, Dept. Analyse Surveillance Environnement, DASE, Service Radioanalyses Chimie Environnement, 91 - Bruyeres-Le-Chatel (France)

    2000-07-01

    The thorium phosphate-diphosphate Th{sub 4}(PO{sub 4}){sub 4}P{sub 2}O{sub 7} (TPD) structure allows the replacement of large amounts of thorium by tetravalent actinides leading to the formation of solid solutions. This compound was obtained in powdered or sintered form after pressing at room temperature at 300-800 MPa then heating at 1250 deg. C for 10-30 hours. The resistance of this material to aqueous corrosion was determined by varying several parameters such as surface, leaching flow, acidity or temperature. It was thus possible to independently determine the influence of each parameter on the leaching rate provided that the saturation of the solution was not obtained. In acidic media, the partial order related to [H{sub 3}O{sup +}] was found to be in the 0.31-0.35 range while, in basic media, the partial order related to [OH{sup -}] was almost the same (0.45). The activation energy (42 kJ/mol) was determined between 4 deg. C and 120 deg. C. Moreover, the addition of phosphate in the leachate slightly increased the TPD dissolution rate. When the saturation of the solution is reached, a gelatinous precipitate controls the thorium and phosphate concentrations. The complete characterization of this solid led to the proposed general formula Th{sub 2}(PO{sub 4}){sub 2}(HPO{sub 4}). n H{sub 2}O which conventional solubility product (at I = 0 M) is very low: K{sup *}{sub S,0} 10{sup -66.6{+-}}{sup 1.2} even in very acidic media. (authors)

  13. Dissolution study of tremolite and anthophyllite: pH effect on the reaction kinetics

    Rozalen, M.; Ramos, M.E.; Gervilla, F.; Kerestedjian, T.; Fiore, S.; Huertas, F.J.

    2014-01-01

    Highlights: • Dissolution rates strongly depend on pH and it is different for each mineral. • Anthophyllite dissolves up to 8 times faster than tremolite in similar conditions. • SEM images show different particle breakage and carbonation effects at basic pHs. • Our results are a good background to develop remediation processes of contaminated sites. - Abstract: The effect of pH on the kinetics of tremolite and anthophyllite dissolution was investigated at 25 °C in batch reactors over the pH range of 1–13.5, in inorganic buffered solutions. Dissolution rates were obtained based on the release of Si and Mg. Results obtained in this study show different behaviors for both minerals. For tremolite, dissolution rates show a noticeable dependence on pH between 1 and 8, decreasing as pH increases and reaching a minimum around neutral conditions. At basic pH this dependence becomes even stronger, but dissolution takes place together with collateral effects of saturation and carbonation. A preferential release of Ca and Mg is observed in acid media, lowering the Mg/Si ratio to the extent that Mg solubility decreases with pH. For anthophyllite, dissolution rates also show a strong dependence on pH, between 1 and 9.5. At the same pH, anthophyllite dissolves up to 8 times faster than tremolite. For pH > 9.5 this dependence is smooth, and it is probably associated with effects of saturation and carbonation. Dissolution is also non-stoichiometric with a faster release of Mg with respect to Si in acid media. SEM observations show differences in the breakage mechanism of the fibers. The anthophyllite particle breakage during dissolution consists of the splitting of bundle fibers parallel to the fiber longitudinal direction. However, for tremolite, other than fiber splitting, particles shorten induced by coalescence of etch pits developed perpendicular to c axe

  14. Feldspar, Infrared Stimulated Luminescence

    Jain, Mayank

    2014-01-01

    This entry primarily concerns the characteristics and the origins of infrared-stimulated luminescence in feldspars.......This entry primarily concerns the characteristics and the origins of infrared-stimulated luminescence in feldspars....

  15. Kinetics of UO2(s) dissolution under reducing conditions: Numerical modelling

    Puigdomenech, I.; Casas, I.; Bruno, J.

    1990-05-01

    A numerical model is presented that describes the dissolution and precipitation of UO 2 (s) under reducing conditions. For aqueous solutions with pH>4, main reaction is: UO 2 (s)+2H 2 O↔U(OH) 4 (aq). The rate constant for the precipitation reaction is found to be log(k p )=-1.2±0.2 h -1 m -2 , while the value for the rate constant of the dissolution reaction is log(k d )=-9.0±0.2 mol/(1 h m 2 ). Most of the experiments reported in the literature show a fast initial dissolution of a surface film of hexavalent uranium oxide. Making the assumption that the chemical composition of the surface coating is U 3 O 7 (s), we have derived a mechanism for this process, and its rate constants have been obtained. The influence of HCO 3 - and CO 3 2- on the mechanism of dissolution and precipitation of UO 2 (s) is still unclear. From the solubility measurements reported, one may conclude that the identity of the aqueous complexes in solution is not well known. Therefore it is not possible to make a mechanistic interpretation of the kinetic data in carbonate medium. (orig.)

  16. Kinetic of the COLUMBO-TANTALITE dissolution in aqueous solutions of hydrofluoric acid

    Rodriguez, Mario; Quiroga, Oscar; Ruiz, Maria del Carmen

    2003-01-01

    The dissolution rate of a columbo-tantalite of the San Luis Province in aqueous solutions of hydrofluoric acid has been studied.Experiments at different temperatures were carried out in a pressure reactor.The experimental results show that the mineral dissolution increases with the reaction time.This effect is greater when the temperature increases from 348 up to 396 K, but it is little 493 K. The experimental data were treated with different models, which have been deduced for the kinetic study of solid-fluid non-catalytic heterogeneous reactions. As a result, the better model that fit the experimental data is a model based on the nucleation and growth theory.This model is physically according to the attack observed by means of scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDXS) on the mineral residues.These residues show an irregular located-type attack

  17. Dissolution kinetics of schwertmannite and ferrihydrite in oxidized mine samples and their detection by differential X-ray diffraction (DXRD)

    Dold, Bernhard

    2003-01-01

    A dissolution test with 9 natural and synthetic schwertmannite and ferrihydrite samples was performed by reaction with 0.2 M ammonium oxalate at pH 3.0 in the dark. The method was coupled with differential X-ray diffraction (DXRD) to successfully detect schwertmannite at low concentrations in oxidized mine tailings. Rapid dissolution was observed for all schwertmannites (> 94% in 60 min) and natural 2-line ferrihydrites (> 85% in 60 min); however, synthetic 2-line and 6-line ferrihydrite dissolved slower (42 and 16% after 60 min, respectively). The results showed that it was not possible to distinguish between natural schwertmannites and ferrihydrites on the basis of their dissolution kinetics. Modeling of the schwertmannite dissolution curves, examinations of mineral shape by scanning electron microscopy, and Fe/S mole ratios of the dissolved fractions indicated that two different schwertmannite particle morphologies (spherical and web-like) occurred. Collapse of spherical (sea-urchin) schwertmannite aggregates seemed to control the dissolution kinetics according to a shrinking core model. In the case of web-like schwertmannite, dissolution could be modeled with a simple first order equation, and structural SO 4 2- may have affected the dissolution kinetics. No relationship was found between ferrihydrite particle shape and dissolution behavior in acid NH 4 -oxalate. A 1-h extraction with 0.2 M NH 4 -oxalate at pH 3.0 in the dark should be adequate to dissolve schwertmannite and natural 2-line ferrihydrite in most samples. In some cases, a fraction of secondary jarosite or goethite may also be dissolved, although at a slower rate. If only schwertmannite is of interest (e.g., determination by DXRD), a 15 min attack should be used to increase selectivity. A truly selective leach of schwertmannite and ferrihydrite should be based on dissolution tests, as a broad variety of dissolution kinetics can be observed in this mineral group

  18. Kinetic model for quartz and spinel dissolution during melting of high-level-waste glass batch

    Pokorny, Richard; Rice, Jarrett A.; Crum, Jarrod V.; Schweiger, Michael J.; Hrma, Pavel

    2013-01-01

    The dissolution of quartz particles and the growth and dissolution of crystalline phases during the conversion of batch to glass potentially affects both the glass melting process and product quality. Crystals of spinel exiting the cold cap to molten glass below can be troublesome during the vitrification of iron-containing high-level wastes. To estimate the distribution of quartz and spinel fractions within the cold cap, we used kinetic models that relate fractions of these phases to temperature and heating rate. Fitting the model equations to data showed that the heating rate, apart from affecting quartz and spinel behavior directly, also affects them indirectly via concurrent processes, such as the formation and motion of bubbles. Because of these indirect effects, it was necessary to allow one kinetic parameter (the pre-exponential factor) to vary with the heating rate. The resulting kinetic equations are sufficiently simple for the detailed modeling of batch-to-glass conversion as it occurs in glass melters. The estimated fractions and sizes of quartz and spinel particles as they leave the cold cap, determined in this study, will provide the source terms needed for modeling the behavior of these solid particles within the flow of molten glass in the melter

  19. A method for phenomenological and chemical kinetics study of autocatalytic reactive dissolution by optical microscopy. The case of uranium dioxide dissolution in nitric acid media

    Marc Philippe

    2018-01-01

    Full Text Available Dissolution is a milestone of the head-end of hydrometallurgical processes, as the stabilization rates of the chemical elements determine the process performance and hold-up. This study aims at better understanding the chemical and physico-chemical phenomena of uranium dioxide dissolution reactions in nitric acid media in the Purex process, which separates the reusable materials and the final wastes of the spent nuclear fuels. It has been documented that the attack of sintering-manufactured uranium dioxide solids occurs through preferential attack sites, which leads to the development of cracks in the solids. Optical microscopy observations show that in some cases, the development of these cracks leads to the solid cleavage. It is shown here that the dissolution of the detached fragments is much slower than the process of the complete cleavage of the solid, and occurs with no disturbing phenomena, like gas bubbling. This fact has motivated the measurement of dissolution kinetics using optical microscopy and image processing. By further discriminating between external resistance and chemical reaction, the “true” chemical kinetics of the reaction have been measured, and the highly autocatalytic nature of the reaction confirmed. Based on these results, the constants of the chemical reactions kinetic laws have also been evaluated.

  20. A method for phenomenological and chemical kinetics study of autocatalytic reactive dissolution by optical microscopy. The case of uranium dioxide dissolution in nitric acid media

    Marc, Philippe; Magnaldo, Alastair; Godard, Jérémy; Schaer, Éric

    2018-03-01

    Dissolution is a milestone of the head-end of hydrometallurgical processes, as the stabilization rates of the chemical elements determine the process performance and hold-up. This study aims at better understanding the chemical and physico-chemical phenomena of uranium dioxide dissolution reactions in nitric acid media in the Purex process, which separates the reusable materials and the final wastes of the spent nuclear fuels. It has been documented that the attack of sintering-manufactured uranium dioxide solids occurs through preferential attack sites, which leads to the development of cracks in the solids. Optical microscopy observations show that in some cases, the development of these cracks leads to the solid cleavage. It is shown here that the dissolution of the detached fragments is much slower than the process of the complete cleavage of the solid, and occurs with no disturbing phenomena, like gas bubbling. This fact has motivated the measurement of dissolution kinetics using optical microscopy and image processing. By further discriminating between external resistance and chemical reaction, the "true" chemical kinetics of the reaction have been measured, and the highly autocatalytic nature of the reaction confirmed. Based on these results, the constants of the chemical reactions kinetic laws have also been evaluated.

  1. Kinetics of carbonate dissolution in CO2-saturated aqueous system at reservoir conditions

    Peng, Cheng; Crawshaw, John P.; Maitland, Geoffrey; Trusler, J. P. Martin

    2014-05-01

    results of the study indicate that the rotating disc technique can allow accurate measurement of the carbonate dissolution rate under surface-reaction-controlled conditions, and that the carbonate dissolution rate typically increases with the increase of temperature, CO2 partial pressure and solution acidity. The study shows that the dissolution of carbonate in CO2-free acidic solutions can be described as a first order heterogeneous reaction; however, this model is not sufficient to describe the reaction kinetics of carbonate minerals in the (CO2 + H2O) system, particularly for high reactivity carbonates, such as calcite, at reservoir conditions. For these systems, both pH and the activity of CO2(aq) influence the dissolution rate. Based on the experimental results, kinetic models have been developed and parameterised to describe the dissolution of different carbonate minerals. The results of this study should facilitate more rigorous modelling of mineral dissolution in deep saline aquifers used for CO2 storage. We gratefully acknowledge the funding of QCCSRC provided jointly by Qatar Petroleum, Shell, and the Qatar Science & Technology Park. Keywords: Carbon Dioxide, Carbonate, High Pressure, High Temperature, Reaction Kinetics.

  2. Kinetics of the isothermal decomposition of zirconium hydride: terminal solid solubility for precipitation and dissolution

    Denisov, E. A.; Kompaniets, T. N.; Voyt, A. P.

    2018-05-01

    The hydrogen permeation technique in the surface-limited regime (SLR) was first used to study the isothermal decomposition of zirconium hydride. It is shown that under isothermal conditions, the hydrogen terminal solid solubility in the α-phase for hydride precipitation (TSSp) and dissolution (TSSd) differ only by 6%, in contrast to the 20-30% indicated in the available literature. It is demonstrated that even the minimum heating/cooling rate (1 C/min) used in the traditional methods of studying TSSp and TSSd is too high to exclude the effect of kinetics on the results obtained.

  3. Kinetics of Ni3S2 sulfide dissolution in solutions of sulfuric and hydrochloric acids

    Palant, A. A.; Bryukvin, V. A.; Vinetskaya, T. N.; Makarenkova, T. A.

    2008-02-01

    The kinetics of Ni3S2 sulfide (heazlewoodite) dissolution in solutions of hydrochloric and sulfuric acids is studied. The process under study in the temperature range of 30 90°C is found to occur in a kinetic regime and is controlled by the corresponding chemical reactions of the Ni3S2 decomposition by solutions of inorganic acids ( E a = 67 92 kJ/mol, or 16 22 kcal/mol). The only exception is the Ni3S2-HCl system at elevated temperatures (60 90°C). In this case, the apparent activation energy decreases sharply to 8.8 kJ/mol (2.1 kcal/mol), which is explained by the catalytic effect of gaseous chlorine formed under these conditions. The studies performed are related to the physicochemical substantiation of the hydrometallurgical processing of the copper-nickel converter mattes produced in the industrial cycle of the Norilsk Mining Company.

  4. Kinetics and thermodynamics of aluminium dissolution in 1.0M sulphuric acid containing chloride ions

    Abdel-Gaber, A.M. [Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426, Ibrahimia, Alexandria 21321 (Egypt)]. E-mail: ashrafmoustafa@yahoo.com; Abd-El-Nabey, B.A. [Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426, Ibrahimia, Alexandria 21321 (Egypt); Sidahmed, I.M. [Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426, Ibrahimia, Alexandria 21321 (Egypt); El-Zayady, A.M. [Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426, Ibrahimia, Alexandria 21321 (Egypt); Saadawy, M. [Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426, Ibrahimia, Alexandria 21321 (Egypt)

    2006-08-01

    The dissolution of aluminium in 1M sulphuric acid solutions containing different chloride ion concentrations (0.01-0.06M) were studied at 25, 30, 35 and 40deg. C using electrochemical impedance spectroscopy (EIS) technique and polarization curves measurements. The kinetic rate equation, under the experimental condition described, was derived and found to verify the following relationship:V=k{sub obs}K{sub 2}C{sub Cl{sup -}}{sup n}1+K{sub 2}C{sub Cl{sup -}}{sup n}where V is the corrosion rate, k{sub obs} and K{sub 2} are the dissolution rate constant of aluminium oxide-chloride complex and the equilibrium constant of chloride ions adsorbed at aluminium oxide surface, respectively. The kinetic and thermodynamic energy parameters were calculated and their values indicate that chloride ions are chemisorbed onto the aluminium oxide surface and the formation of oxide-chloride complex is the rate-determining step.

  5. Study of the dissolution velocity of dispersed solid particles. Development of a calculation method for analyzing the kinetic curves. Extension to the study of composed kinetics

    Jorda, Michel.

    1976-01-01

    The dissolution of a solid in an aqueous phase is studied, the solid consisting of dispersed particles. A continuous colorimetric analysis method is developed to study the dissolution process and a two-parameter optimization method is established to investigate the kinetic curves obtained. This method is based on the differential equation dx/dt=K(1-x)sup(n). (n being the decrease in the dissolution velocity when the dissolved part increases and K a velocity parameter). The dissolution of SO 4 Cu and MnO 4 K in water and UO 3 in SO 4 H 2 is discussed. It is shown that the dissolution velocity of UO 3 is proportional to the concentration of the H + ions in the solution as far as this one is not higher than 0.25N. The study of the temperature dependence of the UO 3 dissolution reaction shows that a transition phase takes place from 25 to 65 0 C between a phase in which the dissolution is controlled by the diffusion of the H + ions and the chemical reaction at the interface and a phase in which the kinetics is only controlled by the diffusion [fr

  6. Kinetics of hydrogen release from dissolutions of ammonia borane in different ionic liquids

    Valero-Pedraza, María José; Martín-Cortés, Alexandra; Navarrete, Alexander; Bermejo, María Dolores; Martín, Ángel

    2015-01-01

    Ammonia borane is a promising hydrogen storage material that liberates hydrogen by thermolysis at moderate temperatures, but it also presents major limitations for practical applications including a long induction time before the initiation of hydrogen release and a difficult regeneration. Previous works have demonstrated that by dissolution of ammonia borane into several ionic liquids, and particularly in 1-butyl-3-methylimidazolium chloride bmimCl, the induction period at the beginning of the thermolysis is eliminated, but some problems persist, including foaming and the formation of a residue after thermolysis that is insoluble in the ionic liquid. In this work, the release of hydrogen from ammonia borane dissolved in different ionic liquids has been analyzed, measuring the kinetics of hydrogen release, visually following the evolution of the sample during the process using pressure glass tube reactors, and analyzing the residue by spectroscopic techniques. While dissolutions of ammonia borane in most ionic liquids analyzed show similar properties as dissolutions in bmimCl, using ionic liquids with bis(trifluoromethylsulfanyl)imide Tf_2N anion the foaming problem is reduced, and in some cases the residue remains dissolved in the ionic liquid, while with ionic liquids with choline anion higher hydrogen yields are achieved that indicate that the decomposition of ammonia borane proceeds through a different path. - Highlights: • Hydrogen release from ammonia borane dissolved in 13 ionic liquids has been studied. • Induction time is shortened and hydrogen release rate is accelerated in all cases. • The best results are obtained using ionic liquids with Tf_2N anion. • Ch cation ionic liquids enable higher H_2 yield, but cyclotriborazane is produced.

  7. A kinetic model of the oxidative dissolution of brannerite, UTi2O6

    Thomas, B.S.; Zhang, Y.

    2003-01-01

    The aqueous dissolution of synthetic brannerite (UTi 2 O 6 ) in an open atmosphere has been investigated. Previous data in the literature have been combined with new experimental work, dealing with the release of uranium from brannerite as a function of solution pH and aqueous carbonate species, in oxygenated solutions. From these data we have developed a conceptual model for uranium release from brannerite consisting of two reaction steps: oxidation of surface uranium(IV) atoms, and subsequent detachment of U(VI) atoms into solution, which is catalysed by surface coordination with protons (acidic media) or carbonate species (alkaline media in equilibrium with the atmosphere). A kinetic rate law is derived for this simple reaction mechanism and fitted to experimental data. The resulting predictive equation for uranium release qualitatively describes the pH-dependent behaviour observed in experiment, and quantitatively gives an upper limit for uranium release from brannerite over a range of conditions and experiment types. (orig.)

  8. Kinetics and thermodynamics of the dissolution of Th1-xMxO2 solid solutions (M = U, Pu)

    Hubert, S.; Heisbourg, G.; Dacheux, N.; Moisy, Ph.; Purans, J.

    2004-01-01

    Kinetics of the dissolution of Th 1-x M x O 2 (M = U, Pu) solid solutions was investigated as a function of several chemical parameters such as pH, substitution ratio, temperature, ionic strength, and electrolyte. Several compositions of Th 1-x U x O 2 and Th 1-x Pu x O 2 were synthesized and characterized before and after leaching by using several methods such as XRD, EXAFS, BET, PIXE, SEM, and XPS. Leaching tests were performed in nitric, hydrochloric or sulfuric media and groundwater. The normalized dissolution rates were evaluated for Th 1-x U x O 2 , and Th 0.88 Pu 0.12 O 2 leading to the determination of the partial order related to the proton concentration, n, and to the corresponding normalized dissolution rate constant at pH = 0, k'T. While for Th enriched solids, the solid solutions Th 1-x U x O 2 have the same dissolution behaviour than ThO 2 with a partial order n ∼ 0.3, in the case of uranium enriched solids, Th 1-x U x O 2 has the same dissolution behaviour than UO 2 with a partial order of n = 1, indicating that uranium oxidation rate becomes the limiting step of the dissolution process. The stoichiometry of the release of both actinides (U or Pu, Th) was verified until the precipitation of thorium occurred in the leachate for pH > 2, while uranium was released in the solution as an uranyl form. For uranium enriched solid solutions, thermodynamic equilibrium was reached after 100 days, and solubility constant of secondary phase was determined. In the case of Th 1-x Pu x O 2 , the dissolution behaviour is similar to that of ThO 2 , but only kinetic aspect of the dissolution can be studied. From the analysis of XPS and EXAFS data on leached and un-leached Th 1-x U x O 2 samples, the dissolution mechanism of solid solutions was explained and will be discussed. The role of the electrolytes on the dissolution of the solid solutions is discussed. Kinetics parameters of dissolution are also given in groundwater and in neutral media

  9. Dissolution kinetics of magnesium hydroxide for CO{sub 2} separation from coal-fired power plants

    Bharadwaj, Hari Krishna [Chemical Engineering Program, School of Energy, Environmental, Biological, and Medical Engineering, University of Cincinnati, Cincinnati, OH 45221-0012 (United States); Lee, Joo-Youp, E-mail: joo.lee@uc.edu [Chemical Engineering Program, School of Energy, Environmental, Biological, and Medical Engineering, University of Cincinnati, Cincinnati, OH 45221-0012 (United States); Li, Xin; Liu, Zhouyang [Chemical Engineering Program, School of Energy, Environmental, Biological, and Medical Engineering, University of Cincinnati, Cincinnati, OH 45221-0012 (United States); Keener, Tim C. [Environmental Engineering Program, School of Energy, Environmental, Biological, and Medical Engineering, University of Cincinnati, Cincinnati, OH 45221-0012 (United States)

    2013-04-15

    Highlights: ► Magnesium hydroxide dissolution was found to be controlled by chemical reaction. ► The intrinsic kinetics has a fractional order between 0.20 and 0.31. ► The true activation energy value was found to have 76 ± 11 kJ/gmol. ► A shrinking-core model predicted experimental data with good accuracy. -- Abstract: The dissolution of magnesium hydroxide in water for the release of magnesium and hydroxyl ions into the solution to maintain suitable alkalinity is a crucial step in the Mg(OH){sub 2}-based CO{sub 2} absorption process. In this study, the rate of dissolution of Mg(OH){sub 2} was investigated under different operating conditions using a pH stat apparatus. The dissolution process was modeled using a shrinking core model and the overall Mg(OH){sub 2} dissolution process was found to be controlled by the surface chemical reaction of Mg(OH){sub 2} with H{sup +} ions. Under the chemical reaction control regime, the dissolution of Mg(OH){sub 2} in alkaline conditions was found not to follow a first-order reaction, and the fractional order of reaction was estimated to lie between 0.20 and 0.31. This suggests that the dissolution reaction is a non-elementary reaction, consisting of a sequence of elementary reactions, via most likely forming a surface magnesium complex. The true activation energy value of 76 ± 11 kJ/gmol was found to be almost twice as much as the observed activation energy value of 42 ± 6 kJ/gmol determined at pH 8.6, and was comparable with the previously reported values. The particle sizes predicted from the intrinsic kinetics determined from the model were in good agreement with the experimentally measured particle sizes during the dissolution process.

  10. Dissolution of crystalline ceramics

    White, W.B.

    1982-01-01

    The present program objectives are to lay out the fundamentals of crystalline waste form dissolution. Nuclear waste ceramics are polycrystalline. An assumption of the work is that to the first order, the release rate of a particular radionuclide is the surface-weighted sum of the release rates of the radionuclide from each crystalline form that contains it. In the second order, of course, there will be synergistic effects. There will be also grain boundary and other microstructural influences. As a first approximation, we have selected crystalline phases one at a time. The sequence of investigations and measurements is: (i) Identification of the actual chemical reactions of dissolution including identification of the solid reaction products if such occur. (ii) The rates of these reactions are then determined empirically to give what may be called macroscopic kinetics. (iii) Determination of the rate-controlling mechanisms. (iv) If the rate is controlled by surface reactions, the final step would be to determine the atomic kinetics, that is the specific atomic reactions that occur at the dissolving interface. Our concern with the crystalline forms are in two areas: The crystalline components of the reference ceramic waste form and related ceramics and the alumino-silicate phases that appear in some experimental waste forms and as waste-rock interaction products. Specific compounds are: (1) Reference Ceramic Phases (zirconolite, magnetoplumbite, spinel, Tc-bearing spinel and perovskite); (2) Aluminosilicate phases (nepheline, pollucite, CsAlSi 5 O 12 , Sr-feldspar). 5 figures, 1 table

  11. A kinetic study of plutonium dioxide dissolution in hydrochloric acid using iron (II) as an electron transfer catalyst

    Fife, K.W.

    1996-09-01

    Effective dissolution of plutonium dioxide has traditionally been accomplished by contact with strong nitric acid containing a small amount of fluoride at temperatures of ∼ 100 C. In spite of these aggressive conditions, PuO 2 dissolution is sometimes incomplete requiring additional contact with the solvent. This work focused on an alternative to conventional dissolution in nitric acid where an electron transfer catalyst, Fe(II), was used in hydrochloric acid. Cyclic voltammetry was employed as an in-situ analytical technique for monitoring the dissolution reaction rate. The plutonium oxide selected for this study was decomposed plutonium oxalate with > 95% of the material having a particle diameter (< 70 microm) as determined by a scanning laser microscopy technique. Attempts to dry sieve the oxide into narrow size fractions prior to dissolution in the HCl-Fe(II) solvent system failed, apparently due to significant interparticle attractive forces. Although sieve splits were obtained, subsequent scanning laser microscopy analysis of the sieve fractions indicated that particle segregation was not accomplished and the individual sieve fractions retained a particle size distribution very similar to the original powder assemblage. This phenomena was confirmed through subsequent dissolution experiments on the various screen fractions which illustrated no difference in kinetic behavior between the original oxide assemblage and the sieve fractions

  12. Non-equilibrium Thermodynamic Dissolution Theory for Multi-Component Solid/Liquid Surfaces Involving Surface Adsorption and Radiolysis Kinetics

    Stout, R B

    2001-01-01

    A theoretical expression is developed for the dissolution rate response for multi-component radioactive materials that have surface adsorption kinetics and radiolysis kinetics when wetted by a multi-component aqueous solution. An application for this type of dissolution response is the performance evaluation of multi-component spent nuclear fuels (SNFs) for long term interim storage and for geological disposition. Typically, SNF compositions depend on initial composition, uranium oxide and metal alloys being most common, and on reactor burnup which results in a wide range of fission product and actinide concentrations that decay by alpha, beta, and gamma radiation. These compositional/burnup ranges of SNFs, whether placed in interim storage or emplaced in a geologic repository, will potentially be wetted by multi-component aqueous solutions, and these solutions may be further altered by radiolytic aqueous species due to three radiation fields. The solid states of the SNFs are not thermodynamically stable when wetted and will dissolve, with or without radiolysis. The following development of a dissolution theory is based on a non-equilibrium thermodynamic analysis of energy reactions and energy transport across a solid-liquid phase change discontinuity that propagates at a quasi-steady, dissolution velocity. The integral form of the energy balance equation is used for this spatial surface discontinuity analysis. The integral formulation contains internal energy functional of classical thermodynamics for both the SNFs' solid state and surface adsorption species, and the adjacent liquid state, which includes radiolytic chemical species. The steady-state concentrations of radiolytic chemical species are expressed by an approximate analysis of the decay radiation transport equation. For purposes of illustration a modified Temkin adsorption isotherm was assumed for the surface adsorption kinetics on an arbitrary, finite area of the solid-liquid dissolution interface. For

  13. Studies on the kinetics of UO2 dissolution in carbonate-bicarbonate medium using sodium hypochlorite as oxidant

    Sharma, J.N.; Bhattacharya, K.; Swami, R.G.; Tangri, S.K.; Mukherjee, T.K.

    1996-01-01

    The dissolution of UO 2 in carbonate-bicarbonate solutions containing sodium hypochlorite as an oxidant has been investigated. The effect of temperature, sodium hypochlorite concentration and stirring speed was examined. In the temperature range of 303 to 318 K, the leaching reaction displayed linear kinetics. Apparent activation energy obtained from the differential approach was found to be 57 kJ mol -1 . This relatively high activation energy value indicates a chemically controlled behavior of UO 2 dissolution. The order of reaction with respect to sodium hypochlorite concentration was found to be unity. (author). 18 refs., 6 figs

  14. Study of the kinetics and mechanism of the dissolution of PUO2 by Cr(II) ion in acidic medium

    Machuron-Mandard, X.

    1991-11-01

    The study of the dissolution of actinides oxides is a topic of particular importance in nuclear energy production. The present study deals with the understanding of the reductive dissolution of PuO 2 in sulfuric acid media under the action of Cr 2+ aq ion. In the first chapter of the document, crystallographic and electronic properties of PuO 2 are described, followed by informations related to its dissolution in acidic media. The second chapter concerns the presentation of the different theories usable to interpret the kinetics of heterogeneous reaction and those for the understanding of electronic transfer applied to semi-conductors. With the help of the above mathematical tools an empirical law rate is established and a reactional model proposed. It appears that the electronic transfer is purely of the heterogenous nature and that the limiting step of the overall process corresponds certainly to the rupture of plutonium oxygen bond [fr

  15. A Compilation of Rate Parameters of Water-Mineral Interaction Kinetics for Application to Geochemical Modeling

    2004-03-01

    Eggleston C. M. (2002) Dissolution kinetics of magnesite in acidic solutions: A hydrothermal atomic force microscopy study assessing step kinetics and...glass dissolution: I. An experimental study of the dissolution rates of basaltic glass as a function of aqueous Al, Si and oxalic acid concentration at...Stillings L. L., Drever J. I., Brantley S. L., Sun Y., and Oxburgh R. (1996) Rates of feldspar dissolution at pH 3-7 with 0-8mM oxalic acid . Chem

  16. The dissolution kinetics of major elements in municipal solid waste incineration bottom ash particles

    Bendz, David; Tüchsen, Peter L.; Christensen, Thomas H.

    2007-12-01

    Leaching and tracer experiments in batches at L/S 20 were performed with 3-month-old MSWI bottom ash separated into eight different particle sizes. The time-dependent leaching of major elements (Ca 2+, K +, Na +, Cl - and SO 4- 2 ) was monitored for up to 747 h. Physical properties of the particles, the specific surface (BET), pore volume and pore volume distribution over pore sizes (BJH) were determined for all particle classes by N 2 adsorption/desorption experiments. Some common features of physical pore structure for all particles were revealed. The specific surface and the particle pore volume were found to be negatively correlated with particle size, ranging from 3.2 m 2/g to 25.7 m 2/g for the surface area and from 0.0086 cm 3/g to 0.091 cm 3/g for the pore volume. Not surprisingly, the specific surface area was found to be the major material parameter that governed the leaching behavior for all elements (Ca 2+, K +, Na +, Cl - and SO 4- 2 ) and particle sizes. The diffusion resistance was determined independently by separate tracer (tritium) experiments. Diffusion gave a significant contribution to the apparent leaching kinetics for all elements during the first 10-40 h (depending on the particle size) of leaching and surface reaction was the overall rate controlling mechanism at late times for all particle sizes. For Ca 2+ and SO 4- 2 , the coupled effect of diffusion resistance and the degree of undersaturation in the intra particle pore volume was found to be a major rate limiting dissolution mechanism for both early and late times. The solubility control in the intra particulate porosity may undermine any attempt to treat bottom ash by washing out the sulfate. Even for high liquid/solid ratios, the solubility in the intra-particular porosity will limit the release rate.

  17. Kinetics of ikaite precipitation and dissolution in seawater-derived brines at sub-zero temperatures to 265 K

    Papadimitriou, Stathys; Kennedy, Hilary; Kennedy, Paul; Thomas, David N.

    2014-09-01

    The kinetics of calcium carbonate hexahydrate (ikaite) precipitation and dissolution were investigated in seawater and seawater-derived brines at sub-zero temperatures using the constant addition experimental technique. The steady state rate of these two processes was found to be a function of the deviation of the solution from equilibrium with respect to ikaite and conformed to the same empirical rate law as the anhydrous CaCO3 polymorphs, calcite and aragonite. In addition to the saturation state of the brine with respect to ikaite, the salinity of the brine and the temperature of the reaction evidently exerted some control on the ikaite precipitation kinetics, while the dissolution kinetics of the polymorph were not noticeably influenced by these two parameters. The experimental salinity and temperature conditions were equivalent to those at thermal equilibrium between brine and ice in the sea ice cover of polar seas. Simple modelling of the CO2 system by extrapolation of the oceanic equivalent to sea ice brines showed that the physical concentration of seawater ions and the changes in ikaite solubility as a function of salinity and temperature, both inherent in the sea ice system, would be insufficient to drive the emergent brines to ikaite supersaturation and precipitation in sea ice down to -8 °C. The loss of dissolved inorganic carbon to the gas phase of sea ice and to sympagic autotrophs are two independent mechanisms which, in nature, could prompt the brine CO2 system towards ikaite supersaturation and precipitation. Under these conditions, the steady state precipitation rate of ikaite was found to be fast enough for rapid formation within short time scales (days to weeks) in sea ice. The observed ikaite dissolution kinetics were also found conducive to short turn-over time scales of a few hours to a few days in corrosive solutions, such as surface seawater.

  18. Long-term kinetic effects and colloid formations in dissolution of LWR spent fuels

    Ahn, T.M.

    1996-11-01

    This report evaluates continuous dissolution and colloid formation during spent-fuel performance under repository conditions in high-level waste disposal. Various observations suggest that reprecipitated layers formed on spent-fuel surfaces may not be protective. This situation may lead to continuous dissolution of highly soluble radionuclides such as C-14, Cl-36, Tc-99, I-129, and Cs-135. However, the diffusion limits of various species involved may retard dissolution significantly. For low-solubility actinides such as Pu-(239+240) or Am-(241+243), various processes regarding colloid formation have been analyzed. The processes analyzed are condensation, dispersion, and sorption. Colloid formation may lead to significant releases of low-solubility actinides. However, because there are only limited data available on matrix dissolution, colloid formation, and solubility limits, many uncertainties still exist. These uncertainties must be addressed before the significance of radionuclide releases can be determined. 118 refs

  19. Long-term kinetic effects and colloid formations in dissolution of LWR spent fuels

    Ahn, T.M.

    1996-11-01

    This report evaluates continuous dissolution and colloid formation during spent-fuel performance under repository conditions in high-level waste disposal. Various observations suggest that reprecipitated layers formed on spent-fuel surfaces may not be protective. This situation may lead to continuous dissolution of highly soluble radionuclides such as C-14, Cl-36, Tc-99, I-129, and Cs-135. However, the diffusion limits of various species involved may retard dissolution significantly. For low-solubility actinides such as Pu-(239+240) or Am-(241+243), various processes regarding colloid formation have been analyzed. The processes analyzed are condensation, dispersion, and sorption. Colloid formation may lead to significant releases of low-solubility actinides. However, because there are only limited data available on matrix dissolution, colloid formation, and solubility limits, many uncertainties still exist. These uncertainties must be addressed before the significance of radionuclide releases can be determined. 118 refs.

  20. SON68 nuclear glass dissolution kinetics: Current state of knowledge and basis of the new GRAAL model

    Frugier, P. [CEA Marcoule, DTCD/SECM/LCLT, BP 17171, 30207 Bagnols-sur-Ceze cedex (France)], E-mail: pierre.frugier@cea.fr; Gin, S.; Minet, Y.; Chave, T. [CEA Marcoule, DTCD/SECM/LCLT, BP 17171, 30207 Bagnols-sur-Ceze cedex (France); Bonin, B. [CEA Saclay, DEN/DIR/DS, 91191 Gif-sur-Yvette cedex (France); Godon, N.; Lartigue, J.-E.; Jollivet, P. [CEA Marcoule, DTCD/SECM/LCLT, BP 17171, 30207 Bagnols-sur-Ceze cedex (France); Ayral, A. [IEM/CNRS-ENSCM Universite Montpellier 2, CC 047, Place Eugene Bataillon, 34095 Montpellier cedex 5 (France); De Windt, L. [ENSMP, CG, 35 rue St Honore, 77305 Fontainebleau cedex (France); Santarini, G. [CEA Saclay HC/CAB, 91191 Gif-sur-Yvette cedex (France)

    2008-10-15

    This article summarizes the present state of knowledge concerning aqueous alteration of R7T7-type nuclear containment glasses, represented mainly by the inactive reference glass designated SON68. Based on this review, we propose to describe the glass alteration kinetics up to and including the final residual rate regime by means of a new mechanistic model known as GRAAL (glassreactivitywithallowanceforthealterationlayer). Phenomenological analysis findings are reviewed for the various glass alteration regimes: interdiffusion, initial rate, rate drop, residual rate and, under very particular circumstances, resumption of alteration. These alteration regimes are associated with predominant mechanisms. Published work interpreting and modeling these mechanisms was examined in detail. There is a broad consensus on the general mechanisms of the initial rate and even the interdiffusion regime, whereas the mechanisms controlling the rate drop remain a subject of dispute not only with regard to nuclear glasses but also for the dissolution of silicate minerals. The reaction affinity responsible for the rate drop is expressed differently by different authors and depending on the underlying theories. The disagreement concerns the nature of the phase (glass or gel) or the activated complex controlling the rate drop, which in turn determines the elements that must be taken into account in the overall affinity term. Progress in recent years, especially in identifying the mechanisms responsible for the residual rate, has shed new light on these issues, allowing us to propose new theoretical foundations for modeling the different kinetic regimes of SON68 nuclear glass dissolution. The GRAAL model considers that water diffusion in the passivating reaction zone (the gel formed under saturation conditions) is a rate-limiting step in the overall glass dissolution kinetics. Moreover, this passivation zone is a soluble phase whose stability is directly dependent on the nature of the

  1. DEVELOPMENT OF A KINETIC MODEL OF BOEHMITE DISSOLUTION IN CAUSTIC SOLUTIONS APPLIED TO OPTIMIZE HANFORD WASTE PROCESSING

    Disselkamp, R.S.

    2011-01-01

    Boehmite (e.g., aluminum oxyhydroxide) is a major non-radioactive component in Hanford and Savannah River nuclear tank waste sludge. Boehmite dissolution from sludge using caustic at elevated temperatures is being planned at Hanford to minimize the mass of material disposed of as high-level waste (HLW) during operation of the Waste Treatment Plant (WTP). To more thoroughly understand the chemistry of this dissolution process, we have developed an empirical kinetic model for aluminate production due to boehmite dissolution. Application of this model to Hanford tank wastes would allow predictability and optimization of the caustic leaching of aluminum solids, potentially yielding significant improvements to overall processing time, disposal cost, and schedule. This report presents an empirical kinetic model that can be used to estimate the aluminate production from the leaching of boehmite in Hanford waste as a function of the following parameters: (1) hydroxide concentration; (2) temperature; (3) specific surface area of boehmite; (4) initial soluble aluminate plus gibbsite present in waste; (5) concentration of boehmite in the waste; and (6) (pre-fit) Arrhenius kinetic parameters. The model was fit to laboratory, non-radioactive (e.g. 'simulant boehmite') leaching results, providing best-fit values of the Arrhenius A-factor, A, and apparent activation energy, E A , of A = 5.0 x 10 12 hour -1 and E A = 90 kJ/mole. These parameters were then used to predict boehmite leaching behavior observed in previously reported actual waste leaching studies. Acceptable aluminate versus leaching time profiles were predicted for waste leaching data from both Hanford and Savannah River site studies.

  2. The effect of antimony presence in anodic copper on kinetics and mechanism of anodic dissolution and cathodic deposition of copper

    Stanković Z.D.

    2008-01-01

    Full Text Available The influence of the presence of Sb atoms, as foreign metal atoms in anode copper, on kinetics, and, on the mechanism of anodic dissolution and cathodic deposition of copper in acidic sulfate solution has been investigated. The galvanostatic single-pulse method has been used. Results indicate that presence of Sb atoms in anode copper increase the exchange current density as determined from the Tafel analysis of the electrode reaction. It is attributed to the increase of the crystal lattice parameter determined from XRD analysis of the electrode material.

  3. Dissolution kinetics of heulandite at pH 2--12 and 25 degrees C

    Ragnarsdottir, K.V.

    1993-01-01

    Because of their favourable cation exchange reactions, heulandite and clinoptilolite have been suggested as being capable of immobilizing radionuclides and therefore could possibly act as an important barrier for nuclear waste. Recent studies of laboratory-reacted minerals indicate, however, that hydrated surface layers tend to accumulate highly hydrolyzable heavy elements. These hydrated layers may therefore be the most important retardants for radionuclides. The dissolution rate of heulandite depends strongly on pH. Based on silica release, the logarithm of the steady-state dissolution rate at pH 2 is -13.1 mol cm -2 s -1 . The logarithm of the rate decreases to -15.8 mol cm -2 s -1 at pH 7.2 and increases again to -14.6 mol cm -2 s -1 at pH 12.2. At low pH, Al is released preferentially to silica; but at intermediate and high pH, the release of silica appears to be congruent relative to Al. The change in dissolution rate with pH indicates that at low pH, the dissolution mechanism is controlled by the detachment of a positively charged Al species, >Al-OH 2 + . Below pH 5, however, a silica-rich surface layer is formed requiring diffusion through the layer. At intermediate and high pH, it is likely that the dissolution rate is controlled by the detachment of a negatively charged silica species, >Si - O - . The reaction order of the hydrogen ion under low pH conditions is 0.7, and the reaction order of the OH - ion is 0.3 at high pH. The measured dissolution rates indicate that a 1 mm heulandite crystal would dissolve in 300,000 yrs if the solution composition is maintained undersaturated. 75 refs., 11 figs., 3 tabs

  4. Dissolution kinetics of smectite in geological repository system of TRU waste

    Sato, Tsutomu

    2005-02-01

    Extensive use of cement for encapsulation, mine timbering, and grouting purposes is envisaged in geological repositories of TRU waste. Degradation of cement materials in the repositories can produce a high pH pore fluid initially ranging from pH 13.0 to 13.5. The high pH pore fluids can migrate and react chemically with the host rock and bentonites which were employed to enhance repository's integrity. These chemical reactions can effect the capacity of the rocks and bentonites in retarding the migration of radionuclides. Smectite, main component of bentonite, can lose some of their desirable properties at the early stages of bentonite-cement fluid interaction. This has been a key research issue in performance assessment of TRU waste disposal. In this study, firstly, the factors affected on dissolution rate of smectite and equations describing dissolution rate were reviewed. Secondly, the effect of dissolved silica on the dissolution behavior of Na-montmorillonite was investigated. Bulk sample flow-through dissolution experiments at alkaline condition (pH 13.3) with different dissolved silica concentrations at different temperatures were performed. Titration experiments were also carried out at similar conditions. Atomic Force Microscopy (AFM) ex situ observations (i.e. on samples from flow-through experiments) was also performed to obtain the dissolution rate. Current results from bulk sample surface titration experiments indicate that dissolved silica has no pronounced effect on the surface titration behavior of Na-montmorillonite at any temperature. However, the trends for the surface titration behavior represent the averaged behavior of all particle sizes (i.e. including colloids) such that within an order of magnitude change cannot be quantified appreciably. Bulk flow-through dissolution experiments coupled with ex situ AFM observations indicate that there is also no effect of dissolved silica with comparatively low concentration of the reacting solution on

  5. Long-term flow/chemistry feedback in a porous medium with heterogenous permeability: Kinetic control of dissolution and precipitation

    Bolton, E.W.; Lasaga, A.C.; Rye, D.M.

    1999-01-01

    The kinetics of dissolution and precipitation is of central importance to understanding the long-term evolution of fluid flows in crustal environments, with implications for problems as diverse as nuclear waste disposal and crustal evolution. The authors examine the dynamics of such evolution for several geologically relevant permeability distributions (models for en-echelon cracks, an isolated sloping fractured zone, and two sloping high-permeability zones that are close enough together to interact). Although the focus is on a simple quartz matrix system, generic features emerge from this study that can aid in the broader goal of understanding the long-term feedback between flow and chemistry, where dissolution and precipitation is under kinetic control. Examples of thermal convection in a porous medium with spatially variable permeability reveal features of central importance to water-rock interaction. After a transient phase, an accelerated rate of change of porosity may be used with care to decrease computational time, as an alternative to the quasi-stationary state approximation (Lichtner, 1988). Kinetic effects produce features not expected by traditional assumptions made on the basis of equilibrium, for example, that cooling fluids are oversaturated and heating fluids are undersaturated with respect to silicic acid equilibrium. Indeed, the authors observe regions of downwelling oversaturated fluid experiencing heating and regions of upwelling, yet cooling, undersaturated fluid. When oscillatory convection is present, the amplitudes of oscillation generally increase with time in near-surface environments, whereas amplitudes tend to decrease over long times near the heated lower boundary. The authors examine the scaling behavior of characteristic length scales, of terms in the solute equation, and of the typical deviation from equilibrium, each as a function of the kinetic rate parameters

  6. Reductive reactivity of iron(III) oxides in the east china sea sediments: characterization by selective extraction and kinetic dissolution.

    Chen, Liang-Jin; Zhu, Mao-Xu; Yang, Gui-Peng; Huang, Xiang-Li

    2013-01-01

    Reactive Fe(III) oxides in gravity-core sediments collected from the East China Sea inner shelf were quantified by using three selective extractions (acidic hydroxylamine, acidic oxalate, bicarbonate-citrate buffered sodium dithionite). Also the reactivity of Fe(III) oxides in the sediments was characterized by kinetic dissolution using ascorbic acid as reductant at pH 3.0 and 7.5 in combination with the reactive continuum model. Three parameters derived from the kinetic method: m 0 (theoretical initial amount of ascorbate-reducible Fe(III) oxides), k' (rate constant) and γ (heterogeneity of reactivity), enable a quantitative characterization of Fe(III) oxide reactivity in a standardized way. Amorphous Fe(III) oxides quantified by acidic hydroxylamine extraction were quickly consumed in the uppermost layer during early diagenesis but were not depleted over the upper 100 cm depth. The total amounts of amorphous and poorly crystalline Fe(III) oxides are highly available for efficient buffering of dissolved sulfide. As indicated by the m 0, k' and γ, the surface sediments always have the maximum content, reactivity and heterogeneity of reactive Fe(III) oxides, while the three parameters simultaneously downcore decrease, much more quickly in the upper layer than at depth. Albeit being within a small range (within one order of magnitude) of the initial rates among sediments at different depths, incongruent dissolution could result in huge discrepancies of the later dissolution rates due to differentiating heterogeneity, which cannot be revealed by selective extraction. A strong linear correlation of the m 0 at pH 3.0 with the dithionite-extractable Fe(III) suggests that the m 0 may represent Fe(III) oxide assemblages spanning amorphous and crystalline Fe(III) oxides. Maximum microbially available Fe(III) predicted by the m 0 at pH 7.5 may include both amorphous and a fraction of other less reactive Fe(III) phases.

  7. Characterisation and dissolution of depleted uranium aerosols produced during impacts of kinetic energy penetrators against a tank

    Chazel, V.; Gerasimo, P.; Debouis, V.; Laroche, P.; Paquet, F

    2003-07-01

    Aerosols produced during impacts of depleted uranium (DU) penetrators against the glacis (sloping armour) and the turret of a tank were sampled. The concentration and size distribution were determined. Activity median aerodynamic diameters were 1 {mu}m (geometric standard deviation, s{sub g} = 3.7) and 2 {mu}m (s{sub g} = 2.5), respectively, for glacis and turret. The mean air concentration was 120 Bq m{sup -3}, i.e. 8.5 mg m{sup -3} of DU. Filters analysed by scanning electron microscopy (SEM) and X ray diffraction showed two types of particles (fine particles and large molten particles) composed mainly of a mixture of uranium and aluminium. The uranium oxides were mostly U{sub 3}O{sub 8}, UO{sub 2.25} and probably UO{sub 3.01} and a mixed compound of U and Al. The kinetics of dissolution in three media (HCO{sub 3}{sup -}, HCl and Gamble's solution) were determined using in-vitro tests. The slow dissolution rates were respectively slow, and intermediate between slow and moderate, and the rapid dissolution fractions were mostly intermediate between moderate and fast. According to the in-vitro results for Gamble's solution, and based on a hypothetical single acute inhalation of 90 Bq, effective doses integrated up to 1 y after incorporation were 0.54 and 0.56 mSv respectively, for aerosols from glacis and turret. In comparison, the ICRP limits are 20 mSv y{sup -1} for workers and 1 mSv y{sup -1} for members of public. A kidney concentration of approximately 0.1 {mu}g U g{sup -1} was predicted and should not, in this case, lead to kidney damage. (author)

  8. Characterisation and dissolution of depleted uranium aerosols produced during impacts of kinetic energy penetrators against a tank

    Chazel, V.; Gerasimo, P.; Debouis, V.; Laroche, P.; Paquet, F.

    2003-01-01

    Aerosols produced during impacts of depleted uranium (DU) penetrators against the glacis (sloping armour) and the turret of a tank were sampled. The concentration and size distribution were determined. Activity median aerodynamic diameters were 1 μm (geometric standard deviation, s g = 3.7) and 2 μm (s g = 2.5), respectively, for glacis and turret. The mean air concentration was 120 Bq m -3 , i.e. 8.5 mg m -3 of DU. Filters analysed by scanning electron microscopy (SEM) and X ray diffraction showed two types of particles (fine particles and large molten particles) composed mainly of a mixture of uranium and aluminium. The uranium oxides were mostly U 3 O 8 , UO 2.25 and probably UO 3.01 and a mixed compound of U and Al. The kinetics of dissolution in three media (HCO 3 - , HCl and Gamble's solution) were determined using in-vitro tests. The slow dissolution rates were respectively slow, and intermediate between slow and moderate, and the rapid dissolution fractions were mostly intermediate between moderate and fast. According to the in-vitro results for Gamble's solution, and based on a hypothetical single acute inhalation of 90 Bq, effective doses integrated up to 1 y after incorporation were 0.54 and 0.56 mSv respectively, for aerosols from glacis and turret. In comparison, the ICRP limits are 20 mSv y -1 for workers and 1 mSv y -1 for members of public. A kidney concentration of approximately 0.1 μg U g -1 was predicted and should not, in this case, lead to kidney damage. (author)

  9. Characterisation and dissolution of depleted uranium aerosols produced during impacts of kinetic energy penetrators against a tank.

    Chazel, V; Gerasimo, P; Dabouis, V; Laroche, P; Paquet, F

    2003-01-01

    Aerosols produced during impacts of depleted uranium (DU) penetrators against the glacis (sloping armour) and the turret of a tank were sampled. The concentration and size distribution were determined. Activity median aerodynamic diameters were 1 microm (geometric standard deviation, sigma(g) = 3.7) and 2 microm (sigma(g) = 2.5), respectively, for glacis and turret. The mean air concentration was 120 Bq m(-3), i.e. 8.5 mg m(-3) of DU. Filters analysed by scanning electron microscopy (SEM) and X ray diffraction showed two types of particles (fine particles and large molten particles) composed mainly of a mixture of uranium and aluminium. The uranium oxides were mostly U3O8, UO2.25 and probably UO3.01 and a mixed compound of U and Al. The kinetics of dissolution in three media (HCO3-, HCl and Gamble's solution) were determined using in-vitro tests. The slow dissolution rates were respectively slow, and intermediate between slow and moderate, and the rapid dissolution fractions were mostly intermediate between moderate and fast. According to the in-vitro results for Gamble's solution, and based on a hypothetical single acute inhalation of 90 Bq, effective doses integrated up to 1 y after incorporation were 0.54 and 0.56 mSv, respectively, for aerosols from glacis and turret. In comparison, the ICRP limits are 20 mSv y(-1) for workers and 1 mSv y(-1) for members of the public. A kidney concentration of approximately 0.1 microg U g(-1) was predicted and should not, in this case, lead to kidney damage.

  10. A New Experimental Design to Study the Kinetics of Solid Dissolution into Liquids at Elevated Temperature

    Wang, Huijun; White, Jesse F.; Sichen, Du

    2018-04-01

    A new method was developed to study the dissolution of a solid cylinder in a liquid under forced convection at elevated temperature. In the new design, a rotating cylinder was placed concentrically in a crucible fabricated by boring four holes into a blank material for creating an internal volume with a quatrefoil profile. A strong flow in the radial direction in the liquid was created, which was evidently shown by computational fluid dynamic (CFD) calculations and experiments at both room temperature and elevated temperature. The new setup was able to freeze the sample as it was at experimental temperature, particularly the interface between the solid and the liquid. This freezing was necessary to obtain reliable information for understanding the reaction mechanism. This was exemplified by the study of dissolution of a refractory in liquid slag. The absence of flow in the radial direction in the traditional setup using a symmetrical cylinder was also discussed. The differences in the findings by past investigators using the symmetrical cylinder are most likely due to the extent of misalignment of the cylinder in the containment vessel.

  11. Mechanisms and kinetics laws of inactive R7T7 reference glass dissolution in water at 90 deg C: initial dissolution rate measurements

    Advocat, T.; Ghaleb, D.; Vernaz, E.

    1993-02-01

    The initial dissolution rate of inactive R7T7 reference glass was measured at 90 deg C in dilute aqueous solutions first at unspecified pH, then with imposed pH values. In distilled water, R7T7 glass corrosion initially involved preferential extraction of boron and network modifier elements (Li, Na, Ca) as long as the solution pH remained acid. When the solution pH became alkaline, glass dissolution was stoichiometric. These two mechanisms were confirmed by dissolution tests in aqueous solutions at imposed pH values under acid and alkaline conditions. The initial dissolution rate r 0 in mole.cm -3 .s -1 also increased significantly in alkaline media when the pH of the aqueous phase increased: in slightly acid media, selective glass dissolution formed a residual, de-alkalinized, hydrated glass that was characterized by transmission electron microscopy and secondary ion mass spectrometry. Under steady-state dissolution conditions, the initial glass corrosion rate (in mole.cm -3 .s -1 ) was: in acid and alkaline media, amorphous and crystallized alteration products formed after complete dissolution of the silicated glass network. The first products formed consisted mainly of Zr, Rare Earths, Fe and Al. (author). 67 refs., 29 figs., 26 tabs., 21 plates

  12. Influence of a microwave radiation on dissolution kinetics of UO2, CeO2, and Co3O4 in nitric environment

    Joret, Laurent

    1995-01-01

    This research thesis addresses the issue of dissolution oxides present in spent nuclear fuels. As previous studies outlined important increases of oxide dissolution rate when submitted to microwaves, the issue is then to apply such a technique to PuO 2 which is the most difficult oxide to dissolve. As plutonium may be handled only in certified laboratories and under strict safety conditions, the author studied the influence of a microwave radiation on the dissolution kinetics of other and various metallic oxides in a nitric environment. The choice of this nitric environment is imposed by conditions met in the nuclear industry. Oxides are chosen according to two criteria: dissolution times ranging from few minutes to few days, various responses to electromagnetic radiation (different values for the real and imaginary parts of their dielectric permittivity). Three oxides are retained: UO 2 and CeO 2 (to model PuO 2 ) and Co 3 O 4 . After a recall of some theoretical aspects of the response of a dielectric material to an electromagnetic field, a comparison between conventional and microwave heating, the author presents the main results obtained by using microwaves in chemistry (organic synthesis, ceramic sintering, acid dissolution). He reports the experimental study of nitric dissolution of oxides by conventional heating, and the dielectric characterisation of the studied oxides. He presents the experimental microwave set-up, and reports and discusses experimental results obtained for the dissolution of UO 2 , CeO 2 and Co 3 O 4 in HNO 3 [fr

  13. Dissolution kinetics of Pd and Pt from automobile catalysts by naturally occurring complexing agents

    Šebek, O.; Mihaljevič, M.; Strnad, L.; Ettler, V.; Ježek, J.; Štědrý, R.; Drahota, P.; Ackerman, Lukáš; Adamec, V.

    2011-01-01

    Roč. 198, December (2011), s. 331-339 ISSN 0304-3894 Institutional research plan: CEZ:AV0Z30130516 Keywords : automobile catalyst * Platinum group elements * mobilisation * leaching * kinetic Subject RIV: DD - Geochemistry Impact factor: 4.173, year: 2011

  14. Development of a kinetic model for the dissolution of the UO2 spent nuclear fuel. Application of the model to the minor radionuclides

    Bruno, J.; Cera, E.; Duro, L.; Pon, J.; Pablo, J. de; Eriksen, Trygve

    1998-05-01

    A kinetic model has been developed in order to explain the evolution of the spent fuel matrix/groundwater system. Mass balance equations have been used to follow the evolution of the system with time. The model has been calibrated by using experimental dissolution data from spent fuel leaching tests from Studsvik and KTH and from synthetic unirradiated UO 2 dissolution tests from VTT. The results of the testing exercise indicate that the combination of mass balance equations together with the kinetic rate laws constitute a useful tool to model and explain experimental dissolution data available in the literature for UO 2 solid phases, including uraninites, unirradiated UO 2 and spent fuel. Although the key processes are well identified and understood, there are still some remaining uncertainties concerning some of the critical parameters of the model. This is particularly true for the density of UO 2 sites prone to oxidation and the rates and mechanisms of the hydrogen peroxide and the combined oxygen and bicarbonate promoted dissolution of UO 2 for oxidant concentration ranges relevant to the spent fuel disposal system. The mass balance kinetic model developed has been extended to minor radionuclides contained in the matrix, i.e. Pu, Tc and Sr. In the case of Pu, the model presented reproduces the behaviour of this critical radionuclide even at early contact times. As it would be expected, Tc seems to follow a different mechanism for its release with respect to the UO 2 matrix dissolution, which is probably linked to the rate of oxidation of Tc metallic inclusions in the fuel. A co- dissolution process of Sr with the UO 2 matrix reproduces the long term dissolution behaviour of this radionuclide, better than the initial Sr release rates

  15. Development of a kinetic model for the dissolution of the UO{sub 2} spent nuclear fuel. Application of the model to the minor radionuclides

    Bruno, J.; Cera, E.; Duro, L.; Pon, J. [QuantiSci SL, Barcelona (Spain); Pablo, J. de [UPC, Barcelona (Spain). Dept. Enginyeria Quimica; Eriksen, Trygve [Royal Inst. of Tech., Stockholm (Sweden). Dept. of Nuclear Chemistry

    1998-05-01

    A kinetic model has been developed in order to explain the evolution of the spent fuel matrix/groundwater system. Mass balance equations have been used to follow the evolution of the system with time. The model has been calibrated by using experimental dissolution data from spent fuel leaching tests from Studsvik and KTH and from synthetic unirradiated UO{sub 2} dissolution tests from VTT. The results of the testing exercise indicate that the combination of mass balance equations together with the kinetic rate laws constitute a useful tool to model and explain experimental dissolution data available in the literature for UO{sub 2} solid phases, including uraninites, unirradiated UO{sub 2} and spent fuel. Although the key processes are well identified and understood, there are still some remaining uncertainties concerning some of the critical parameters of the model. This is particularly true for the density of UO{sub 2} sites prone to oxidation and the rates and mechanisms of the hydrogen peroxide and the combined oxygen and bicarbonate promoted dissolution of UO{sub 2} for oxidant concentration ranges relevant to the spent fuel disposal system. The mass balance kinetic model developed has been extended to minor radionuclides contained in the matrix, i.e. Pu, Tc and Sr. In the case of Pu, the model presented reproduces the behaviour of this critical radionuclide even at early contact times. As it would be expected, Tc seems to follow a different mechanism for its release with respect to the UO{sub 2} matrix dissolution, which is probably linked to the rate of oxidation of Tc metallic inclusions in the fuel. A co- dissolution process of Sr with the UO{sub 2} matrix reproduces the long term dissolution behaviour of this radionuclide, better than the initial Sr release rates 49 refs, 22 figs, 2 tables

  16. Solubility and dissolution kinetics study of uranium phosphates and vanadates: implications for the front end of the electronuclear cycle

    Cretaz, F.

    2013-01-01

    In the current context of restart of the nuclear energy, the needs in uranium are expected to increase significantly. Moreover, in a perspective of sustainable development, the exploitation, the treatment and the purification of uranium ores need to be optimized. It is thus necessary to determine reliable thermodynamic data (and especially solubility constants) for the systems of interest, especially uranium(VI) phosphates and vanadates. In this aim, a multi parametric study of the dissolution of meta-torbernite Cu 0.8 (H 3 O) 0.2 (UO 2 ) 2 (PO 4 ) 2.8 H 2 O, meta-autunite Ca(UO 2 ) 2 (PO 4 ) 2.6 H 2 O, meta-ankoleite K 2 (UO 2 ) 2 (PO 4 ) 2.6 H 2 O and carnotite K 2 (UO 2 ) 2 (VO 4 ) 2.3 H 2 O was undertaken. First, analogues of these four minerals were synthesized, based only on dry chemistry process for carnotite or on wet chemistry methods for the phosphate phases. They were then extensively characterized (in terms of structure, microstructure and chemical composition). It particularly highlighted the similar structures of such compounds. The anionic groups (PO 4 3- or V 2 O 8 6- ) and uranyl form parallel layers between which counter cations (Cu 2+ , Ca 2+ or K + ) and water molecules are inserted. However, the counter cations present in the interlayer space of the three phosphate phases present different lability. The synthetic phases were also compared to their natural analogues, except for meta-ankoleite, which allowed us to point out significant differences in the composition (presence of impurities in natural samples) and the morphology (grain size). The dissolution of these phases was then studied from a kinetic and thermodynamic point of view, through leaching tests in static and dynamic conditions, in various acid media (sulfuric, nitric and hydrochloric) and at different temperatures. In these conditions, the dissolution of meta-autunite was found to be un-congruent due to the precipitation of uranyl phosphate then avoiding the determination of

  17. Kinetic Controls on the Desorption/Dissolution of Sorbed U(VI) and their Influence on Reactive Transport

    Zachara, John M.; Chongxuan Liu; Qafoku, Nikolla P.; McKinley, James P.; Catalano, Jeffrey G.; Brown, Gordon E. Jr.; Davis, James A.

    2006-01-01

    A number of published studies have sought to understand geochemical kinetic process of uranium (U) that are relevant to nuclear waste sites and repositories by studying the weathering of U ore bodies and downgradient transport of weathering products. Such studies have provided important insights on processes operative over many thousand to millions of years. This project also seeks knowledge on the geochemical kinetics of U, but for shorter in-ground time periods (e.g., 20-50 years) relevant to DOE legacy waste sites. Several representative field sites were selected for intense study at Hanford as part of EMSP research to provide: (1) fundamental insights on intermediate duration geochemical events of U controlling fate and transport, and (2) key scientific information needed for remedial action assessment and informed decision making. The site discussed in this poster is the 300 A uranium plume. This plume is located at the south end of Hanford and discharges directly to the Columbia River. The plume resulted from the discharge of fuels fabrication wastes (nitric acid solutions containing U and Cu) and cladding dissolution wastes (basic sodium aluminate) to the North and South Process Ponds between 1943 and 1975 near the Columbia River. A Kd-based remedial action assessment fifteen years ago predicted that the plume would dissipate to concentrations below the DWS within 10 y. As a result of this assessment, an interim, MNA remedial decision was agreed to by DOE and state/federal regulators. It has been 15 y since the above assessment, and groundwater concentrations have not decreased (attenuated) as projected. Stakeholders are now demanding remedial intervention, and DOE seeks science-based conceptual and numeric models for more accurate future projections. The objectives are: (1) Identify the chemical speciation (e.g., adsorption complexes precipitates), mineral residence, and physical location of contaminant U in a depth sequence of sediments from the disposal

  18. Kinetic Controls on the Desorption/Dissolution of Sorbed U(VI) and Their Influence on Reactive Transport

    J. M. Zachara; C. Liu; N. Qafoku; J. P. McKinley; J. A. Davis; D. Stoliker; Y. Arai; J. G. Catalano; G. E. Brown, Jr.

    2007-01-01

    A number of published studies have sought to understand geochemical kinetic process of uranium (U) that are relevant to nuclear waste sites and repositories by studying the weathering of U ore bodies and downgradient transport of weathering products. Such studies have provided important insights on processes operative over many thousand to millions of years. This project also seeks knowledge on the geochemical kinetics of U, but for shorter in-ground time periods (e.g., 20-50 years) relevant to DOE legacy waste sites. Several representative field sites were selected for intense study at Hanford as part of EMSP research to provide: (1) fundamental insights on intermediate duration geochemical events of U controlling fate and transport, and (2) key scientific information needed for remedial action assessment and informed decision making. The site discussed in this poster is the 300 A uranium plume. This plume is located at the south end of Hanford and discharges directly to the Columbia River. The plume resulted from the discharge of fuels fabrication wastes (nitric acid solutions containing U and Cu) and cladding dissolution wastes (basic sodium aluminate) to the North and South Process Ponds between 1943 and 1975 near the Columbia River. A Kd-based remedial action assessment fifteen years ago predicted that the plume would dissipate to concentrations below the DWS within 10 y. As a result of this assessment, an interim, MNA remedial decision was agreed to by DOE and state/federal regulators. It has been 15 y since the above assessment, and groundwater concentrations have not decreased (attenuated) as projected. Stakeholders are now demanding remedial intervention, and DOE seeks science-based conceptual and numeric models for more accurate future projections. The objectives are: (1) Identify the chemical speciation (e.g., adsorption complexes or precipitates), mineral residence, and physical location of contaminant U in a depth sequence of sediments from the

  19. The electrode kinetics of the evolution and dissolution of oxygen at the urania-zirconia interfaces

    Badwal, S.P.S.; Bevan, D.J.M.; Bockris, J.O'M.

    1980-01-01

    In order to assess the potential of urania-yttria fluorite-type solid solutions as electrodes for high-temperature electrolysis of steam, oxygen evolution and dissolution reactions have been studied at the (Usub(0.7)Ysub(0.3))Osub (2+x)/YSZ interface. A current-interruption technique was used to separate overpotential and resistive potential drop. In oxygen and air the overpotential-current curves obey the Tafel law, suggesting that a charge-transfer process is rate determining. Activation energies of 120 kJ mole -1 and 165 kJ mole -1 were obtained for the cathodic reaction in oxygen and air respectively. The capacitance obtained from galvanostatic transients varied with potential, temperature, and oxygen partial pressure. The average value of n, the number of electrons involved in the overall charge-transfer reaction, was determined to be 4.01 from reversible potential measurements. The overpotential losses are small for porous electrodes at high psub(O 2 ). A mechanism for the oxygen transfer reaction has been proposed and its limitations discussed. (author)

  20. Kinetics of dissolution of a biocide soda-lime glass powder containing silver nanoparticles

    Esteban-Tejeda, L.; Silva, A. C. da; Mello-Castanho, S. R.; Pacharroman, C.; Moya, J. S.

    2013-01-01

    In the present study we have studied the lixiviation kinetics of silver nanoparticles, as well as the solubility of a particulate system ( 2 lixiviation followed a Jander model (α 2 /4 ≈ Kt). It has been proven that nanostructured soda-lime glass/nAg composed by particles <30 μm with a 20 wt% of silver are a strong biocide versus Gram-positive, Gram-negative bacteria and yeasts. This soda-lime glass/nAg acts as a perfect dispenser of silver nanoparticles to the liquid media, avoiding the fast increasing of its concentration over the toxicity limit for human cells and for the environment.

  1. Colloid-facilitated effects on migration of radionuclides in fractured rock with a kinetic solubility-limited dissolution model

    Jen Chunping; Tien Nengchuan

    2010-01-01

    Nuclides can move with groundwater either as solutes or colloids, where the latter mechanism generally results in much shorter traveling time as the nuclides interact strongly with solid phases, such as actinides. In the performance assessment, it is therefore essential to assess the relative importance of these two transport mechanisms for different nuclides. The relative importance of colloids depends on the nature and concentration of the colloids in groundwater. Plutonium (Pu), neptunium (Np), uranium (U) and americium (Am) are four nuclides of concern for the long-term emplacement of nuclear wastes at potential repository sites. These four actinides have a high potential for migrating if attached to iron oxide, clay or silica colloids in the groundwater.Strong sorption of the actinides by colloids in the groundwater may facilitate the transport of these nuclides along potential flow paths. The solubility-limited dissolution model can be used to assess the safety of the release of nuclear waste in geological disposal sites. Usually, it has been assumed that the solubility of the waste form is constant. If a nuclide reaches its solubility limit at an inner location near the waste form, it is unlikely that the same nuclide will reach its solubility limit at an outer location unless this nuclide has a parent nuclide. It is unlikely that the daughter nuclides will exceed their solubility limit due to decay of their parent nuclide. The present study investigates the effect of colloids on the transport of solubility-limited nuclides under the kinetic solubility-limited dissolution (KSLD) boundary condition in fractured media. The release rate of the nuclides is proportional to the difference between the saturation concentration and the inlet aqueous concentration of the nuclides. The presence of colloids decreases the aqueous concentration of nuclides and, thus, increases the release flux of nuclides from the waste form. (authors)

  2. The Thermal Expansion Of Feldspars

    Hovis, G. L.; Medford, A.; Conlon, M.

    2009-12-01

    Hovis and others (1) investigated the thermal expansion of natural and synthetic AlSi3 feldspars and demonstrated that the coefficient of thermal expansion (α) decreases significantly, and linearly, with increasing room-temperature volume (VRT). In all such feldspars, therefore, chemical expansion limits thermal expansion. The scope of this work now has been broadened to include plagioclase and Ba-K feldspar crystalline solutions. X-ray powder diffraction data have been collected between room temperature and 925 °C on six plagioclase specimens ranging in composition from anorthite to oligoclase. When combined with thermal expansion data for albite (2,3,4) a steep linear trend of α as a function of VRT emerges, reflecting how small changes in composition dramatically affect expansion behavior. The thermal expansion data for five synthetic Ba-K feldspars ranging in composition from 20 to 100 mole percent celsian, combined with data for pure K-feldspar (3,4), show α-VRT relationships similar in nature to the plagioclase series, but with a slope and intercept different from the latter. Taken as a group all Al2Si2 feldspars, including anorthite and celsian from the present study along with Sr- (5) and Pb-feldspar (6) from other workers, show very limited thermal expansion that, unlike AlSi3 feldspars, has little dependence on the divalent-ion (or M-) site occupant. This apparently is due to the necessitated alternation of Al and Si in the tetrahedral sites of these minerals (7), which in turn locks the tetrahedral framework and makes the M-site occupant nearly irrelevant to expansion behavior. Indeed, in feldspar series with coupled chemical substitution it is the change away from a 1:1 Al:Si ratio that gives feldspars greater freedom to expand. Overall, the relationships among α, chemical composition, and room-temperature volume provide useful predictive tools for estimating feldspar thermal expansion and give insight into the controls of expansion behavior in

  3. Hydrothermal alteration of the glass R7T7. Glass dissolution kinetics at 150 and 2500, role of neo-formed phases

    Caurel, J.

    1990-01-01

    The glass R7T7 is chosen in France for vitrification of solution from reprocessing. Safety requires the knowledge of R7T7 long term behavior in deep geologic formations. Temperature dependence of leaching between 50 and 300 0 C is studied by static tests for 7 days. An activation energy of 30kJ/Mole is calculated between 50; 75 or 100 0 C and 250 0 C. Results suggest similar corrosion mechanisms between 90-100 and 250 0 C by a complete change between 250 and 275 0 C. Glass corrosion kinetics at 150 0 C and 250 0 C between 1 day and 1 year evidence the precipitation of aluminosilicates and formation of thick amorphous gels progressively enriched with silica. Glass dissolution at 150 0 C and 250 0 C is simulated with the geochemical DISSOL code. Results suggest that dissolution kinetics are controlled by activity of H 4 SiO 4 in solution only. Silica contained into the gel controls corrosion kinetics different from 0. Even if the nature of dissolution mechanisms does not seem modified between 150 and 250 0 C, sample cracking at 250 0 C induces an increase of dissolved glass that does not allow a direct comparison of corrosion kinetics between 150 and 250 0 C [fr

  4. Heterogeneous dissolution kinetics as a method of the granulometric analysis of polydispersed solids

    Melichar, F.; Pourova, D.; Simova, L.; Zvonickova, J.

    1976-05-01

    The principles of determining the granulometric composition of polydisperse solids from kinetic data on the solubilities thereof are given in the theoretical part of the report. The conditions are stated under which characteristic curves (equations) may be determined. These equations define the relationship between the dissolved polydisperse fraction and the relative decrease of the characteristic size of the polydisperse particles. The characteristic curves are specific for the given granulometric polydispersion state. The experimentally determined characteristic curves, which are expressed analytically by means of an equivalent function, are analyzed using three independent methods, which make it possible to determine the granulometric composition of the dissolved polydispersion: the method of the ''reversed geometrical model'', the Akselrud model method, the granulometric atlas method. The granulometric compositions determined by these methods are compared and discussed. The methods proposed may be considered as further applicable methods in the granulometric particle analysis within the size range of 1 to 700 μm defining predominantly the granulometric spectrum of the primary dispersion, i.e. the deagglomerated particles. (author)

  5. Synthesis, characterization, kinetic and thermodynamic studies of the dissolution of ThO2 and of solid solutions Th1-xMxO2 (M = U, Pu)

    Heisbourg, G.

    2003-12-01

    The aim of this work was to understand the mechanisms of dissolution of ThO 2 and of thorium mixed oxides such as Th 1-x U x O 2 and Th 1-x Pu x O 2 in aqueous, oxygenated or inert media. Several solids have been synthesized by precipitation in oxalic medium: Th 1-x U x O 2 (x= 0.11; 0.24; 0.37; 0.53; 0.67; 0.81 and 0.91) and Th 1-x Pu x O 2 (x= 0.13; 0.32 and 0.66). They have been characterized by XRD, SEM, TEM, XPS, XAS, PIXE and EPMA. The sintering conditions of these materials have been studied and optimized in order to obtain sintered samples with a measured density very near the theoretical densities. A kinetic study of the dissolution of ThO 2 and of solid solutions Th 1-x U x O 2 has been carried out in several aqueous media (HNO 3 , HCl, H 2 SO 4 ) in terms of several parameters: protons concentration, temperature, pH, ionic strength, nature of the electrolyte solution and uranium molar ratio for the solid solutions Th 1-x U x O 2 in order to determine the kinetic laws of dissolution of the solid solutions having different compositions comparatively to ThO 2 . The leaching tests carried out in natural waters of compositions near those of the deep geologic sites considered for the storage of nuclear wastes have shown that the dissolution of the solids was bound to the complexing effect of the constitutional ions of the water considered. The leaching tests carried out on sintered samples of the same composition have led to the same normalized dissolution velocities. The thermodynamic aspect of the dissolution of the solid solutions Th 1-x U x O 2 in nitric medium has been studied at last. (O.M.)

  6. What classic greywacke (litharenite) can reveal about feldspar diagenesis: An example from Permian Rotliegend sandstone in Hessen, Germany

    Molenaar, Nicolaas; Felder, Marita; Bär, Kristian; Götz, Annette E.

    2015-08-01

    Rotliegend siliciclastic sediments in southern Hessen (Germany) are a good example of dissolution of detrital feldspars, which is a common feature in many sandstones. Dissolution occurred after mechanical compaction of the lithic-rich sandstone, which experienced framework collapse with pores and pore connections filled and obstructed by deformed ductile lithic grains (pseudomatrix) thereby reducing pore space to microporosity., The advanced degree of compaction and reduced porosity caused low permeability and low hydraulic conductivity of the rock mass. This is further reduced by the presence of wackes and shales that occur intercalated with the sandstones. Feldspar dissolution thus took place in low permeable sediments when large-scale flow of meteoric or acidic fluids is ruled out as a cause of feldspar dissolution. Mineral precipitation (illite, kaolinite, and albite) took place within pseudomatrix and detrital matrix as well as in secondary pores created by feldspar dissolution. Feldspar was the source for the authigenesis. The system was thus closed during burial after framework collapse, and diagenetic reactants in the form of detrital components were already present within the system. The original mass was preserved, but redistributed and diagenetic minerals were the local sinks for the dissolved reactants, precipitating within the system. This also suggests that burial diagenesis in general might be more mass conservative than usually assumed. Rotliegend sandstones thus form a case where, despite of the lack of external exchange of mass by fluid flow, major diagenetic processes did take place and significantly modified the original mineralogy and texture. Feldspar diagenesis can take place from other processes than mere large-scale flushing of open systems as often supposed. It implies that the volumes of rock affected by feldspar diagenesis may be much larger than anticipated based upon the common hold believe that feldspar diagenesis is linked to

  7. Experimental investigation of the effects of aqueous species on the dissolution kinetics of R7T7 glass; Etude experimentale de l`influence d`especes aqueuses sur la cinetique de dissolution du verre nucleaire R7T7

    Gin, S

    1994-10-01

    This contribution to the study of aqueous corrosion of the French ``R7T7`` reference nuclear containment glass includes a bibliographic survey of prior investigations, highlighting the problems encountered in interpreting the interactions in systems containing clay materials in contact with the glass. An experimental methodology is proposed to investigate the effects of inorganic aqueous species separately from those of a few organic acids on the dissolution mechanisms and kinetics of R7T7 glass at 90 deg. C. The experimental results discussed support the idea that several glass network forming elements may have a kinetically limiting role. The most likely hypothesis to account for the absence of saturation conditions with respect to the glass in certain clay media involves the formation of complexes with kinetically limiting metallic elements such as aluminum released by glass corrosion. This work contributes to a better understanding of the basic mechanisms of nuclear glass dissolution in a geological repository environment. It facilitates the interpretation of glass alteration studies in realistic or actual solutions and may contribute to specifying near field chemical barriers in the form of additives (amorphous silica, aluminum hydroxides or phosphates) around the glass disposal package to enhance the stability of the glass matrix. (author). 148 refs., 40 figs., 32 tabs., 1 append.

  8. Effects of Bacterial Siderophore and Biofilm Synthesis on Silicate Mineral Dissolution Kinetics: Results from Experiments with Targeted Mutants

    Van Den Berghe, M. D.; West, A. J.; Nealson, K. H.

    2018-05-01

    This project aims to characterize and quantify the specific microbial mechanisms and metabolic pathways responsible for silicate mineral dissolution and micronutrient acquisition directly from mineral phases.

  9. The dissolution rate of silicate glasses and minerals: an alternative model based on several activated complexes

    Berger, G.

    1997-01-01

    Most of the mineral reactions in natural water-rock systems progress at conditions close to the chemical equilibrium. The kinetics of these reactions, in particular the dissolution rate of the primary minerals, is a major constrain for the numerical modelling of diagenetic and hydrothermal processes. In the case of silicates, recent experimental studies have pointed out the necessity to better understand the elementary reactions which control the dissolution process. This article presents several models that have been proposed to account for the observed dissolution rate/chemical affinity relationships. The case of glasses (R7T7), feldspars and clays, in water, in near neutral pH aqueous solutions and in acid/basic media, are reviewed. (A.C.)

  10. Hydroxylamine a potential reagent for dissolution off gas scrubbing in nuclear spent fuel reprocessing: kinetics of the iodine reduction

    Cau Dit Coumes, C.; Devisme, F.; Chopin, J.; Vargas, S.

    1996-01-01

    Iodine, which can be released inside the containment buildings when accident occurs, can be traced, in normal operating conditions, at the back end of the fuel cycle. Hydroxylamine has been selected as a regent of potential interest to trap iodine in the dissolution off gas treatment. The kinetics of the reaction between hydroxylamine and iodine has been studied in a narrow range of pH(1-2), with hydroxylamine in excess (ratios of hydroxylamine to iodine initial concentrations varying from 2 to 40), at constant temperature (30 deg. C) and ionic strength (0.1 mol/l). Spectrophotometry and voltametry have been coupled for analytical solved using a investigation. The problem of the rapid mixing of the reactants has been solved using a continuous reactor. Tri-iodine has been shown non reactive towards hydroxylamine. An initial rate law have been proposed, pointing out the first order of the reaction with respect to hydroxylamine and iodine, and the inhibitory effect and hydrogen ions. Nitrous acid has been identified as a transitory product. Nitrous oxide and nitrogen monoxide have been detected by gas chromatography, the ratio of the amounts of products formed depending on acidity. The complexity of the overall reaction has been ascribed to the competition of hour reactions (I 2 + I I 3 - NH 3 OH + + 2 I 2 + H 2 O ->HNO 2 + 4 I - + 5 H + ; NH 3 OH + + HNO 2 -> N 2 O + 2 H 2 O + H-+ 2HNO 2 + 2 I - + 2H-+ -> 2 NO + I 2 + H 2 O). (authors)

  11. Hydroxylamine a potential reagent for dissolution off gas scrubbing in nuclear spent fuel reprocessing: kinetics of the iodine reduction

    Cau Dit Coumes, C.; Devisme, F. [CEA Centre d`Etudes de la Vallee du Rhone, 30 - Marcoule (France). Dept. d`Exploitation du Retraitement et de Demantelement; Chopin, J.; Vargas, S.

    1996-12-31

    Iodine, which can be released inside the containment buildings when accident occurs, can be traced, in normal operating conditions, at the back end of the fuel cycle. Hydroxylamine has been selected as a regent of potential interest to trap iodine in the dissolution off gas treatment. The kinetics of the reaction between hydroxylamine and iodine has been studied in a narrow range of pH(1-2), with hydroxylamine in excess (ratios of hydroxylamine to iodine initial concentrations varying from 2 to 40), at constant temperature (30 deg. C) and ionic strength (0.1 mol/l). Spectrophotometry and voltametry have been coupled for analytical solved using a investigation. The problem of the rapid mixing of the reactants has been solved using a continuous reactor. Tri-iodine has been shown non reactive towards hydroxylamine. An initial rate law have been proposed, pointing out the first order of the reaction with respect to hydroxylamine and iodine, and the inhibitory effect and hydrogen ions. Nitrous acid has been identified as a transitory product. Nitrous oxide and nitrogen monoxide have been detected by gas chromatography, the ratio of the amounts of products formed depending on acidity. The complexity of the overall reaction has been ascribed to the competition of hour reactions (I{sub 2} + I <=> I{sub 3}{sup -}NH{sub 3}OH{sup +} + 2 I{sub 2} + H{sub 2}O ->HNO{sub 2} + 4 I{sup -} + 5 H{sup +}; NH{sub 3}OH{sup +} + HNO{sub 2} -> N{sub 2}O + 2 H{sub 2}O + H-+ 2HNO{sub 2} + 2 I{sup -} + 2H-+ -> 2 NO + I{sub 2} + H{sub 2}O). (authors). 12 refs.

  12. Hydrothermal alteration of plagioclase and growth of secondary feldspar in the Hengill Volcanic Centre, SW Iceland

    Larsson, D.; Grönvold, K.; Oskarsson, N.; Gunnlaugsson, E.

    2002-05-01

    Dissolution of igneous feldspar and the formation and occurrence of secondary feldspar in tholeiitic basalts from the Hengill volcanic centre, in SW Iceland was studied by microprobe analysis of cuttings from two ca. 2000 m deep geothermal wells. Well NG-7 in Nesjavellir represents a geothermal system in a rift zone where the intensity of young, insignificantly altered intrusions increases with depth. Well KhG-1 in Kolviðarhóll represents the margin of a rift zone where the intensity of intrusives is lower and the intensity of alteration higher. This marginal well represents altered basaltic crust in an early retrograde state. The secondary plagioclase in both wells is mainly oligoclase, occurring in association with K-feldspar and chlorite±actinolite. The texture of this assemblage depends on the lithology and intensity of alteration. In Nesjavellir (NG-7) the composition of secondary albite-oligoclase is correlated with the host-rock composition. This connection is not apparent in more intensely altered samples from Kolviðarhóll (KhG-1). The influence of temperature on composition of secondary Na-feldspar is unclear in both wells although Ca is expected to increase with temperature. Any temperature dependence may be suppressed by the influence of rock composition in Nesjavellir and by retrograde conditions at Kolviðarhóll. The absence of clear compositional gradients between igneous plagioclase and secondary feldspar and between Na-feldspar and K-feldspar suggests that secondary feldspars formed by dissolution precipitation reactions.

  13. Theoretical study of the dissolution kinetics of galena and cerussite in an abandoned mining area (Zaida mine, Morocco)

    El Alaoui, Lamiae; Dekayir, Abdelilah

    2018-05-01

    In the abandoned mine in Zaida, the pit lakes filled with water constitute significant water reserves. In these lakes, the waters are permanently in contact with ore deposit (cerussite and galena). The modelling of the interaction of waters with this mineralization shows that cerussite dissolves more rapidly than galena. This dissolution is controlled by the pH and dissolved oxygen concentration in solution. The lead concentrations recorded in these lakes come largely from the dissolution of cerussite.

  14. Dissolution kinetics for alumina in cryolite melts. Distribution of alumina in the electrolyte of industrial aluminium cells

    Kobbeltvedt, Ove

    1997-12-31

    This thesis contributes to the understanding of which factors determine the rate of dissolution of alumina added to the bath in alumina reduction cells. Knowing this may help reduce the occurrences of operation interruptions and thus make it possible to produce aluminium using less energy. When alumina powder was added to a stirred cryolite melt, the alumina dissolved in two distinct main stages. In the first stage, the dissolution rate was very high, which reflects dissolution of single alumina grains that are being dispersed in the bath upon addition. In the second stage, lumps of alumina infiltrated with bath dissolved at a rate considerably slower than that of the first stage. The formation of these alumina agglomerates is the most important contributor to slow dissolution. The parameters varied in the experiments were convection, batch size, and temperature of the bath and of the added alumina. Increased gas stirring of the bath speeded up dissolution in both stages but the size of the batch was of little significance. Increasing the bath temperature had no effect in the first stage but speeded up dissolution considerably in the second stage. Compared to adding alumina at room temperature, preheating it to a high temperature (600 {sup o}C) increased the dissolution rate in the first stage while preheating to lower temperatures (100-300 {sup o}C) decreased the dissolution rate. In the second stage, preheating slowed the dissolution. The two latter phenomena of reduced dissolution rates are ascribed to the removal of moisture from the alumina upon preheating. The bath flow and the distribution of alumina in the bath were measured in four different types of cells. It was found that if a certain asymmetry of the magnetic field traverse to the cell was present, due to the presence of risers, then loops of high velocity bath flow occurred near the short ends of the cell. Thus, alumina added near the short ends is effectively transferred away from the feeding

  15. Thermodynamic and Kinetic Aspects of the Dissolution of Quartz-Kaolinite Mixtures by Alkalis Aspects thermodynamiques et cinétiques de la dissolution des mélanges quartz-kaolinite par les alcalis

    Labrid J.

    2006-11-01

    Full Text Available Mineral-alkali interactions have received considerable attention in the recent literature dealing with enhanced oil recovery techniques and clay stabilization treatments. One of the critical factors to be considered is alkali consumption. Alkalinity decrease occurs through several mechanisms, which are ion exchange, precipitation, reaction with crude oil components, and dissolution of minerals. This paper describes the dissolution process. An original kinetic model is proposed to describe the alkaline dissolution of a clayey sandstone. This model is based first on results concerning quartz dissolution/condensation processes. It is also based on new experimental data, which demonstrate the inhibiting effect of aluminum and, as the reaction proceeds, the precipitation of an aluminosilicate whose the chemical composition has been determined. From these data, a kinetic scheme has been conceived in which adsorption of different chemical species is assumed to occur onto solid surfaces. These species play a more or less important role according to the extent of the reaction. In the mechanisms considered, the argillaceous fraction of the rock provides silicon and aluminum which inhibit the dissolution of the matrix while silicon coming from quartz interferes with clay attack. The kinetic model depicts the coupling of elementary dissolution processes and calculates dissolved silicon and aluminum. It has been tested for various operating conditions, providing initial reaction rates for quartz and clay. Results emphasize the definitive advantage of carbonate compared to other alkaline chemicals owing to the relative low pH of solutions, which is particularly favorable for promoting inhibition by aluminum and, as a general rule, for reducing mineral dissolution. Ce résumé contient des formules (*** qui ne peuvent s'afficher à l'écran L'emploi des agents alcalins pour améliorer la récupération du pétrole a été préconisé à l'origine dans le but

  16. [Energy related studies utilizing K-feldspar thermochronology

    1992-01-01

    In our second year of current funding cycle, we have investigated the Ar diffusion properties and microstructures of K-feldspars and the application of domain theory to natural K-feldspars. We completed a combined TEM and argon diffusion study of the effect of laboratory heat treatment on the microstructure and kinetic properties of K-feldspar. We conclude in companion papers that, with one minor exception, no observable change in the diffusion behavior occurs during laboratory extraction procedures until significant fusion occurs at about 1100 degrees C. The effect that is observed involves a correlation between the homogenization of cryptoperthite lamelle and the apparent increase in retentivity of about 5% of the argon in the K-feldspar under study. We can explain this effect of both as an artifact of the experiment or the loss of a diffusion boundary. Experiments are being considered to resolve this question. Refinements have been made to our experimental protocol that appears that greatly enhance the retrieval of multi-activation energies from K-feldspars. We have applied the multi-domain model to a variety of natural environments (Valles Caldera, Red River fault, Appalachian basin) with some surprising results. Detailed 40 Ar/ 39 Ar coverage of the Red River shear zone, thought to be responsible for the accommodation of a significant fraction of the Indo-Asian convergence, strongly suggests that our technique can precisely date both the termination of ductile strike-slip motion and the initiation of normal faulting. Work has continued on improving our numerical codes for calculating thermal histories and the development of computer based graphing tools has significantly increased our productivity

  17. Quantifying Silica Reactivity in Subsurface Environments: Reaction Affinity and Solute Matrix Controls on Quartz and SiO2 Glass Dissolution Kinetics

    Dove, Patricia M.

    1999-01-01

    Our goal is to develop a quantitative and mechanistic understanding of amorphous silica, SiO2(am), dissolution kinetics in aqueous solutions. A knowledge of fundamental controls on the reactivity of simple Si-O bonded phases is the baseline of behavior for understanding highly complex silica phases. In the Earth, silicate minerals comprise >70% of the crust and dominate virtually every subsurface system. More importantly for the objectives of this EMSP project, the silicates are important because compositionally complex glasses will become the front line of defense in containing radioactive wastes in the nation's long term and interim storage strategies. To date, the behavior of SiO2(am) is largely inferred from studies of the better known crystalline polymorphs (e.g. alpha-quartz). In the first step towards constructing a general model for amorphous silica reactivity in the complex fluid compositions of natural waters, we are determining the dissolution behavior as a function of temperature, solution pH and cation concentration. With these data we are determining relationships between SiO2 glass structure and dissolution rates in aqueous solutions, as described below

  18. Dissolution processes

    Silver, G.L.

    1976-01-01

    This review contains more than 100 observations and 224 references on the dissolution phenomenon. The dissolution processes are grouped into three categories: methods of aqueous attack, fusion methods, and miscellaneous observations on phenomena related to dissolution problems

  19. Atmospheric weathering and silica-coated feldspar: analogy with zeolite molecular sieves, granite weathering, soil formation, ornamental slabs, and ceramics.

    Smith, J V

    1998-03-31

    Feldspar surfaces respond to chemical, biological, and mechanical weathering. The simplest termination is hydroxyl (OH), which interacts with any adsorption layer. Acid leaching of alkalis and aluminum generated a silica-rich, nanometers-thick skin on certain feldspars. Natural K, Na-feldspars develop fragile surfaces as etch pits expand into micrometer honeycombs, possibly colonized by lichens. Most crystals have various irregular coats. Based on surface-catalytic processes in molecular sieve zeolites, I proposed that some natural feldspars lose weakly bonded Al-OH (aluminol) to yield surfaces terminated by strongly bonded Si-OH (silanol). This might explain why some old feldspar-bearing rocks weather slower than predicted from brief laboratory dissolution. Lack of an Al-OH infrared frequency from a feldspar surface is consistent with such a silanol-dominated surface. Raman spectra of altered patches on acid-leached albite correspond with amorphous silica rather than hydroxylated silica-feldspar, but natural feldspar may respond differently. The crystal structure of H-exchanged feldspar provides atomic positions for computer modeling of complex ideas for silica-terminated feldspar surfaces. Natural weathering also depends on swings of temperature and hydration, plus transport of particles, molecules, and ionic complexes by rain and wind. Soil formation might be enhanced by crushing granitic outcrops to generate new Al-rich surfaces favorable for chemical and biological weathering. Ornamental slabs used by architects and monumental masons might last longer by minimizing mechanical abrasion during sawing and polishing and by silicifying the surface. Silica-terminated feldspar might be a promising ceramic surface.

  20. Sub-minute kinetics of human red cell fumarase: 1 H spin-echo NMR spectroscopy and 13 C rapid-dissolution dynamic nuclear polarization.

    Shishmarev, Dmitry; Wright, Alan J; Rodrigues, Tiago B; Pileio, Giuseppe; Stevanato, Gabriele; Brindle, Kevin M; Kuchel, Philip W

    2018-03-01

    Fumarate is an important probe of metabolism in hyperpolarized magnetic resonance imaging and spectroscopy. It is used to detect the release of fumarase in cancer tissues, which is associated with necrosis and drug treatment. Nevertheless, there are limited reports describing the detailed kinetic studies of this enzyme in various cells and tissues. Thus, we aimed to evaluate the sub-minute kinetics of human red blood cell fumarase using nuclear magnetic resonance (NMR) spectroscopy, and to provide a quantitative description of the enzyme that is relevant to the use of fumarate as a probe of cell rupture. The fumarase reaction was studied using time courses of 1 H spin-echo and 13 C-NMR spectra. 1 H-NMR experiments showed that the fumarase reaction in hemolysates is sufficiently rapid to make its kinetics amenable to study in a period of approximately 3 min, a timescale characteristic of hyperpolarized 13 C-NMR spectroscopy. The rapid-dissolution dynamic nuclear polarization (RD-DNP) technique was used to hyperpolarize [1,4- 13 C]fumarate, which was injected into concentrated hemolysates. The kinetic data were analyzed using recently developed FmR α analysis and modeling of the enzymatic reaction using Michaelis-Menten equations. In RD-DNP experiments, the decline in the 13 C-NMR signal from fumarate, and the concurrent rise and fall of that from malate, were captured with high spectral resolution and signal-to-noise ratio, which allowed the robust quantification of fumarase kinetics. The kinetic parameters obtained indicate the potential contribution of hemolysis to the overall rate of the fumarase reaction when 13 C-NMR RD-DNP is used to detect necrosis in animal models of implanted tumors. The analytical procedures developed will be applicable to studies of other rapid enzymatic reactions using conventional and hyperpolarized substrate NMR spectroscopy. Copyright © 2018 John Wiley & Sons, Ltd.

  1. Modeling of the Dissolution Kinetics of Arbutus Wild Berries-Based Tablets as Evaluated by Electric Conductivity

    Abbas-Aksil, T.; Benamara, S.

    2015-01-01

    Lyophilized powder (LP) from Algerian arbutus wild berries (Arbutus unedo L.) was obtained. This present paper reports about the dissolution (releasing) properties of LP-based tablets, evaluated through the electric conductivity (EC) of distilled water which is employed as surrounding medium, at three different temperatures (291, 298 and 309 K). In addition to this, secondary physicochemical characteristics such as elementary analysis, color and compressibility were evaluated. Regarding the modeling of ionic transfer, among the three tested models, namely Peleg, Singh et al. and Singh and Kulshestha, the latter seems to be the most appropriate (R2 = 0.99), particularly in the case of compacted tablets under 2000 Pa. The temperature dependence of the dissolution process was also studied applying Arrhenius equation (R2>0.8) which allowed to deduce the activation energy, ranging from 18.7 to 21.4 kJ.mol -1 according to the model and compression force employed. (author)

  2. GLAMOR - Or How We Achieved A Common Understanding On The Decrease Of Glass Dissolution Kinetics Through International Cooperation

    Van Iseghem, Pierre; Aerstens, Marc; Gin, Stephane; Grambow, Bernd; Strachan, Denis M.; McGrail, B. Peter; Wicks, George G.; McMenamin, Thomas

    2011-01-01

    The objective of the EC funded GLAMOR project was to achieve a common understanding of the processes that control the decrease of the dissolution rate of high-level waste glass in water when silica becomes saturated. Is affinity control or a protective layer dominating? The following steps were taken: (1) review of the literature, (2) selection ofselect an experimental dataset, and selection of the models r(t) and GM2003, and (3) application apply by the GLAMOR partners of the models to the datasets. The main focus has beenwas on dissolution tests in pure water at different values of surface-to-volume and pH. Some of the main conclusions were: (1) both affinity and protective layer concepts must be considered in the interpretation of the rate decreasing stage, (2) the residual dissolution rate observed beyond the silica saturation stage is far more important in view of the long-term performance of the glass, and deserves more attention in future R and D. In the GLAMOR final report, we also discussed in detail the modeling parameters, such as the silica saturation concentration, the silica diffusion coefficient, the silica retention factor in the reaction layer, and the water diffusion coefficient.

  3. Radionuclide transport in fractured porous media -- Analytical solutions for a system of parallel fractures with a kinetic solubility-limited dissolution model

    Li, S.H.; Chen, C.T.

    1997-01-01

    Analytical solutions are developed for the problem of radionuclide transport in a system of parallel fractures situated in a porous rock matrix. A kinetic solubility-limited dissolution model is used as the inlet boundary condition. The solutions consider the following processes: (a) advective transport in the fractures, (b) mechanical dispersion and molecular diffusion along the fractures, (c) molecular diffusion from a fracture to the porous matrix, (d) molecular diffusion within the porous matrix in the direction perpendicular to the fracture axis, (e) adsorption onto the fracture wall, (f) adsorption within the porous matrix, and (g) radioactive decay. The solutions are based on the Laplace transform method. The general transient solution is in the form of a double integral that is evaluated using composite Gauss-Legendre quadrature. A simpler transient solution that is in the form of a single integral is also presented for the case that assumes negligible longitudinal dispersion along the fractures. The steady-state solutions are also provided. A number of examples are given to illustrate the effects of the following important parameters: (a) fracture spacings, (b) dissolution-rate constants, (c) fracture dispersion coefficient, (d) matrix retardation factor, and (e) fracture retardation factor

  4. In-vitro analysis of the dissolution kinetics and systemic availability of plutonium ingested in the form of 'hot' particles from the Semipalatinsk NTS.

    Conway, M; León Vintró, L; Mitchell, P I; García-Tenorio, R; Jimenez-Ramos, M C; Burkitbayev, M; Priest, N D

    2009-05-01

    In-vitro leaching of radioactive 'hot' particles isolated from soils sampled at the Semipalatinsk Nuclear Test Site has been carried out in order to evaluate the fraction of plutonium activity released into simulated human stomach and small intestine fluids during digestion. Characterisation of the particles (10-100 Bq(239,240)Pu) and investigation of their dissolution kinetics in simulated fluids has been accomplished using a combination of high-resolution alpha-spectrometry, gamma-spectrometry and liquid scintillation counting. The results of these analyses indicate that plutonium transfer across the human gut following the ingestion of 'hot' particles can be up to two orders of magnitude lower than that expected for plutonium in a more soluble form, and show that for areas affected by local fallout, use of published ingestion dose coefficients, together with bulk radionuclide concentrations in soil, may lead to a considerable overestimation of systemic uptake via the ingestion pathway.

  5. In-vitro analysis of the dissolution kinetics and systemic availability of plutonium ingested in the form of 'hot' particles from the Semipalatinsk NTS

    Conway, M. [School of Physics, University College Dublin, Belfield, Dublin 4 (Ireland); Leon Vintro, L. [School of Physics, University College Dublin, Belfield, Dublin 4 (Ireland)], E-mail: luis.leon@ucd.ie; Mitchell, P.I. [School of Physics, University College Dublin, Belfield, Dublin 4 (Ireland); Garcia-Tenorio, R.; Jimenez-Ramos, M.C. [Departamento de Fisica, Universidad de Sevilla, 41012 Sevilla (Spain); Burkitbayev, M. [Department of Inorganic Chemistry, Al-Farabi Kazakh National University, Almaty (Kazakhstan); Priest, N.D. [School of Health and Social Sciences, Middlesex University, Queensway, Enfield EN3 4SA (United Kingdom)

    2009-05-15

    In-vitro leaching of radioactive 'hot' particles isolated from soils sampled at the Semipalatinsk Nuclear Test Site has been carried out in order to evaluate the fraction of plutonium activity released into simulated human stomach and small intestine fluids during digestion. Characterisation of the particles (10-100 Bq {sup 239,240}Pu) and investigation of their dissolution kinetics in simulated fluids has been accomplished using a combination of high-resolution alpha-spectrometry, gamma-spectrometry and liquid scintillation counting. The results of these analyses indicate that plutonium transfer across the human gut following the ingestion of 'hot' particles can be up to two orders of magnitude lower than that expected for plutonium in a more soluble form, and show that for areas affected by local fallout, use of published ingestion dose coefficients, together with bulk radionuclide concentrations in soil, may lead to a considerable overestimation of systemic uptake via the ingestion pathway.

  6. Principles of Thermal Expansion in Feldspars

    Hovis, Guy; Medford, Aaron; Conlon, Maricate; Tether, Allison; Romanoski, Anthony

    2010-05-01

    Following the recent thermal expansion work of Hovis et al. (1) on AlSi3 feldspars, we have investigated the thermal expansion of plagioclase, Ba-K, and Ca-K feldspar crystalline solutions. X-ray powder diffraction data were collected between room temperature and 925 °C on six natural plagioclase specimens ranging in composition from anorthite to oligoclase, the K-exchanged equivalents of these plagioclase specimens, and five synthetic Ba-K feldspars with compositions ranging from 25 to 99 mol % BaAl2Si2O8. The resulting thermal expansion coefficients (α) for volume have been combined with earlier results for end-member Na- and K-feldspars (2,3). Unlike AlSi3 feldspars, Al2Si2 feldspars, including anorthite and celsian from the present study plus Sr- and Pb-feldspar from other workers (4,5), show essentially constant and very limited thermal expansion, regardless of divalent cation size. In the context of structures where the Lowenstein rule (6) requires Al and Si to alternate among tetrahedra, the proximity of bridging Al-O-Si oxygen ions to divalent neighbors (ranging from 0 to 2) produces short Ca-O (or Ba-O) bonds (7,8) that apparently are the result of local charge-balance requirements (9). Gibbs et al. (10) suggest that short bonds such as these have a partially covalent character. This in turn stiffens the structure. Thus, for feldspar series with coupled substitution the change away from a purely divalent M-site occupant gives the substituting (less strongly bonded) monovalent cations increasingly greater influence on thermal expansion. Overall, then, thermal expansion in the feldspar system is well represented on a plot of α against room-temperature volume, where one sees a quadrilateral bounded by data for (A) AlSi3 feldspars whose expansion behavior is controlled largely by the size of the monovalent alkali-site occupant, (B) Al2Si2 feldspars whose expansion is uniformly limited by partially-covalent bonds between divalent M-site occupants and

  7. Feldspar 40Ar/39Ar dating of ICDP PALEOVAN cores

    Engelhardt, Jonathan Franz; Sudo, Masafumi; Stockhecke, Mona; Oberhänsli, Roland

    2017-11-01

    Volcaniclastic fall deposits in ICDP drilling cores from Lake Van, Turkey, contain sodium-rich sanidine and calcium-rich anorthoclase, which both comprise a variety of textural zoning and inclusions. An age model records the lake's history and is based on climate-stratigraphic correlations, tephrostratigraphy, paleomagnetics, and earlier 40Ar/39Ar analyses (Stockhecke et al., 2014b). Results from total fusion and stepwise heating 40Ar/39Ar analyses presented in this study allow for the comparison of radiometric constraints from texturally diversified feldspar and the multi-proxy lacustrine age model and vice versa. This study has investigated several grain-size fractions of feldspar from 13 volcaniclastic units. The feldspars show textural features that are visible in cathodoluminescence (CL) or back-scattered electron (BSE) images and can be subdivided into three dominant zoning-types: (1) compositional zoning, (2) round pseudo-oscillatory zoning and (3) resorbed and patchy zoning (Ginibre et al., 2004). Round pseudo-oscillatory zoning records a sensitive alternation of Fe and Ca that also reflects resorption processes. This is only visible in CL images. Compositional zoning reflects anticorrelated anorthite and orthoclase contents and is visible in BSE. Eleven inverse isochron ages from total fusion and three from stepwise heating analyses fit the age model. Four experiments resulted in older inverse isochron ages that do not concur with the model within 2σ uncertainties and that deviate from 1 ka to 17 ka minimum. C- and R-type zoning are interpreted as representing growth in magma chamber cupolas, as wall mushes, or in narrow conduits. Persistent compositions of PO-type crystals and abundant surfaces recording dissolution features correspond to formation within a magma chamber. C-type zoning and R-type zoning have revealed an irregular incorporation of melt and fluid inclusions. These two types of zoning in feldspar are interpreted as preferentially

  8. Dissolution kinetics of metal coating in HNO3-scCO2 micro-emulsion using QCM

    Ju, Min Su; Koh, Moon Sung; Park, Kwang Heon; Kim, Hak Won; Kim, Hong Doo

    2005-01-01

    Radioactive contamination is rising because of an increasing number of nuclear facilities. Among the decontamination methods, the surface decontamination method is especially important. Conventional chemical decontamination methods for surface decontamination cause not only secondary radioactive wastes, but also corrosion and defects on the surface of equipment. Therefore, we require a new surface decontamination method. If CO 2 is used as a solvent for decontamination of radioactive contaminants, the wastes can be effectively reduced by recycling the CO 2 . Supercritical fluid has many good points as a process solvent, including low viscosity, negligible surface tension, and variable selectivity. And supercritical fluids have physical properties of both liquid and gas, such as good penetration with a high dissolution capability. A number of workers applied supercritical CO 2 solvent for cleaning precision devices and waste treatments. Since supercritical CO 2 has its mild critical point at 31 .deg. C and 73.8bar as well as low surface tension, it is a potentially suitable cleaning substance. The operational costs of CO 2 cleaning were estimated to be lower than other cleaning processes. However supercritical CO 2 has limited solubility about contaminated material. To tackle these problem, we researched various aspects of surfactants. Quartz Crystal Microbalance (QCM) is a thickness-shear mode resonator in which the acoustic wave propagates in a direction perpendicular to the crystal surface. The use of QCM as a chemical sensor has its origins in the work of Sauerbrey and King who carried out micro-gravimetric measurements in the gas phase. It was assumed in their work that a thin film applied to a thickness-shear-mode device could be treated in sensor measurements, and a shift in the resonance frequency of an oscillating AT-cut crystal could be correlated quantitatively with a change in mass added to or removed from the surface of the device. Now, the QCM

  9. Probing luminescence centers in Na rich feldspar

    Prasad, Amit Kumar; Lapp, Torben; Kook, Myung Ho

    2016-01-01

    our understanding of the luminescence mechanisms and recombination sites, in a sample of Na rich plagioclase feldspar (oligoclase). Both the UV and violet–blue emissions show resonant excitations arising from a distribution of energy levels. We propose, contrary to the general understanding...

  10. Carbon dioxide storage in marine sediments - dissolution, transport and hydrate formation kinetics from high-pressure experiments

    Bigalke, N. K.; Savy, J. P.; Pansegrau, M.; Aloisi, G.; Kossel, E.; Haeckel, M.

    2009-12-01

    By satisfying thermodynamic framework conditions for CO2 hydrate formation, pressures and temperatures of the deep marine environment are unique assets for sequestering CO2 in clathrates below the seabed. However, feasibility and safety of this storage option require an accurate knowledge of the rate constants governing the speed of physicochemical reactions following the injection of the liquefied gas into the sediments. High-pressure experiments designed to simulate the deep marine environment open the possibility to obtain the required parameters for a wide range of oceanic conditions. In an effort to constrain mass transfer coefficients and transport rates of CO2 in(to) the pore water of marine sediments first experiments were targeted at quantifying the rate of CO2 uptake by de-ionized water and seawater across a two-phase interface. The nature of the interface was controlled by selecting p and T to conditions within and outside the hydrate stability field (HSF) while considering both liquid and gaseous CO2. Concentration increase and hydrate growth were monitored by Raman spectroscopy. The experiments revealed anomalously fast transport rates of dissolved CO2 at conditions both inside and outside the HSF. While future experiments will further elucidate kinetics of CO2 transport and hydrate formation, these first results could have major significance to safety-related issues in the discussion of carbon storage in the marine environment.

  11. Thermo-optical properties of optically stimulated luminescence in feldspars

    Poolton, N.R.J.; Bøtter-Jensen, L.; Johnsen, O.

    1995-01-01

    Optically stimulated luminescence processes in feldspars are subject to competing thermal enhancement and quenching processes: this article describes the thermal enhancement effects for orthoclase, albite and plagioclase feldspars. It is demonstrated that certain lattice vibrational modes can be ...

  12. Impacts of seawater saturation state (ΩA = 0.4-4.6) and temperature (10, 25 °C) on the dissolution kinetics of whole-shell biogenic carbonates

    Ries, Justin B.; Ghazaleh, Maite N.; Connolly, Brian; Westfield, Isaac; Castillo, Karl D.

    2016-11-01

    Anthropogenic increase of atmospheric pCO2 since the Industrial Revolution has caused seawater pH to decrease and seawater temperatures to increase-trends that are expected to continue into the foreseeable future. Myriad experimental studies have investigated the impacts of ocean acidification and warming on marine calcifiers' ability to build protective shells and skeletons. No studies, however, have investigated the combined impacts of ocean acidification and warming on the whole-shell dissolution kinetics of biogenic carbonates. Here, we present the results of experiments designed to investigate the effects of seawater saturation state (ΩA = 0.4-4.6) and temperature (10, 25 °C) on gross rates of whole-shell dissolution for ten species of benthic marine calcifiers: the oyster Crassostrea virginica, the ivory barnacle Balanus eburneus, the blue mussel Mytilus edulis, the conch Strombus alatus, the tropical coral Siderastrea siderea, the temperate coral Oculina arbuscula, the hard clam Mercenaria mercenaria, the soft clam Mya arenaria, the branching bryozoan Schizoporella errata, and the coralline red alga Neogoniolithon sp. These experiments confirm that dissolution rates of whole-shell biogenic carbonates decrease with calcium carbonate (CaCO3) saturation state, increase with temperature, and vary predictably with respect to the relative solubility of the calcifiers' polymorph mineralogy [high-Mg calcite (mol% Mg > 4) ≥ aragonite > low-Mg calcite (mol% Mg carbonates. Furthermore, the severity of the temperature effects on gross dissolution rates also varied with respect to carbonate polymorph solubility, with warming (10-25 °C) exerting the greatest effect on biogenic high-Mg calcite, an intermediate effect on biogenic aragonite, and the least effect on biogenic low-Mg calcite. These results indicate that both ocean acidification and warming will lead to increased dissolution of biogenic carbonates in future oceans, with shells/skeletons composed of the more

  13. Quantifying Silica Reactivity in Subsurface Environments: Reaction Affinity and Solute Matrix Controls on Quartz and SiO2 Glass Dissolution Kinetics

    Dove, Patricia M.

    2000-01-01

    During the three years of this project, Professor Dove's laboratory made tremendous progress in understanding controls on amorphous silica dissolution kinetics in aqueous solutions. Our findings have already received considerable attention. In hydrothermal and low temperature studies, the work focused on determining quantitative and mechanistic controls on the most abundant silica polymorphs in Earth environments--quartz and amorphous silica. Our studies achieved goals set forth in the original proposal to establish a new quantitative understanding of amorphous silica dissolution. This support has resulted in 10 journal, 12 abstracts and 2 thesis publications. The PI and students were also recognized with 6 awards during this period. The 1998 EMSP conference in Chicago was an important meeting for our project. The symposium, enabled P.I. Dove to establish valuable contacts with ''users'' having specific needs for the findings of our EMSP project related to the urgency of problems in the Tanks Focus Area (TFA). Since that time, our working relations developed as Dove interacted with TFA scientists and engineers on the problems of waste glass properties. These interactions refined our experimental objectives to better meet their needs. Dove presented the results of EMSP research findings to a TFA subgroup at a Product Acceptance Workshop held in Salt Lake City during December 1998. The travel costs to attend this unanticipated opportunity were paid from EMSP project funds. In January 2000, Dove also attended a similar meeting in Atlanta with PNNL, SRL and BNF scientists/engineers to discuss new issues and make another level of decisions on the Product Acceptance goals. Our EMSP-funded research interfaced very well with the ongoing studies of Dr. Pete McGrail and colleagues in the Applied Geochemistry Group at PNNL. The value of our work to ''users'' was further demonstrated when Dove's EMSP-funded Postdoc, Dr. Jonathan Icenhower was hired by the same PNNL group. With

  14. Radioluminescence dating: the IR emission of feldspar

    Schilles, Thomas.; Habermann, Jan

    2000-01-01

    A new luminescence reader for radioluminescence (RL) measurements is presented. The system allows detection of RL emissions in the near infrared region (IR). Basic bleaching properties of the IR-RL emission of feldspars are investigated. Sunlight-bleaching experiments as a test for sensitivity changes are presented. IR-bleaching experiments were carried out to obtain information about the underlying physical processes of the IR-RL emission

  15. Kiglapait Feldspar States 5 to Review

    Morse, S. A.

    2017-12-01

    The 1305 Ga Kiglapait Intrusion of coastal Labrador records the crystallization of troctolite through olivine gabbro to magnetite- and apatite-bearing rocks to monoclinic sanidine- mesoperthite-ferrosyenite below an inverted stratigraphy of a thin Upper Border Zone. The crystallization history was about 1 Ma. ¶The evolutionary history of Kiglapait feldspars in an 8.4 km thick magma chamber runs from plagioclase An70 at 5 kbar and 1250°C, cooling through to ferrosyenite with mesoperthite and two feldspars at 3 kbar and 1,000°C. The residual magma encountered the binodal solvus and finished crystallizing as an azeotrope with plagioclase (Or 21, An 15) and sanidine (Or 52, An 8) in liquid (Xor = 1/3; An 11). Cooling in the subsolidus brought the feldspars to compositions An15-Or 3, An0-Or 80-85 at 800-730°C. Metastable mesoperthite on the coherent solvus in various stages of late equilibration persists in the local assemblages. Arrested to complete feldspar symplectites suggest the local presence of a vapor phase. ¶Splits of the final Or-rich feldspar were found by mass spectrometry to have a dominant quantity of Rb and 87Sr/86Sr along with % amounts of Ba; in contrast, the plag fraction has very low Rb and 87Sr/86Sr. The estimated timing of the isotopic segregation was plausibly continuous with major-element fractionation or perhaps at the moment(s) of exsolution. ¶The cooling record of the solidified intrusion at 3 kbar is shown by 40Ar/39Ar data to have been rapid, reaching an ambient temperature near 240°C within the first 20 Ma, compared to the ambient country-rock temperature before intrusion of 350°C. The difference suggests a late uplift of the region after the Kiglapait magmatism. ¶Contributions from Y. Yu, T. Krogh, M. Hamilton, D. Lindsley, D. DePaolo, M. Jercinovic and S.R. Hart are especially acknowledged.

  16. Microfluidic Leaching of Soil Minerals: Release of K+ from K Feldspar

    Ciceri, Davide; Allanore, Antoine

    2015-01-01

    The rate of K+ leaching from soil minerals such as K-feldspar is believed to be too slow to provide agronomic benefit. Currently, theories and methods available to interpret kinetics of mineral processes in soil fail to consider its microfluidic nature. In this study, we measure the leaching rate of K+ ions from a K-feldspar-bearing rock (syenite) in a microfluidic environment, and demonstrate that at the spatial and temporal scales experienced by crop roots, K+ is available at a faster rate than that measured with conventional apparatuses. We present a device to investigate kinetics of mineral leaching at an unprecedented simultaneous resolution of space (~101-102 μm), time (~101-102 min) and fluid volume (~100-101 mL). Results obtained from such a device challenge the notion that silicate minerals cannot be used as alternative fertilizers for tropical soils. PMID:26485160

  17. Dissolution kinetics of UO2: Flow-through tests on UO2.00 pellets and polycrystalline schoepite samples in oxygenated, carbonate/bicarbonate buffer solutions at 25 degree C

    Nguyen, S.N.; Weed, H.C.; Leider, H.R.; Stout, R.B.

    1991-10-01

    The modelling of radionuclide release from waste forms is an important part of the performance assessment of a potential, high-level radioactive waste repository. Since spent fuel consists of UO 2 containing actinide elements and other fission products, it is necessary to determine the principal parameters affecting UO 2 dissolution and quantify their effects on the dissolution rate before any prediction of long term release rates of radionuclides from the spent fuel can be made. As part of a complex matrix to determine the dissolution kinetics of UO 2 as a function of time, pH, carbonate/bicarbonate concentration and oxygen activity, we have measured the dissolution rates at 25 degrees C of: (1) UO 2 pellets; (2) UO 2.00 powder and (3) synthetic dehydrated schoepite, UO 3 .H 2 O using a single-pass flow through system in an argon-atmosphere glove box. Carbonate, carbonate/bicarbonate, and bicarbonate buffers with concentrations ranging from 0.0002 M to 0.02 M and pH values form 8 to 11 have been used. Argon gas mixtures containing oxygen (from 0.002 to 0.2 atm) and carbon dioxide (from 0 to 0.011 atm) were bubbled through the buffers to stabilize their pH values. 12 refs., 2 tabs

  18. Study of the thorium phosphate-diphosphate (TPD) dissolution: kinetic aspect - thermodynamic aspect: analysis of the neo-formed phases; Etude de la dissolution du phosphate diphosphate de thorium: - aspect cinetique - aspect thermodynamique: analyse des phases neoformees

    Thomas, A.Ch

    2000-10-06

    The aim of this work is to study the aqueous corrosion of the thorium phosphate-diphosphate (TPD), of the formula Th{sub 4}(PO{sub 4}){sub 4}P{sub 2}O{sub 7}, in the framework of the actinides immobilization. In order to complete the anterior studies concerning solid solutions where thorium is substituted by a tetravalent ion (uranium (IV) or plutonium (IV)) in the TPD structure, compounds of thorium and neptunium phosphate-diphosphate, of formula Th{sub 4-x}Np{sub x}(PO{sub 4}){sub 4}P{sub 2}O{sub 7}, have been prepared. Furthermore, a new chemical way of synthesis has been investigated in order to sinter solids solution of thorium and uranium phosphate-diphosphate (TUPD) in good conditions. The TPD dissolution study showed two principals steps. The first one corresponds to the control of element concentration by the material dissolution whereas the second corresponds to the formation of secondary precipitates for which thermodynamic equilibrium controls the concentration of the species in solution. Leaching tests have been performed varying several independent parameters in order to determine the TPD dissolution rate. The partial orders related to the protons or to the hydroxide ions have been found between 0.35 and 0.45 whereas the apparent dissolution rate constants are in the range 1.10{sup -5} for 9.10{sup -5} g.m{sup -2}.j{sup -1} for acidic and basic media. The neo-formed phases have been characterized after the dissolution of TPD and TUPD. We found that the TPD leaching in acidic medium leads to the formation of the crystallized thorium phosphate-hydrogen-phosphate (TPHP), of formula Th{sub 2}(PO{sub 4}){sub 2}(HPO{sub 4}), x H{sub 2}O, whereas the TUPD dissolution leads to the TPHP and an other compound, of formula (UO{sub 2}){sub 3}(PO{sub 4}){sub 2}, 5 H{sub 2}O. We calculated its solubility product which is in good agreement with those found in the literature. The phases formed during the leaching of solids containing plutonium; americium or curium (Th

  19. Thermal quenching of luminescence processes in feldspars

    Poolton, N.R.J.; Bøtter-Jensen, L.; Duller, G.A.T.

    1995-01-01

    , which display very different behaviour. The first involves the internal transitions of common transition metal ions. The second is typical of centres not displaying excited states within the band gap that are likely to arise from direct recombination between the conduction band and the ground state......The technique of optically stimulated luminescence has important uses in the dose evaluation of irradiated feldspars. The luminescence process involves the eviction of electrons from donor traps, charge transfer through the conduction band, and recombination at acceptor sites; each...

  20. Kinetics of dissolution of sapphire in melts in the CaO-Al2O3-SiO2 system

    Shaw, Cliff S. J.; Klausen, Kim B.; Mao, Huahai

    2018-05-01

    The dissolution rate of sapphire in melts in the CAS system of varying silica activity, viscosity and degree of alumina saturation has been determined at 1600 °C and 1.5 GPa. After an initiation period of up to 1800 s, dissolution is controlled by diffusion of cations through the boundary layer adjacent to the dissolving sapphire. The dissolution rate decreases with increasing silica activity, viscosity and molar Al2O3/CaO. The calculated diffusion matrix for each solvent melt shows that CAS 1 and 9 which have molar Al2O3/CaO of 0.33 and 0.6 and dissolution rate constants of 0.65 × 10-6 and 0.59 × 10-6 m/s0.5 have similar directions and magnitudes of diffusive coupling: DCaO-Al2O3 and DAl2O3-CaO are both negative are approximately equal. The solvent with the fastest dissolution rate: CAS 4, which has a rate constant of 1.5 × 10-6 m/s0.5 and Al2O3/CaO of 0.31 has positive DCaO-Al2O3 and negative DAl2O3-CaO and the absolute values vary by a factor of 4. Although many studies show that aluminium is added to the melts via the reaction: Si4+ =Al3+ + 0.5Ca2+ the compositional profiles show that this reaction is not the only one involved in accommodating the aluminium added during sapphire dissolution. Rather, aluminium is incorporated as both tetrahedrally coordinated Al charge balanced by Ca and as aluminium not charge balanced by Ca (termed Alxs). This reaction: AlIV -Ca =Alxs +CaNBO where CaNBO is a non-bridging oxygen associated with calcium, may involve the formation of aluminium triclusters. The shape of the compositional profiles and oxide-oxide composition paths is controlled by the aluminium addition reaction. When Alxs exceeds 2%, CaO diffusion becomes increasingly anomalous and since the bond strength of Alxs correlates with CaO/CaO + Al2O3, the presence of more than 2% Alxs leads to significantly slower dissolution than when Alxs is absent or at low concentration. Thus, dissolution is controlled by diffusion of cations through the boundary layer, but this

  1. Experimental study of kinetic and mechanism of dissolution of apatite structured minerals. Application to the prediction of the long term behavior of an actinides storage host matrix

    Chairat, C.

    2005-11-01

    The motivation for this study is to assess the potential of using apatite structured ceramics as long-lived actinide storage hosts. To assess their ability to resist aqueous corrosion, the dissolution of natural fluoro-apatite and synthetic Nd-britholite (neodymium is a proxy for the trivalent actinides) was studied. Mineral surfaces were characterized using a combined spectrometric, electrokinetic and potentiometric approach and dissolution rates were measured in closed and open system reactors as a function of solution composition. Experimental results suggest apatitic minerals dissolve via distinct step sequence: 1) fluoride release, 2) release of the calcium situated in the M1, and 3) the simultaneous removal of phosphate and calcium II via the breaking of only Ca-O bonds. TST based rate equations based in this mechanism accurately describe fluoro-apatite and synthetic britholite dissolution rates as a function of solution composition. Nd release rates are limited by precipitation of Nd-rhabdophane. (author)

  2. Luminescence and ESR properties of Brazilian feldspars

    Bitencourt, J.F.S.; Silva, D.M.; Silva, P.H.; Kinoshita, A.; Munita, C.S.; Tatumi, S.H.

    2006-01-01

    The IRSL and TL responses of three different feldspar crystals have been analysed. TL measurements were taken in the ultraviolet UV (290-370nm) and the visible VIS (340-610nm) regions of the spectrum. For the UV region and for a natural sample, peaks were observed at 283, 287 and 310 deg. C for grey, white and pink crystals, respectively. For samples irradiated after prior preheating, it was noted that TL peaks occurred at about 200 deg. C for all the samples; irradiation with high doses above 500Gy induced the formation of one additional peak at 170 deg. C. The VIS region results were similar to those for the UV. ESR experiments have been developed to verify the influence of radiation and heat treatments on the centres and preliminary results showed great variation in the intensities of [TiO 4 ] - , Al-O - -Al and Fe 3+ centres

  3. The dissolution of chalcopyrite in chloride media

    Ibanez, T.; Velasquez, L.

    2013-01-01

    The aim of this investigation is to determinate the effects of parameters and additives on the kinetics of dissolution of chalcopyrite on moderated conditions by means of dissolutions test with chalcopyrite concentrate and pure chalcopyrite in shake flasks and instrumented stirred reactors. A study of the dissolution of chalcopyrite in chloride solutions has demonstrated that the rate of dissolution of chalcopyrite is strongly dependent on the potential of the solution within a range of 540 to 630 mV (versus SHE). Leaching at pH around 2.5 results in increased rates of copper dissolution suggesting the possibility to keep the solution potential within the range. Both pyrite and silver ions enhance the dissolution of chalcopyrite and this effect increases when both species are present. The MnO 2 has a negative effect on the dissolution increasing the solution potential to values where the rate decreases considerably. (Author)

  4. Na-rich feldspar as a luminescence dosimeter in infrared stimulated luminescence (IRSL) dating

    Sohbati, Reza; Murray, Andrew; Jain, Mayank

    2013-01-01

    on geological origin and erosion history, but the dosimetry of K-rich feldspar grains extracted from rocks is complicated because the internal dose rate is very dependent on the original feldspar grain size. The in situ grain size information is lost during the crushing process used to separate the grains...... settings for which independent age control is available. The blue and yellow luminescence emissions are measured for IR stimulation at 50 °C (IR50), and post-IR IR stimulation at 290 °C (pIRIR290). Thermal stability experiments imply that the corresponding signals in both emissions have comparable thermal...... stabilities and that all signals have similar recombination kinetics and are thermally stable over geological timescales. The IR50 doses measured using blue and yellow emissions are similar to or lower than quartz doses while pIRIR290 blue doses are higher than those from yellow emission and quartz doses...

  5. Quantitative analysis of time-resolved infrared stimulated luminescence in feldspars

    Pagonis, Vasilis, E-mail: vpagonis@mcdaniel.edu [McDaniel College, Physics Department, Westminster, MD 21157 (United States); Ankjærgaard, Christina [Soil Geography and Landscape Group & Netherlands Centre for Luminescence dating, Wageningen University, PO Box 47, 6700 AA Wageningen (Netherlands); Jain, Mayank [Center for Nuclear Technologies, Technical University of Denmark, DTU Risø Campus, Roskilde (Denmark); Chithambo, Makaiko L. [Department of Physics and Electronics, Rhodes University, PO BOX 94, Grahamstown 6140 (South Africa)

    2016-09-15

    Time-resolved infrared-stimulated luminescence (TR-IRSL) from feldspar samples is of importance in the field of luminescence dating, since it provides information on the luminescence mechanism in these materials. In this paper we present new analytical equations which can be used to analyze TR-IRSL signals, both during and after short infrared stimulation pulses. The equations are developed using a recently proposed kinetic model, which describes localized electronic recombination via tunneling between trapped electrons and recombination centers in luminescent materials. Recombination is assumed to take place from the excited state of the trapped electron to the nearest-neighbor center within a random distribution of luminescence recombination centers. Different possibilities are examined within the model, depending on the relative importance of electron de-excitation and recombination. The equations are applied to experimental TR-IRSL data of natural feldspars, and good agreement is found between experimental and modeling results.

  6. CALCIUM CARBONATE DISSOLUTION RATE IN LIMESTONE CONTACTORS

    The rate of carbonate mineral dissolution from limestone was studied using a rotating disk apparatus and samples of limestone of varied composition. The purpose of this study was to determine the effect of limestone composition on the kinetics of carbonate mineral dissolution. Th...

  7. The dissolution kinetics and apparent solubility of natural apatite in closed reactors at temperatures from 5 to 50 degrees C and pH from 1 to 6

    Harouiya, N.; Chairat, C.; Kohler, S.J.; Gout, R.; Oelkers, E.H. [Univ Toulouse 3, CNRS, UMR 5563, F-31400 Toulouse (France); Chairat, C. [CEA, LCLT SECM DTCD, Lab Etud Comportement Long Terme, F-30207 Bagnols Sur Ceze, (France)

    2007-07-01

    The apparent solubility and dissolution rates of natural apatite were measured in closed-system reactors as a function of temperature from 5 to 50 degrees C and pH from 1 to 6. The temporal release rates of Ca, P, and F during the experiments are approximately consistent with stoichiometric dissolution in all experiments. One advantage of closed-system experiments is that they allow determination of reactive fluid evolution and dissolution rates at far-from to near-to equilibrium conditions. Surface area normalized apatite dissolution rates, r, obtained in all experiments are consistent with r = A{sub A}a{sub H{sup +}}{sup n}exp(E{sub A}/RT)(1 -exp(-A/{sigma} RT)) where A{sub A} stands for a rate constant equal to 4 * 10{sup -3} mol/cm{sup 2}/s, a{sub H{sup +}}) denotes the activity of the aqueous H{sup +}, n designates a reaction order equal to 0.6, E{sub A} symbolizes an activation energy equal to 11.0 kcal/mol, A refers to the chemical affinity of the dissolving apatite, {sigma} stands for Temkin's average stoichiometric number equal to 5; R designates the gas constant, and T represents absolute temperature. Logarithms of apparent equilibrium constants obtained from experiments performed at 3 {<=} pH {<=} 5.6 for the apatite dissolution reaction: Ca{sub 5}(PO{sub 4}){sub 3}F + 3H{sup +} = 5Ca{sup 2+} + 3HPO{sub 4}{sup 2-} + F{sup -} are found to be - 29.5 {+-} 0.6, - 29.4 {+-} 0.9 and - 29.9 {+-} 1.3 at 5, 25, and 50 degrees C, respectively. (authors)

  8. Mathematical modeling of drug dissolution.

    Siepmann, J; Siepmann, F

    2013-08-30

    The dissolution of a drug administered in the solid state is a pre-requisite for efficient subsequent transport within the human body. This is because only dissolved drug molecules/ions/atoms are able to diffuse, e.g. through living tissue. Thus, generally major barriers, including the mucosa of the gastro intestinal tract, can only be crossed after dissolution. Consequently, the process of dissolution is of fundamental importance for the bioavailability and, hence, therapeutic efficacy of various pharmaco-treatments. Poor aqueous solubility and/or very low dissolution rates potentially lead to insufficient availability at the site of action and, hence, failure of the treatment in vivo, despite a potentially ideal chemical structure of the drug to interact with its target site. Different physical phenomena are involved in the process of drug dissolution in an aqueous body fluid, namely the wetting of the particle's surface, breakdown of solid state bonds, solvation, diffusion through the liquid unstirred boundary layer surrounding the particle as well as convection in the surrounding bulk fluid. Appropriate mathematical equations can be used to quantify these mass transport steps, and more or less complex theories can be developed to describe the resulting drug dissolution kinetics. This article gives an overview on the current state of the art of modeling drug dissolution and points out the assumptions the different theories are based on. Various practical examples are given in order to illustrate the benefits of such models. This review is not restricted to mathematical theories considering drugs exhibiting poor aqueous solubility and/or low dissolution rates, but also addresses models quantifying drug release from controlled release dosage forms, in which the process of drug dissolution plays a major role. Copyright © 2013 Elsevier B.V. All rights reserved.

  9. Luminescence characterization of a sodium rich feldspar

    Correcher, V.; Sanchez M, L.; Garcia G, J.; Rivera, T.

    2006-01-01

    This paper reports on the radioluminescence (RL) and thermoluminescence (TL) properties of a sodium rich feldspar ((Na,K)[AlSi 3 O 8 ]) with a mean molecular composition of orthoclase (Or) and albite (Ab) of Or 1 Ab 99 . Despite the complexity of the luminescence signals of the sample, it is possible to determine six different emission bands at about 300, 380, 420, 460, 550 and 680 nm. The 300 nm emission can be associated to structural defects related to the recombination process in which the Na + ion diffusion-limited is involved. The UV-blue emission band at (i) 380 nm is characteristic of mineral phases containing SiO 4 tetrahedral and could be related to intrinsic defects in the lattice, (ii) the 420 nm band could be associated to the presence of Cu (II) ions placed next to the hole traps or the recombination on a centre formed from a hole-oxygen atom adjacent to two Al atoms (Al-O-Al) and (iii) the 460 nm waveband could be due to the presence of Ti 4+ . The green and red emissions are respectively associated to the presence of Mn 2+ and Fe 3+ ions. The ratio between the relative intensities, peaked at 290 (the more intense waveband) and 550 nm is about 10:1 in both TL and RL; this fact indicates that the efficiency of recombination centres does no changes regardless on the type of the process. (Author)

  10. Sorption of cesium and uranium to Feldspar

    Wijland, G.C.; Pennders, R.M.J.

    1990-07-01

    Within safety assessment studies, for nuclear waste disposal in deep geologic formations, calculation for the migration of radionuclides through the geosphere are often carried out with models taking sorption into account. In the past 8 years the insight grew that other physico-chemical processes, besides sorption, could affect migration behaviour. While the currently used transport models were being improved taking either linear or non-linear sorption into account, the coupling of geochemical and transport models came into scope. In spite of these developments models which are still based on the sorption theory are frequently applied in studying migration behaviour of radionuclides. This is caused by the necessity of making preliminary pronouncements, while coupled models are still in stage of development and thermodynamic data are very limited available. Therefore one has to obtain insight in the reliability of the models based on the sorption theory. within the sorption database there is a lack of knowledge about mineralogy, composition of the fluid and the experimental conditions underlying the data. Therefore the Expert Group on geochemical Modelling supported by the Finnish proposal in order to obtain insight in the possible deviation of the sorption coefficients that can be estimated from experiments performed with standard samples, fluid composition and experimental conditions. Nine laboratories from OECD membership countries took part in this intercalibration study. In the framework of the Dutch safety assessment studies the Dutch National Institute of Public health and Environmental protection (RIVM) has decided to participate in this exercise. In this report the results are presented of sorption experiments for cesium and natural Uranium to Feldspar. (H.W.). 4 refs.; 1 fig.; 7 tabs

  11. Effect of pH on the dissolution kinetics of zero-valent iron in the presence of EDDHA and EDTA

    Lodge, Alexander M.; Pierce, Eric M.; Wellman, Dawn M.; Rodriguez, Elsa A.

    2007-01-01

    The effect of environmental factors (e.g., pH, solution composition, and temperature) that affect the longevity of Fe(0) barriers in the subsurface are difficult to quantify independently from changes that occur to the passivating layer. Therefore, to quantify the rate of Fe(0) dissolution under conditions which maintain the pO2 at a relatively constant level and minimize the formation of a passivating layer on the metal surface, a series of experiments have been conducted with the single-pass flow-through (SPFT) apparatus. These experiments were conducted over the pH range from 7.0 to 12.0 at 90 C in the presence of 5 mM EDDHA or 5 mM EDTA. The organic acids, EDDHA and EDTA, helped to maintain the aqueous Fe concentration below saturation with respect to Fe-bearing alteration phases and minimize the formation of a partially oxidized surface film. Results suggest the corrosion of Fe(0) is relatively insensitive to pH and the forward or maximum dissolution rate is 3 to 4 orders of magnitude higher than when a passive film and corrosion products are present

  12. Lead-isotope inhomogeneity in Precambrian igneous K-feldspars

    Ludwig, K.R.; Silver, L.T.

    1977-01-01

    Stepwise PB-removal experiments, using both vacuum volatilization and HF-leaching techniques, on acid-washed K-feldspar concentrates from Precambrian igneous rocks show that all contain some unsupported radiogenic Pb. Two types of radiogenic Pb were recognised. One has a 'normal' isotopic composition, with relative abundances of 206 Pb, 207 Pb and 208 Pb consistent with the age and U-Th contents of the rocks. The other type of unsupported radiogenic lead in the feldspars is apparently pure 206 Pb, derived from long-term migration and accumulation of radioactive daughter(s) of 238 U. This 'pure' 206 Pb lead occupies different sites from the 'normal' radiogenic lead, and tends to show a release maximum during vacuum volatilization at about 1150 0 C. The usefulness of stepwise vacuum volatilization may be limited by the tendency of a small amount of radiogenic lead to concentrate in the least volatile fraction. Stepwise partial HF attacks appear to give at least as good separation of radiogenic from original feldspar lead, and are recommended as a routine procedure for isotopic analyses of Precambrian feldspars. The fact that most of the five K-feldspars examined contained unsupported radiogenic lead implies that caution must be used in applying total-sample lead analyses of Precambrian feldspars to problems of lead-isotope evolution in crustal rocks. (author)

  13. Can cathodoluminescence of feldspar be used as provenance indicator?

    Scholonek, Christiane; Augustsson, Carita

    2016-05-01

    We have studied feldspar from crystalline rocks for its textural and spectral cathodoluminescence (CL) characteristics with the aim to reveal their provenance potential. We analyzed ca. 60 rock samples of plutonic, volcanic, metamorphic, and pegmatitic origin from different continents and of 16 Ma to 2 Ga age for their feldspar CL textures and ca. 1200 feldspar crystals from these rocks for their CL color spectra. Among the analyzed rocks, igneous feldspar is most commonly zoned, whereby oscillatory zoning can be confirmed to be typical for volcanic plagioclase. The volcanic plagioclase also less commonly contains twin lamellae that are visible in CL light than crystals from other rock types. Alkali feldspar, particularly from igneous and pegmatitic rocks, was noted to be most affected by alteration features, visible as dark spots, lines and irregular areas. The size of all textural features of up to ca. 150 μm, in combination with possible alteration in both the source area and the sedimentary system, makes the CL textures of feldspar possible to use for qualitative provenance research only. We observed alkali feldspar mostly to luminesce in a bluish color and sometimes in red, and plagioclase in green to yellow. The corresponding CL spectra are dominated by three apparent intensity peaks at 440-520 nm (mainly blue), 540-620 nm (mainly green) and 680-740 nm (red to infrared). A dominance of the peak in the green wavelength interval over the blue one for plagioclase makes CL particularly useful for the differentiation of plagioclase from alkali feldspar. An apparent peak position in red to infrared at < 710 nm for plagioclase mainly is present in mafic rocks. Present-day coastal sand from Peru containing feldspar with the red to infrared peak position mainly exceeding 725 nm for northern Peruvian sand and a larger variety for sand from southern Peru illustrates a discriminative effect of different source areas. We conclude that the provenance application

  14. Dissolution of aluminium

    Uriarte Hueda, A.; Berberana Eizmendi, M.; Pereira Sanchez, G.

    1968-01-01

    The dissolution of aluminum with acid solutions ( nitric acid-mercuric nitrate) and alkaline solutions (sodium hydroxide-sodium nitrate) has been studied. The instantaneous dissolution rate (IDR) has been studied in function of the concentration of the used reagents and the dissolution temperature. The complete dissolution has been included in the second part of this report, to know the total dissolution time, the consume of reagents and the stability of the resultant solutions. (Author)

  15. Comparison of the Kinetic Rate Law Parameters for the Dissolution of Natural and Synthetic Autunite in the Presence of Aqueous Bicarbonate Ions

    Gudavalli, Ravi; Katsenovich, Yelena; Wellman, Dawn M.; Idarraga, Melina; Lagos, Leonel; Tansel, Berrin

    2013-08-02

    Bicarbonate is one of the most significant components within the uranium geochemical cycle. In aqueous solutions, bicarbonate forms strong complexes with uranium. As such, aqueous bicarbonate may significantly increase the rate of uranium release from uranium minerals. Quantifying the relationship of aqueous bicarbonate concentration to the rate of uranium release during dissolution is critical to understanding the long-term fate of uranium within the environment. Single-pass flow-through (SPTF) experiments were conducted to estimate the rate of uranium release from Na meta-autunite as a function of bicarbonate (0.0005-0.003 M) under the pH range of 6-11 and a temperature range of 5-60oC. Consistent with the results of previous investigation, the rate of uranium release exhibited minimal dependency on temperature; but were strongly dependent on pH. Increasing aqueous bicarbonate concentrations afforded comparable increases in the rate of release of uranium. Most notably under low pH conditions the aqueous bicarbonate resulted in up to 370 fold increases in the rate of uranium release in relative to the rate of uranium release in the absence of bicarbonate. However, the effect of aqueous bicarbonate on the release of uranium was significantly less under higher pH conditions. It is postulated that at high pH values, surface sites are saturated with carbonate, thus the addition of more bicarbonate would have less effect on uranium release.

  16. Biotite and chlorite weathering at 25 degrees C: the dependence of pH and (bi)carbonate on weathering kinetics, dissolution stoichiometry, and solubility; and the relation to redox conditions in granitic aquifers

    Malmstroem, M.; Banwart, S. [Royal Inst. of Technology, Stockholm (Sweden). Dept. of Inorganic Chemistry; Duro, L. [Universidad Politecnica de Cataluna, Barcelona (Spain). Dept. de Ingneria Quimica; Wersin, P.; Bruno, J. [MBT Technologia Ambiental, Cerdanyola (Spain)

    1995-01-01

    We have studied the kinetics and thermodynamics of biotite and chlorite weathering in the pH range 2dissolution is highly non-stoichiometric and pH dependent in the whole pH region. By XPD we have identified a clay mineral to be the main weathering product formed. A model of biotite dissolution and the formation of secondary solubility controlling minerals, such as Fe(III)-hydroxide, Na-clay, quartz and gibbsite is used to explain experimental equilibrium concentrations of silicon, iron, aluminium and magnesium. The model predict redox potentials in the range of -200-400 mV at neutral pH and qualitatively agrees with field data reported in the literature. We use observed iron release rate to make conservative estimates of timescales of 1. the depletion of molecular oxygen from deep aquifers (810{sup 2}-10{sup 2} year); and 2. the development of characteristic Fe(III) concentrations (10{sup -5} M in 10{sup -}1 years). The Fe(III)-bearing clay minerals formed during these experiments are similar to the fracture-filling-material observed at the Aespoe Hard Rock Laboratory. Such clays can provide reducing capacity to a repository. They can help maintain anoxic conditions by consuming oxygen that enters the repository during the construction and operation phases thereby helping maintain the redox stability of the repository regarding canister corrosion. The half-life of oxygen trapped in the repository at the time of closure depends on the rate of oxygen uptake by Fe(II) minerals, sulfide minerals and organic carbon. Fe(II)-clay minerals are important to the redox stability of a repository, as well as providing a sorption barrier to radionuclide migration. 107 refs, 52 figs, 35 tabs.

  17. Assessment of bleaching of K-feldspar grains

    Zhang Jiafu; Li Shenghua; Tso, M-Y.W.

    2001-01-01

    Based on the difference in the bleaching rate between IRSL and TL signals, a new method of assessing the bleaching of sedimentary feldspar is proposed. All measurements for De and the bleaching factor (normalized ratio of IRSL to TL) are carried out on the same grain. K-feldspar grains from two sediments, a marine and an alluvium, from Hong Kong were tested. Their bleaching factors indicate that bleaching of the marine sediment was not uniform, whereas the latter was relatively homogeneous. Furthermore, the relatively well-bleached grains in each sample were identified

  18. OSL-thermochronometry of feldspar from the KTB borehole, Germany

    Guralnik, Benny; Jain, Mayank; Herman, Frédéric

    2015-01-01

    a new thermochronometer based on the infrared stimulated luminescence (IRSL) from feldspar, and validate the extrapolation of its response to artificial radiation and heat in the laboratory to natural environmental conditions. Specifically, we present a new detailed Na-feldspar IRSL thermochronology...... the current geothermal gradient, or (ii) inverted into a geothermal palaeogradient of 29±2 °C km−1, integrating natural thermal conditions over the last ∼65 ka. The demonstrated ability to invert a depth–luminescence dataset into a meaningful geothermal palaeogradient opens new venues for reconstructing...

  19. Synthesis, characterization, kinetic and thermodynamic studies of the dissolution of ThO{sub 2} and of solid solutions Th{sub 1-x}M{sub x}O{sub 2} (M = U, Pu); Synthese, caracterisation et etudes cinetique et thermodynamique de la dissolution de ThO{sub 2} et des solutions solides Th{sub 1-x}M{sub x}O{sub 2} (M = U, Pu)

    Heisbourg, G

    2003-12-01

    The aim of this work was to understand the mechanisms of dissolution of ThO{sub 2} and of thorium mixed oxides such as Th{sub 1-x}U{sub x}O{sub 2} and Th{sub 1-x}Pu{sub x}O{sub 2} in aqueous, oxygenated or inert media. Several solids have been synthesized by precipitation in oxalic medium: Th{sub 1-x}U{sub x}O{sub 2} (x= 0.11; 0.24; 0.37; 0.53; 0.67; 0.81 and 0.91) and Th{sub 1-x}Pu{sub x}O{sub 2} (x= 0.13; 0.32 and 0.66). They have been characterized by XRD, SEM, TEM, XPS, XAS, PIXE and EPMA. The sintering conditions of these materials have been studied and optimized in order to obtain sintered samples with a measured density very near the theoretical densities. A kinetic study of the dissolution of ThO{sub 2} and of solid solutions Th{sub 1-x}U{sub x}O{sub 2} has been carried out in several aqueous media (HNO{sub 3}, HCl, H{sub 2}SO{sub 4}) in terms of several parameters: protons concentration, temperature, pH, ionic strength, nature of the electrolyte solution and uranium molar ratio for the solid solutions Th{sub 1-x}U{sub x}O{sub 2} in order to determine the kinetic laws of dissolution of the solid solutions having different compositions comparatively to ThO{sub 2}. The leaching tests carried out in natural waters of compositions near those of the deep geologic sites considered for the storage of nuclear wastes have shown that the dissolution of the solids was bound to the complexing effect of the constitutional ions of the water considered. The leaching tests carried out on sintered samples of the same composition have led to the same normalized dissolution velocities. The thermodynamic aspect of the dissolution of the solid solutions Th{sub 1-x}U{sub x}O{sub 2} in nitric medium has been studied at last. (O.M.)

  20. Dissolution Methods Database

    U.S. Department of Health & Human Services — For a drug product that does not have a dissolution test method in the United States Pharmacopeia (USP), the FDA Dissolution Methods Database provides information on...

  1. Time-resolved luminescence from feldspars: New insight into fading

    Tsukamoto, S.; Denby, P.M.; Murray, A.S.

    2006-01-01

    Time-resolved infrared optically stimulated luminescence (IR-OSL) signals of K- and Na-feldspar samples extracted from sediments were measured in UV, blue and red detection windows, using a fast photon counter and pulsed IR stimulation (lambda = 875 nm). We observe that the relative contribution ...

  2. Hydroxylamine as a potential reagent for dissolution off gas scrubbing in spent fuel reprocessing: kinetics of the iodine reduction. An example of similarity between the studies on the chemistry of iodine in reactor safety and in spent fuel reprocessing

    Cau Dit Coumes, C; Devisme, F [Commissariat a l` Energie Atomique, CE/VRH, Bagnols-sur-Ceze (France); Vargas, S; Chopin-Dumas, J [Laboratoire d` Electrochimie Inorganique, ENSSPICAM, Marseille (France)

    1996-12-01

    Iodine, which can be released inside the containment building when an accident occurs, can be traced, in normal operating conditions, at the back end of the fuel cycle. Hydroxylamine has been selected as a reagent of potential interest to trap iodine in the dissolution off gas treatment. The kinetics of the reaction between hydroxylamine and iodine has been studied in a narrow range of pH (1-2), with hydroxylamine in excess (ratios of hydroxylamine to iodine initial concentrations varying from 2 to 40), at constant temperature (30{sup o}C) and ionic strength (0.1 mol/L). Spectrophotometry and voltametry have been coupled for analytical investigation. The problem of the rapid mixing of the reactants has been solved using a continuous reactor. Triiodide has been shown non reactive towards hydroxylamine. An initial rate law has been proposed, pointing out the first order of the reaction with respect to hydroxylamine and iodine, and the inhibitory effect of iodide and hydrogen ions. Nitrous acid has been identified as a transitory product. Nitrous oxide and nitrogen monoxide have been detected by gas chromatography, the ratio of the amounts of products formed depending on acidity. The complexity of the overall reaction has been ascribed to the competition of four reactions as previously proposed in the literature. (author) 8 figs., 1 tab., 13 refs.

  3. Hydroxylamine as a potential reagent for dissolution off gas scrubbing in spent fuel reprocessing: kinetics of the iodine reduction. An example of similarity between the studies on the chemistry of iodine in reactor safety and in spent fuel reprocessing

    Cau Dit Coumes, C.; Devisme, F.; Vargas, S.; Chopin-Dumas, J.

    1996-01-01

    Iodine, which can be released inside the containment building when an accident occurs, can be traced, in normal operating conditions, at the back end of the fuel cycle. Hydroxylamine has been selected as a reagent of potential interest to trap iodine in the dissolution off gas treatment. The kinetics of the reaction between hydroxylamine and iodine has been studied in a narrow range of pH (1-2), with hydroxylamine in excess (ratios of hydroxylamine to iodine initial concentrations varying from 2 to 40), at constant temperature (30 o C) and ionic strength (0.1 mol/L). Spectrophotometry and voltametry have been coupled for analytical investigation. The problem of the rapid mixing of the reactants has been solved using a continuous reactor. Triiodide has been shown non reactive towards hydroxylamine. An initial rate law has been proposed, pointing out the first order of the reaction with respect to hydroxylamine and iodine, and the inhibitory effect of iodide and hydrogen ions. Nitrous acid has been identified as a transitory product. Nitrous oxide and nitrogen monoxide have been detected by gas chromatography, the ratio of the amounts of products formed depending on acidity. The complexity of the overall reaction has been ascribed to the competition of four reactions as previously proposed in the literature. (author) 8 figs., 1 tab., 13 refs

  4. Laboratory fading rates of various luminescence signals from feldspar-rich sediment extracts

    Thomsen, Kristina Jørkov; Murray, A.S.; Jain, Mayank

    2008-01-01

    Feldspar as a retrospective dosimeter is receiving more and more attention because of its useful luminescence properties; in particular the dose response curve extends to significantly higher doses than quartz. However, feldspars have one major disadvantage; both the thermoluminescence (TL...

  5. Climatic aridity over India 11,000 years ago: Evidence from feldspar distribution in shelf sediments

    Hashimi, N.H.; Nair, R.R.

    Feldspars and quartz contents of sand and silt fractions of forty three samples from the western continental shelf of India were determined by the X-ray diffraction method. The results indicate that the feldspar content in the relict (9000...

  6. Dissolution studies of synthetic soddyite and uranophane

    Casas, I.; Perez, I.; Torrero, E.; Bruno, J.; Cera, E.; Duro, L.

    1997-09-01

    The dissolution of synthetically obtained soddyite and uranophane has been studied in solutions of low ionic strength. These are the likely final phases of the oxidative alternation pathway of uranium dioxide. The thermodynamic and kinetic dissolution properties of these phases have been determined at different bicarbonate concentrations. The solubilities determined in the experiments with soddyite correspond fairly well to the theoretical model calculated with a log K 0 s0 =3.9±0.7. For uranophane, the best fitting was obtained for a log K 0 s0 =11.7±0.6. The dissolution rate in the presence of bicarbonate gave for soddyite an average value of 6.8(±4.4) 10 -10 mol m -2 s -1 . For uranophane, under the same experimental conditions, the following dissolution rate equation has been derived: r 0 (mol m -2 s -1 )=10 -9±2. [HCO 3 - ] 0.69±0.09 2

  7. Simfuel dissolution studies in granitic groundwater

    Casas, I.; Caceci, M.S.; Bruno, J.; Sandino, A.; Ollila, K.

    1991-09-01

    The dissolution behavior of an unirradiated chemical analogue of spent nuclear fuel (SIMFUEL) has been studied in the presence of two different synthetic groundwater at 25 deg C and under both oxic and anoxic conditions. The release of U, Mo, Ba, Y and Sr was monitored during static (batch) leaching experiments of long duration (about 250 days). Preliminary results from continuous flow-through reactor experiments are also reported. The results obtained indicate the usefulness and limitations of SIMFUEL in the study of the kinetics and mechanism of dissolution of the minor components of spent nuclear fuel. Molybdenum, barium and strontium have shown a trend to congruent dissolution with the SIMFUEL matrix after a higher initial fractional release. Yttrium release has been found to be solubility controlled under the experimental conditions. A clear dependence on the partial pressure of O 2 of the rates of dissolution of uranium has been observed

  8. SIMFUEL dissolution studies in granitic groundwater

    Casas, I.; Caceci, M.S.; Bruno, J; Sandino, A.

    1991-09-01

    The dissolution behavior of an unirradiated chemical analogue of spent nuclear fuel (SIMFUEL) has been studied in the presence of two different synthetic groundwaters at 25 degrees C and under both oxic and anoxic conditions. The release of U, Mo, Ba, Y and Sr was monitored during static (batch) leaching experiments of long duration (about 250 days). Preliminary results from continuous flow-through reactor experiments are also reported. The results obtained indicate the usefulness and limitations of SIMFUEL in the study of the kinetics and mechanism of dissolution of the minor components of spent nuclear fuel. Molybdenum, barium and strontium have shown a trend of congruent dissolution with the SIMFUEL matrix after a higher initial fractional release has been found to be solubility controlled under the experimental conditions. A clear dependence on the partial pressure of O 2 of the rate of dissolution of uranium has been observed. (au)

  9. UO2 dissolution rates: A review

    McKenzie, W.F.

    1992-09-01

    This report reviews literature data on UO 2 dissolution kinetics and provides a framework for guiding future experimental studies as well as theoretical modeling studies. Under oxidizing conditions, UO 2 dissolution involves formation of an oxidized surface layer which is then dissolved by formation of aqueous complexes. Higher oxygen pressures or other oxidants are required at higher temperatures to have dissolution rates independent of oxygen pressure. At high oxygen pressures (1-5 atm, 25-70 C), the dissolution rate has a one-half order dependence on oxygen pressure, whereas at oxygen pressures below 0.2 atm, Grandstaff (1976), but nobody else, observed a first-order dependence on dissolution rate. Most people found a first-order dependence on carbonate concentration; Posey-Dowty (1987) found independence of carbonate at pH 7 to 8.2. Dissolution rates increase with temperature except in experiments involving granitic groundwater. Dissolution rates were generally greater under acid or basic conditions than near neutral pH

  10. Measurement of the dose in quartz in the presence of feldspar contamination

    Wallinga, J.; Murray, A.S.; Bøtter-Jensen, L.

    2002-01-01

    To allow the determination of the dose in quartz in the presence of feldspar contamination. the quartz-to-feldspar optically stimulated luminescence (OSL) ratio needs to be maximised. Experiments were carried Out to find the optimum procedure to bleach the feldspar by exposure to infrared light...

  11. Modelling of the UO2 dissolution mechanisms in synthetic groundwater solutions. Dissolution experiments carried out under oxic conditions

    Cera, E.; Grive, M.; Bruno, J.; Ollila, K.

    2001-02-01

    The analytical data generated during the last three years within the 4th framework program of the European Community at VTT Chemical Technology concerning UO 2 dissolution under oxidising conditions have been modelled in the present work. The modelling work has been addressed to perform a kinetic study of the dissolution data generated by Ollila (1999) under oxidising conditions by using unirradiated uranium dioxide as solid sample. The average of the normalised UO 2 dissolution rates determined by using the initial dissolution data generated in all the experimental tests is (6.06 ± 3.64)* 10 -7 mol m -2 d -1 . This dissolution rate agrees with most of the dissolution rates reported in the literature under similar experimental conditions. The results obtained in this modelling exercise show that the same bicarbonate promoted oxidative dissolution processes operate for uranium dioxide, as a chemical analogue of the spent fuel matrix, independently of the composition of the aqueous solution used. (orig.)

  12. Bleaching of the thermoluminescence of feldspars by sunlight

    Robertson, G.B.; Prescott, J.R.; Hutton, J.T.

    1991-01-01

    Feldspars are an important component of materials used for thermoluminescence (TL) and photoluminescence (PL) dating of sediments; and successful dating implies a knowledge of the degree of re-setting by exposure to sunlight of the stored luminescence energy. We have studied the bleaching by full sunlight of the TL of six alkali feldspars of representative composition and of one oligoclase. The high potassium and high sodium feldspars are the brightest, and are also the least easily bleached, whereas those of intermediate (K-Na) composition bleach quickly. On a time scale of upwards of 16 h, all samples would have bleached enough for them to be useful for TL dating. A search was made for individual glow curve peaks that bleach particularly quickly (and are thus similar to the well-known 325 o C peak used in the TL dating of quartz). In the samples studied, there was only one glow curve peak that was selectively susceptible to bleaching: the 280 o C peak in oligoclase. (author)

  13. Isochron measurements of naturally irradiated K-feldspar grains

    Li Bo; Li Shenghua; Wintle, Ann G.; Zhao Hui

    2007-01-01

    The equivalent doses of K-feldspar grains in a range of grain sizes from 90 to 250μm diameter were measured using a single-aliquot regenerative-dose protocol for the infrared stimulated luminescence (IRSL) signals for two samples of desert sand. The equivalent doses for each sample were compared with that for the 125-150μm grains of quartz from the same samples. The results suggested that the K-feldspar equivalent doses were underestimated because of anomalous fading. Measurements of the decay of the IRSL signals following laboratory irradiation for these two samples, and an additional one from a previously published isochron study, showed anomalous fading during the period of laboratory storage. The decay rate was about 3% per decade for all samples and was independent of the grain size used. Using plots of equivalent doses for K-feldspars as a function of their calculated internal dose rate, and the quartz equivalent dose as a function of grain size, it was concluded that the IRSL signal derived from the internal dose rate had not faded over the 13,000 years that had elapsed since the grains were deposited

  14. Stoneware tile manufacturing using rice straw ash as feldspar replacement

    Alvaro Guzman, A.; John Torres, L.; Martha Cedeno, V.; Silvio Delvasto, A.; Vicente Amigo, B.; Enrique Sanchez, V.

    2013-01-01

    In this research are presented the results of using rice straw ash (RSA) in low proportions as substitute of feldspar for manufacturing stoneware tiles. Specimens of semidry triaxial mixtures, where feldspar was substituted for different percentages (25 % and 50 %) of RSA, were prepared by uniaxial pressing, followed by drying and sintering. Physical and mechanical properties of sintered bodies were evaluated. Porcelain stoneware tile specimens C0 and CF25 reached bending strength and water absorption values were in accordance with standard ISO 13006 (Annex G, BIa) ( ≥ 35 MPa and ≤ 0.5 %, respectively). However, in porcelain stoneware tile specimens CF50 due to bloating phenomenon was not possible obtain commercial tiles in accordance with standard ISO 13006. By using Scanning Electron Microscopy (SEM) needles of primary and secondary mullite were identified in a vitreous phase; and by using X-Ray Diffraction (XRD) mullite and quartz phases were identified. It was concluded that feldspar can be substituted positively by RSA in stoneware tile pastes. (Author)

  15. Dissolution of UO2 in redox conditions

    Casas, I.; Pablo de, J.; Rovira, M.

    1998-01-01

    The performance assessment of the final disposal of the spent nuclear fuel in geological formations is strongly dependent on the spent fuel matrix dissolution. Unirradiated uranium (IV) dioxide has shown to be very useful for such purposes. The stability of UO 2 is very dependent on vault redox conditions. At reducing conditions, which are expected in deep groundwaters, the dissolution of the UO 2 -matrix can be explained in terms of solubility, while under oxidizing conditions, the UO 2 is thermodynamically unstable and the dissolution is kinetically controlled. In this report the parameters which affect the uranium solubility under reducing conditions, basically pH and redox potential are discussed. Under oxidizing conditions, UO 2 dissolution rate equations as a function of pH, carbonate concentration and oxidant concentration are reported. Dissolution experiments performed with spent fuel are also reviewed. The experimental equations presented in this work, have been used to model independent dissolution experiments performed with both unirradiated and irradiated UO 2 . (Author)

  16. Dissolution of minerals with rough surfaces

    de Assis, Thiago A.; Aarão Reis, Fábio D. A.

    2018-05-01

    We study dissolution of minerals with initial rough surfaces using kinetic Monte Carlo simulations and a scaling approach. We consider a simple cubic lattice structure, a thermally activated rate of detachment of a molecule (site), and rough surface configurations produced by fractional Brownian motion algorithm. First we revisit the problem of dissolution of initial flat surfaces, in which the dissolution rate rF reaches an approximately constant value at short times and is controlled by detachment of step edge sites. For initial rough surfaces, the dissolution rate r at short times is much larger than rF ; after dissolution of some hundreds of molecular layers, r decreases by some orders of magnitude across several time decades. Meanwhile, the surface evolves through configurations of decreasing energy, beginning with dissolution of isolated sites, then formation of terraces with disordered boundaries, their growth, and final smoothing. A crossover time to a smooth configuration is defined when r = 1.5rF ; the surface retreat at the crossover is approximately 3 times the initial roughness and is temperature-independent, while the crossover time is proportional to the initial roughness and is controlled by step-edge site detachment. The initial dissolution process is described by the so-called rough rates, which are measured for fixed ratios between the surface retreat and the initial roughness. The temperature dependence of the rough rates indicates control by kink site detachment; in general, it suggests that rough rates are controlled by the weakest microscopic bonds during the nucleation and formation of the lowest energy configurations of the crystalline surface. Our results are related to recent laboratory studies which show enhanced dissolution in polished calcite surfaces. In the application to calcite dissolution in alkaline environment, the minimal values of recently measured dissolution rate spectra give rF ∼10-9 mol/(m2 s), and the calculated rate

  17. Thermodynamic stability and kinetics of perovskite dissolution

    Nesbitt, H W; Bancroft, G M; Fyfe, W S; Karkhanis, S N; Nishijima, A [Western Ontario Univ., London (Canada); Shin, S [National Chemical Lab. for Industry, Tsukuba (Japan)

    1981-01-29

    Perovskite, a SYNROC host mineral for nuclear wastes, is thermodynamically unstable in natural waters and in association with common minerals. Leach experiments demonstrate that CaTiO/sub 3/ (perovskite), SrTiO/sub 3/ and BaTiO/sub 3/ are as reactive as some silicate glasses below 100/sup 0/C, but leach much more slowly than glasses above 100/sup 0/C.

  18. Numerical modelling of multicomponent LNAPL dissolution kinetics ...

    subsequent removal of free phase liquid, still the organic compounds are present .... Since the flow through porous media is mainly restricted to the pore space ..... initial and boundary conditions for the numerical scheme are given in table 2.

  19. Luminescence from potassium feldspars stimulated by infrared and green light

    Duller, G.A.T.; Bøtter-Jensen, L.

    1993-01-01

    A series of experiments are reported which investigate stimulated luminescence from potassium feldspar. The aim is to provide a basic phenomenological description of the response of the material to stimulation by heat, infrared radiation (875 DELTA 80 nm) and a green light wavelength band from 5 15...... to 560 nm. Two conclusions are drawn: firstly it is suggested that the majority of the trapped charge responsible for the infrared stimulated luminescence signal does not give rise to a thermoluminescence signal, and secondly that a large traction of the two optically stimulated luminescence signals...

  20. Dissolution of covalent adaptable network polymers in organic solvent

    Yu, Kai; Yang, Hua; Dao, Binh H.; Shi, Qian; Yakacki, Christopher M.

    2017-12-01

    It was recently reported that thermosetting polymers can be fully dissolved in a proper organic solvent utilizing a bond-exchange reaction (BER), where small molecules diffuse into the polymer, break the long polymer chains into short segments, and eventually dissolve the network when sufficient solvent is provided. The solvent-assisted dissolution approach was applied to fully recycle thermosets and their fiber composites. This paper presents the first multi-scale modeling framework to predict the dissolution kinetics and mechanics of thermosets in organic solvent. The model connects the micro-scale network dynamics with macro-scale material properties: in the micro-scale, a model is developed based on the kinetics of BERs to describe the cleavage rate of polymer chains and evolution of chain segment length during the dissolution. The micro-scale model is then fed into a continuum-level model with considerations of the transportation of solvent molecules and chain segments in the system. The model shows good prediction on conversion rate of functional groups, degradation of network mechanical properties, and dissolution rate of thermosets during the dissolution. It identifies the underlying kinetic factors governing the dissolution process, and reveals the influence of different material and processing variables on the dissolution process, such as time, temperature, catalyst concentration, and chain length between cross-links.

  1. Uranium carbide dissolution in nitric solution: Sonication vs. silent conditions

    Virot, Matthieu; Szenknect, Stéphanie; Chave, Tony; Dacheux, Nicolas; Moisy, Philippe; Nikitenko, Sergey I.

    2013-01-01

    The dissolution of uranium carbide (UC) in nitric acid media is considered by means of power ultrasound (sonication) or magnetic stirring. The induction period required to initiate UC dissolution was found to be dramatically shortened when sonicating a 3 M nitric solution (Ar, 20 kHz, 18 W cm −2 , 20 °C). At higher acidity, magnetic stirring offers faster dissolution kinetics compared to sonication. Ultrasound-assisted UC dissolution is found to be passivated after ∼60% dissolution and remains incomplete whatever the acidity which is confirmed by ICP–AES, LECO and SEM–EDX analyses. In general, the kinetics of UC dissolution is linked to the in situ generation of nitrous acid in agreement with the general mechanism of UC dissolution; the nitrous acid formation is reported to be faster under ultrasound at low acidity due to the nitric acid sonolysis. The carbon balance shared between the gaseous, liquid, and solid phases is strongly influenced by the applied dissolution procedure and HNO 3 concentration

  2. Uranium carbide dissolution in nitric solution: Sonication vs. silent conditions

    Virot, Matthieu; Szenknect, Stéphanie; Chave, Tony; Dacheux, Nicolas; Moisy, Philippe; Nikitenko, Sergey I.

    2013-10-01

    The dissolution of uranium carbide (UC) in nitric acid media is considered by means of power ultrasound (sonication) or magnetic stirring. The induction period required to initiate UC dissolution was found to be dramatically shortened when sonicating a 3 M nitric solution (Ar, 20 kHz, 18 W cm-2, 20 °C). At higher acidity, magnetic stirring offers faster dissolution kinetics compared to sonication. Ultrasound-assisted UC dissolution is found to be passivated after ∼60% dissolution and remains incomplete whatever the acidity which is confirmed by ICP-AES, LECO and SEM-EDX analyses. In general, the kinetics of UC dissolution is linked to the in situ generation of nitrous acid in agreement with the general mechanism of UC dissolution; the nitrous acid formation is reported to be faster under ultrasound at low acidity due to the nitric acid sonolysis. The carbon balance shared between the gaseous, liquid, and solid phases is strongly influenced by the applied dissolution procedure and HNO3 concentration.

  3. To the problem of paleodosimetrical information stability in alkali feldspars

    Huett, Galina; Jaek, Ivar

    1997-01-01

    The stability of holes of the centres of recombination in alkali feldspars, extracted from sediments, is studied. For the emission centres with 410 and 570 nm the energy of activation of thermal quenching is obtained (> 2 eV). Problems of fading and difference between thermoluminescence (TL) and optically stimulated luminescence (OSL), as well as bleach abilities, are discussed. Values of thermal activation energy (> 2 eV) obtained for two different emission bands (410 and 570 nm) in alkali feldspars prove the upper limit of dating (c 10 5 years). The absence of a permanent channel of fading is supported by experimental data. Differences in bleach ability, as well as in residuals of TL and OSL response dating signals, are explained within the frame of the proposed model of identity of defects responsible for those signals. It is supposed that better bleach ability of the OSL signal is connected with optical selection of more transparent grains (or more easily bleach able centres). The applicability of the orange band of emission (570 nm) for dating is recommended for future study

  4. New insights into the oleate flotation response of feldspar particles of different sizes: Anisotropic adsorption model.

    Xu, Longhua; Tian, Jia; Wu, Houqin; Deng, Wei; Yang, Yaohui; Sun, Wei; Gao, Zhiyong; Hu, Yuehua

    2017-11-01

    The anisotropic adsorption of sodium oleate (NaOL) on feldspar surfaces was investigated to elucidate the different flotation properties of feldspar particles of four different size ranges. Microflotation experiments showed that the feldspar flotation recovery of particles with sizes spanning different ranges decreased in the order 0-19>19-38>45-75>38-45μm. Zeta potential and FTIR measurements showed that NaOL was chemically adsorbed on the Al sites of the feldspar surface. The anisotropic surface energies and broken bond densities estimated by density functional theory calculations showed that, although feldspar mostly exposed (010) and (001) surfaces, only the (001) surfaces contained the Al sites needed for NaOL adsorption. The interaction energies calculated by molecular dynamics simulations confirmed the more favorable NaOL adsorption on (001) than (010) surfaces, which may represent the main cause for the anisotropic NaOL adsorption on feldspar particles of different sizes. SEM measurements showed that the main exposed surfaces on coarse and fine feldspar particles were the side (010) and basal (001) ones, respectively. A higher fraction of Al-rich (001) surfaces is exposed on fine feldspar particles, resulting in better floatability compared with coarse particles. XPS and adsorption measurements confirmed that the Al content on the feldspar surface varied with the particle size, explaining the different NaOL flotation of feldspar particles of different sizes. Therefore, the present results suggest that coarsely ground ore should be used for the separation of feldspar gangue minerals. Further improvements in the flotation separation of feldspar from associated valuable minerals can be achieved through selective comminution or grinding processes favoring the exposure of (010) surfaces. Copyright © 2017 Elsevier Inc. All rights reserved.

  5. Advances in heterogeneous autocatalytic reactions applied to uranium dissolution - 5317

    Marc, P.; Magnaldo, A.; Godard, J.; Schaer, E.

    2015-01-01

    Dissolution and the solubilization of the chemical elements is a milestone of the head-end of hydrometallurgical processes. When dissolving spent nuclear fuels, additional constraints are added due to the permanent need to strictly control and limit the hold-up. Thus the need for kinetic modeling concerning the dissolution of spent nuclear fuels in nitric acid. This study aims at better understanding the chemical and physical-chemical phenomena of uranium dioxide dissolution reactions in nitric medium. It has been documented that the nitric acid attack of sintering-manufactured uranium dioxide solids occurs through preferential attack sites. This non uniform attack leads to the development of cracks in the solids. Optical microscopy observations show that in some cases, the development of these cracks can lead to the solid cleavage. In this case, we show that the dissolution of the detached fragments is much slower than the time required for the complete cleavage of the solid. These points motivated the measurements of dissolution kinetics using optical microscopy and image processing. A comparison of the measured kinetics with the diffusion kinetics by the mean of the external resistance fraction allows discriminating between measured kinetics corresponding to the chemical reaction or mass-transport limitation. This capability to measure, for the very first time, the 'true' chemical kinetics of the reaction has enabled the confirmation of the highly autocatalytic nature of the reaction, and first evaluation of the constants of the chemical reactions kinetic laws. These data are fundamental to set the kinetic parameters of the chemical reactions in a future model of the dissolution of uranium dioxide sintered pellets. (authors)

  6. K-Ar dating: incomplete extraction of radiogenic argon from alkali feldspar - a comment

    Baksi, A.K.

    1984-01-01

    In a recent paper, McDowell (1983) discussed the difficulties involved in obtaining accurate K-Ar ages on alkali feldspar samples. These difficulties primarily stem from the fact that the feldspars melt at high temperatures and lack structural volatiles which could flush out all of the 40 Ar* from the viscous melt at temperatures below 1600 0 C. Evidently, if feldspar samples could be satisfactorily melted at lower temperatures by the use of a suitable flux, complete release of 40 Ar* should occur. McDowell (1983) also commented on the lack of a suitable feldspar standard sample for argon dating work. This comment will briefly address these two problems. (Auth.)

  7. Dissolution of nuclear fuels

    Uriarte Hueda, A.; Berberana Eizmendi, M.; Rainey, R.

    1968-01-01

    A laboratory study was made of the instantaneous dissolution rate (IDR) for unirradiated uranium metal rods and UO 2 , PuO 2 and PuO 2 -UO 2 pellets in boiling nitric acid alone and with additives. The uranium metal and UO 2 dissolved readily in nitric acid alone; PuO 2 dissolved slowly even with the addition of fluoride; PuO 2 -UO 2 pellets containing as much as 35% PuO 2 in UO 2 gave values of the instantaneous dissolution rate to indicate can be dissolved with nitric acid alone. An equation to calculate the time for complete dissolution has been determinate in function of the instantaneous dissolution rates. The calculated values agree with the experimental. Uranium dioxide pellets from various sources but all having a same density varied in instantaneous dissolution rate. All the pellets, however, have dissolved ved in the same time. The time for complete dissolution of PuO 2 -UO 2 pellets, having the same composition, and the concentration of the used reagents are function of the used reagents are function of the fabrication method. (Author) 8 refs

  8. Effect of alteration phase formation on the glass dissolution rate

    Ebert, W.L.

    1997-01-01

    The dissolution rates of many glasses have been observed to increase upon the formation of certain alteration phases. While simulations have predicted the accelerating effect of formation of certain phases, the phases predicted to form in computer simulations are usually different than those observed to form in experiments. This is because kinetically favored phases form first in experiments, while simulations predict the thermodynamically favored phases. Static dissolution tests with crushed glass have been used to measure the glass dissolution rate after alteration phases form. Because glass dissolution rates are calculated on a per area basis, an important effect in tests conducted with crushed glass is the decrease in the surface area of glass that is available for reaction as the glass dissolves. This loss of surface area must be taken into account when calculating the dissolution rate. The phases that form and their effect on the dissolution rate are probably related to the glass composition. The impact of phase formation on the glass dissolution rate also varies according to the solubility products of the alteration phases and how the orthocilicic acid activity is affected. Insight into the relationship between the glass dissolution rate, solution chemistry and alteration phase formation is provided by the results of accelerated dissolution tests

  9. Effect of alteration phase formation on the glass dissolution rate

    Ebert, W L [Argonne National Laboratory, Chemical Technology Div. (United States)

    1997-07-01

    The dissolution rates of many glasses have been observed to increase upon the formation of certain alteration phases. While simulations have predicted the accelerating effect of formation of certain phases, the phases predicted to form in computer simulations are usually different than those observed to form in experiments. This is because kinetically favored phases form first in experiments, while simulations predict the thermodynamically favored phases. Static dissolution tests with crushed glass have been used to measure the glass dissolution rate after alteration phases form. Because glass dissolution rates are calculated on a per area basis, an important effect in tests conducted with crushed glass is the decrease in the surface area of glass that is available for reaction as the glass dissolves. This loss of surface area must be taken into account when calculating the dissolution rate. The phases that form and their effect on the dissolution rate are probably related to the glass composition. The impact of phase formation on the glass dissolution rate also varies according to the solubility products of the alteration phases and how the orthocilicic acid activity is affected. Insight into the relationship between the glass dissolution rate, solution chemistry and alteration phase formation is provided by the results of accelerated dissolution tests.

  10. Kinetics of dissolution of {alpha}-Fe{sub 2}O{sub 3} and {gamma}-Fe{sub 2}O{sub 3} in EDTA and NTA-based formulations

    Ranganathan, S. [Dept. of Chemical Engineering, Univ. of New Brunswick, Fredericton, N.B. (Canada); Srinivasan, M.P. [Water and Steam Chemistry Lab. of Bhabha Atomic Research Centre (BARC) (India); Narasimhan, S.V. [Bhabha Atomic Research Centre (India); Raghavan, P.S. [Madras Christian Coll., Chennai (India); Gopalan, R. [Dept. of Chemistry, Madras Christian Coll., Chennai (India)

    2004-06-01

    The dissolution studies were carried out on haematite ({alpha}-Fe{sub 2}O{sub 3}) and maghemite ({gamma}-Fe{sub 2}O{sub 3}) in two different formulations of ethylenediaminetetraacetic acid (EDTA) and nitrilotriaceticacid (NTA). The rate constants were calculated using the ''inverse cubic rate law.'' The leaching of the metal ions from the oxide is controlled partly by the Fe(II)-L{sub n} (L is a complexing ligand and n is the number of ligands attached to Fe{sup 2+}), a dissolution product arising from the oxides having Fe{sup 2+} in the lattice. The addition of Fe(II)-L{sub n} along with the formulation greatly increased the initial rate of dissolution. The effect of the addition of Fe(II)-L as a reductant on the dissolution of {alpha}-Fe{sub 2}O{sub 3} was not the same as in the case of {gamma}-Fe{sub 2}O{sub 3}. The rate constants (k{sub obs}) for the dissolution of {alpha}-Fe{sub 2}O{sub 3} and {gamma}-Fe{sub 2}O{sub 3} in the presence of ascorbic acid were less in the EDTA formulation than in the NTA formulation. The studies using Fe(II)-NTA and Fe(II)-EDTA with varying compositions of citric acid and ascorbic acid revealed that a minimum quantity of the chelant is sufficient to initiate the dissolution process, which can be further controlled by the reductants and weaker chelants such as citric acid. (orig.)

  11. Chrysotile dissolution rates: Implications for carbon sequestration

    Thom, James G.M.; Dipple, Gregory M.; Power, Ian M.; Harrison, Anna L.

    2013-01-01

    Highlights: • Uncertainties in serpentine dissolution kinetics hinder carbon sequestration models. • A pH dependent, far from equilibrium dissolution rate law for chrysotile. • F chrysotile (mol/m 2 /s) = 10 −0.21pH−10.57 at 22 °C over pH 2–10. • Laboratory dissolution rates consistent with mine waste weathering observations. • Potential for carbon sequestration in mine tailings and aquifers is assessed. - Abstract: Serpentine minerals (e.g., chrysotile) are a potentially important medium for sequestration of CO 2 via carbonation reactions. The goals of this study are to report a steady-state, far from equilibrium chrysotile dissolution rate law and to better define what role serpentine dissolution kinetics will have in constraining rates of carbon sequestration via serpentine carbonation. The steady-state dissolution rate of chrysotile in 0.1 m NaCl solutions was measured at 22 °C and pH ranging from 2 to 8. Dissolution experiments were performed in a continuously stirred flow-through reactor with the input solutions pre-equilibrated with atmospheric CO 2 . Both Mg and Si steady-state fluxes from the chrysotile surface, and the overall chrysotile flux were regressed and the following empirical relationships were obtained: F Mg =-0.22pH-10.02;F Si =-0.19pH-10.37;F chrysotile =-0.21pH-10.57 where F Mg , F Si , and F chrysotile are the log 10 Mg, Si, and molar chrysotile fluxes in mol/m 2 /s, respectively. Element fluxes were used in reaction-path calculations to constrain the rate of CO 2 sequestration in two geological environments that have been proposed as potential sinks for anthropogenic CO 2 . Carbon sequestration in chrysotile tailings at 10 °C is approximately an order of magnitude faster than carbon sequestration in a serpentinite-hosted aquifer at 60 °C on a per kilogram of water basis. A serpentinite-hosted aquifer, however, provides a larger sequestration capacity. The chrysotile dissolution rate law determined in this study has

  12. Stability of IRSL signals from sedimentary K-feldspar samples

    Thomsen, Kristina Jørkov; Murray, A.S.; Jain, Mayank

    2011-01-01

    for potassium-rich sedimentary feldspars. We show that the natural post-IR IRSL (pIRIR) signal from a 3.6 Ma old sample is in apparent saturation on a laboratory generated dose response curve, i.e. it does not show detectable fading in nature although a low fading rate is observed on laboratory time scales. We...... be explained in terms of either a single- or multiple-trap model. We present evidence that may suggest that at least part of pIRIR signal is derived from a high temperature trap (∼550°C thermoluminescence (TL) peak), although again the data can also be explained in terms of a single-trap model. Finally, we...

  13. Developing a numerical simulation for fading in feldspar

    Larsen, A.; Greilich, S.; Jain, M.; Murray, A.S.

    2009-01-01

    Most models describing anomalous fading in feldspars are based on analytical solutions. As an alternative approach we present an entirely numerical model based on statistical sampling that simulates stepwise the charge creation/trapping and recombination in a given phosphor. We assume the number density of electrons and holes at any time to be equal, although the model is not bound to that assumption. The model is flexible enough to be used on any combination of geological and laboratory timescales and for any defined configuration of defects. Using this approach we observed reorganization of nearest-neighbor distances with time. The best agreement with experimental data is achieved if we assume the crystal to consist of small subvolumes (nanocrystals) only within which charge carriers are allowed to recombine.

  14. Aluminum Target Dissolution in Support of the Pu-238 Program

    McFarlane, Joanna [ORNL; Benker, Dennis [ORNL; DePaoli, David W [ORNL; Felker, Leslie Kevin [ORNL; Mattus, Catherine H [ORNL

    2014-09-01

    Selection of an aluminum alloy for target cladding affects post-irradiation target dissolution and separations. Recent tests with aluminum alloy 6061 yielded greater than expected precipitation in the caustic dissolution step, forming up to 10 wt.% solids of aluminum hydroxides and aluminosilicates. We present a study to maximize dissolution of aluminum metal alloy, along with silicon, magnesium, and copper impurities, through control of temperature, the rate of reagent addition, and incubation time. Aluminum phase transformations have been identified as a function of time and temperature, using X-ray diffraction. Solutions have been analyzed using wet chemical methods and X-ray fluorescence. These data have been compared with published calculations of aluminum phase diagrams. Temperature logging during the transients has been investigated as a means to generate kinetic and mass transport data on the dissolution process. Approaches are given to enhance the dissolution of aluminum and aluminosilicate phases in caustic solution.

  15. Thermoluminescence of annealed and shock-loaded feldspar

    Hartmetz, C.P.

    1988-01-01

    Samples of oligoclase and bytownite were shock-loaded to a variety of pressures, and annealed for a variety of temperatures and times. The effect of Mrad doses of gamma-rays on oligoclase TL were also studied. After these treatments, thermoluminescence (TL) and X-ray diffraction (XRD) measurements were made to: (1) determine the effects of shock on terrestrial feldspar and compare with variations in the TL emission of ordinary chondrites (OCs); (2) determine if disordering in feldspar was responsible for any related changes in TL properties of OCs; (3) determine if the combined effect of shock plus annealing causes the changes in TL properties; (4) see if radiation damage from cosmic ray exposure plays a role in the TL variations; (5) examine the implications of this work to the thermal and shock histories of OCs. The lightly shock-loaded and annealed oligoclase samples have a dominant peak temperature of 120-140 C, identical to type 3.3-3.5 OCs. The heavily shocked samples dominant peak is at 230C, similar to type > 3.5 OCs . While the heavily annealed/disordered oligoclase samples have a peak at 280C, this peak is rarely observed in OCs. Radiation damage from Mrad doses of gamma-rays produced no change in peak temperature, but facilitated the shift to higher peak temperatures. The TL sensitivity of the shocked samples decreased by a factor of 25. Samples annealed at low temperatures (438-533C) showed a factor of 2 decrease in TL, but at the highest temperatures, the TL was a factor of 8 higher

  16. Dating Last Interglacial Coastal Systems Using New Feldspar Luminescence Technologies

    Lamothe, M.

    2017-12-01

    The recent explosion in new luminescence dating technologies offers new opportunities to explore Quaternary marine coastal facies and landforms. However, tectonic and climatic processes controlling the development of Pleistocene coastal lithosomes are commonly obscured by their poorly constrained geological age. Luminescence dating of feldspar probes one order of magnitude deeper into geological time than radiocarbon and more than 5 times the current age range of quartz optically-stimulated luminescence, routinely used in luminescence dating. However, feldspar luminescence stimulated by infrared photons (eg IRSL) is hampered by anomalous fading. Successful correction methods developed by us over the last 15 years did produce sound chronologies but the fading-corrected ages carried large uncertainties. New approaches initiated by other laboratories, mainly in Europe, have isolated high temperature post-IRSL luminescence as this signal seems to be only slightly affected by fading. However, the gain in stability seems to be lessened due to bleachibility issues, generating age overestimations. We developed a novel protocol known as post-isothermal IRSL dating (Pit-IR) that focuses on a dual system of luminescence signals, probing low (50C) and medium (225C) temperature IRSL signals following isothermal treatments of various intensities. These protocols have been tested on Last interglacial coastal sediments in strikingly different GIA contexts along the Atlantic coastal areas of SE USA as well as from Morocco, Brazil and LIG sites in the Mediterranean basin. A systematic analysis of these results would suggest that a) falling-stages sequences are more commonly preserved as the OSL/IRSL ages are preferentially dating from the end of the MIS5e high stand and b) MIS5a marine sediments may be detectable away from areas generally thought to be affected by peripheral bulge collapse.

  17. Kinetics of optically - and thermally - induced diffusion and dissolution of silver in evaporated As33S33.5Se33.5 amorphous films: their properties and structure

    Krbal, M.; Wágner, T.; Frumar, M.; Vlček, Milan; Frumarová, Božena

    2006-01-01

    Roč. 47, č. 2 (2006), s. 193-197 ISSN 0031-9090. [Solid State Chemistry VI. Praha, 13.09.2004-17.09.2004] Institutional research plan: CEZ:AV0Z40500505 Keywords : diffusion and dissolution * As-S-Se films Subject RIV: CA - Inorganic Chemistry Impact factor: 0.577, year: 2006

  18. Spent fuel dissolution mechanisms

    Ollila, K.

    1993-11-01

    This study is a literature survey on the dissolution mechanisms of spent fuel under disposal conditions. First, the effects of radiolysis products on the oxidative dissolution mechanisms and rates of UO 2 are discussed. These effects have mainly been investigated by using electrochemical methods. Then the release mechanisms of soluble radionuclides and the dissolution of the UO 2 matrix including the actinides, are treated. Experimental methods have been developed for measuring the grain-boundary inventories of radionuclides. The behaviour of cesium, strontium and technetium in leaching tests shows different trends. Comparison of spent fuel leaching data strongly suggests that the release of 90 Sr into the leachant can be used as a measure of the oxidation/dissolution of the fuel matrix. Approaches to the modelling UO 2 , dissolution are briefly discussed in the next chapter. Lastly, the use of natural material, uraninite, in the evaluation of the long-term performance of spent fuel is discussed. (orig.). (81 ref., 37 figs., 8 tabs.)

  19. Feldspar basalts in lunar soil and the nature of the lunar continents

    Reid, A. M.; Ridley, W. I.; Harmon, R. S.; Warner, J.; Brett, R.; Jakes, P.; Brown, R. W.

    1974-01-01

    It is found that 25% on the Apollo-14 glasses have the same composition as the glasses in two samples taken from the Luna-16 column. The compositions are equivalent to feldspar basalt and anorthosite gabbro, and are similar to the feldspar basalts identified from Surveyor-7 analysis for lunar continents.

  20. Full analysis of feldspar texture and crystal structure by combining X-ray and electron techniques

    Balic Zunic, Tonci; Piazolo, Sandra; Katerinopoulou, Anna

    2013-01-01

    identification plus crystal structure refinement of all components in a feldspar intergrowth. This procedure was applied to perthitic intergrowths in feldspars from two different pegmatites in the Larvik plutonic complex in the southern part of the Oslo region, Norway. It revealed that the two starting high...

  1. Developing Effective Separation of Feldspar and Quartz While Recycling Tailwater by HF Pretreatment

    Weiqing Wang

    2018-04-01

    Full Text Available The effect of hydrofluoric acid (HF pretreatment on flotation of feldspar and quartz using dodecylamine (DDA as collector was investigated by micro-flotation, zeta potential, pyrene fluorescence spectroscopy, attenuated total reflection flourier transformed infrared spectroscopy (ATR-FTIR, scanning electron microscope (SEM, X-ray photoelectron spectroscopy (XPS and bench scale flotation. The micro-flotation tests revealed that there was little difference in the flotation of feldspar and quartz at pH 2, using H2SO4 as pH regulator. After HF pretreatment, the floatability of feldspar significantly increased while the floatability of quartz showed no change. HF pretreatment resulted in leaching of SiO2 and enrichment of Na, K and Al on the feldspar surface. Consequently, the negative surface charge of feldspar increased at pH 2, which allowed for the flotation separation of the feasible minerals. This took place via an increased electrostatic adsorption between DDA and Na, K, Al on the feldspar surface, which effectively increased its hydrophobicity and as a result, improved the floatability of feldspar. An alternative process which exhibited effective separation of quartz and feldspar while recycling the tailwater from the flotation was proposed.

  2. Bio-beneficiation of kaolin and feldspar and its effect on fired

    Presence of iron compounds as impurities in kaolin and feldspar, impart reddish colour to ceramic products manufactured using these minerals. The quality of kaolin and feldspar was enriched mainly through iron removal by biological methods. Bacteria isolated from kaolin of Indian origin were used for bioleaching.

  3. Application of Cathodoluminescence to The Study of Feldspars: Imaging and Spectrometry

    Fonseca, Rute; Couto, Helena

    2017-12-01

    Cathodoluminescence (CL) studies were carried out on polished thin sections of different feldspar samples (from migmatites, granites, aplite-pegmatites and granitic aggregates) using a hot cathode CL equipment HC3-LM coupled to an optical microscope and to a spectrometer (SpectraPro 2300i and a CCD Pixis 400B detector and the software Winspec32) from the Faculty of Sciences of University of Porto. The system was operated at 14kV and a filament current of 0.18 mA. The samples were coated with a thin gold film using a Cressington 108 Auto device. Luminescence images were acquired during the CL analysis with an adapted digital video-camera (KAPPA PS 40C-285 (DX) with dual stage Peltier cooling) and an acquisition time between 351ms and 3,52s. The CL study, including imaging and spectrometry, proved to be an important tool to complement the feldspar petrography as it contributes to the identification of features not observed under optical microscope. The application of the Cathodoluminescence to feldspar allows distinguishing between potassic feldspar and plagioclase, differentiating generations of feldspar and displaying internal zoning and growth areas, among other. The spectrometry complements the CL imaging. It allows obtaining a qualitative level of emission intensity, which permits the interpretation of the nature of this luminescence in each feldspar. Bands shown in the spectra are related to the existing activator elements. In the present study, it was found an association of each feldspar to different spectra and respective colour. The plagioclases exhibit yellow or green luminescence. The activator element is Mn2+, showing a broad emission band between 550 - 570 nm specially detected on this type of feldspars, due to the replacement of K+ for Mn2+. The potassium feldspars have more or less intense blue colour associated with various activators elements: the activator element is Cu2+ showing a broad emission band between 420±5 nm. This emission band can be

  4. Iron oxides photochemical dissolution

    Blesa, M.A.; Litter, M.I.

    1987-01-01

    This work was intended to study the light irradiation influence of diverse wave-lengths on iron oxides dissolution in aqueous solutions. The objectives of this work were: the exploration of photochemical processes with the aim of its eventual application in: a) decontamination and chemical cleaning under special conditions; b) materials for solar energy conversion. (Author)

  5. Plutonium oxide dissolution

    Gray, J.H.

    1992-01-01

    Several processing options for dissolving plutonium oxide (PuO 2 ) from high-fired materials have been studied. The scoping studies performed on these options were focused on PuO 2 typically generated by burning plutonium metal and PuO 2 produced during incineration of alpha contaminated waste. At least two processing options remain applicable for dissolving high-fired PuO 2 in canyon dissolvers. The options involve solid solution formation of PuO 2 With uranium oxide (UO 2 ) and alloying incinerator ash with aluminum. An oxidative dissolution process involving nitric acid solutions containing a strong oxidizing agent, such as cerium (IV), was neither proven nor rejected. This uncertainty was due to difficulty in regenerating cerium (IV) ions during dissolution. However, recent work on silver-catalyzed dissolution of PuO 2 with persulfate has demonstrated that persulfate ions regenerate silver (II). Use of persulfate to regenerate cerium (IV) or bismuth (V) ions during dissolution of PuO 2 materials may warrant further study

  6. Formation of halloysite from feldspar: Low temperature, artificial weathering versus natural weathering

    Parham, Walter E.

    1969-01-01

    Weathering products formed on surfaces of both potassium and plagioclase feldspar (An70), which were continuously leached in a Soxhlet extraction apparatus for 140 days with 7.21 of distilled water per day at a temperature of approximately 78°C, are morphologically identical to natural products developed on potassium feldspars weathered under conditions of good drainage in the humid tropics. The new products, which first appear as tiny bumps on the feldspar surface, start to develop mainly at exposed edges but also at apparently random sites on flat cleavage surfaces. As weathering continues, the bumps grow outward from the feldspar surface to form tapered projections, which then develop into wide-based thin films or sheets. The thin sheets of many projections merge laterally to form one continuous flame-shaped sheet. The sheets formed on potassium feldspars may then roll to form tubes that are inclined at a high angle to the feldspar surface. Etch pits of triangular outline on the artificially weathered potassium feldspars serve as sites for development of continuous, non-rolled, hollow tubes. It is inferred from its morphology that this weathering product is halloysite or its primitive form. The product of naturally weathered potassium feldspars is halloysite . 4H2O.The flame-shaped films or sheets formed on artificially weathered plagioclase feldspar do not develop into hollow tubes, but instead give rise to a platy mineral that is most probably boehmite. These plates form within the flame-shaped films, and with continued weathering are released as the film deteriorates. There is no indication from this experiment that platy pseudohexagonal kaolinite forms from any of these minerals under the initial stage of weathering.

  7. Determinants of marriage dissolution

    Rahim, Mohd Amirul Rafiq Abu; Shafie, Siti Aishah Mohd; Hadi, Az'lina Abdul; Razali, Nornadiah Mohd; Azid @ Maarof, Nur Niswah Naslina

    2015-10-01

    Nowadays, the number of divorce cases among Muslim couples is very worrisome whereby the total cases reported in 2013 increased by half of the total cases reported in the previous year. The questions on the true key factors of dissolution of marriage continue to arise. Thus, the objective of this study is to reveal the factors that contribute to the dissolution of marriage. A total of 181 cases and ten potential determinants were included in this study. The potential determinants considered were age at marriage of husband and wife, educational level of husband and wife, employment status of husband and wife, income of husband and wife, the number of children and the presence at a counseling session. Logistic regression analysis was used to analyze the data. The findings revealed that four determinants, namely the income of husband and wife, number of children and the presence at a counselling session were significant in predicting the likelihood of divorce among Muslim couples.

  8. Collective dissolution of microbubbles

    Michelin, Sébastien; Guérin, Etienne; Lauga, Eric

    2018-04-01

    A microscopic bubble of soluble gas always dissolves in finite time in an undersaturated fluid. This diffusive process is driven by the difference between the gas concentration near the bubble, whose value is governed by the internal pressure through Henry's law, and the concentration in the far field. The presence of neighboring bubbles can significantly slow down this process by increasing the effective background concentration and reducing the diffusing flux of dissolved gas experienced by each bubble. We develop theoretical modeling of such diffusive shielding process in the case of small microbubbles whose internal pressure is dominated by Laplace pressure. We first use an exact semianalytical solution to capture the case of two bubbles and analyze in detail the shielding effect as a function of the distance between the bubbles and their size ratio. While we also solve exactly for the Stokes flow around the bubble, we show that hydrodynamic effects are mostly negligible except in the case of almost-touching bubbles. In order to tackle the case of multiple bubbles, we then derive and validate two analytical approximate yet generic frameworks, first using the method of reflections and then by proposing a self-consistent continuum description. Using both modeling frameworks, we examine the dissolution of regular one-, two-, and three-dimensional bubble lattices. Bubbles located at the edge of the lattices dissolve first, while innermost bubbles benefit from the diffusive shielding effect, leading to the inward propagation of a dissolution front within the lattice. We show that diffusive shielding leads to severalfold increases in the dissolution time, which grows logarithmically with the number of bubbles in one-dimensional lattices and algebraically in two and three dimensions, scaling respectively as its square root and 2 /3 power. We further illustrate the sensitivity of the dissolution patterns to initial fluctuations in bubble size or arrangement in the case

  9. Study on the dissolution of uranium dibutyl phosphate deposits

    Rufus, A.L.; Sathyaseelan, V.S.; Velmurugan, S.; Narasimhan

    2008-01-01

    An insoluble sticky complex of uranium dibutyl phosphate (U-DBP) formed on the inner surfaces of a reprocessing facility can host radioactive nuclides resulting in radiation exposure hazard. Removal of this layer will greatly result in the reduction of radiation field. Hence, dissolution studies with synthetically prepared U-DBP were carried out. A two-step dissolution process consisting of an initial oxidation with acid permanganate followed by reduction with NAC (NTA, Ascorbic acid and Citric acid) was used. Oxidation kinetics of DBP by permanganate, dissolution of synthetic U-DBP complex as a powder and also as a film over SS surface was studied. XRF and SEM techniques were used to monitor the process of dissolution. Material compatibility of welded SS-304 specimens was also studied. It was found that the two-step process was more efficient when compared to either permanganate or NAC treatment alone. (author)

  10. Study on the dissolution of uranium dibutyl phosphate deposits

    Rufus, A.L.; Sathyaseelan, V.S.; Velmurugan, S.; Narasimhan [Bhabha Atomic Research Centre Facilities, Water and Steam Chemistry Div., Kalpakkam (India)], E-mail: svn@igcar.gov.in

    2008-07-01

    An insoluble sticky complex of uranium dibutyl phosphate (U-DBP) formed on the inner surfaces of a reprocessing facility can host radioactive nuclides resulting in radiation exposure hazard. Removal of this layer will greatly result in the reduction of radiation field. Hence, dissolution studies with synthetically prepared U-DBP were carried out. A two-step dissolution process consisting of an initial oxidation with acid permanganate followed by reduction with NAC (NTA, Ascorbic acid and Citric acid) was used. Oxidation kinetics of DBP by permanganate, dissolution of synthetic U-DBP complex as a powder and also as a film over SS surface was studied. XRF and SEM techniques were used to monitor the process of dissolution. Material compatibility of welded SS-304 specimens was also studied. It was found that the two-step process was more efficient when compared to either permanganate or NAC treatment alone. (author)

  11. The dissolution of chalcopyrite in chloride media; Lixiviacion de la calcopirita en medios clorurados

    Ibanez, T.; Velasquez, L.

    2013-06-01

    The aim of this investigation is to determinate the effects of parameters and additives on the kinetics of dissolution of chalcopyrite on moderated conditions by means of dissolutions test with chalcopyrite concentrate and pure chalcopyrite in shake flasks and instrumented stirred reactors. A study of the dissolution of chalcopyrite in chloride solutions has demonstrated that the rate of dissolution of chalcopyrite is strongly dependent on the potential of the solution within a range of 540 to 630 mV (versus SHE). Leaching at pH around 2.5 results in increased rates of copper dissolution suggesting the possibility to keep the solution potential within the range. Both pyrite and silver ions enhance the dissolution of chalcopyrite and this effect increases when both species are present. The MnO{sub 2} has a negative effect on the dissolution increasing the solution potential to values where the rate decreases considerably. (Author)

  12. Single-grain dating of young sediments using the pIRIR signal from feldspar

    Reimann, Tony; Thomsen, Kristina Jørkov; Jain, Mayank

    2012-01-01

    In this article we test for the first time the potential of single-grains of K-rich feldspar to date well-bleached and poorly bleached sediments using a post-IR IRSL (pIRIR) protocol. We measure natural dose distributions using K-rich feldspars from four coastal samples applying the pIRIR protocol.......5%.The analysis of the well-bleached samples shows that only the brightest 30% of the grains give pIRIR single-grain ages in agreement with the age control; this effect may arise from the suggested correlation between blue emission and potassium content of individual grains. Comparison of single......-grain quartz and feldspar dose distributions from the poorly bleached samples shows that quartz is relatively better bleached; nevertheless, selection of a reliable ‘minimum’ feldspar dose was achieved using two different statistical models....

  13. Further investigations into pulsed optically stimulated luminescence from feldspars using blue and green light

    Ankjærgaard, Christina; Jain, Mayank; Kalchgruber, R.

    2009-01-01

    The purpose of this paper is to investigate characteristics of luminescence signals resulting from pulsed optical stimulation of feldspars and thereby to understand the underlying processes giving rise to the signal. Fourteen different feldspar specimens were investigated using time-resolved opti......The purpose of this paper is to investigate characteristics of luminescence signals resulting from pulsed optical stimulation of feldspars and thereby to understand the underlying processes giving rise to the signal. Fourteen different feldspar specimens were investigated using time...... suggests that the TR-OSL signal decay is governed by the recombination process and not by the excited state lifetime. Furthermore data from the TR-OSL signal dependence on stimulation time and preheat temperature suggest that the recombination process may not be a sum of exponentials, although the model...... cannot be rejected definitively....

  14. Some evidence of uranium in volcanic feldspar rocks in the state of Sonora

    Marquina M, O. E. [Uranio Mexicano, Mexico City

    1983-05-15

    Description is given of four projects of exploration and survey for uranium associated with tertiary volcanic feldspar rocks importantly dispersed in the State of Sonora and being carried out by Uranium Mexicano.

  15. Optically stimulated luminescence characteristics of natural and doped quartz and alkali feldspars

    Huett, G.; Jaek, I.; Brodski, L. [Institute of Geology at Tallinn Technical University, Tallinn (Estonia); Vasilchenko, V. [Institute of Experimental Physics and Technology of Tartu University, Tartu (Estonia)

    1999-05-01

    Natural alkali feldspars and quartz were doped by Tl and Cu by thermodiffusion and electrodiffusion technology. As a result of doping, intensive UV emission bands were created. The OSL stimulation spectra of irradiated natural and doped quartz and alkali feldspars were measured in the span of 400-1300 nm using UV emission of Tl at 280 nm and of Cu at 380 nm. One-trap centre conception was confirmed for high-temperature palaeodosimetrical TL peaks and OSL stimulation spectrum bands: for alkali feldspars at 880 and 420 nm and visible region of the spectrum for quartz. A thermooptical mechanism of the optical depopulation of the corresponding trap is confirmed in alkali feldspars, but there is no evidence for processes of this kind in quartz. An analogy between the physical background of OSL properties of both minerals is discussed.

  16. Optically stimulated luminescence characteristics of natural and doped quartz and alkali feldspars

    Huett, G.; Jaek, I.; Brodski, L.; Vasilchenko, V.

    1999-01-01

    Natural alkali feldspars and quartz were doped by Tl and Cu by thermodiffusion and electrodiffusion technology. As a result of doping, intensive UV emission bands were created. The OSL stimulation spectra of irradiated natural and doped quartz and alkali feldspars were measured in the span of 400-1300 nm using UV emission of Tl at 280 nm and of Cu at 380 nm. One-trap centre conception was confirmed for high-temperature palaeodosimetrical TL peaks and OSL stimulation spectrum bands: for alkali feldspars at 880 and 420 nm and visible region of the spectrum for quartz. A thermooptical mechanism of the optical depopulation of the corresponding trap is confirmed in alkali feldspars, but there is no evidence for processes of this kind in quartz. An analogy between the physical background of OSL properties of both minerals is discussed

  17. Evaluation of The Use of Bentonite, Kaolin and Feldspar For Immobilizing The Uranium Radionuclide Slugdewaste

    Prayitno

    2006-01-01

    The experimental investigation on the mixture of bentonite, kaolin, feldspar, sludge waste and with the ratio of bentonite, kaolin, feldspar for evaluating its effectiveness has been done. Experimentally, this investigation is the preliminary study of the use of bentonite, kaolin, feldspar as a material for the immobilization of sludge waste containing material element especially uranium. This investigation was conducted by mixing waste (2,5; 5; 7.5; 10; 12.5 and 15 %) of total weight sludge waste and bentonite, kaolin, feldspar with of 800, 900 and 1000 o C temperature. The obtained the process condition in which the uranium fraction immobilized could be kept in the limit of safety standard for the sludge waste. Therefore, it could be concluded that the addition of hay ash as an additive in the formation of block monolith tend to minimize the leached sludge waste in the leaching media. (author)

  18. Paleodosimetrical properties of sodium alkali feldspars and problems of luminescence dating of sediments

    Huett, Galina; Jaek, Ivar

    1996-01-01

    Emission spectra of natural alkali feldspars extracted from sediments are studied using a CCD-camera based high sensitivity spectrometer. Applying a semiconductor laser (860± 1 nm), two dominant emission bands, blue (410 nm) and orange (570 nm), are revealed in infrared optically stimulated luminescence (IROSL) spectra for the most of the sediments from Scandinavian sections. Luminescence and dosimetric al properties of the hole traps, the induced orange emission band typical of sodium alkali feldspars are studied. As a result, high light bleach ability but low stability of the dosimetric al information lit sodium alkali feldspars are established. Problems of luminescence dating of sediments based on the mixture of potassium-sodium alkali feldspars are discussed. (author)

  19. Understanding the ice nucleation characteristics of feldspars suspended in solution

    Kumar, Anand; Marcolli, Claudia; Kaufmann, Lukas; Krieger, Ulrich; Peter, Thomas

    2017-04-01

    Chemical) and 5 wt% lanolin (Fluka Chemical) is emulsified with a rotor-stator homogenizer for 40 s at a rotation frequency of 7000 rpm. 4 - 10 mg of this mixture is pipetted in an aluminum pan (closed hermetically), placed in the DSC and subjected to three freezing cycles. The first and the third freezing cycles are executed at a cooling rate of 10 K/min to control the stability of the sample. The second freezing cycle is executed at a 1 K/min cooling rate and is used for evaluation. Freezing temperatures are obtained by evaluating the onset of the freezing signal in the DSC curve and plotted against water activity. Results Based on Koop et al. (2000), a general decreasing trend in ice nucleation efficiency of the mineral samples with increasing solute concentrations is expected. Interestingly, feldspars (microcline, sanidine, plagioclase) in very dilute solutions of ammonia and ammonium salts (water activity close to one) show an increase in ice nucleation efficiency of 4 to 6 K compared to that in pure water. Similar trends but less pronounced are observed for kaolinite while quartz shows barely any effect. Therefore, there seem to be specific interactions between the feldspar surface and ammonia and/or ammonium ions which result in an increase in freezing temperatures at low solute concentrations. The surface ion exchange seems to be secondary for this effect since it is also present in ammonia solution. We hypothesize that ammonia adsorbs on the aluminol/silanol groups present on feldspar (viz. aluminosilicate surface) surfaces (Nash and Marshall, 1957; Belchinskaya et al., 2013). Hence allowing one of the N-H bonds to stick outwards from the surface, facing towards the bulk water and providing a favorable template for ice to grow. The current study gives an insight into the ice nucleation behavior of aluminosilicate minerals when present in conjunction with chemical species, eg. ammonium/sulfates, which is of high atmospheric relevance. References Koop et al., (2000

  20. Use of rice straw ash as substitute of feldspar in triaxial porcelain

    Guzmán, Álvaro; Delvasto, Silvio; Sánchez, Enrique; Amigó Borrás, Vicente

    2013-01-01

    [EN] The substitution of raw materials for processing high energy consumption materials by agricultural and agro-industrial wastes causes a positive impacts on the environment preservation. One of these residues is rice straw, which according to FAO estimation, its annual production is about 600 million tons. In this research was studied the use of rice straw ash (RSA) as substitute of the use of feldspar in the whiteware production. Clay-feldspar-quartz porcelains are referred to...

  1. Quantitative analysis of time-resolved infrared stimulated luminescence in feldspars

    Pagonis, Vasilis; Ankjærgaard, Christina; Jain, Mayank

    2016-01-01

    Time-resolved infrared-stimulated luminescence (TR-IRSL) from feldspar samples is of importance in the field of luminescence dating, since it provides information on the luminescence mechanism in these materials. In this paper we present new analytical equations which can be used to analyze TR-IR....... The equations are applied to experimental TR-IRSL data of natural feldspars, and good agreement is found between experimental and modeling results....

  2. [Study on the fine structure of K-feldspar of Qichun granite].

    Du, Deng-Wen; Hong, Han-Lie; Fan, Kan; Wang, Chao-Wen; Yin, Ke

    2013-03-01

    Fine structure of K-feldspar from the Qichun granite was investigated using X-ray diffraction (XRD), Fourier infrared absorption spectroscopy (FTIR), and inductively coupled plasma mass spectrometry methods to understand the evolution of the granitic magmatism and its correlation to molybdenite mineralization. The XRD results showed that K-feldspar of the potassic alteration veins has higher ordering index and triclinicity and is namely microcline with triclinic symmetry. K-feldspar of the early cretaceous granite has relatively lower ordering index and has widening [131] peak and is locally triclinic ordering. K-feldspar of the late cretaceous granite has lowest ordering index and sharp [131] peak and is honiogeneously monoclinic. The FTIR results showed that the IR spectra of the Qichun K-feldspar are similar to that of orthoclase reported by Farmer (1974). The 640 cm-1 absorption band increases while the 540 cm-' absorption band decreases with increase in K-feldspar ordering index, also, the 1,010 cm-1 absorption band separates into 1,010 and 1,046 cm-1 absorption bands, with a change in the band shape from widening to sharp outline. The ICP-MS results suggested that K-feldspar of the early cretaceous granite has relatively higher metal elements and rare earth elements, and the granite exhibits better mineralization background, K-feldspar of the potassic alteration veins has markedly lower Sr and Ba, indicating that the alteration fluid originated from the granitic magmatism, and hence, potassic alteration is a good indicator for molybdenite exploration.

  3. Solubility limits on radionuclide dissolution

    Kerrisk, J.F.

    1984-12-31

    This paper examines the effects of solubility in limiting dissolution rates of a number of important radionuclides from spent fuel and high-level waste. Two simple dissolution models were used for calculations that would be characteristics of a Yucca Mountain repository. A saturation-limited dissolution model, in which the water flowing through the repository is assumed to be saturated with each waste element, is very conservative in that it overestimates dissolution rates. A diffusion-limited dissolution model, in which element-dissolution rates are limited by diffusion of waste elements into water flowing past the waste, is more realistic, but it is subject to some uncertainty at this time. Dissolution rates of some elements (Pu, Am, Sn, Th, Zr, Sm) are always limited by solubility. Dissolution rates of other elements (Cs, Tc, Np, Sr, C, I) are never solubility limited; their release would be limited by dissolution of the bulk waste form. Still other elements (U, Cm, Ni, Ra) show solubility-limited dissolution under some conditions. 9 references, 3 tables.

  4. In vitro release of ketoprofen suppositories using the USP basket and the flow-through cell dissolution methods.

    Medina, José Raúl; Padilla, Adrián Roberto; Hurtado, Marcela; Cortés, Alma Rosa; Domínguez-Ramírez, Adriana Miriam

    2014-05-01

    In order to study the release characteristics of ketoprofen suppositories under the hydrodynamic environment generated by USP Apparatus 1 and 4, the dissolution profiles of the Mexican reference product (100 mg) were determined. Phosphate buffer pH 8 and 1% sodium lauryl sulfate (SLS) aqueous solutions were proved as dissolution mediums. Baskets were rotated at 100 rpm with USP Apparatus 1 and different flow rates from 16-32 mL/min with USP Apparatus 4 were used. Drug samples were taken and quantified during 60 min by UV analysis at 260 nm. Mean dissolution time (MDT) and dissolution efficiency (DE) were calculated by model-independent methods. Data were also fitted to several kinetic models. Poor dissolution was found in both dissolution mediums when USP basket method was used ( 0.99). The results suggest the need to establish an adequate dissolution method to evaluate the release kinetics of ketoprofen from suppositories.

  5. Biorelevant dissolution media

    Ilardia-Arana, David; Kristensen, Henning G; Müllertz, Anette

    2006-01-01

    Biorelevant dissolution media containing bile salt and lecithin at concentrations appropriate for fed and fasted state are useful when testing oral solid formulations of poorly water-soluble drugs. Dilution of amphiphile solutions affects the aggregation state of the amphiphiles because bile salt...... is partitioned between the aqueous phase and the aggregates. The aim of the investigation was to study the effect of dilution on the size distribution of aggregates and its effect on the solubilization capacity. Clear buffered solutions of four intestinal amphiphiles (sodium glycocholate, lecithin, monoolein...

  6. Comparative evaluation of methods to quantify dissolution of nanomaterials

    Hartmann, Nanna B.; Kruse, Susanne; Baun, Anders

    2015-01-01

    Effects and behaviour of nanomaterials in the environment depends on the materials' specific physical and chemical properties and for certain nanomaterials (e.g., Ag, ZnO and CuO) aqueous solubility is of outmost importance. The solubility of metals salts is normally described as a maximum...... dissolved concentration or by the solubility constant (Ksp). For nanomaterials it is essential to also assess solubility kinetics as nanomaterials will often not dissolve instantaneously upon contact with artificial aqueous media or natural waters. Dissolution kinetics will thereby influence their short...... and long-term environmental fate as well as laboratory test results. This highlights the need to evaluate and improve the reliability of methods applied to assess the solubility kinetics of nanomaterials. Based on existing OECD guidelines and guidance documents on aqueous dissolution of metals and metal...

  7. On-line monitoring of lithium carbonate dissolution

    Sun, Yuzhu; Song, Xingfu; Wang, Jin; Luo, Yan; Yu, Jianguo [National Engineering Research Center for Integrated Utilization Salt Lake Resources, East China University of Science and Technology, Shanghai (China)

    2009-11-15

    Dissolution of lithium carbonate (Li{sub 2}CO{sub 3}) in aqueous solution was investigated using three on-line apparatuses: the concentration of Li{sub 2}CO{sub 3} was measured by electrical conductivity equipment; CLD (Chord Length Distribution) was monitored by FBRM (Focused Beam Reflectance Measurement); crystal image was observed by PVM (Particle Video Microscope). Results show dissolution rate goes up with a decrease of particle size, and with an increase in temperature; stirring speed causes little impact on dissolution; ultrasound facilitates dissolution obviously. The CLD evolution and crystal images of Li{sub 2}CO{sub 3}powders in stirred fluid were observed detailedly by FBRM and PVM during dissolution. Experimental data were fitted to Avrami model, through which the activation energy was found to be 34.35 kJ/mol. PBE (Population Balance Equation) and moment transform were introduced to calculate dissolution kinetics, obtaining correlation equations of particle size decreasing rate as a function of temperature and undersaturation. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. IRSL dating of K-feldspars: Modelling natural dose response curves to deal with anomalous fading and trap competition

    Kars, Romee H.; Wallinga, Jakob

    2009-01-01

    We recently proposed a model that reconstructs the natural dose response curve for K-rich feldspars, using laboratory fading measurements and dose response as input parameters. The model is based on the relationship between recombination centre density and trap lifetime. In this study we test the working of the model by comparing modelled feldspar ages with known quartz OSL ages of the same samples and with anomalous fading-corrected feldspar ages. The modelled feldspar ages are in good agreement with quartz OSL ages and corrected feldspar ages, opening possibilities for future use of the model on samples without independent age constraints. Furthermore, we investigate the effects of trap competition on the build-up of IRSL signal using two new variations of the model. Results show that incorporating trap competition into the model reduces the agreement between feldspar IRSL ages and quartz OSL ages.

  9. Use of rice straw ash as substitute of feldspar in triaxial porcelain

    Alvaro Guzman, A.; Silverio Delvasto, A.; Enrique Sanchez, V.; Vicente Amigo, B.

    2013-01-01

    The substitution of raw materials for processing high energy consumption materials by agricultural and agro-industrial wastes causes a positive impacts on the environment preservation. One of these residues is rice straw, which according to FAO estimation, its annual production is about 600 million tons. In this research was studied the use of rice straw ash as substitute of the use of feldspar in the white ware production. Clay-feldspar-quartz porcelains are referred to as triaxial white ware. Specimens of semidry triaxial mixtures, where feldspar was substituted for different percentages of CTA, were prepared by uniaxial pressing, followed by drying and sintering. Physical and mechanical properties of sintered bodies were evaluated. The porosity and the compressive strength of the fired pieces do increase with additions of up to 75% of CTA in substitution of feldspar. Their mineralogical phases were determined by DRX and SEM; grains of quartz, and needles of primary and secondary mullite were identified in a vitreous phase. It was concluded that feldspar can be substituted positively by CTA in white ware pastes. (Author) 22 refs.

  10. OSL, TL and IRSL emission spectra of sedimentary quartz and feldspar samples

    Lomax, Johanna; Mittelstraß, Dirk; Kreutzer, Sebastian; Fuchs, Markus

    2015-01-01

    This contribution presents a variety of different luminescence emission spectra from sedimentary feldspar and quartz samples under various stimulation modes. These are green stimulated quartz (OSL-) spectra, quartz TL spectra, feldspar IRSL and post-IR IRSL spectra. A focus was set at recording OSL and IRSL spectra at elevated stimulation temperatures such as routinely applied in luminescence dating. This was to test whether optical stimulation at elevated temperatures results in a shift of emission peaks. For OSL emissions of quartz, this has so far not been tested. In case of feldspar emissions, post-IR IRSL conditions, hence IRSL emissions at a low temperature, directly followed by high temperature post-IRSL emissions, are explicitly investigated. All spectra were recorded using a new system incorporated into a Lexsyg luminescence reader. Thus, this study, besides presenting new spectral data, also serves as a feasibility study for this new device. It is shown that (a) the new device is capable of automatically measuring different sorts of spectra, also at elevated temperatures, (b) known thermally and optically stimulated peak emissions of quartz and feldspar are confirmed, (c) obtained IRSL and OSL spectra indicate that there is no significant relation between peak emission and stimulation temperature. - Highlights: • We have measured OSL, IRSL and TL emission spectra of sedimentary quartz and feldspar samples. • Spectral analyses were performed at elevated stimulation temperatures. • Emission spectra show very little variation with stimulation temperatures.

  11. Hydrothermal alteration of deep fractured granite: Effects of dissolution and precipitation

    Nishimoto, Shoji; Yoshida, Hidekazu

    2010-03-01

    This paper investigates the mineralogical effects of hydrothermal alteration at depth in fractures in granite. A fracture accompanied by an alteration halo and filled with clay was found at a depth of 200 m in a drill core through Toki granite, Gifu, central Japan. Microscopic observation, XRD, XRF, EPMA and SXAM investigations revealed that the microcrystalline clays consist of illite, quartz and pyrite and that the halo round the fracture can be subdivided into a phyllic zone adjacent to the fracture, surrounded by a propylitic zone in which Fe-phyllosilicates are present, and a distinctive outer alteration front characterized by plagioclase breakdown. The processes that result in these changes took place in three successive stages: 1) partial dissolution of plagioclase with partial chloritization of biotite; 2) biotite dissolution and precipitation of Fe-phyllosilicate in the dissolution pores; 3) dissolution of K-feldspar and Fe-phyllosilicate, and illite precipitation associated with development of microcracks. These hydrothermal alterations of the granite proceed mainly by a dissolution-precipitation process resulting from the infiltration of hydrothermal fluid along microcracks. Such infiltration causes locally high mobility of Al and increases the ratio of fluid to rock in the alteration halo. These results contribute to an understanding of how granitic rock becomes altered in orogenic fields such as the Japanese island arc.

  12. Use of micro-reactors to obtain new insights into the factors influencing tricalcium silicate dissolution

    Suraneni, Prannoy; Flatt, Robert J.

    2015-01-01

    A micro-reactor approach, developed previously, is used to study the early dissolution of tricalcium silicate. This approach uses micron-sized gaps mimicking particles in close contact to understand dissolution, nucleation, and growth processes. The main factors influencing the dissolution kinetics of tricalcium silicate are presented. We show that the presence of defects caused by polishing does not affect the extent of dissolution. A strong effect of aluminum in solution reducing the extent of dissolution is however identified. This effect is highly dependent on the pH, and is much lower above pH 13. We show also that superplasticizers reduce the extent of dissolution; however, the exact reason for this effect is not clear.

  13. The effect of preheating on the IRSL signal from feldspar

    Murray, A.S.; Buylaert, J.P.; Thomsen, Kristina Jørkov

    2009-01-01

    between the loss of blue IRSL and TL signals with preheating, and the effect of prior IRSL on the TL signal. Using IRSL measured at 50 °C and a SAR protocol, we then examine the dependence on preheat temperature of equivalent dose (De), laboratory fading rate (g), and the resulting luminescence age, from...... is consistent with a kinetic analysis of sensitivity-corrected IRSL data. The corollary to our observations is that shallow (unstable) traps do not give rise to a significant IRSL signal....

  14. The Relationship Between the Evolution of an Internal Structure and Drug Dissolution from Controlled-Release Matrix Tablets.

    Kulinowski, Piotr; Hudy, Wiktor; Mendyk, Aleksander; Juszczyk, Ewelina; Węglarz, Władysław P; Jachowicz, Renata; Dorożyński, Przemysław

    2016-06-01

    In the last decade, imaging has been introduced as a supplementary method to the dissolution tests, but a direct relationship of dissolution and imaging data has been almost completely overlooked. The purpose of this study was to assess the feasibility of relating magnetic resonance imaging (MRI) and dissolution data to elucidate dissolution profile features (i.e., kinetics, kinetics changes, and variability). Commercial, hydroxypropylmethyl cellulose-based quetiapine fumarate controlled-release matrix tablets were studied using the following two methods: (i) MRI inside the USP4 apparatus with subsequent machine learning-based image segmentation and (ii) dissolution testing with piecewise dissolution modeling. Obtained data were analyzed together using statistical data processing methods, including multiple linear regression. As a result, in this case, zeroth order release was found to be a consequence of internal structure evolution (interplay between region's areas-e.g., linear relationship between interface and core), which eventually resulted in core disappearance. Dry core disappearance had an impact on (i) changes in dissolution kinetics (from zeroth order to nonlinear) and (ii) an increase in variability of drug dissolution results. It can be concluded that it is feasible to parameterize changes in micro/meso morphology of hydrated, controlled release, swellable matrices using MRI to establish a causal relationship between the changes in morphology and drug dissolution. Presented results open new perspectives in practical application of combined MRI/dissolution to controlled-release drug products.

  15. Metasomatic alkali-feldspar syenites (episyenites) of the Proterozoic Suomenniemi rapakivi granite complex, southeastern Finland

    Suikkanen, E.; Rämö, O. T.

    2017-12-01

    Peralkaline to marginally metaluminous alkali-feldspar syenites and quartz alkali-feldspar syenites are hosted by subalkaline, ferroan rapakivi granites in the 1644 Ma Suomenniemi complex of southeastern Finland. These alkali syenites form NW-oriented dikes and small (fingerprints are, within error, identical to those of the subalkaline granites of the complex. We propose that the Suomenniemi alkali-feldspar syenites are episyenites, formed as the result of pervasive local metasomatism of the subalkaline granites caused by high-temperature oxidizing peralkaline fluids. The process led to major geochemical changes, e.g., addition of Na, Al and Fe3 +, depletion of Si and Fe2 +, and partial to complete recrystallization of the granites along fluid pathways.

  16. Iron removal on feldspar by using Averrhoa bilimbii as bioleaching agent

    Amin, Muhammad; Aji, Bramantyo B.; Supriyatna, Yayat Iman; Bahfie, Fathan

    2017-01-01

    Investigation of Averrhoa bilimbii as bioleaching agent was carried out. Parameters of leaching duration, acid concentration, and temperature were performed in iron removal process. Feldspar with sized 149 µm was diluted in 30 ml acid solution in order to reduce its iron content. The experimental results showed a good technical feasibility of the process which iron oxide content of feldspar was decreased from 2.24% to 0.29%. The lowest iron concentration remained was obtained after 5 hours of leaching treatment at 60 °C, and concentrated (100 vol%) Averrhoa bilimbii extract as bioleaching agent. SEM characterizations were carried out on the feldspar before and after the leaching treatment. The result shows that there were no significant effect of leaching process on the ore morphology.

  17. Understanding optically stimulated charge movement in quartz and feldspar using time-resolved measurements

    Ankjærgaard, Christina

    . Although, results are only presented for some quartz and feldspar samples, they were found to be very similar within the each group during the course of this work.Thermoluminescence (TL) and optically stimulated luminescence (OSL) from quartz and feldspar are widely used in accident dosimetry...... stimulation energy. The thesis first delves into three main methodological developments, namely (i) research and development of the equipment for TR-OSL measurements, (ii) finding the best method for multiple-exponential analysis of a TR-OSL curve, and (iii) optimisation of the pulsing configuration...... of the equipment for TR-OSL measurements, (ii) finding the best method for multiple-exponential analysis of a TR-OSL curve, and (iii) optimisation of the pulsing configuration for the best separation of quartz OSL from a mixed quarts-feldspar sample. It then proceeds to study the different charge transport...

  18. Identifying well-bleached quartz using the different bleaching rates of quartz and feldspar luminescence signals

    Murray, A.S.; Thomsen, Kristina Jørkov; Masuda, N.

    2012-01-01

    When dating older sedimentary deposits using quartz, there are no unambiguous methods for identifying the presence of incomplete bleaching. Current statistical analysis of dose distributions depends entirely on the assumption that incomplete bleaching and mixing are the main causes of any excess...... dispersion in the distribution; the only existing way to test this assumption is using independent age control. Here we suggest a new approach to this question, based on the differential bleaching rates of quartz and feldspar luminescence signals. We first present data that confirm the differences...... in relative bleaching rates of quartz optically stimulated luminescence (OSL) and feldspar luminescence stimulated at 50 °C by infrared light (IR50) and feldspar luminescence stimulated at 290 °C by infrared light after a stimulation at 50 °C (pIRIR290), and use recently deposited samples to determine...

  19. Salinity-Dependent Adhesion Response Properties of Aluminosilicate (K-Feldspar) Surfaces

    Lorenz, Bärbel; Ceccato, Marcel; Andersson, Martin Peter

    2017-01-01

    is composed predominantly of quartz with some clay, but feldspar grains are often also present. While the wettability of quartz and clay surfaces has been thoroughly investigated, little is known about the adhesion properties of feldspar. We explored the interaction of model oil compounds, molecules...... in well sorted sandstone. Adhesion forces, measured with the chemical force mapping (CFM) mode of atomic force microscopy (AFM), showed a low salinity effect on the fresh feldspar surfaces. Adhesion force, measured with -COO(H)-functionalized tips, was 60% lower in artificial low salinity seawater (LS......, ∼1500 ppm total dissolved solids) than in the high salinity solution, artificial seawater (HS, ASW, ∼35 600 ppm). Adhesion with the -CH3 tips was as much as 30% lower in LS than in HS. Density functional theory calculations indicated that the low salinity response resulted from expansion of the electric...

  20. Optimising the separation of quartz and feldspar optically stimulated luminescence using pulsed excitation

    Ankjaergaard, C.; Jain, M.; Thomsen, K.J.; Murray, A.S.

    2010-01-01

    In luminescence dating, the two most commonly used natural minerals, quartz and feldspar, are exposed to different dose rates in the natural environment, and so record different doses. The luminescence signals also have different stabilities. For accurate dosimetry, the signals from these two minerals must be separated, either by physical separation of the mineral grains, or by instrumental separation of the luminescence signals. The luminescence signals from quartz and feldspar have different luminescence lifetimes under pulsed optical stimulation. This difference in lifetime can be used to discriminate between the two signals from a mixed quartz-feldspar sample. The purpose of this study is to identify optimum measurement conditions for the best separation of quartz OSL from that of feldspar in a mixed sample using pulsed stimulation and time-resolved OSL. We integrate the signal from 5 μs after the LEDs are switched off until just before the LEDs are switched on again, with the pulse on-time equal to the pulse off-time of 50 μs. By using only the initial interval of the pulsed OSL decay curve (equivalent to 0.2 s of CW-OSL using blue light at 50 mW cm -2 ) we find that the quartz to feldspar pulsed OSL intensity ratio is at a maximum. By using these parameters with an additional infrared (IR) stimulation at 175 o C before measurement (to further reduce the feldspar signal intensity), we obtain a factor of 25 enhancement in signal separation compared to that from a conventional prior-IR CW measurement. This ratio can be further improved if the counting window in the pulse off-time is restricted to detect between 20 and 50 μs instead of the entire off-period.

  1. Natural radioactivity and Rare Earth elements in feldspar samples, Central Eastern desert, Egypt

    Walley El-Dine, Nadia, E-mail: nadia_walley5@hotmail.co [Department of physics, Faculty of girls for Art, Science and Education, Ain Shams University, Heliopolis, Cairo (Egypt); El-Shershaby, Amal [Department of physics, Faculty of girls for Art, Science and Education, Ain Shams University, Heliopolis, Cairo (Egypt); Afifi, Sofia [Nuclear Materials Authority (Egypt); Sroor, Amany; Samir, Eman [Department of physics, Faculty of girls for Art, Science and Education, Ain Shams University, Heliopolis, Cairo (Egypt)

    2011-05-15

    The pegmatite bodies of the Eastern Desert of Egypt are widely distributed especially along the Marsa-Alam-Idfu road. The Abu Dob area covers about 150 km{sup 2} of the Arabian Nubian shield at the central part of the Eastern Desert of Egypt. Most of the pegmatite is zoned; the zonation starts with milky quartz at the core followed by alkali feldspar at the margins. The feldspars vary in color from rose to milky and in composition from K-feldspar to Na-feldspar, sometimes interactions of both types are encountered. Thirteen feldspar samples were collected from different locations in the Abu Dob area for measuring the natural radioactivity of {sup 238}U, {sup 232}Th and {sup 40}K using an HPGe detector. The variation in concentration of radionuclides for the area under investigation can be classified into regions of high, medium and low natural radioactivity. The average concentration in BqKg{sup -1} has been observed to be from 9.5 to 183675.7 BqKg{sup -1} for {sup 238}U, between 6.1 and 94,314.2 BqKg{sup -1} for {sup 232}Th and from 0 to 7894.6 BqKg{sup -1} for {sup 40}K. Radium equivalent activities (Ra{sub eq}), dose rate (D{sub R}) and external hazard (H{sub ex}) have also been determined. In the present work, the concentration of rare earth elements are measured for two feldspar samples using two techniques, Environmental Scanning Electron microscope XIL 30 ESEM, Philips, and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). The existence of rare earth elements in this area are very high and can be used in different important industries.

  2. Natural radioactivity and Rare Earth elements in feldspar samples, Central Eastern desert, Egypt

    Walley El-Dine, Nadia; El-Shershaby, Amal; Afifi, Sofia; Sroor, Amany; Samir, Eman

    2011-01-01

    The pegmatite bodies of the Eastern Desert of Egypt are widely distributed especially along the Marsa-Alam-Idfu road. The Abu Dob area covers about 150 km 2 of the Arabian Nubian shield at the central part of the Eastern Desert of Egypt. Most of the pegmatite is zoned; the zonation starts with milky quartz at the core followed by alkali feldspar at the margins. The feldspars vary in color from rose to milky and in composition from K-feldspar to Na-feldspar, sometimes interactions of both types are encountered. Thirteen feldspar samples were collected from different locations in the Abu Dob area for measuring the natural radioactivity of 238 U, 232 Th and 40 K using an HPGe detector. The variation in concentration of radionuclides for the area under investigation can be classified into regions of high, medium and low natural radioactivity. The average concentration in BqKg -1 has been observed to be from 9.5 to 183675.7 BqKg -1 for 238 U, between 6.1 and 94,314.2 BqKg -1 for 232 Th and from 0 to 7894.6 BqKg -1 for 40 K. Radium equivalent activities (Ra eq ), dose rate (D R ) and external hazard (H ex ) have also been determined. In the present work, the concentration of rare earth elements are measured for two feldspar samples using two techniques, Environmental Scanning Electron microscope XIL 30 ESEM, Philips, and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). The existence of rare earth elements in this area are very high and can be used in different important industries.

  3. Development of Dissolution Test Method for Drotaverine ...

    Development of Dissolution Test Method for Drotaverine ... Methods: Sink conditions, drug stability and specificity in different dissolution media were tested to optimize a dissolution test .... test by Prism 4.0 software, and differences between ...

  4. Electrons in feldspar I: On the wavefunction of electrons trapped at simple lattice defects

    Poolton, H.R.J.; Wallinga, J.; Murray, A.S.

    2002-01-01

    The purpose of this article is to make an initial consideration of the physical properties of electrons trapped at classic hydrogenic lattice defects in feldspar. We are particularly interested to determine the radial extent of the electron wavefunctions in the ground and excited states. It is sh......The purpose of this article is to make an initial consideration of the physical properties of electrons trapped at classic hydrogenic lattice defects in feldspar. We are particularly interested to determine the radial extent of the electron wavefunctions in the ground and excited states...

  5. Determination of potassium in feldspars by beta counting using a GM multicounter system

    Boetter-Jensen, L; Mejdahl, V

    1985-01-01

    A gas flow multicounter system developed at Risoe National laboratory for low-level beta counting applications was adopted for measuring potassium in feldspars extracted from archaeological and geological materials, in connection with TL dating work. A guard counter reduces the background by using an anticoincidence technique. Calibration was accomplished by measuring KCl and a feldspar standard. A potassium content of 1% yields a net beta count rate (background subtracted) of about 40 c.p.h.; the background is around 15 c.p.h. The precision in repeated measurements is better than 2% and the estimated accuracy is about 3%.

  6. On the shape of continuous wave infrared stimulated luminescence signals from feldspars: A case study

    Pagonis, V.; Jain, Mayank; Thomsen, Kristina Jørkov

    2014-01-01

    The continuous-wave IRSL (CW-IRSL) signals from feldspars are known to decay in a non-exponential manner, and their exact mathematical description is of great importance in dosimetric and dating studies. This paper investigates the possibility of fitting experimental CW-IRSL curves from a variety...... to guide future modeling work on luminescence processes in feldspars. Small statistical differences were found between K-rich and Na-rich fractions of the same sample. However, the experimental data shows that the parameters depend on the irradiation dose, but do not depend on the time elapsed after...

  7. Effects of alteration product precipitation on glass dissolution

    Strachan, Denis M.; Neeway, James J.

    2014-06-01

    Understanding the mechanisms that control the durability of nuclear waste glass is paramount if reliable models are to be constructed so that the glass dissolution rate in a given geological repository can be calculated. Presently, it is agreed that (boro)silicate glasses dissolve in water at a rate dependent on the solution concentration of orthosilicic acid (H4SiO4) with higher [H4SiO4] leading to lower dissolution rates. Once the reaction has slowed as a result of the buildup of H4SiO4, another increase in the rate has been observed that corresponds to the precipitation of certain silica-bearing alteration products. However, it has also been observed that the concentration of silica-bearing solution species does not significantly decrease, indicating saturation, while other glass tracer elements concentrations continue to increase, indicating that the glass is still dissolving. In this study, we have used the Geochemist’s Workbench code to investigate the relationship between glass dissolution rates and the precipitation rate of a representative zeolitic silica-bearing alteration product, analcime [Na(AlSi2O6)∙H2O]. To simplify the calculations, we suppressed all alteration products except analcime, gibbsite (Al(OH)3), and amorphous silica. The pseudo-equilibrium-constant matrix for amorphous silica was substituted for the glass pseudo-equilibrium-constant matrix because it has been shown that silicate glasses act as a silica-only solid with respect to kinetic considerations. In this article, we present the results of our calculations of the glass dissolution rate at different values for the analcime precipitation rate constant and the effects of varying the glass dissolution rate constant at a constant analcime precipitation rate constant. From the simulations we conclude, firstly, that the rate of glass dissolution is dependent on the kinetics of

  8. Transient refractory material dissolution by a volumetrically-heated melt

    Seiler, Jean Marie, E-mail: jean-marie.seiler@cea.fr [CEA, DEN, DTN, 17 Rue des Martyrs, 38054 Grenoble Cedex 9 (France); Ratel, Gilles [CEA, DEN, DTN, 17 Rue des Martyrs, 38054 Grenoble Cedex 9 (France); Combeau, Hervé [Institut Jean Lamour, UMR 7198, Lorraine University, Ecole des Mines de Nancy, Parc de Saurupt, 54042 Nancy Cedex (France); Gaus-Liu, Xiaoyang; Kretzschmar, Frank; Miassoedov, Alexei [Karlsruhe Institut of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)

    2014-12-15

    Highlights: • We describe a test investigating ceramic dissolution by a molten non-eutectic melt. • The evolution of the interface temperature between melt and refractory is measured. • A theoretical model describing dissolution kinetics is proposed. • When dissolution stops, interface temperature is the liquidus temperature of the melt. - Abstract: The present work addresses the question of corium–ceramic interaction in a core catcher during a core-melt accident in a nuclear power plant. It provides an original insight into transient aspects concerning dissolution of refractory material by a volumetrically heated pool. An experiment with simulant material (LIVECERAM) is presented. Test results clearly show that dissolution of solid refractory material can occur in a non-eutectic melt at a temperature which is lower than the melting temperature of the refractory material. During the dissolution transient, the interface temperature rises above the liquidus temperature, corresponding to the instantaneous average composition of the melt pool. With constant power dissipation in the melt and external cooling of the core-catcher, a final steady-state situation is reached. Dissolution stops when the heat flux (delivered by the melt to the refractory) can be removed by conduction through the residual thickness of the ceramic, with T{sub interface} = T{sub liquidus} (calculated for the average composition of the final liquid pool). The final steady state corresponds to a uniform pool composition and uniform interface temperature distribution. Convection in the pool is governed by natural thermal convection and the heat flux distribution is therefore similar to what would be obtained for a single component pool. An interpretation of the experiment with two model-based approaches (0D and 1D) is presented. The mass transfer kinetics between the interface and the bulk is controlled by a diffusion sublayer within the boundary layer. During the dissolution transient

  9. Luminescence at the end of the tunnelling - Investigating charge transfer mechanisms and luminescence dating methods for feldspar minerals

    Kars, R.H.

    2014-01-01

    This thesis comprises analyses of mineral physics with an application in geology and archeology. The thesis contributes to the development of feldspar luminescence dating methods in order to extend the applicable age range of feldspar luminescence dating in the Quaternary (last 2.6 Ma). The research

  10. Application of pulsed OSL to the separation of the luminescence components from a mixed quartz/feldspar sample

    Denby, P.M.; Botter-Jensen, L.; Murray, A.S.; Thomsen, K.J.; Moska, P.

    2006-01-01

    It is known that the pulsed optically stimulated luminescence (OSL) characteristics of quartz and feldspars are very different. These differences can be used to preferentially discriminate against the feldspar signal in mixed quartz-bar feldspar mineral assemblages, or in separated quartz contaminated with a feldspar signal. We have developed instrumentation for the study of high-speed pulse stimulated OSL. Our system uses the standard blue/IR LED stimulation unit of a Riso reader (allowing stimulation pulses down to 1-2μs duration) and can thus be applied to the routine analysis of samples. Using this stimulation source, and high-speed photon timing, the OSL yield can be monitored throughout the pulsing cycle and subsequent OSL decay. It is found that the total photon yield per unit stimulation power in pulsed mode is, for quartz, twice and, for feldspar, nearly four times, that in continuous wave mode. Observation of this OSL signal, between stimulation pulses, is seen to be characteristic of the mineral being examined, and has been used to preferentially discriminate against feldspar contamination in a mixed quartz/feldspar sample. Simple implementation of this technique by gating the counting period, so that counts are only accumulated during a windowed period, reduces the feldspar signal to 1.6% of its original value relative to that of the quartz

  11. Beneficiation of feldspar ore for application in the ceramic industry: Influence of composition on the physical characteristics

    M.E. Gaied

    2015-03-01

    Experimental studies indicate that an acceptable concentrate for industrial application can be obtained from these rocks. The feldspar yield was used to evaluate the process efficiency. Besides, the cone shrinkage, water absorption, degree of vitrification, mechanical properties (flexural strength and dielectric behaviour were used to monitor the quality of the recovered feldspars.

  12. Testing feldspar luminescence dating of young archaeological heated materials using potshards from Pella (Tell Tabqat Fahl) in the Jordan valley

    Khasswneh, Sahar Al; Murray, Andrew Sean; Bourke, Stephen

    2017-01-01

    Recent developments in the use of more stable feldspar signals in the luminescence dating of sediments offer the possibility of obtaining accurate feldspar luminescence ages for ceramic artefacts; this is especially interesting in locations which do not provide suitable quartz extracts. Here we e...

  13. Mesoporous Silica Molecular Sieve based Nanocarriers: Transpiring Drug Dissolution Research.

    Pattnaik, Satyanarayan; Pathak, Kamla

    2017-01-01

    Improvement of oral bioavailability through enhancement of dissolution for poorly soluble drugs has been a very promising approach. Recently, mesoporous silica based molecular sieves have demonstrated excellent properties to enhance the dissolution velocity of poorly water-soluble drugs. Current research in this area is focused on investigating the factors influencing the drug release from these carriers, the kinetics of drug release and manufacturing approaches to scale-up production for commercial manufacture. This comprehensive review provides an overview of different methods adopted for synthesis of mesoporous materials, influence of processing factors on properties of these materials and drug loading methods. The drug release kinetics from mesoporous silica systems, the manufacturability and stability of these formulations are reviewed. Finally, the safety and biocompatibility issues related to these silica based materials are discussed. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

  14. Uranothorite solid solutions: From synthesis to dissolution

    Costin, Dan-Tiberiu

    2012-01-01

    USiO 4 coffinite appears as one of the potential phases formed in the back-end of the alteration of spent fuel, in reducing storage conditions. A study aiming to assess the thermodynamic data associated with coffinite through an approach based on the preparation of Th 1-x U x SiO 4 uranothorite solid solutions was then developed during this work. First, the preparation of uranothorite samples was successfully undertaken in hydrothermal conditions. However, the poly-phased samples systematically formed for x ≥ 0,2 underlined the kinetic hindering linked with the preparation of uranium-enriched samples, including coffinite end-member. Nevertheless, the characterization of the various samples led to confirm the formation of an ideal solid solution and allowed the constitution of a spectroscopic database. The purification of the samples was then performed by the means of different protocols based on physical (dispersion-centrifugation) or chemical (selective dissolution of secondary phases) methods. This latter led to a complete of the impurities (Th 1-y U y O 2 mixed oxide and amorphous silica) through successive washing steps in acid then basic media. Finally, dissolution experiments were undertaken on uranothorite samples (0 ≤ xexp. ≤ 0,5) and allowed pointing out the influence of composition, pH and temperature on the normalized dissolution rate of the compounds. Also, the associated thermodynamic data, such as activation energy, indicate that the reaction is controlled by surface reactions. Once the equilibrium is reached, the analogous solubility constants were determined for each composition studied, then allowing the extrapolation to coffinite value. It was then finally possible to conclude on the inversion of coffinitisation reaction with temperature. (author) [fr

  15. Biotite and chlorite weathering at 25 degrees C: the dependence of pH and (bi)carbonate on weathering kinetics, dissolution stoichiometry, and solubility; and the relation to redox conditions in granitic aquifers

    Malmstroem, M.; Banwart, S.

    1995-01-01

    We have studied the kinetics and thermodynamics of biotite and chlorite weathering in the pH range 2 2 -10 2 year); and 2. the development of characteristic Fe(III) concentrations (10 -5 M in 10 - 1 years). The Fe(III)-bearing clay minerals formed during these experiments are similar to the fracture-filling-material observed at the Aespoe Hard Rock Laboratory. Such clays can provide reducing capacity to a repository. They can help maintain anoxic conditions by consuming oxygen that enters the repository during the construction and operation phases thereby helping maintain the redox stability of the repository regarding canister corrosion. The half-life of oxygen trapped in the repository at the time of closure depends on the rate of oxygen uptake by Fe(II) minerals, sulfide minerals and organic carbon. Fe(II)-clay minerals are important to the redox stability of a repository, as well as providing a sorption barrier to radionuclide migration. 107 refs, 52 figs, 35 tabs

  16. Quantitative analysis of time-resolved infrared stimulated luminescence in feldspars

    Pagonis, Vasilis; Ankjærgaard, Christina; Jain, Mayank

    2016-01-01

    Time-resolved infrared-stimulated luminescence (TR-IRSL) from feldspar samples is of importance in the field of luminescence dating, since it provides information on the luminescence mechanism in these materials. In this paper we present new analytical equations which can be used to analyze TR-IR...

  17. Determining the K-content of single-grains of feldspar for luminescence dating

    Smedley, R.K.; Duller, G.A.T.; Pearce, N.J.G.; Roberts, H.M.

    2012-01-01

    Feldspars form a solid-solution series whereby the K-content may range from 0 to 14%. LA-ICP-MS measurements for density-separated single-grains of feldspar yielded realistic concentrations of K within the range of those naturally occurring, and also highlighted the difficulty in isolating the pure end members during density-separation. No direct relationship was found between the thermal stability of the infrared-stimulated luminescence (IRSL) signal and measured K-content of individual grains. However, the brightest IRSL and post-IR IRSL signals originated from grains with ∼12% K-content. All grains giving a measurable signal had K-content between 6 and 13%, therefore it is suggested that an internal K-content of 10 ± 2% can be assumed for routine single-grain dating of density-separated K-feldspars. - Highlights: ► Measure range of K for single-grains of density separated feldspar using LA-ICP-MS. ► Single-grain thermal stability and brightness do not directly relate to K-content. ► Brightest 3 grains measured ∼12% K and provided the majority of the IRSL signals.

  18. Dynamics of the deep red Fe3+ photoluminescence emission in feldspar

    Prasad, Amit Kumar; Jain, Mayank

    2018-01-01

    be exploited for site discrimination within a complex feldspar sample. The radiative relaxation in Fe3+ (4T1 → 6A1) is shown to be a dynamic process depending on whether the ion is excited using resonant or non-resonant transition. We suggest that during resonant excitation, the excited state of Fe3+ undergoes...

  19. Validating post IR-IRSL dating on K-feldspars through comparison with quartz OSL ages

    Kars, R.H.; Busschers, F.S.; Wallinga, J.

    2012-01-01

    Recent developments have opened up the possibilities of using potassium feldspar for dating Pleistocene sediments; a stable (less-fading) part of the infrared stimulated luminescence (IRSL) signal can be selected by largely depleting the unstable part of the IR signal, using a combination of thermal

  20. Determination of Potassium in Feldspars by Beta Counting Using a GM Multicounter System

    Bøtter-Jensen, Lars; Mejdahl, V.

    1985-01-01

    A gas flow multicounter system developed at Riso National Laboratory for low-level beta counting applications was adopted for measuring potassium in feldspars extracted from archaeological and geological materials, in connection with TL dating work. A guard counter reduces the background by using...

  1. Red-IR stimulated luminescence in K-feldspar: Single or multiple trap origin?

    Andersen, Martin Thalbitzer; Jain, Mayank; Tidemand-Lichtenberg, Peter

    2012-01-01

    We investigate on the origins of the infra-red stimulated luminescence (IRSL) signals in 3 potassium feldspars based on IR-red spectroscopy (700–1050 nm) using a fiber-coupled tunable Ti:Sapphire laser, in combination with different thermal and optical (pre)treatments of the samples. We also...

  2. Limits to depletion of blue-green light stimulated luminescence in feldspars: Implications for quartz dating

    Jain, M.; Singhvi, A.K.

    2001-01-01

    stimulation curve of otherwise pure quartz. In this study, the functional relationship between the infra-red stimulated luminescence (IRSL) and BGSL of feldspars, (1) at different preheats, and (2) with IR bleaching at different stimulation temperatures and durations, is examined. The results suggest two trap...

  3. Radiation-induced growth and isothermal decay of infrared-stimulated luminescence from feldspar

    Guralnik, Benny; Li, Bo; Jain, Mayank

    2015-01-01

    the growth and decay of laboratory-regenerated luminescence signals. Here we review a selection of common models describing the response of infrared stimulated luminescence (IRSL) of feldspar to constant radiation and temperature as administered in the laboratory. We use this opportunity to introduce...

  4. Dependence of (anomalous) fading of infra-red stimulated luminescence on trap occupancy in feldspars

    Morthekai, P.; Jain, Mayank; Gach, Grzegorz

    2013-01-01

    Dose dependency of anomalous fading of infra-red stimulated luminescence (IRSL) from feldspars has been investigated using radiations of different ionisation qualities. The rate of fading of the IRSL signal after proton irradiation (9.4–30%/decade) is on an average almost twice compared...

  5. Testing the application of quartz and feldspar luminescence dating to MIS 5 Japanese marine deposits

    Thiel, Christine; Tsukamoto, Sumiko; Tokuyasu, Kayoko

    2015-01-01

    The applicability of both quartz and feldspar luminescence dating was tested on twenty-five samples from a marine succession now forming a coastal cliff at Oga Peninsula, Honshu Island, Japan. The quartz optically stimulated luminescence (OSL) signal shows thermal instability and linear modulated...

  6. Mechanical behavior of alumina and alumina-feldspar based ceramics in an acetic acid (4%) environment

    Stumpf, Aisha S.G.; Bergmann, Carlos P.; Vicenzi, Juliane; Fetter, Rebecca; Mundstock, Karina S.

    2009-01-01

    This study investigates the mechanical properties of alumina-feldspar based ceramics when exposed to an aggressive environment (acetic acid 4%). Alumina ceramics containing different concentrations of feldspar (0%, 1%, 5%, 10%, or 40%) were sintered at either 1300, 1600, or 1700 o C. Flaws (of width 0%, 30%, or 50%) were introduced into the specimens using a saw. Half of these ceramic bodies were exposed to acetic acid. Their flexural strength, K IC , and porosity were measured and the fractured samples were evaluated using scanning electronic- and optical microscopy. It was found that in the ceramic bodies sintered at 1600 o C, feldspar content up to 10% improved flexural strength and K IC, and reduced porosities. Generally, it was found that acetic acid had a weakening effect on the flexural strength of samples sintered at 1700 o C but a beneficial effect on K IC of ceramics sintered at 1600 o C. It was concluded that alumina-based ceramics with feldspar content up to 10% and sintered at higher temperatures would perform better in an aggressive environment similar to oral cavity.

  7. Controlled evaluation of silver nanoparticle dissolution using atomic force microscopy.

    Kent, Ronald D; Vikesland, Peter J

    2012-07-03

    Incorporation of silver nanoparticles (AgNPs) into an increasing number of consumer products has led to concern over the potential ecological impacts of their unintended release to the environment. Dissolution is an important environmental transformation that affects the form and concentration of AgNPs in natural waters; however, studies on AgNP dissolution kinetics are complicated by nanoparticle aggregation. Herein, nanosphere lithography (NSL) was used to fabricate uniform arrays of AgNPs immobilized on glass substrates. Nanoparticle immobilization enabled controlled evaluation of AgNP dissolution in an air-saturated phosphate buffer (pH 7.0, 25 °C) under variable NaCl concentrations in the absence of aggregation. Atomic force microscopy (AFM) was used to monitor changes in particle morphology and dissolution. Over the first day of exposure to ≥10 mM NaCl, the in-plane AgNP shape changed from triangular to circular, the sidewalls steepened, the in-plane radius decreased by 5-11 nm, and the height increased by 6-12 nm. Subsequently, particle height and in-plane radius decreased at a constant rate over a 2-week period. Dissolution rates varied linearly from 0.4 to 2.2 nm/d over the 10-550 mM NaCl concentration range tested. NaCl-catalyzed dissolution of AgNPs may play an important role in AgNP fate in saline waters and biological media. This study demonstrates the utility of NSL and AFM for the direct investigation of unaggregated AgNP dissolution.

  8. Dissolution performance of plutonium nitride based fuel materials

    Aneheim, E.; Hedberg, M. [Nuclear Chemistry, Chemistry and Chemical Engineering, Chalmers University of Technology, Kemivaegen 4, Gothenburg, SE41296 (Sweden)

    2016-07-01

    Nitride fuels have been regarded as one viable fuel option for Generation IV reactors due to their positive features compared to oxides. To be able to close the fuel cycle and follow the Generation IV concept, nitrides must, however, demonstrate their ability to be reprocessed. This means that the dissolution performance of actinide based nitrides has to be thoroughly investigated and assessed. As the zirconium stabilized nitrides show even better potential as fuel material than does the pure actinide containing nitrides, investigations on the dissolution behavior of both PuN and (Pu,Zr)N has been undertaken. If possible it is desirable to perform the fuel dissolutions using nitric acid. This, as most reprocessing strategies using solvent-solvent extraction are based on a nitride containing aqueous matrix. (Pu,Zr)N/C microspheres were produced using internal gelation. The spheres dissolution performance was investigated using nitric acid with and without additions of HF and Ag(II). In addition PuN fuel pellets were produced from powder and their dissolution performance were also assessed in a nitric acid based setting. It appears that both PuN and (Pu,Zr)N/C fuel material can be completely dissolved in nitric acid of high concentration with the use of catalytic amounts of HF. The amount of HF added strongly affects dissolution kinetics of (Pu, Zr)N and the presence of HF affects the 2 solutes differently, possibly due to inhomogeneity o the initial material. Large additions of Ag(II) can also be used to facilitate the dissolution of (Pu,Zr)N in nitric acid. PuN can be dissolved by pure nitric acid of high concentration at room temperature while (Pu, Zr)N is unaffected under similar conditions. At elevated temperature (reflux), (Pu,Zr)N can, however, also be dissolved by concentrated pure nitric acid.

  9. Optimization of dissolution process parameters for uranium ore concentrate powders

    Misra, M.; Reddy, D.M.; Reddy, A.L.V.; Tiwari, S.K.; Venkataswamy, J.; Setty, D.S.; Sheela, S.; Saibaba, N. [Nuclear Fuel Complex, Hyderabad (India)

    2013-07-01

    Nuclear fuel complex processes Uranium Ore Concentrate (UOC) for producing uranium dioxide powder required for the fabrication of fuel assemblies for Pressurized Heavy Water Reactor (PHWR)s in India. UOC is dissolved in nitric acid and further purified by solvent extraction process for producing nuclear grade UO{sub 2} powder. Dissolution of UOC in nitric acid involves complex nitric oxide based reactions, since it is in the form of Uranium octa oxide (U{sub 3}O{sub 8}) or Uranium Dioxide (UO{sub 2}). The process kinetics of UOC dissolution is largely influenced by parameters like concentration and flow rate of nitric acid, temperature and air flow rate and found to have effect on recovery of nitric oxide as nitric acid. The plant scale dissolution of 2 MT batch in a single reactor is studied and observed excellent recovery of oxides of nitrogen (NO{sub x}) as nitric acid. The dissolution process is automated by PLC based Supervisory Control and Data Acquisition (SCADA) system for accurate control of process parameters and successfully dissolved around 200 Metric Tons of UOC. The paper covers complex chemistry involved in UOC dissolution process and also SCADA system. The solid and liquid reactions were studied along with multiple stoichiometry of nitrous oxide generated. (author)

  10. Dissolution of FFTF vendor fuel

    Lerch, R.E.

    1979-08-01

    Dissolution experiments were performed on FFTF vendor fuel (both mechanically mixed and coprecipitated) during 1974, 1975, and 1976. A marked improvement was noted in the completeness of fuel dissolution from 1974 to 1976. The reason for this is unknown but may have been attributable to slight changes in fuel fabrication conditions. In general, the bulk of the fuel pellets tested dissolved to greater than 99.9% in nitric acid alone

  11. Dissolution of FFTF vendor fuel

    Lerch, R.E.

    1979-08-01

    Dissolution experiments were performed on FFTF vendor fuel (both mechanically mixed and coprecipitated) during 1974, 1975, and 1976. A marked improvement was noted in the completeness of fuel dissolution from 1974 to 1976. The reason for this is unknown but may have been attributable to slight changes in fuel fabrication conditions. In general, the bulk of the fuel pellets tested dissolved to greater than 99.9% in nitric acid alone.

  12. Understanding optically stimulated charge movement in quartz and feldspar using time-resolved measurements

    Ankjaergaard, C.

    2010-02-01

    Thermoluminescence (TL) and optically stimulated luminescence (OSL) from quartz and feldspar are widely used in accident dosimetry and luminescence dating. In order to improve already existing methods or to develop new methods towards extending the current limits of the technique, it is important to understand the charge movement within these materials. Earlier studies have primarily focussed on examination of the trap behaviour; however, this only tells half of the story as OSL is a combination of charge stimulation and recombination. By using time-resolved OSL (TR-OSL), one can directly examine the recombination route(s), and thus obtain insight into the other half of the process involved in luminescence emission. This thesis studies the TR-OSL and optically stimulated phosphorescence signals from quartz and feldspars spanning several orders of magnitude in time (few ns to the seconds time scale) in order to identify various charge transport mechanisms in the different time regimes. The techniques employed are time-resolved OSL, continuous-wave OSL, TL, optically stimulated exo-electron (OSE) emission and time-resolved OSE. These different techniques are used in combination with variable thermal or optical stimulation energy. The thesis first delves into three main methodological developments, namely (i) research and development of the equipment for TR-OSL measurements, (ii) finding the best method for multiple-exponential analysis of a TR-OSL curve, and (iii) optimisation of the pulsing configuration for the best separation of quartz OSL from a mixed quarts-feldspar sample. It then proceeds to study the different charge transport mechanisms subsequent to an optical stimulation pulse in quartz and feldspars. The results obtained for quartz conclude that the main lifetime component in quartz represents an excited state lifetime of the recombination centre, and the more slowly decaying components on the millisecond to seconds time scale arise from charge recycling

  13. Understanding optically stimulated charge movement in quartz and feldspar using time-resolved measurements

    Ankjaergaard, C.

    2010-02-15

    Thermoluminescence (TL) and optically stimulated luminescence (OSL) from quartz and feldspar are widely used in accident dosimetry and luminescence dating. In order to improve already existing methods or to develop new methods towards extending the current limits of the technique, it is important to understand the charge movement within these materials. Earlier studies have primarily focussed on examination of the trap behaviour; however, this only tells half of the story as OSL is a combination of charge stimulation and recombination. By using time-resolved OSL (TR-OSL), one can directly examine the recombination route(s), and thus obtain insight into the other half of the process involved in luminescence emission. This thesis studies the TR-OSL and optically stimulated phosphorescence signals from quartz and feldspars spanning several orders of magnitude in time (few ns to the seconds time scale) in order to identify various charge transport mechanisms in the different time regimes. The techniques employed are time-resolved OSL, continuous-wave OSL, TL, optically stimulated exo-electron (OSE) emission and time-resolved OSE. These different techniques are used in combination with variable thermal or optical stimulation energy. The thesis first delves into three main methodological developments, namely (i) research and development of the equipment for TR-OSL measurements, (ii) finding the best method for multiple-exponential analysis of a TR-OSL curve, and (iii) optimisation of the pulsing configuration for the best separation of quartz OSL from a mixed quarts-feldspar sample. It then proceeds to study the different charge transport mechanisms subsequent to an optical stimulation pulse in quartz and feldspars. The results obtained for quartz conclude that the main lifetime component in quartz represents an excited state lifetime of the recombination centre, and the more slowly decaying components on the millisecond to seconds time scale arise from charge recycling

  14. Dissolution glow curve in LLD

    Haverkamp, U.; Wiezorek, C.; Poetter, R.

    1990-01-01

    Lyoluminescence dosimetry is based upon light emission during dissolution of previously irradiated dosimetric materials. The lyoluminescence signal is expressed in the dissolution glow curve. These curves begin, depending on the dissolution system, with a high peak followed by an exponentially decreasing intensity. System parameters that influence the graph of the dissolution glow curve, are, for example, injection speed, temperature and pH value of the solution and the design of the dissolution cell. The initial peak does not significantly correlate with the absorbed dose, it is mainly an effect of the injection. The decay of the curve consists of two exponential components: one fast and one slow. The components depend on the absorbed dose and the dosimetric materials used. In particular, the slow component correlates with the absorbed dose. In contrast to the fast component the argument of the exponential function of the slow component is independent of the dosimetric materials investigated: trehalose, glucose and mannitol. The maximum value, following the peak of the curve, and the integral light output are a measure of the absorbed dose. The reason for the different light outputs of various dosimetric materials after irradiation with the same dose is the differing solubility. The character of the dissolution glow curves is the same following irradiation with photons, electrons or neutrons. (author)

  15. Mathematical characterization of continuous wave infrared stimulated luminescence signals (CW-IRSL) from feldspars

    Pagonis, V.; Phan, Huy; Goodnow, Rebecca; Rosenfeld, Sara; Morthekai, P.

    2014-01-01

    Continuous-wave infrared stimulated luminescence signals (CW-IRSL) from feldspars have been the subject of many experimental studies, due to their importance in luminescence dating and dosimetry. Accurate mathematical characterization of the shape of these CW-IRSL signals in feldspars is of practical and theoretical importance, especially in connection with “anomalous fading” of luminescence signals in dating studies. These signals are known to decay in a non-exponential manner and their exact mathematical shape as a function of stimulation time is an open research question. At long stimulation times the IRSL decay has been shown experimentally to follow a power law of decay, and previous researchers have attempted to fit the overall shape of these signals empirically using the well known Becquerel function (or compressed hyperbola decay law). This paper investigates the possibility of fitting CW-IRSL curves using either the Becquerel decay law, or a recently developed analytical equation based on localized electronic recombination of donor–acceptor pairs in luminescent materials. It is shown that both mathematical approaches can give excellent fits to experimental CW-IRSL curves, and the precision of the fitting process is studied by analyzing a series of curves measured using a single aliquot of a feldspar sample. Both fitting equations are solutions of differential equations involving numerically similar time dependent recombination probabilities k(t). It is concluded that both fitting equations provide approximately equivalent mathematical descriptions of the CW-IRSL curves in feldspars, and can be used as mathematical representations of the shape of CW-IRSL signals. - Highlights: • Feldspar CW-IRSL curves fitted using Becquerel decay law and new analytical equation. • Both mathematical approaches give excellent fits to experimental CW-IRSL curves. • Series of experimental CW-IRSL curves analyzed using both fitting expressions. • The time

  16. On the effect of optical and isothermal treatments on luminescence signals from feldspars

    Pagonis, Vasilis; Polymeris, George; Kitis, George

    2015-01-01

    During luminescence dosimetry and luminescence dating applications it is often necessary to precondition the geological samples by applying a thermal or optical treatment before measuring the luminescence signal. In luminescence applications using apatites or feldspars, measurement of continuous-wave infrared or optically stimulated signals (CW-IRSL and CW-OSL) are customarily preceded by either an isothermal heating of the samples at a fixed temperature for a short time interval, or alternatively by optically bleaching the samples using light from LEDs with the appropriate wavelength. This paper presents new analytical equations which can be used to describe these commonly employed double experimental procedures. The equations are based on a recently published model which assumes that tunneling processes are taking place in random distributions of donor–acceptor pairs. The concentration of charge carriers during the CW-IRSL or CW-OSL experiment is expressed in terms of the parameters of the preceding thermal or optical bleaching procedure, and depends also on the distribution of distances between electron and hole pairs. The analytical equations in this paper are compared with experimental data from a feldspar sample which undergoes an isothermal procedure followed by measurement of the CW-IRSL signal. Additional comparisons with experiment are provided using a feldspar sample which undergoes an infrared bleaching process, followed by measurement of the CW-OSL signal. These results and conditions under which the equations can be used are discussed within the framework of the model. - Highlights: • CW-IRSL and CW-OSL measurements are preceded by heating or optical bleaching. • New analytical equations are derived to describe these double experimental procedures. • Equations are compared with data from a feldspar sample following isothermal procedure. • Equations are compared with data from a feldspar sample following optical bleaching.

  17. Developing a quality by design approach to model tablet dissolution testing: an industrial case study.

    Yekpe, Ketsia; Abatzoglou, Nicolas; Bataille, Bernard; Gosselin, Ryan; Sharkawi, Tahmer; Simard, Jean-Sébastien; Cournoyer, Antoine

    2017-11-02

    This study applied the concept of Quality by Design (QbD) to tablet dissolution. Its goal was to propose a quality control strategy to model dissolution testing of solid oral dose products according to International Conference on Harmonization guidelines. The methodology involved the following three steps: (1) a risk analysis to identify the material- and process-related parameters impacting the critical quality attributes of dissolution testing, (2) an experimental design to evaluate the influence of design factors (attributes and parameters selected by risk analysis) on dissolution testing, and (3) an investigation of the relationship between design factors and dissolution profiles. Results show that (a) in the case studied, the two parameters impacting dissolution kinetics are active pharmaceutical ingredient particle size distributions and tablet hardness and (b) these two parameters could be monitored with PAT tools to predict dissolution profiles. Moreover, based on the results obtained, modeling dissolution is possible. The practicality and effectiveness of the QbD approach were demonstrated through this industrial case study. Implementing such an approach systematically in industrial pharmaceutical production would reduce the need for tablet dissolution testing.

  18. Simulation study of effects of initial particle size distribution on dissolution

    Wang, G.; Xu, D.S.; Ma, N.; Zhou, N.; Payton, E.J.; Yang, R.; Mills, M.J.; Wang, Y.

    2009-01-01

    Dissolution kinetics of γ' particles in binary Ni-Al alloys with different initial particle size distributions (PSD) is studied using a three-dimensional (3D) quantitative phase field model. By linking model inputs directly to thermodynamic and atomic mobility databases, microstructural evolution during dissolution is simulated in real time and length scales. The model is first validated against analytical solution for dissolution of a single γ' particle in 1D and numerical solution in 3D before it is applied to investigate the effects of initial PSD on dissolution kinetics. Four different types of PSD, uniform, normal, log-normal and bimodal, are considered. The simulation results show that the volume fraction of γ' particles decreases exponentially with time, while the temporal evolution of average particle size depends strongly on the initial PSD

  19. Etude cinetique et thermodynamique de la dissolution de la fluorapatite dans l'acide phosphorique

    Brahim, K.; Khattech, I.; Dubes, J.P.; Jemal, M.

    2005-01-01

    A modification on the reversal cells of a C-80 SETARAM calorimeter allows a Joule effect in the reaction cells to determine a transfer function in experimental conditions close to those of dissolution of a solid in a liquid. The calorimeter was then used to determine in isothermal conditions both thermodynamic and kinetic parameters associated with dissolution of synthetic fluorapatite in phosphoric acid solutions. Due to the rapidity of reaction, the heat flow recordings were deconvoluted and the resulting curves were analyzed iteratively to obtain the rates of digestion and the enthalpy of dissolution at 298 K of fluorapatite in phosphoric acid solution containing 10, 18 or 30 wt% P 2 O 5 . The results agree with a two-step dissolution mechanism. The first step is the dissolution of the solid in phosphoric acid, and the second is the formation of the complex Ca(H 2 PO 4 ) +

  20. Dissolution behaviour of 238U, 234U and 230Th deposited on filters from personal dosemeters.

    Becková, Vera; Malátová, Irena

    2008-01-01

    Kinetics of dissolution of (238)U, (234)U and (230)Th dust deposited on filters from personal alpha dosemeters was studied by means of a 26-d in vitro dissolution test with a serum ultrafiltrate simulant. Dosemeters had been used by miners at the uranium mine 'Dolní Rozínka' at Rozná, Czech Republic. The sampling flow-rate as declared by the producer is 4 l h(-1) and the sampling period is typically 1 month. Studied filters contained 125 +/- 6 mBq (238)U in equilibrium with (234)U and (230)Th; no (232)Th series nuclides were found. Half-time of rapid dissolution of 1.4 d for (238)U and (234)U and slow dissolution half-times of 173 and 116 d were found for (238)U and (234)U, respectively. No detectable dissolution of (230)Th was found.

  1. Dissolution behaviour of 238U, 234U and 230Th deposited on filters from personal dosemeters

    Beckova, V.; Malatova, I.

    2008-01-01

    Kinetics of dissolution of 238 U, 234 U and 230 Th dust deposited on filters from personal alpha dosemeters was studied by means of a 26-d in vitro dissolution test with a serum ultra-filtrate simulant. Dosemeters had been used by miners at the uranium mine 'Dolni Rozinka' at Rozna, Czech Republic. The sampling flow-rate as declared by the producer is 4 l h -1 and the sampling period is typically 1 month. Studied filters contained 125 ± 6 mBq 238 U in equilibrium with 234 U and 230 Th; no 232 Th series nuclides were found. Half-time of rapid dissolution of 1.4 d for 238 U and 234 U and slow dissolution half-times of 173 and 116 d were found for 238 U and 234 U, respectively. No detectable dissolution of 230 Th was found. (authors)

  2. Dissolution of aluminium; Disolucion de aluminio

    Uriarte Hueda, A; Berberana Eizmendi, M; Pereira Sanchez, G

    1968-07-01

    The dissolution of aluminum with acid solutions ( nitric acid-mercuric nitrate) and alkaline solutions (sodium hydroxide-sodium nitrate) has been studied. The instantaneous dissolution rate (IDR) has been studied in function of the concentration of the used reagents and the dissolution temperature. The complete dissolution has been included in the second part of this report, to know the total dissolution time, the consume of reagents and the stability of the resultant solutions. (Author)

  3. Faster dissolution of PuO2 in nitrous media by means of electrolytic oxidation

    Baumgaertner, F.; Kim, J.I.; Luckner, N.; Brueckl, N.; Lieberer, E.

    1984-03-01

    The contribution shows that the dissolution of PuO 2 in HNO 3 can be accelerated considerably by means of electrolytic oxidation. A glass apparatus has been developed which uses platinum electrodes providing for sufficient contact between electrodes and solids. Increase of temperature, acid concentration, and electrode current density, and a good contact between electrode and metal oxide will improve the dissolution kinetics. The reaction could be made even faster by addition of Ce 4+ . (orig.) [de

  4. Revisiting classical silicate dissolution rate laws under hydrothermal conditions

    Pollet-Villard, Marion; Daval, Damien; Saldi, Giuseppe; Knauss, Kevin; Wild, Bastien; Fritz, Bertrand

    2015-04-01

    In the context of geothermal energy, the relative intensities of primary mineral leaching and secondary mineral precipitation can affect porosity and permeability of the reservoir, thereby influencing its hydraulic performance and the efficiency of the geothermal power station. That is why the prediction of reaction kinetics of fluid/rock interactions represents a critical issue in this context. Moreover, in several geothermal systems such as the one of Soultz-sous-Forêts (Alsace, France), the circulation of aqueous fluids induces only modest modifications of their chemical composition. Therefore, fluid-rock interactions take place at close-to-equilibrium conditions, where the rate-affinity relations are poorly known and intensively debated [1]. To describe more precisely the dissolution processes, our strategy consists in investigating the dissolution of the main cleavages of K-spar minerals (one of the prevalent primary minerals in the reservoir of Soultz-sous-Forêts geothermal system) over a wide range of Gibbs free energy (ΔG) conditions. The aims are to decipher the impact of crystallographic orientation and microstructural surface modifications on the dissolution kinetics and to propose a relation between K-spar dissolution rate and ΔG. Our experimental work relies on a coupled approach which combines classical experiments of K-spar dissolution monitored by aqueous chemical analyses (ICP-AES) and innovative techniques of nm- to μm-scale characterization of solid surface (SEM, AFM, VSI) [2]. Our results confirm that K-spar dissolution is an anisotropic process: we measure a tenfold factor between the slowest and the fastest-dissolving surfaces. Moreover, the formation of etch pits on surfaces during their alteration has been evidenced on all of the different faces that have been studied. This complex evolution of the surface topography casts doubt of the relevance of a surface model based on shrinking particles and represents a possible cause of an

  5. Detrital K-feldspar thermochronology of the Nanaimo Group: Characterization of Basement and Extraregional Basin Contributions

    Isava, V.; Grove, M.; Mahoney, J. B.; Kimbrough, D. L.

    2016-12-01

    The Late Cretaceous-Early Paleogene Nanaimo Group covers the contact between Triassic basement Wrangellia terrane and the Jurassic-Cretaceous Coast Plutonic Complex (CPC) in southern British Columbia. Prior detrital zircon U-Pb and Hf studies indicate a change in sediment source for the Nanaimo basin, from the primitive CPC in Santonian-Early Campanian time to an isotopically evolved continental extraregional source during the late Campanian/Maastrictian. Two notably different areas have been proposed as potential source regions: (1) the Idaho/Boulder batholith and Belt Supergroup, and (2) the Mojave/Salinia segment of structurally disrupted late Cretaceous southern California margin. Single crystal 40Ar/39Ar laser fusion of ca. 100-200 grains apiece from seven detrital K-feldspar samples from Santonian-Maastrichtian strata of the northern Nanaimo Group constrain the history of the sediments' source regions. The two oldest samples, from the K-feldspar poor Comox and Extension Fms., display a monotonic increasing distribution of cooling ages 80-125 Ma that reflects shallow erosion of the CPC. In contrast, Late Campanian strata of the Cedar District and De Courcy Fms. exhibit a more pronounced cluster of cooling ages 80-95 Ma as well as a greater proportion of Jurassic ages that represent progressively deeper erosion of the CPC. Evidence for an extraregional sediment source appears abruptly in the Geoffrey Fm. by 72 Ma, matching the time of local-to-extraregional shift indicated in detrital zircon U-Pb studies. Over 90% of the detrital K-feldspars from these arkosic sandstones yield cooling ages of 70-80 Ma, with sparse older ages associated with the CPC. Samples from the successively younger Spray and Gabriola Fms. also yield >90% K-feldspar ages younger than 80 Ma and exhibit age maxima of 68 Ma and 65 Ma, respectively. These results are distinct from detrital zircon U-Pb and K-feldspar 40Ar/39Ar ages of the southern Sierra Nevada, Mojave/Salina, and northern

  6. Complex Diffusion Mechanisms for Li in Feldspar: Re-thinking Li-in-Plag Geospeedometry

    Holycross, M.; Watson, E. B.

    2017-12-01

    In recent years, the lithium isotope system has been applied to model processes in a wide variety of terrestrial environments. In igneous settings, Li diffusion gradients have been frequently used to time heating episodes. Lithium partitioning behavior during decompression or cooling events drives Li transfer between phases, but the extent of Li exchange may be limited by its diffusion rate in geologic materials. Lithium is an exceptionally fast diffuser in silicate media, making it uniquely suited to record short-lived volcanic phenomena. The Li-in-plagioclase geospeedometer is often used to time explosive eruptions by applying laboratory-calibrated Li diffusion coefficients to model concentration profiles in magmatic feldspar samples. To quantify Li transport in natural scenarios, experimental measurements are needed that account for changing temperature and oxygen fugacity as well as different feldspar compositions and crystallographic orientation. Ambient pressure experiments were run at RPI to diffuse Li from a powdered spodumene source into polished sanidine, albite, oligoclase or anorthite crystals over the temperature range 500-950 ºC. The resulting 7Li concentration gradients developed in the mineral specimens were evaluated using laser ablation ICP-MS. The new data show that Li diffusion in all feldspar compositions simultaneously operates by both a "fast" and "slow" diffusion mechanism. Fast path diffusivities are similar to those found by Giletti and Shanahan [1997] for Li diffusion in plagioclase and are typically 10 to 20 times greater than slow path diffusivities. Lithium concentration gradients in the feldspar experiments plot in the shape of two superimposed error function curves with the slow diffusion regime in the near-surface of the crystal. Lithium diffusion is most sluggish in sanidine and is significantly faster in the plagioclase feldspars. It is still unclear what diffusion mechanism operates in nature, but the new measurements may impact

  7. Rapid and gradual modes of aerosol trace metal dissolution in seawater

    Katherine Rose Marie Mackey

    2015-01-01

    Full Text Available Atmospheric deposition is a major source of trace metals in marine surface waters and supplies vital micronutrients to phytoplankton, yet measured aerosol trace metal solubility values are operationally defined and there are relatively few multi-element studies on aerosol-metal solubility in seawater. Here we measure the solubility of aluminum (Al, cadmium (Cd, cobalt (Co, copper (Cu, iron (Fe, manganese (Mn, nickel (Ni, lead (Pb, and zinc (Zn from natural aerosol samples in seawater over a 7 day period to (1 evaluate the role of extraction time in trace metal dissolution behavior and (2 explore how the individual dissolution patterns could influence biota. Dissolution behavior occurs over a continuum ranging from rapid dissolution, in which the majority of soluble metal dissolved immediately upon seawater exposure (Cd and Co in our samples, to gradual dissolution, where metals dissolved slowly over time (Zn, Mn, Cu, and Al in our samples. Additionally, dissolution affected by interactions with particles was observed in which a decline in soluble metal concentration over time occurred (Fe and Pb in our samples. Natural variability in aerosol chemistry between samples can cause metals to display different dissolution kinetics in different samples, and this was particularly evident for Ni, for which samples showed a broad range of dissolution rates. The elemental molar ratio of metals in the bulk aerosols was 23,189Fe: 22,651Al: 445Mn: 348Zn: 71Cu: 48Ni: 23Pb: 9Co: 1Cd, whereas the seawater soluble molar ratio after 7 days of leaching was 11Fe: 620Al: 205Mn: 240Zn: 20Cu: 14Ni: 9Pb: 2Co: 1Cd. The different kinetics and ratios of aerosol metal dissolution have implications for phytoplankton nutrition, and highlight the need for unified extraction protocols that simulate aerosol metal dissolution in the surface ocean.

  8. The effect of Ti and Nb on nitrogen dissolution reaction in stainless steel melt

    Jang, Min Whan; Hong, In Kook; Pak, Jong Jin; Song, Hyo Seok; Lee, Yong Deuk

    2002-01-01

    A kinetic study of nitrogen dissolution in STS304 stainless steel melt containing Ti and Nb has been carried out at 1500 degree C using an induction furnace and a levitation melting furnace. At low O and S levels, the nitrogen dissolution rate showed the first-order kinetics being controlled by the mass transfer of nitrogen in the melt. Ti addition to STS304 stainless melt significantly retarded the nitrogen dissolution rate by the formation of solid Ti oxide layer adhered on the melt surface. Nb did not affect the rate of nitrogen dissolution. In the levitation melting experiment where the oxide layer was removed from the melt surface, Ti did not retard the nitrogen dissolution rate. Simultaneous addition of Ti and Al increased the dissolution rate by the formation of non-wetting Al 2 O 3 on the melt surface. A small addition of CaO-Al 2 O 3 synthetic flux to Ti containing melt was very effective to remove the oxide layer, hence to increase the nitrogen dissolution rate

  9. The effect of Ti and Nb on nitrogen dissolution reaction in stainless steel melt

    Jang, Min Whan; Hong, In Kook; Pak, Jong Jin [Hanyang Univ., Ansan (Korea, Republic of); Song, Hyo Seok; Lee, Yong Deuk [POSCO, Pohang (Korea, Republic of)

    2002-03-01

    A kinetic study of nitrogen dissolution in STS304 stainless steel melt containing Ti and Nb has been carried out at 1500 degree C using an induction furnace and a levitation melting furnace. At low O and S levels, the nitrogen dissolution rate showed the first-order kinetics being controlled by the mass transfer of nitrogen in the melt. Ti addition to STS304 stainless melt significantly retarded the nitrogen dissolution rate by the formation of solid Ti oxide layer adhered on the melt surface. Nb did not affect the rate of nitrogen dissolution. In the levitation melting experiment where the oxide layer was removed from the melt surface, Ti did not retard the nitrogen dissolution rate. Simultaneous addition of Ti and Al increased the dissolution rate by the formation of non-wetting Al{sub 2}O{sub 3} on the melt surface. A small addition of CaO-Al{sub 2}O{sub 3} synthetic flux to Ti containing melt was very effective to remove the oxide layer, hence to increase the nitrogen dissolution rate.

  10. Dissolution Threats and Legislative Bargaining

    Becher, Michael; Christiansen, Flemming Juul

    2015-01-01

    Chief executives in many parliamentary democracies have the power to dissolve the legislature. Despite a well-developed literature on the endogenous timing of parliamentary elections, political scientists know remarkably little about the strategic use of dissolution power to influence policymaking....... To address this gap, we propose and empirically evaluate a theoretical model of legislative bargaining in the shadow of executive dissolution power. The model implies that the chief executive's public support and legislative strength, as well as the time until the next constitutionally mandated election...

  11. Actor bonds after relationship dissolution

    Skaates, Maria Anne

    2000-01-01

    Most of the presented papers at the 1st NoRD Workshop can be classified as belonging to the business marketing approach to relationship dissolution. Two papers were conceptual, and the remaining six were empirical studies. The first conceptual study by Skaates (2000) focuses on the nature...... of the actor bonds that remain after a business relationship has ended. The study suggests that an interdisciplinary approach would provide a richer understanding of the phenomenon; this could be achieved by using e.g. Bourdieu's sociological concepts in dissolution research....

  12. Further investigations into pulsed optically stimulated luminescence from feldspars using blue and green light

    Ankjaergaard, C.; Jain, M.; Kalchgruber, R.; Lapp, T.; Klein, D.; McKeever, S.W.S.; Murray, A.S.; Morthekai, P.

    2009-01-01

    The purpose of this paper is to investigate characteristics of luminescence signals resulting from pulsed optical stimulation of feldspars and thereby to understand the underlying processes giving rise to the signal. Fourteen different feldspar specimens were investigated using time-resolved optically stimulated luminescence (TR-OSL), and these signals can be mathematically described as a sum of 4 exponential components (a, b, c, d). The slowest component, d, increases with the duration of the light pulse as expected from the exponential model. The stimulation temperature dependence experiment suggests that the TR-OSL signal decay is governed by the recombination process and not by the excited state lifetime. Furthermore data from the TR-OSL signal dependence on stimulation time and preheat temperature suggest that the recombination process may not be a sum of exponentials, although the model cannot be rejected definitively.

  13. Strontium and argon isotopes in naturally weathered biotites, muscovites and feldspars

    Clauer, N.

    1981-01-01

    A Rb-Sr and K-Ar isotopical study on progressively weathered biotites, muscovites and feldspars from plutonic and eruptive rocks shows that their continental weathering is a complex phenomenon controlled by environmental conditions. During weathering of biotites, the K-Ar couple often mimics the Rb-Sr couple. The radiogenic Sr and Ar isotopes are systematically leached out, but the behaviour of the elemental Rb, K, Sr and Ar depends upon the environment. In contrast, the Sr and Ar balances of muscovites are maintained, even during very intensive weathering. In mixtures of feldspars, the common Sr seems to be leached out preferentially to the radiogenic isotope, while the K-Ar balance is maintained. (Auth.)

  14. Potassium self-diffusion in a K-rich single-crystal alkali feldspar

    Hergemöller, Fabian; Deicher, Manfred; Wolf, Herbert; Brenner, Florian; Hutter, Herbert; Abart, Rainer; Stolwijk, Nicolaas A.

    The paper reports potassium diffusion measurements performed on gem-quality single-crystal alkali feldspar in the temperature range from 1169 to 1021 K. Natural sanidine from Volkesfeld, Germany was implanted with {}^{43}K at the ISOLDE/CERN radioactive ion-beam facility normal to the (001) crystallographic plane. Diffusion coefficients are well described by the Arrhenius equation with an activation energy of 2.4 eV and a pre-exponential factor of 5×10^{-6}m^{2}/s, which is more than three orders of magnitude lower than the {}^{22}Na diffusivity in the same feldspar and the same crystallographic direction. State-of-the-art considerations including ionic conductivity data on the same crystal and Monte Carlo simulations of diffusion in random binary alloy structures point to a correlated motion of K and Na through the interstitialcy mechanism.

  15. FTIR measurements of OH in deformed quartz and feldspars of the South Tibetan Detachment, Greater Himalaya

    Jezek, L.; Law, R. D.; Jessup, M. J.; Searle, M. P.; Kronenberg, A. K.

    2017-12-01

    OH absorption bands due to water in deformed quartz and feldspar grains of mylonites from the low-angle Lhotse Detachment (of the South Tibetan Detachment System, Rongbuk Valley north of Mount Everest) have been measured by Fourier Transform Infrared (FTIR) Spectroscopy. Previous microstructural studies have shown that these rocks deformed by dislocation creep at high temperature conditions in the middle crust (lower - middle amphibolite facies), and oxygen isotope studies suggest significant influx of meteoric water. OH absorption bands at 3400 cm-1 of quartz mylonites from the footwall of the Lhotse Detachment Fault are large, with the character of the molecular water band due to fluid inclusions in milky quartz. Mean water contents depend on structural position relative to the core of the Lhotse Detachment, from 1000 ppm (OH/106 Si) at 420 m below the fault to 11,350 (+/-1095) ppm near its center. The gradient in OH content shown by quartz grains implies influx of meteoric water along the Lhotse Detachment from the Tibetan Plateau ground surface to middle crustal depths, and significant fluid penetration into the extruding Himalayan slab by intergranular, permeable fluid flow processes. Feldspars of individual samples have comparable water contents to those of quartz and some are wetter. Large water contents of quartz and feldspar may have contributed to continued deformation and strain localization on the South Tibetan Detachment System. Dislocation creep in quartz is facilitated by water in laboratory experiments, and the water contents of the Lhotse fault rocks are similar to (and even larger than) water contents of quartz experimentally deformed during water weakening. Water contents of feldspars are comparable to those of plagioclase aggregates deformed experimentally by dislocation and diffusion creep under wet conditions.

  16. Biochemical evolution. I. Polymerization on internal, organophilic silica surfaces of dealuminated zeolites and feldspars

    Smith, Joseph V.

    1998-01-01

    Catalysis at mineral surfaces might generate replicating biopolymers from simple chemicals supplied by meteorites, volcanic gases, and photochemical gas reactions. Many ideas are implausible in detail because the proposed mineral surfaces strongly prefer water and other ionic species to organic ones. The molecular sieve silicalite (Union Carbide; = Al-free Mobil ZSM-5 zeolite) has a three-dimensional, 10-ring channel system whose electrically neutral Si-O surface strongly adsorbs organic species over water. Three -O-Si tetrahedral bonds lie in the surface, and the fourth Si-O points inwards. In contrast, the outward Si-OH of simple quartz and feldspar crystals generates their ionic organophobicity. The ZSM-5-type zeolite mutinaite occurs in Antarctica with boggsite and tschernichite (Al-analog of Mobil Beta). Archean mutinaite might have become de-aluminated toward silicalite during hot/cold/wet/dry cycles. Catalytic activity of silicalite increases linearly with Al-OH substitution for Si, and Al atoms tend to avoid each other. Adjacent organophilic and catalytic Al-OH regions in nanometer channels might have scavenged organic species for catalytic assembly into specific polymers protected from prompt photochemical destruction. Polymer migration along weathered silicic surfaces of micrometer-wide channels of feldspars might have led to assembly of replicating catalytic biomolecules and perhaps primitive cellular organisms. Silica-rich volcanic glasses should have been abundant on the early Earth, ready for crystallization into zeolites and feldspars, as in present continental basins. Abundant chert from weakly metamorphosed Archaean rocks might retain microscopic clues to the proposed mineral adsorbent/catalysts. Other framework silicas are possible, including ones with laevo/dextro one-dimensional channels. Organic molecules, transition-metal ions, and P occur inside modern feldspars. PMID:9520372

  17. Bleaching of the thermoluminescence of feldspars by selected wavelengths present in sunlight

    Robertson, G.B.; Prescott, J.R.; Hutton, J.T.

    1993-01-01

    Feldspars occur in many sediments, and dating them by thermoluminescence (TL) requires a knowledge of how efficiently sunlight bleaches these minerals. The relative bleaching efficiencies of various wavelengths have been investigated for four alkali feldspars and an oligoclase, using the natural TL of the samples and the artificial TL induced by laboratory irradiation, bleached by wavelengths in the range 322-550 nm. Ultraviolet wavelengths are more efficient than the longer wavelengths at bleaching all the glow-curve peaks and are responsible for most of the phototransfer from high-temperature peaks to low-temperature peaks. Some feldspars show an initial increase in TL intensity with bleaching. Two sanidines of similar bulk composition but different TL glow curves show different dependences on bleaching wavelength. In a sodic sanidine with a dominant 240 o C peak the energy required to bleach to 50% was a thousand times greater at 550 nm than at 322 nm. In contrast, another sanidine with a complex glow curve between 150 and 450 o C showed a much slower change in the 330 o C peak with wavelength - a factor of 10 between 322 and 550 nm - with a region between 400 and 500 nm which was almost independent of wavelength. This behaviour is explained by competing mechanisms of phototransfer and bleaching which depend on wavelength in different ways. (author)

  18. Possible reasons for anomalous fading in alkali feldspars used for luminescence dating of Quaternary deposits

    Jaek, Ivar

    2007-09-01

    Full Text Available According to many publications, alkali feldspars are characterized by specific athermal (anomalous fading of their thermoluminescence and optically-stimulated luminescence. This phenomenon is manifested as spontaneous decline in luminescence intensity over relatively long (months and years time after laboratory irradiation, possibly due to tunnelling of electrons from lattice defects and impurities acting as dosimetric traps. It can hamper reliable luminescent dating of Quaternary deposits on the basis of feldspar extractions due to possible unpredictable underestimation of the ages. In this paper we present some experimental results related to the manifestation of the phenomenon. It is found that, in general case, the assumed long-term anomalous fading cannot be connected to electron tunnelling from the deep dosimetric traps. At the same time, some decrease in the dosimetric luminescence signal observable in just irradiated feldspar samples can really be caused by tunnelling. However, the probability of this process quickly goes down, already within some days after irradiation. Interpretation of some other short- and long-term anomalous fading-like effects requires involvement of radiation- and thermo-induced ionic processes.

  19. Marital dissolution: an economic analysis.

    Hunter, K A

    1984-01-01

    A longitudinal analysis of factors affecting marital dissolution in the United States is presented using data from the Coleman-Rossi Retrospective Life History. Factors considered include labor force participation of both spouses, wage growth, size of family unit, age at marriage, and educational status. The study is based on the economic analysis approach developed by Gary S. Becker and others.

  20. Peculiar Feldspar And Quartz Inclusions Within Zircons From Anorthosites, North Eastern Desert, Egypt

    Eliwa, H. A.; Dawoud, M. I.; Khalaf, I. M.; Negendank, J. F.; Itaya, T.

    2004-12-01

    Zircons from three anorthosite outcrops along Wadi Dib area, north Eastern Desert of Egypt contain abundant and conspicuous inclusions of quartz, feldspar, amphibole and apatite. These anorthosites, as (50-100m thick) layers, represent the top of mafic-ultramafic intrusions exhibiting rhythmic layering visible by reputation of melanocratic and leucocratic layers. Field and microscopic studies exhibit that these anorthosites were affected by the action of residual magmatic solutions associated with the late stage crystallization of the younger granites, which modified their mineralogical composition. They are composed totally of plagioclase with subordinate amount of clinoenstatite, augite, amphibole, biotite, K-feldspar, and quartz. Accessories are magnetite, ilmenite, apatite and zircon. The abundance and the mode of occurrence of K-feldspar, quartz, and biotite with apatite and zircon among the megacrysts suggest their formation is ascribed to the interaction with the residual solutions. The microprobe data exhibit difference between feldspar and amphiboles contained herein zircons and those as anorthosite mineral constituents. The genetic relationship between zircons and their inclusions suggests later growth of zircons than inclusions and most probably at the final stage of rock modification. Zircons are magmatic and found in the interstitial feldspar and quartz among plagioclase megacrysts in aggregates or as individual grains. The microscopic and SEM images investigation exhibit that most zircons are subhedral to euhedral equant and prismatic crystals. Most zircons have same range of crystal morphologies and internal growth structures with predominance of prism /{100/} and pyramid /{101/} and occasionally prism /{110/} and pyramid /{111/}. No evidences for poly-faceted grains, inherited cores or later overgrowths were detected. CL images distinguished zircons with visible core-rim structures and others with regular and continuous growth zones contained herein

  1. Beneficiation of feldspar ore for application in the ceramic industry: Influence of composition on the physical characteristics

    Gaied, M.E.; Gallala, W.

    2015-01-01

    In this study, physical and physicochemical experiments were carried out to improve the quality of feldspar ore in Sidi Aïch massive, located in the Gafsa region of south-western Tunisia. After determination of the mineralogical and the chemical composition, flotation methods were applied. In this study, non-hydrofluoric acid flotation methods used in feldspar-quartz separation were compared with each other and with the conventional HF/amine method. The results showed that conventional HF/ami...

  2. Alkali feldspar syenites with shoshonitic affinities from Chhotaudepur area: Implication for mantle metasomatism in the Deccan large igneous province

    K.R. Hari

    2014-03-01

    Full Text Available Two petrologically distinct alkali feldspar syenite bodies (AFS-1 and AFS-2 from Chhotaudepur area, Deccan Large Igneous Province are reported in the present work. AFS-1 is characterized by hypidiomorphic texture and consists of feldspar (Or55Ab43 to Or25Ab71, ferro-pargasite/ferro-pargasite hornblende, hastingsite, pyroxene (Wo47, En5, Fs46, magnetite and biotite. AFS-2 exhibits panidiomorphic texture with euhedral pyroxene (Wo47-50, En22-39, Fs12–31 set in a groundmass matrix of alkali feldspar (Or99Ab0.77 to Or1.33Ab98, titanite and magnetite. In comparison to AFS-1, higher elemental concentrations of Ba, Sr and ∑REE are observed in AFS-2. The average peralkaline index of the alkali feldspar syenites is ∼1 indicating their alkaline nature. Variation discrimination diagrams involving major and trace elements and their ratios demonstrate that these alkali feldspar syenites have a shoshonite affinity but emplaced in a within-plate and rifting environment. No evidence of crustal contamination is perceptible in the multi-element primitive mantle normalized diagram as well as in terms of trace elemental ratios. The enrichment of incompatible elements in the alkali feldspar syenites suggests the involvement of mantle metasomatism in their genesis.

  3. Dissolution kinetics and mechanism of pandermite in acetic acid ...

    STORAGESEVER

    2010-06-07

    Jun 7, 2010 ... Borax is widely used in welding and brazing of metals and more recently, ... cleansing, high-energy fuels, cutting fluids and catalysts. *Corresponding .... temperature was reached, a given amount of pandermite was added to ...

  4. Kinetics of yttrium dissolution from waste ceramic dust

    STOPIC SRECKO R.; FRIEDRIH BERND G.

    2016-01-01

    Yttrium is a silvery transition metal and has similar chemical properties to lanthanoids. Because of this similarity, yttrium belongs to rare earth elements. Ytttrium and yttrium oxide are mostly used in fluoroscent lamps, production of electrodes, in electronic filters, lasers, superconductors and as additives in various materials to improve their properties. Yttrium is mainly recovered from the minerals monazite [(Ce,La,Th,Nd,Y)PO4] and xenotime YPO4.The presence of radioactive elements suc...

  5. Dissolution Kinetics of Icel-Aydincik Dolomite in Hydrochloric Acid

    NJD

    Department of Mining Engineering, Faculty of Engineering and Architecture, Cukurova University, Balcali, ... 65 °C. It was observed that heterogeneous chemical reactions ..... Dolomite, Ph.D. thesis, Cukurova University, Adana, Turkey, 2004.

  6. Electrochemistry and dissolution kinetics of magnetite and ilmenite

    White, A.F.; Peterson, M.L.; Hochella, M.F.

    1994-01-01

    Natural samples of magnetite and ilmenite were experimentally weathered in pH 1-7 anoxic solutions at temperatures of 2-65 ??C. Reaction of magnetite is described as [Fe2+Fe23+]O4(magnetite) + 2H+ ??? ??[Fe23+]O3(maghemite) + Fe2+ + H2O. Dynamic polarization experiments using magnetite electrodes confirmed that this reaction is controlled by two electrochemical half cells, 3[Fe2+Fe23+]O4(magnetite) ??? 4??[Fe23+]O3(maghemite) + Fe2+ + 2e- and [Fe2+Fe23+]O4(magnetite) + 8 H+ + 2e- ??? 3Fe2+ + 4H2O, which result in solid state Fe3+ reduction, formation of an oxidized layer and release of Fe(II) to solution. XPS data revealed that iron is present in the ferric state in the surfaces of reacted magnetite and ilmenite and that the Ti Fe ratio increased with reaction pH for ilmenite. Short-term (<36 h) release rates of Fe(II) were linear with time. Between pH 1 and 7, rates varied between 0.3 and 13 ?? 10-14 mol ?? cm-2 ?? s-1 for magnetite and 0.05 and 12.3 ?? 10-14 mol ?? cm-2 ?? s-1 for ilmenite. These rates are two orders of magnitude slower than electrochemical rates determined by Tafel and polarization resistance measurements. Discrepancies are due to both differences in geometric and BET surface area estimates and in the oxidation state of the mineral surface. In long-term closed-system experiments (<120 days), Fe(II) release slowed with time due to the passivation of the surfaces by increasing thicknesses of oxide surface layers. A shrinking core model, coupling surface reaction and diffusion transport, predicted that at neutral pH, the mean residence time for sand-size grains of magnetite and ilmenite will exceed 107 years. This agrees with long-term stability of these oxides in the geologic record. ?? 1994.

  7. Dissolution rates of over-the-counter painkillers: a comparison among formulations.

    Alemanni, Matteo; Gatoulis, Sergio C; Voelker, Michael

    2016-06-01

    We wanted to compare the dissolution profile of several over-the-counter analgesics to understand whether the different formulation techniques employed to enhance absorption were associated with variations in the dissolution rate, a parameter known to affect drug absorption. We considered 5 formulations currently marketed in Italy: aspirin tablets (Aspirina Dolore e Infiammazione®), ibuprofen tablets and liquid capsules (Moment®), ibuprofen lysine tablets (Nurofenimmedia®) and dexketoprofen trometamol tablets (Enantyum®). Dissolution tests were performed according to the current USP/NF monograph dissolution procedure. Drug dissolution was evaluated at 1, 3, 6, 15, and 30 minutes since the start of the test. Dissolution was evaluated at three different pH: 1.2, 4.5 and 6.8. Every test was repeated 12 times. The aspirin formulation was by far the most rapid dissolving formulation, among those tested, with more than 80% of the tablet dissolved at 6 minutes for every pH considered. At pH 1.2 and 4.5, only the dexketoprofen formulation was able to reach the dissolution level of aspirin at 30 minutes, but had lower levels of dissolution at the previous time points. Instead, at pH 6.8, most of the formulations approached aspirin dissolution level, but only after 15 minutes. Ibuprofen capsules had the slowest kinetics, with a lag phase the first 6 minutes. Different formulation strategies can lead to great differences in the dissolution rates even among drugs of the same class, suggesting that enhancements in the formulation of painkillers can lead to improvements in drug absorption, and thus in the onset of analgesia.

  8. Solvents effects on crystallinity and dissolution of β-artemether.

    Xu, Jianghui; Singh, Vikramjeet; Yin, Xianzhen; Singh, Parbeen; Wu, Li; Xu, Xiaonan; Guo, Tao; Sun, Lixin; Gui, Shuangying; Zhang, Jiwen

    2017-03-01

    β-artemether (ARM) is a widely used anti-malarial drug isolated from the Chinese antimalarial plant, Artemisia annua. The solvent effects on crystal habits and dissolution of ARM were thoroughly investigated and discussed herein. The ARM was recrystallized in nine different solvents of varied polarity, namely, methanol, ethanol, isopropanol, tetrahydrofuran, dichloromethane, trichloromethane, ethyl acetate, acetone and hexane by solvent evaporation method. The obtained crystals were morphologically characterized using scanning electron microscope (SEM). The average sizes of crystals were 1.80-2.64 μm calculated from microscopic images using Image-Pro software. No significant change in chemical structure was noticed after recrystallization and the specific band at 875 cm -1 wavenumber (C-O-O-C) confirmed the presence of most sensitive functional group in the ARM chemical structure. The existence and production of two polymorphic forms, polymorph A and polymorph B, was confirmed by differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD). The data suggested that the fabrication of polymorph B can be simply obtained from the recrystallization of ARM in a specific solvent. Significant effects of solvent polarity, crystals shapes and sizes on drug dissolution were noticed during in vitro dissolution test. The release kinetics were calculated and well fitted by the Higuchi and Hixon-Crowell models. The ARM-methanol and ARM-hexane showed highest and slowest dissolution, respectively, due to the effects of solvent polarity and crystal morphologies. Overall, proper selection of the solvents for the final crystallization of ARM helps to optimize dissolution and bioavailability for a better delivery of anti-malarial drug.

  9. Dissolution test for glibenclamide tablets

    Elisabeth Aparecida dos Santos Gianotto

    2007-10-01

    Full Text Available The aim of this work is to develop and validate a dissolution test for glibenclamide tablets. Optimal conditions to carry out the dissolution test are 500 mL of phosphate buffer at pH 8.0, paddles at 75 rpm stirring speed, time test set to 60 min and using equipment with six vessels. The derivative UV spectrophotometric method for determination of glibenclamide released was developed, validated and compared with the HPLC method. The UVDS method presents linearity (r² = 0.9999 in the concentration range of 5-14 µg/mL. Precision and recoveries were 0.42% and 100.25%, respectively. The method was applied to three products commercially available on the Brazilian market.

  10. Mesoporous silica formulation strategies for drug dissolution enhancement: a review.

    McCarthy, Carol A; Ahern, Robert J; Dontireddy, Rakesh; Ryan, Katie B; Crean, Abina M

    2016-01-01

    Silica materials, in particular mesoporous silicas, have demonstrated excellent properties to enhance the oral bioavailability of poorly water-soluble drugs. Current research in this area is focused on investigating the kinetic profile of drug release from these carriers and manufacturing approaches to scale-up production for commercial manufacture. This review provides an overview of different methods utilized to load drugs onto mesoporous silica carriers. The influence of silica properties and silica pore architecture on drug loading and release are discussed. The kinetics of drug release from mesoporous silica systems is examined and the manufacturability and stability of these formulations are reviewed. Finally, the future prospects of mesoporous silica drug delivery systems are considered. Substantial progress has been made in the characterization and development of mesoporous drug delivery systems for drug dissolution enhancement. However, more research is required to fully understand the drug release kinetic profile from mesoporous silica materials. Incomplete drug release from the carrier and the possibility of drug re-adsorption onto the silica surface need to be investigated. Issues to be addressed include the manufacturability and regulation status of formulation approaches employing mesoporous silica to enhance drug dissolution. While more research is needed to support the move of this technology from the bench to a commercial medicinal product, it is a realistic prospect for the near future.

  11. Compilation of kinetic data for geochemical calculations

    Arthur, R.C.; Savage, D.; Sasamoto, Hiroshi; Shibata, Masahiro; Yui, Mikazu

    2000-01-01

    Kinetic data, including rate constants, reaction orders and activation energies, are compiled for 34 hydrolysis reactions involving feldspars, sheet silicates, zeolites, oxides, pyroxenes and amphiboles, and for similar reactions involving calcite and pyrite. The data are compatible with a rate law consistent with surface reaction control and transition-state theory, which is incorporated in the geochemical software package EQ3/6 and GWB. Kinetic data for the reactions noted above are strictly compatible with the transition-state rate law only under far-from-equilibrium conditions. It is possible that the data are conceptually consistent with this rate law under both far-from-equilibrium and near-to-equilibrium conditions, but this should be confirmed whenever possible through analysis of original experimental results. Due to limitations in the availability of kinetic data for mine-water reactions, and in order to simplify evaluations of geochemical models of groundwater evolution, it is convenient to assume local-equilibrium in such models whenever possible. To assess whether this assumption is reasonable, a modeling approach accounting for couple fluid flow and water-rock interaction is described that can be use to estimate spatial and temporal scale of local equilibrium. The approach is demonstrated for conditions involving groundwater flow in fractures at JNC's Kamaishi in-situ tests site, and is also used to estimate the travel time necessary for oxidizing surface waters to migrate to the level of a HLW repository in crystalline rock. The question of whether local equilibrium is a reasonable assumption must be addressed using an appropriate modeling approach. To be appropriate for conditions at the Kamaishi site using the modeling approach noted above, the fracture fill must closely approximate a porous mine, groundwater flow must be purely advective and diffusion of solutes across the fracture-host rock boundary must not occur. Moreover, the mineralogical and

  12. Effect of ageing of K-feldspar on its ice nucleating efficiency in immersion, deposition and contact freezing modes

    Peckhaus, Andreas; Bachmann, Felix; Hoffmann, Nadine; Koch, Michael; Kiselev, Alexei; Leisner, Thomas

    2015-04-01

    Recently K-feldspar was identified as one of the most active atmospheric ice nucleating particles (INP) of mineral origin [1]. Seeking the explanation to this phenomena we have conducted extensive experimental investigation of the ice nucleating efficiency of K-feldspar in three heterogeneous freezing modes. The immersion freezing of K-feldspar was investigated with the cold stage using arrays of nanoliter-size droplets containing aqueous suspension of polydisperse feldspar particles. For contact freezing, the charged droplets of supercooled water were suspended in the laminar flow of the DMA-selected feldspar-containing particles, allowing for determination of freezing probability on a single particle-droplet contact [2]. The nucleation and growth of ice via vapor deposition on the crystalline surfaces of macroscopic feldspar particles have been investigated in the Environmental Scanning Electron Microscope (ESEM) under humidified nitrogen atmosphere. The ice nucleation experiments were supplemented with measurements of effective surface area of feldspar particles and ion chromatography (IC) analysis of the leached framework cations (K+, Na+, Ca2+, Mg2+). In this contribution we focus on the role of surface chemistry influencing the IN efficiency of K-feldspar, in particular the connection between the degree of surface hydroxylation and its ability to induce local structural ordering in the interfacial layer in water molecules (as suggested by recent modeling efforts). We mimic the natural process of feldspar ageing by suspending it in water or weak aqueous solution of carbonic acid for different time periods, from minutes to months, and present its freezing efficiency as a function of time. Our immersion freezing experiments show that ageing have a nonlinear effect on the freezing behavior of feldspar within the investigated temperature range (-40°C to -10°C). On the other hand, deposition nucleation of ice observed in the ESEM reveals clear different pattern

  13. Anodic dissolution and corrosion of alloy Cu30Ni in chloride solutions

    Zolotarev, E.I.

    1989-01-01

    The anodic and corrosion behavior of alloy Cu30Ni is studied in a solution of 3 N NaCl + 0.01 N HCl by a radiometric method using gamma isotopes of 58 Co (as a marker for Ni) and 64 Cu in combination with electrochemical measurements. It was established that under stationary conditions there was uniform dissolution of the alloy both during free corrosion and anodic polarization. The authors obtained partial anodic dissolution curves for the components of the alloy. It was shown that the dissolution kinetics differed from the mechanisms controlling dissolution of the corresponding pure metals. During corrosion of the alloy in an oxygen atmosphere a back precipitation of copper on the surface of the alloy was not observed. The characteristics observed in the corrosion-electrochemical behavior of the alloy in concentrated chloride solutions can be explained by the presence of Ni on the surface of the dissolving alloy

  14. Comparison of the properties of various optically stimulated luminescence signals from potassium feldspar

    Fu Xiao; Zhang Jiafu; Zhou Liping

    2012-01-01

    Various optically stimulated luminescence signals from K-feldspar have been used to determine the equivalent doses of sediment samples. Understanding the properties of these optical signals is critical to evaluate their applicability and limitations to optical dating. In this paper, some properties of IRSL, post-IR OSL and post-IR IRSL signals (detected in the UV region using U-340 filters) from a museum sample of K-feldspar were investigated by analyzing the relationships between optical and TL signals, and the effect of optical bleaching and heating on optical signals. The trap parameters of the different optical signals were calculated using the pulse annealing method. The results show that this sample exhibits two regenerated TL peaks at ∼140 and ∼330 °C. Corresponding to the low temperature TL peak, the OSL and post-IR OSL signals appear to be more associated with lower temperature TL than the IRSL signal measured at 50 °C. Corresponding to the high temperature TL peak, the post-IR IRSL signals mainly originate from the more thermally stable traps associated with the high temperature TL, compared with the IRSL and post-IR OSL signals. However, the post-IR IRSL 225°C signal is shown to be hard to be bleached by blue light and simulated sunlight, compared with the IRSL 50°C and low temperature post-IR IRSL signals. The implication for optical dating is that the elevated temperature post-IR IRSL signals can be preferentially applied over other signals from K-feldspar, but it is desirable that the effectiveness of the pre-depositional zeroing of these signals is assessed.

  15. OSL and IRSL characteristics of quartz and feldspar from southern California, USA

    Lawson, Michael J.; Roder, Belinda J.; Stang, Dallon M.; Rhodes, Edward J.

    2012-01-01

    Southern California comprises of a wide range of diverse landscapes and environments, from high mountains with glacial and periglacial sediments to deserts with large sand dunes, extensive alluvial fans and ephemeral playas. Highly active tectonic processes has exposed ancient (c. 2 Ga) plutonic and metamorphic basement from deep within the crust, while similar Palaeozoic, Mesozoic and Cenozoic rocks are also common. A rich array of volcanic lithologies extending into the late Quaternary complement many thick sedimentary sequences that formed in equally diverse ancient environments typical of an accreting active continental margin. In some locations, notably in the Coachella Valley close to Palm Springs and the Salton Sea, low OSL sensitivity and poor characteristics restrict the application of the quartz SAR protocol to date late Pleistocene and Holocene fluvial sediments. In other locations such as the Malibu coastline, high sensitivity of the quartz OSL signal is observed, despite local source rocks being dominated by volcanic lithologies. Problems of poor quartz characteristics, along with uncertainty in predicting quartz OSL behavior for future dating campaigns poses a significant problem for projects, in particular for neotectonic contexts. While K-feldspar has been used extensively to date eolian and fluvial sediments in southern California, little information regarding signal stability is available. We explore the characteristics of both quartz and feldspar sub-samples from eolian, fluvial, lacustrine environments, in order to help develop mineral selection criteria for optical dating applications and clarify these issues. The importance of radiation quenching in quartz grains recently eroded from bedrock and the role of fires in enhancing OSL sensitivity are considered. The relative bleachability of quartz and feldspar fractions, along with thermal stability considerations is discussed. A simple test for quartz OSL signal contamination based on thermal

  16. Role of nitrous acid during the dissolution of UO2 in nitric acid

    Deigan, N.; Pandey, N.K.; Kamachi Mudali, U.; Joshi, J.B.

    2016-01-01

    Understanding the dissolution behaviour of sintered UO 2 pellet in nitric acid is very important in designing an industrial scale dissolution system for the plutonium rich fast reactor MOX fuel. In the current article we have established the role of nitrous acid on the dissolution kinetics of UO 2 pellets in nitric acid. Under the chemical conditions that prevail in a typical Purex process, NO and NO 2 gases gets generated in the process streams. These gases produce nitrous acid in nitric acid medium. In addition, during the dissolution of UO 2 in nitric acid medium, nitrous acid is further produced in-situ at the pellet solution interface. As uranium dissolves oxidatively in nitric acid medium wherein it goes from U(IV) in solid to U(VI) in liquid, presence of nitrous acid (a good oxidizing agent) accelerates the reaction rate. Hence for determining the reaction mechanism of UO 2 dissolution in nitric acid medium, knowing the nitrous acid concentration profile during the course of dissolution is important. The current work involves the measurement of nitrous acid concentration during the course of dissolution of sintered UO 2 pellets in 8M starting nitric acid concentration as a function of mixing intensity from unstirred condition to 1500 RPM

  17. Time-resolved infrared stimulated luminescence signals in feldspars: Analysis based on exponential and stretched exponential functions

    Pagonis, V.; Morthekai, P.; Singhvi, A.K.; Thomas, J.; Balaram, V.; Kitis, G.; Chen, R.

    2012-01-01

    Time-resolved infrared-stimulated luminescence (TR-IRSL) signals from feldspar samples have been the subject of several recent experimental studies. These signals are of importance in the field of luminescence dating, since they exhibit smaller fading effects than the commonly employed continuous-wave infrared signals (CW-IRSL). This paper presents a semi-empirical analysis of TR-IRSL data from feldspar samples, by using a linear combination of exponential and stretched exponential (SE) functions. The best possible estimates of the five parameters in this semi-empirical approach are obtained using five popular commercially available software packages, and by employing a variety of global optimization techniques. The results from all types of software and from the different fitting algorithms were found to be in close agreement with each other, indicating that a global optimum solution has likely been reached during the fitting process. Four complete sets of TR-IRSL data on well-characterized natural feldspars were fitted by using such a linear combination of exponential and SE functions. The dependence of the extracted fitting parameters on the stimulation temperature is discussed within the context of a recently proposed model of luminescence processes in feldspar. Three of the four feldspar samples studied in this paper are K-rich, and these exhibited different behavior at higher stimulation temperatures, than the fourth sample which was a Na-rich feldspar. The new method of analysis proposed in this paper can help isolate mathematically the more thermally stable components, and hence could lead to better dating applications in these materials. - Highlights: ► TR-IRSL from four feldspars were analyzed using exponential and stretched exponential functions. ► A variety of global optimization techniques give good agreement. ► Na-rich sample behavior is different from the three K-rich samples. ► Experimental data are fitted for stimulation temperatures

  18. Oster pluton (Central Karelia) - the ancient massif of two-feldspar granites of Baltic Shield

    Kovalenko, A.V.; Rizvanova, N.G.

    2000-01-01

    Geochronological study of two-feldspar granites forming the Oster pluton in the Central Karelia was performed using the methods of U-Pb- and Sm-Nd-dating. U-Pb isotope data for zircons from granite of the Oster pluton correspond to the age of 2876±21 mln. years, whereas Sm-Nd isotope data obtained for three samples of the garnet correspond to the age varying from 3.0 to 3.5 bln. years. The ancient age of granites of the Oster pluton is explained by the presence of a sufficiently powerful crust in the region by that moment [ru

  19. Optical dating using feldspar from Quaternary alluvial and colluvial sediments from SE Brazilian Plateau, Brazil

    Tatumi, Sonia H.; Peixoto, Maria Naise O.; Moura, Josilda R.S.; Mello, Claudio L.; Carmo, Isabela O.; Kowata, Emilia A.; Yee, Marcio; Brito, Silvio Luiz M.; Gozzi, Giuiliano; Kassab, Luciana R.P.

    2003-01-01

    Opticallly stimulated luminescence (OSL) dating has been applied to a wide variety of materials such as loess, sand dunes, colluvium, alluvium, volcanic products, etc., helping geologic geomorphologic studies. OSL dating results using feldspar crystals extracted from alluvial and colluvial deposits of SE Brazilian Plateau will be presented in this work. The methodology used is based on the regeneration method, with multiple aliquot protocol. A total of 23 sample ages were obtained spanning 6.5-97.2 kyr. Results of radioactive contents and comparison with radiocarbon ages will be discussed

  20. Modeling of the shape of infrared stimulated luminescence signals in feldspars

    Pagonis, Vasilis; Jain, Mayank; Murray, Andrew S.

    2012-01-01

    This paper presents a new empirical model describing infrared (IR) stimulation phenomena in feldspars. In the model electrons from the ground state of an electron trap are raised by infrared optical stimulation to the excited state, and subsequently recombine with a nearest-neighbor hole via...... corresponds to a fast rate of recombination processes taking place along the infrared stimulated luminescence (IRSL) curves. The subsequent decay of the simulated IRSL signal is characterized by a much slower recombination rate, which can be described by a power-law type of equation.Several simulations...

  1. Structures of the K- and Na-components of two-phase feldspar from Primorskii Krai

    Organova, N.I.; Marsii, I.M.; Zakharov, N.D.; Nasedkin, V.V.; Borisovskii, S.B.; Rozhdestvenskaya, I.V.; Ivanova, T.I.

    1999-01-01

    The structures of two components of the decomposed solid solution of an alkali feldspar are refined. These structures exhibit at least two specific features: (1) the complete phase separation into pure K and pure Na phases and (2) an anomalous distribution of Al atoms over four crystallographically independent positions of silicon-aluminum tetrahedra in the Na-component (different from its usual distribution). To explain the results obtained, the ideas of synergetics are invoked (the geological history of the specimen includes a powerful explosion, which threw out the material from the volcano to the Earth's surface)

  2. Mechanistic analysis of solute transport in an in vitro physiological two-phase dissolution apparatus.

    Mudie, Deanna M; Shi, Yi; Ping, Haili; Gao, Ping; Amidon, Gordon L; Amidon, Gregory E

    2012-10-01

    In vitro dissolution methodologies that adequately capture the oral bioperformance of solid dosage forms are critical tools needed to aid formulation development. Such methodologies must encompass important physiological parameters and be designed with drug properties in mind. Two-phase dissolution apparatuses, which contain an aqueous phase in which the drug dissolves (representing the dissolution/solubility component) and an organic phase into which the drug partitions (representing the absorption component), have the potential to provide meaningful predictions of in vivo oral bioperformance for some BCS II, and possibly some BCS IV drug products. Before such an apparatus can be evaluated properly, it is important to understand the kinetics of drug substance partitioning from the aqueous to the organic medium. A mass transport analysis was performed of the kinetics of partitioning of drug substance solutions from the aqueous to the organic phase of a two-phase dissolution apparatus. Major assumptions include pseudo-steady-state conditions, a dilute aqueous solution and diffusion-controlled transport. Input parameters can be measured or estimated a priori. This paper presents the theory and derivation of our analysis, compares it with a recent kinetic approach, and demonstrates its effectiveness in predicting in vitro partitioning profiles of three BCS II weak acids in four different in vitro two-phase dissolution apparatuses. Very importantly, the paper discusses how a two-phase apparatus can be scaled to reflect in vivo absorption kinetics and for which drug substances the two-phase dissolution systems may be appropriate tools for measuring oral bioperformance. Copyright © 2012 John Wiley & Sons, Ltd.

  3. Acid-catalyzed kinetics of indium tin oxide etching

    Choi, Jae-Hyeok; Kim, Seong-Oh; Hilton, Diana L. [School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore); Centre for Biomimetic Sensor Science, Nanyang Technological University, 50 Nanyang Drive, 637553 (Singapore); Cho, Nam-Joon, E-mail: njcho@ntu.edu.sg [School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore); Centre for Biomimetic Sensor Science, Nanyang Technological University, 50 Nanyang Drive, 637553 (Singapore); School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, 637459 (Singapore)

    2014-08-28

    We report the kinetic characterization of indium tin oxide (ITO) film etching by chemical treatment in acidic and basic electrolytes. It was observed that film etching increased under more acidic conditions, whereas basic conditions led to minimal etching on the time scale of the experiments. Quartz crystal microbalance was employed in order to track the reaction kinetics as a function of the concentration of hydrochloric acid and accordingly solution pH. Contact angle measurements and atomic force microscopy experiments determined that acid treatment increases surface hydrophilicity and porosity. X-ray photoelectron spectroscopy experiments identified that film etching is primarily caused by dissolution of indium species. A kinetic model was developed to explain the acid-catalyzed dissolution of ITO surfaces, and showed a logarithmic relationship between the rate of dissolution and the concentration of undisassociated hydrochloric acid molecules. Taken together, the findings presented in this work verify the acid-catalyzed kinetics of ITO film dissolution by chemical treatment, and support that the corresponding chemical reactions should be accounted for in ITO film processing applications. - Highlights: • Acidic conditions promoted indium tin oxide (ITO) film etching via dissolution. • Logarithm of the dissolution rate depended linearly on the solution pH. • Acid treatment increased ITO surface hydrophilicity and porosity. • ITO film etching led to preferential dissolution of indium species over tin species.

  4. Correlation of basic TL, OSL and IRSL properties of ten K-feldspar samples of various origins

    Sfampa, I.K. [Aristotle University of Thessaloniki, Nuclear Physics Laboratory, 54124 Thessaloniki (Greece); Polymeris, G.S. [Institute of Nuclear Sciences, Ankara University, 06100 Besevler, Ankara (Turkey); Pagonis, V. [McDaniel College, Physics Department, Westminster, MD 21157 (United States); Theodosoglou, E. [Department of Mineralogy-Petrology-Economic Geology, School of Geology, Aristotle University of Thessaloniki, 54124 Thessaloniki (Greece); Tsirliganis, N.C. [Laboratory of Radiation Applications and Archaeological Dating, Department of Archaeometry and Physicochemical Measurements, ‘Athena’ R.& I.C., Kimmeria University Campus, GR67100 Xanthi (Greece); Kitis, G., E-mail: gkitis@auth.gr [Aristotle University of Thessaloniki, Nuclear Physics Laboratory, 54124 Thessaloniki (Greece)

    2015-09-15

    Highlights: • OSL and IRSL bleaching behavior of ten K-feldspar samples is presented. • OSL and IRSL decay curves were component resolved using tunneling model. • The growth of integrated OSL and IRSL signals versus time was described by new expression based on tunneling model. • Correlation between TL, OSL and IRSL signals and of all properties with K-feldspar structure was discussed. - Abstract: Feldspars stand among the most widely used minerals in dosimetric methods of dating using thermoluminescence (TL), optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL). Having very good dosimetric properties, they can in principle contribute to the dating of every site of archaeological and geological interest. The present work studies basic properties of ten naturally occurring K-feldspar samples belonging to three feldspar species, namely sanidine, orthoclase and microcline. The basic properties studied are (a) the influence of blue light and infrared stimulation on the thermoluminescence glow-curves, (b) the growth of OSL, IRSL, residual TL and TL-loss as a function of OSL and IRSL bleaching time and (c) the correlation between the OSL and IRSL signals and the energy levels responsible for the TL glow-curve. All experimental data were fitted using analytical expressions derived from a recently developed tunneling recombination model. The results show that the analytical expressions provide excellent fits to all experimental results, thus verifying the tunneling recombination mechanism in these materials and providing valuable information about the concentrations of luminescence centers.

  5. IR-RF dating of sand-sized K-feldspar extracts: A test of accuracy

    Buylaert, Jan-Pieter; Jain, Mayank; Murray, A.S.

    2012-01-01

    In this paper we use a recently developed radioluminescence (RL) attachment to the Risø TL/OSL reader to test the InfraRed-RadioFluorescence (IR-RF) dating method applied to K-feldspar rich extracts from our known-age archive samples. We present experiments to characterise the instrument performa......In this paper we use a recently developed radioluminescence (RL) attachment to the Risø TL/OSL reader to test the InfraRed-RadioFluorescence (IR-RF) dating method applied to K-feldspar rich extracts from our known-age archive samples. We present experiments to characterise the instrument...... performance and to test the reproducibility of IR-RF measurements. These experiments illustrate the high sensitivity and dose rate of our RL system, the negligible influence of the turntable movement on IR-RF signals and the effectiveness of the built in 395 nm LED at bleaching IR-RF signals. We measure IR......-RF ages on a set of samples with independent age control using a robust analytical method, which is able to detect any possible sensitivity change. Our IR-RF ages do not agree well with the independent age control; the ages of the younger samples (20–45 ka) are significantly over-estimated while the ages...

  6. Comparative study of ice nucleating efficiency of K-feldspar in immersion and deposition freezing modes

    Hiron, T.; Hoffmann, N.; Peckhaus, A.; Kiselev, A. A.; Leisner, T.; Flossmann, A. I.

    2016-12-01

    One of the main challenges in understanding the evolution of Earth's climate resides in the understanding the role of ice nucleation on the development of tropospheric clouds as well as its initiation. K-feldspar is known to be a very active ice nucleating particle and this study focuses on the characterization of its activity in two heterogeneous nucleation modes, immersion and deposition freezing.We use a newly built humidity-controlled cold stage allowing the simultaneous observation of up to 2000 identical 0.6-nanoliter droplets containing suspension of mineral dust particles. The droplets are first cooled down to observe immersion freezing, the obtained ice crystals are then evaporated and finally, the residual particles are exposed to the water vapor supersaturated with respect to ice.The ice nucleation abilities for the individual residual particles are then compared for the different freezing modes and correlation between immersion ice nuclei and deposition ice nuclei is investigated.Based on the electron microscopy analysis of the residual particles, we discuss the possible relationship between the ice nucleation properties of feldspar and its microstructure. Finally, we discuss the atmospheric implications of our experimental results, using DESCAM, a 1.5D bin-resolved microphysics model.

  7. Calcination/dissolution residue treatment

    Knight, R.C.; Creed, R.F.; Patello, G.K.; Hollenberg, G.W.; Buehler, M.F.; O'Rourke, S.M.; Visnapuu, A.; McLaughlin, D.F.

    1994-09-01

    Currently, high-level wastes are stored underground in steel-lined tanks at the Hanford site. Current plans call for the chemical pretreatment of these wastes before their immobilization in stable glass waste forms. One candidate pretreatment approach, calcination/dissolution, performs an alkaline fusion of the waste and creates a high-level/low-level partition based on the aqueous solubilities of the components of the product calcine. Literature and laboratory studies were conducted with the goal of finding a residue treatment technology that would decrease the quantity of high-level waste glass required following calcination/dissolution waste processing. Four elements, Fe, Ni, Bi, and U, postulated to be present in the high-level residue fraction were identified as being key to the quantity of high-level glass formed. Laboratory tests of the candidate technologies with simulant high-level residues showed reductive roasting followed by carbonyl volatilization to be successful in removing Fe, Ni, and Bi. Subsequent bench-scale tests on residues from calcination/dissolution processing of genuine Hanford Site tank waste showed Fe was separated with radioelement decontamination factors of 70 to 1,000 times with respect to total alpha activity. Thermodynamic analyses of the calcination of five typical Hanford Site tank waste compositions also were performed. The analyses showed sodium hydroxide to be the sole molten component in the waste calcine and emphasized the requirement for waste blending if fluid calcines are to be achieved. Other calcine phases identified in the thermodynamic analysis indicate the significant thermal reconstitution accomplished in calcination

  8. CHARACTERIZATION AND ALUMINUM DISSOLUTION DEMONSTRATION WITH A 3 LITER TANK 51H SAMPLE

    Hay, M; John Pareizs, J; Cj Bannochie, C; Michael Stone, M; Damon Click, D; Daniel McCabe, D

    2008-01-01

    A 3-liter sludge slurry sample was sent to SRNL for demonstration of a low temperature aluminum dissolution process. The sludge was characterized before and after the aluminum dissolution. Post aluminum dissolution sludge settling and the stability of the decanted supernate were also observed. The characterization of the as-received 3-liter sample of Tank 51H sludge slurry shows a typical high aluminum HM sludge. The XRD analysis of the dried solids indicates Boehmite is the predominant crystalline form of aluminum in the sludge solids. However, amorphous phases of aluminum present in the sludge would not be identified using this analytical technique. The low temperature (55 C) aluminum dissolution process was effective at dissolving aluminum from the sludge. Over the three week test, ∼42% of the aluminum was dissolved out of the sludge solids. The process appears to be selective for aluminum with no other metals dissolving to any appreciable extent. At the termination of the three week test, the aluminum concentration in the supernate had not leveled off indicating more aluminum could be dissolved from the sludge with longer contact times or higher temperatures. The slow aluminum dissolution rate in the test may indicate the dissolution of the Boehmite form of aluminum however; insufficient kinetic data exists to confirm this hypothesis. The aluminum dissolution process appears to have minimal impact on the settling rate of the post aluminum dissolution sludge. However, limited settling data were generated during the test to quantify the effects. The sludge settling was complete after approximately twelve days. The supernate decanted from the settled sludge after aluminum dissolution appears stable and did not precipitate aluminum over the course of several months. A mixture of the decanted supernate with Tank 11 simulated supernate was also stable with respect to precipitation

  9. Impact of dissolution and carbonate precipitation on carbon storage in basalt

    Wells, R. K.; Xiong, W.; Tadeoye, J.; Menefee, A.; Ellis, B. R.; Skemer, P. A.; Giammar, D.

    2016-12-01

    The spatial evolution of silicate mineral dissolution, carbonate precipitation, and the transport of fluids influence the viability of carbon storage in basalt reservoirs. Dissolution of natural basalt and subsequent carbonate precipitation in systems with different transport processes operating were characterized using static and flow-through (5 mL/hr) experiments at 50, 100, and 150 °C, and 100 bar CO2. Intact samples and cores with milled pathways that simulate fractures were tested. Spatial and mineralogical patterns in dissolution and precipitation were analyzed using optical and electron microscopy, microCT scanning, and surface roughness data. Precipitates and fluid chemistry were analyzed using Raman spectroscopy, SEM-EDS, and ICP-MS. Analysis of the bulk solution and surface topography suggests dissolution of olivine and pyroxene grains begins within hours of the start of the experiments. In flow-through experiments, total effluent cation concentrations reach a peak concentration within a few hours then drop towards a steady state within a few days. In static experiments, the initial rate of cation release is faster than it is after several weeks. In both cases Ca2+, Mg2+, and Fe2+ are the dominant cations in solution in the initial stages of reaction. Lower concentrations of Na2+, K+, and Al3+, and the preservation of feldspar and matrix grains after several weeks of reaction indicate the slow reactivity of these minerals. As the reaction progresses, the surface roughness increases steadily with cavities developing at the sites of olivine and pyroxene grains. Post-reaction analysis of basalt samples reacted at static conditions with milled pathways reveals that both siderite and amorphous silica precipitated within diffusion-limited zones as early as 4-6 weeks. Siderite abundance varies with distance along the pathway with the highest concentration of carbonates 1-2 cm below the fracture opening. Siderite precipitates are large enough to fill fracture

  10. Attenuation of glass dissolution in the presence of natural additives

    Sang, Jing C.; Barkatt, Aaron [Department of Chemistry, The Catholic University of America, Washington, DC (United States); O`Keefe, John A. [National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, MD (United States)

    1996-11-01

    The dissolution kinetics of silicate glasses in aqueous environments in systems which included a variety of natural crystalline solids in addition to the glass itself and the aqueous phase are reported. The results demonstrate the possibility of a dramatic decrease in the rate of dissolution of silicate glass in the presence of certain varieties of olivine-based materials. This decrease in dissolution rate was shown to be due to the fact that these additives consist mostly of Mg-based material but also contain minor amounts of Al and Ca. The combined presence of Mg with these minor species affected the corrosion rate of the glass as a whole, including its most soluble components such as boron. This study has potentially important implications to the durability of glasses exposed to natural environments. The results may be relevant to the use of active backfill materials in burial sites for nuclear waste glasses, as well as to better understanding of the environmental degradation of natural and ancient glasses.

  11. The dissolution phenomenon of lysozyme crystals

    Mueller, C.; Ulrich, J. [Martin Luther University Halle-Wittenberg, Department of Thermal Separation Processes, Centre of Engineering Science, Halle/Saale (Germany)

    2012-02-15

    Dissolution studies on lysozyme crystals were carried out since the observed dissolution pattern look different from non-protein dissolved crystals. The Tetragonal, High Temperature and Low Temperature Orthorhombic morphologies, crystallized using sodium chloride, were chosen and the influence of different pH, salt and protein concentration on their dissolution was investigated. An increase in pH and/or salt concentration can modify the dissolution behaviour. The pattern of the crystals during the dissolution process will, therefore, develop differently. Frequently a skeleton like crystal pattern followed by a falling apart of the crystals is observed. The multi-component character of the lysozyme crystal (protein, water, buffer, salt) as well as ''solvatomorphism'' gives first insights in the phenomena happening in the dissolution process. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Plutonium dioxide dissolution in glass

    Vienna, J.D.; Alexander, D.L.; Li, Hong [and others

    1996-09-01

    In the aftermath of the Cold War, the U.S. Department of Energy`s (DOE) Office of Fissile Materials Disposition (OFMD) is charged with providing technical support for evaluation of disposition options for excess fissile materials manufactured for the nation`s defense. One option being considered for the disposition of excess plutonium (Pu) is immobilization by vitrification. The vitrification option entails immobilizing Pu in a host glass and waste package that are criticality-safe (immune to nuclear criticality), proliferation-resistant, and environmentally acceptable for long-term storage or disposal. To prove the technical and economic feasibility of candidate vitrification options it is necessary to demonstrate that PuO{sub 2} feedstock can be dissolved in glass in sufficient quantity. The OFMD immobilization program has set a Pu solubility goal of 10 wt% in glass. The life cycle cost of the vitrification options are strongly influenced by the rate at which PUO{sub 2} dissolves in glass. The total number of process lines needed for vitrification of 50 t of Pu in 10 years is directly dependent upon the time required for Pu dissolution in glass. The objective of this joint Pacific Northwest National Laboratory (PNNL) - Savannah River Technology Center (SRTC) study was to demonstrate a high Pu solubility in glass and to identify on a rough scale the time required for Pu dissolution in the glass. This study was conducted using a lanthanide borosilicate (LaBS) glass composition designed at the SRTC for the vitrification of actinides.

  13. Plutonium dioxide dissolution in glass

    Vienna, J.D.; Alexander, D.L.; Li, Hong

    1996-09-01

    In the aftermath of the Cold War, the U.S. Department of Energy's (DOE) Office of Fissile Materials Disposition (OFMD) is charged with providing technical support for evaluation of disposition options for excess fissile materials manufactured for the nation's defense. One option being considered for the disposition of excess plutonium (Pu) is immobilization by vitrification. The vitrification option entails immobilizing Pu in a host glass and waste package that are criticality-safe (immune to nuclear criticality), proliferation-resistant, and environmentally acceptable for long-term storage or disposal. To prove the technical and economic feasibility of candidate vitrification options it is necessary to demonstrate that PuO 2 feedstock can be dissolved in glass in sufficient quantity. The OFMD immobilization program has set a Pu solubility goal of 10 wt% in glass. The life cycle cost of the vitrification options are strongly influenced by the rate at which PUO 2 dissolves in glass. The total number of process lines needed for vitrification of 50 t of Pu in 10 years is directly dependent upon the time required for Pu dissolution in glass. The objective of this joint Pacific Northwest National Laboratory (PNNL) - Savannah River Technology Center (SRTC) study was to demonstrate a high Pu solubility in glass and to identify on a rough scale the time required for Pu dissolution in the glass. This study was conducted using a lanthanide borosilicate (LaBS) glass composition designed at the SRTC for the vitrification of actinides

  14. Experimental early crystallization of K-feldspar in granitic systems. Implications on the origin of magmatic fabrics in granitic rocks

    Díaz-Alvarado, J.

    2017-07-01

    One of the most outstanding characteristics of some granodioritic to granitic rocks is the presence of K-feldspar megacrysts. For instance, granodiorites and monzogranites of the Spanish Central System batholith present variable amounts of large (up to 10cm in length) euhedral K-feldspar crystals. The porphyritic textures, the euhedral shape, the alignment of plagioclase and biotite inclusions and the magmatic fabrics point to a magmatic origin for these megacrysts. This work presents a phase equilibria study in a high-K2O granodioritic system. A series of experiments were conducted with a granodioritic composition (GEMbiot) to study the crystallization sequence at the emplacement conditions in the Gredos massif, i.e. 4 H2O wt.% and 0.4GPa. Experimental results show that orthopiroxene is the liquidus phase at 1010ºC, which reacts with the H2O-rich melt to stabilize biotite between 980 and 940ºC. Plagioclase crystallizes at around 910ºC, and K-feldspar crystallizes in the matrix between 750 and 700ºC when the crystal fraction is around 0.5. However, at 850 ºC, a pelite-doped experiment shows euhedral K-feldspar (≈5vol%) in both the reactive xenolith domain together with cordierite and the granodioritic domain, where the K2O wt.% rise from 4.5 in the normal experiment to 5.9 in the doped experiment. These results suggest that the bulk-assimilation process promotes the bulk and heterogeneous K2O enrichment in a huge granodioritic magma volume, which triggers an early crystallization of K-feldspar megacrysts. Because of this early crystallization of the megacrysts, the magmatic foliations defined by K-feldspar megacrysts are formed during and after the emplacement processes and are highly influenced by tectonic kinematics.

  15. Experimental study of kinetic and mechanism of dissolution of apatite structured minerals. Application to the prediction of the long term behavior of an actinides storage host matrix; Etude experimentale de la cinetique et des mecanismes d'alteration de mineraux apatitiques. Application au comportement d'une ceramique de confinement d'actinides mineurs

    Chairat, C

    2005-11-15

    The motivation for this study is to assess the potential of using apatite structured ceramics as long-lived actinide storage hosts. To assess their ability to resist aqueous corrosion, the dissolution of natural fluoro-apatite and synthetic Nd-britholite (neodymium is a proxy for the trivalent actinides) was studied. Mineral surfaces were characterized using a combined spectrometric, electrokinetic and potentiometric approach and dissolution rates were measured in closed and open system reactors as a function of solution composition. Experimental results suggest apatitic minerals dissolve via distinct step sequence: 1) fluoride release, 2) release of the calcium situated in the M1, and 3) the simultaneous removal of phosphate and calcium II via the breaking of only Ca-O bonds. TST based rate equations based in this mechanism accurately describe fluoro-apatite and synthetic britholite dissolution rates as a function of solution composition. Nd release rates are limited by precipitation of Nd-rhabdophane. (author)

  16. Zirconium-nickel crystals—hydrogen accumulators: Dissolution and penetration of hydrogen atoms in alloys

    Matysina, Z. A.; Zaginaichenko, S. Yu.; Shchur, D. V.; Gabdullin, M. T.; Kamenetskaya, E. A.

    2016-07-01

    The calculation of the free energy, thermodynamic equilibrium equations, and kinetic equations of the intermetallic compound Zr2NiH x has been carried out based on molecular-kinetic concepts. The equilibrium hydrogen concentration depending on the temperature, pressure, and energy parameters has been calculated. The absorption-desorption of hydrogen has been studied, and the possibility of the realization of the hysteresis effect has been revealed. The kinetics of the dissolution and permeability of hydrogen is considered, the time dependence of these values has been found, and conditions for the extremum character of their time dependence have been determined. Relaxation times of the dissolution and permeability of hydrogen into the alloy have been calculated. The calculation results are compared with the experimental data available in the literature.

  17. Dissolution behavior of irradiated mixed oxide fuel with short stroke shearing for fast reactor reprocessing

    Ikeuchi, Hirotomo; Sano, Yuichi; Shibata, Atsuhiro; Koizumi, Tsutomu; Washiya, Tadahiro

    2013-01-01

    An efficient dissolution process was established for future reprocessing in which mixed-oxide (MOX) fuels with high plutonium contents and dissolver solution with high heavy-metal (HM) concentrations (more than 500 g dm -3 ) will be treated. This dissolution process involves short stroke shearing of fuels (∼10 mm in length). The dissolution kinetics of irradiated MOX fuels and the effects of the Pu content, HM concentration, and fuel form on the dissolution rate were investigated. Irradiated fuel was found to dissolve as 10 2 -10 3 times fast as non-irradiated fuel, but the rate decreased with increasing Pu content. Kinetic analysis based on the fragmentation model, which considers the penetration and diffusion of nitric acid through fuel matrices prior to chemical reaction, indicated that the dissolution rate of irradiated fuel was affected not only by the volume ratio of liquid to solid (L/S ratio) but also by the exposed surface area per unit mole of nitric acid (A/m ratio). The penetration rate of nitric acid is expected to be decreased at high HM concentrations by a reduction in the L/S ratio, but enhanced by shearing the fuel pieces with short strokes and thus enlarging the A/m ratio. (author)

  18. Affinity functions for modeling glass dissolution rates

    Bourcier, W.L. [Lawrence Livermore National Lab., CA (United States)

    1997-07-01

    Glass dissolution rates decrease dramatically as glass approach ''saturation'' with respect to the leachate solution. Most repository sites are chosen where water fluxes are minimal, and therefore the waste glass is most likely to dissolve under conditions close to ''saturation''. The key term in the rate expression used to predict glass dissolution rates close to ''saturation'' is the affinity term, which accounts for saturation effects on dissolution rates. Interpretations of recent experimental data on the dissolution behaviour of silicate glasses and silicate minerals indicate the following: 1) simple affinity control does not explain the observed dissolution rate for silicate minerals or glasses; 2) dissolution rates can be significantly modified by dissolved cations even under conditions far from saturation where the affinity term is near unity; 3) the effects of dissolved species such as Al and Si on the dissolution rate vary with pH, temperature, and saturation state; and 4) as temperature is increased, the effect of both pH and temperature on glass and mineral dissolution rates decrease, which strongly suggests a switch in rate control from surface reaction-based to diffusion control. Borosilicate glass dissolution models need to be upgraded to account for these recent experimental observations. (A.C.)

  19. Application of pulsed OSL to the separation of the luminescence components from a mixed quartz/feldspar sample

    Denby, Phil M.; Bøtter-Jensen, L.; Murray, A.S.

    2006-01-01

    with a feldspar signal. We have developed instrumentation for the study of high-speed pulse stimulated OSL. Our system uses the standard blue/IR LED stimulation unit of a Riso reader (allowing stimulation pulses down to 1-2 mu s duration) and can thus be applied to the routine analysis of samples. Using...... that counts are only accumulated during a windowed period, reduces the feldspar signal to 1.6% of its original value relative to that of the quartz. (c) 2006 Elsevier Ltd. All rights reserved....

  20. Optimization of Dissolution Compartments in a Biorelevant Dissolution Apparatus Golem v2, Supported by Multivariate Analysis

    Ivan Stupák

    2017-11-01

    Full Text Available Biorelevant dissolution instruments represent an important tool for pharmaceutical research and development. These instruments are designed to simulate the dissolution of drug formulations in conditions most closely mimicking the gastrointestinal tract. In this work, we focused on the optimization of dissolution compartments/vessels for an updated version of the biorelevant dissolution apparatus—Golem v2. We designed eight compartments of uniform size but different inner geometry. The dissolution performance of the compartments was tested using immediate release caffeine tablets and evaluated by standard statistical methods and principal component analysis. Based on two phases of dissolution testing (using 250 and 100 mL of dissolution medium, we selected two compartment types yielding the highest measurement reproducibility. We also confirmed a statistically ssignificant effect of agitation rate and dissolution volume on the extent of drug dissolved and measurement reproducibility.

  1. Accumulated phenocrysts and origin of feldspar porphyry in the Chanho area, western Yunnan, China

    Xu, Xing-Wang; Jiang, Neng; Yang, Kai; Zhang, Bao-Lin; Liang, Guang-He; Mao, Qian; Li, Jin-Xiang; Du, Shi-Jun; Ma, Yu-Guang; Zhang, Yong; Qin, Ke-Zhang

    2009-12-01

    The No. 1 feldspar porphyry in the Chanho area, western Yunnan, China is characterized by the development of deformed glomeroporphyritic aggregates (GA) that contain diagnostic gravity settling textures. These textures include interlocking curved grain boundaries caused by compaction, bent twins, and arch-like structures. The GAs are accumulated phenocrysts (AP) and antecrysts. The unstable textural configurations such as extensive penetrative microfractures that are restricted within the AP and fractured cores of zircon grains, all suggest that the GAs are transported fragments of fractured cumulates that formed in a pre-emplacement magma chamber rather than form in situ at the current intrusion site. Compositions of minerals and melt as represented by different mineral aggregates formed at various stages of the magmatic process and their relations to the composition of porphyry bodies in the Chanho area indicate that the porphyritic melt for the No. 1 feldspar porphyry experienced two stages of melt mixing. Pulses of potassic melt flowed into a pre-emplacement magma chamber and mixed with crystallizing dioritic magma containing phenocrysts resulted in the first hybrid alkaline granitic melt. The mixing caused denser phenocrysts to settle and aggregate to form cumulates. Secondly, new dioritic melt was injected into the magma chamber and was mixed with the previously formed hybrid alkaline granitic melt to produce syenitic melt. Geochron data, including U-Pb age of zircon and 39Ar/ 40Ar age of hornblende and oligoclase phenocrysts, indicate that hornblende and oligoclase phenocrysts, as well as the core of zircon grains, were antecrysts that formed in a number of crystallization events between 36.3 and 32.78 Ma. Gravity settling of phenocrysts took place at about 33.1 to 32.78 Ma and melts with deformed GAs were transported upwards and emplaced into the current site at 32 Ma. Results of this research indicate that the No. 1 feldspar porphyry was a shallow

  2. Dissolution, agglomerate morphology, and stability limits of protein-coated silver nanoparticles.

    Martin, Matthew N; Allen, Andrew J; MacCuspie, Robert I; Hackley, Vincent A

    2014-09-30

    Little is understood regarding the impact that molecular coatings have on nanoparticle dissolution kinetics and agglomerate formation in a dilute nanoparticle dispersion. Dissolution and agglomeration processes compete in removing isolated nanoparticles from the dispersion, making quantitative time-dependent measurements of the mechanisms of nanoparticle loss particularly challenging. In this article, we present in situ ultra-small-angle X-ray scattering (USAXS) results, simultaneously quantifying dissolution, agglomeration, and stability limits of silver nanoparticles (AgNPs) coated with bovine serum albumin (BSA) protein. When the BSA corona is disrupted, we find that the loss of silver from the nanoparticle core is well matched by a second-order kinetic rate reaction, arising from the oxidative dissolution of silver. Dissolution and agglomeration are quantified, and morphological transitions throughout the process are qualified. By probing the BSA-AgNP suspension around its stability limits, we provide insight into the destabilization mechanism by which individual particles rapidly dissolve as a whole rather than undergo slow dissolution from the aqueous interface inward, once the BSA layer is breached. Because USAXS rapidly measures over the entire nanometer to micrometer size range during the dissolution process, many insights are also gained into the stabilization of NPs by protein and its ability to protect the labile metal core from the solution environment by prohibiting the diffusion of reactive species. This approach can be extended to a wide variety of coating molecules and reactive metal nanoparticle systems to carefully survey their stability limits, revealing the likely mechanisms of coating breakdown and ensuing reactions.

  3. Dissolution of uranium and plutonium particles: simulations using the Mercer equation

    Cowan, C.E.; Jenne, E.A.

    1983-10-01

    There is a need to be able to predict the amount of plutonium that will be in solution at a given time from dissolution of particles in order to better predict the environmental behavior and possible adverse effects of plutonium spills. The equation developed by Mercer (1967) to simulate the dissolution of particles in lungs was parameterized and used to simulate the dissolution of a population of plutonium or uranium particles in the soil. Parameter values for the size distribution of particles in soil, and the density of the particles were found; however, values for the shape factors, and the dissolution rate were virtually non-existent. The calculated mass dissolved was most sensitive to the median diameter of the population of particles and least sensitive to the geometric standard deviation. A given percent change in the shape parameter and the dissolution rate resulted in approximately an equal percent change in the mass dissolved. Provided that the population of particles follows a log-normal distribution, the particles are homogeneous in composition and the dissolution can be represented by first-order kinetics, this equation can probably be applied with slight modification to estimate the mass dissolved at a given time. 66 references, 7 figures, 4 tables

  4. Timing of the deglaciation in southern Patagonia: Testing the applicability of K-Feldspar IRSL

    Blomdin, Robin; Murray, Andrew S.; Thomsen, Kristina Jørkov

    2012-01-01

    need evaluation against an absolute chronology. The aim of this project is to investigate the applicability of OSL dating to sediments from southern Patagonia; in particular, we examine the dating potential of K-feldspar IRSL signals. Samples were collected from landforms interpreted as being deposited...... to our individual dose estimates based on the over-dispersion (OD) observed in laboratory gamma dose recovery experiments (22% for small aliquots and 18% for single grains). Then the possible effects of incomplete bleaching and differential fading are examined. For our natural samples we observe...... environmental ODs between 30 and 130% and mean residual doses between ∼30 and 80 Gy. Minimum age models are used to identify the part of the dose population that is most likely to have been well-bleached and results from these models are compared. The models give ages that are consistent with each other...

  5. Pre-treatment of desalination feed seawater by Jordanian Tripoli, Pozzolana and Feldspar: batch experiments

    AIMAN E. AL-RAWAJFEH

    2011-06-01

    Full Text Available In this research, composites of layered double hydroxide (LDH with three Jordanian natural raw materials: Tripoli (T, Pozzolana (P and Feldspar (F were prepared by co-precipitation and have been used for feed seawater pre-treatment. The data reveals that percent adsorption decreased with increase in initial concentration, but the actual amount of adsorbed ions per unit mass of LDH/T-P-F increased with increase in metal ion concentrations. The values of ΔG were negative and within 21 to 26 kJ/mol, while the values of and ΔS were positive, with ΔH within the range of 0.1 to 25 kJ/mol. The values of ΔH, ΔS and ΔG indicate the favorability of physisorption and show that the LDH/T-P-F composites have a considerable potential as adsorbents for the removal of ions from seawater.

  6. Photoionization of radiation-induced traps in quartz and alkali feldspars.

    Hütt, G; Jaek, I; Vasilchenko, V

    2001-01-01

    For the optimization of luminescence dating and dosimetry techniques on the basis of the optically stimulated luminescence, the stimulation spectra of quartz and alkali feldspars were measured in the spectral region of 250-1100 nm using optically stimulated afterglow. Optically stimulated luminescence in all studied spectral regions is induced by the same kind of deep traps, that produce thermoluminescence in the regions of palaeodosimetric peaks for both minerals. The mechanism for photoionization of deep traps was proposed as being due to delocalization of the excited state of the corresponding lattice defects. The excited state overlaps the zone states; i.e. is situated in the conduction band. Because of the high quantum yield of deep electron trap ionization in the UV spectral region, the present aim was to study the possibility of using UV-stimulation for palaeodose reconstruction.

  7. Photoionization of radiation-induced traps in quartz and alkali feldspars

    Huett, G.; Jaek, I.; Vasilchenko, V.

    2001-01-01

    For the optimization of luminescence dating and dosimetry techniques on the basis of the optically stimulated luminescence, the stimulation spectra of quartz and alkali feldspars were measured in the spectral region of 250-1100 nm using optically stimulated afterglow. Optically stimulated luminescence in all studied spectral regions is induced by the same kind of deep traps, that produce thermoluminescence in the regions of palaeodosimetric peaks for both minerals. The mechanism for photoionization of deep traps was proposed as being due to delocalization of the excited state of the corresponding lattice defects. The excited state overlaps the zone states; i.e. is situated in the conduction band. Because of the high quantum yield of deep electron trap ionization in the UV spectral region, the present aim was to study the possibility of using UV-stimulation for palaeodose reconstruction

  8. Photoionization of radiation-induced traps in quartz and alkali feldspars

    Huett, G. E-mail: hutt@pdos.gi.ee; Jaek, I.; Vasilchenko, V

    2001-01-15

    For the optimization of luminescence dating and dosimetry techniques on the basis of the optically stimulated luminescence, the stimulation spectra of quartz and alkali feldspars were measured in the spectral region of 250-1100 nm using optically stimulated afterglow. Optically stimulated luminescence in all studied spectral regions is induced by the same kind of deep traps, that produce thermoluminescence in the regions of palaeodosimetric peaks for both minerals. The mechanism for photoionization of deep traps was proposed as being due to delocalization of the excited state of the corresponding lattice defects. The excited state overlaps the zone states; i.e. is situated in the conduction band. Because of the high quantum yield of deep electron trap ionization in the UV spectral region, the present aim was to study the possibility of using UV-stimulation for palaeodose reconstruction.

  9. Partial replacement of the feldspar waste of flat glass ceramics for masses in white

    Porto, V.S.; Araujo, A.M.B.; Morais, C.R.S.; Cavalcanti, M.S.L.

    2012-01-01

    In all the industrial production process requires the consumption of raw materials exaggerated the traditional scarcity of incurring the same. To reverse this situation, one of the possible actions is the search for alternative technologies that aim to replace these materials by waste that exhibit similar characteristics. This study aims to verify the possibility of partially replacing feldspar by waste flat glass ceramic mass for white, since this type of waste, when subjected to high temperatures can act as a flux. For this research, initially the raw materials were characterized using the techniques of energy dispersive spectroscopy X-ray (EDX) and X-ray diffraction. Then, test pieces were prepared to be burned at temperatures between 1000 and 1250 ° C, which were submitted to tests of porosity to absorb water. The results are within the standards required by the standards established for ceramic products, which confirms the feasibility of such waste to act as a flux in ceramic white masses. (author)

  10. Dissolution process of atmospheric aerosol particles into cloud droplets; Processus de dissolution des aerosols atmospheriques au sein des gouttes d'eau nuageuses

    Desboeufs, K

    2001-01-15

    Clouds affect both climate via the role they play in the Earth's radiation balance and tropospheric chemistry since they are efficient reaction media for chemical transformation of soluble species. Cloud droplets are formed in the atmosphere by condensation of water vapour onto aerosol particles, the cloud condensation nuclei (CCN). The water soluble fraction of these CCN governs the cloud micro-physics, which is the paramount factor playing on the radiative properties of clouds. Moreover, this soluble fraction is the source of species imply in the oxidation/reduction reactions in the aqueous phase. Thus, it is of particular importance to understand the process controlling the solubilization of aerosols in the cloud droplets. The main purpose of this work is to investigate experimentally and theoretically the dissolution of particles incorporated in the aqueous phase. From the studies conducted up to now, we have identify several factors playing on the dissolution reaction of aerosols. However, the quantification of the effects of these factors is difficult since the current means of study are not adapted to the complexity of cloud systems. First, this work consisted to perform a experimental system, compound by an open flow reactor, enabling to follow the kinetic of dissolution in conditions representative of cloud. This experimental device is used to a systematic characterisation of the known factors playing on the dissolution, i.e. pH, aerosol nature, aerosol weathering... and also for the identification and the quantification of the effects of other factors: ionic strength, acid nature, clouds processes. These experiments gave quantitative results, which are used to elaborate a simple model of aerosol dissolution in the aqueous phase. This model considers the main factors playing on the dissolution and results in a general mechanism of aerosol dissolution extrapolated to the cloud droplets. (author)

  11. Dissolution process of atmospheric aerosol particles into cloud droplets; Processus de dissolution des aerosols atmospheriques au sein des gouttes d'eau nuageuses

    Desboeufs, K.

    2001-01-15

    Clouds affect both climate via the role they play in the Earth's radiation balance and tropospheric chemistry since they are efficient reaction media for chemical transformation of soluble species. Cloud droplets are formed in the atmosphere by condensation of water vapour onto aerosol particles, the cloud condensation nuclei (CCN). The water soluble fraction of these CCN governs the cloud micro-physics, which is the paramount factor playing on the radiative properties of clouds. Moreover, this soluble fraction is the source of species imply in the oxidation/reduction reactions in the aqueous phase. Thus, it is of particular importance to understand the process controlling the solubilization of aerosols in the cloud droplets. The main purpose of this work is to investigate experimentally and theoretically the dissolution of particles incorporated in the aqueous phase. From the studies conducted up to now, we have identify several factors playing on the dissolution reaction of aerosols. However, the quantification of the effects of these factors is difficult since the current means of study are not adapted to the complexity of cloud systems. First, this work consisted to perform a experimental system, compound by an open flow reactor, enabling to follow the kinetic of dissolution in conditions representative of cloud. This experimental device is used to a systematic characterisation of the known factors playing on the dissolution, i.e. pH, aerosol nature, aerosol weathering... and also for the identification and the quantification of the effects of other factors: ionic strength, acid nature, clouds processes. These experiments gave quantitative results, which are used to elaborate a simple model of aerosol dissolution in the aqueous phase. This model considers the main factors playing on the dissolution and results in a general mechanism of aerosol dissolution extrapolated to the cloud droplets. (author)

  12. The dependence of orange-red IRSL decay curves of potassium feldspars on sample temperature

    Fattahi, Morteza

    2004-01-01

    This paper presents the effects of stimulation temperature on the infrared stimulated orange-red (600-650 nm) luminescence emission (orange-red infrared simulated luminescence (IRSL)) in potassium feldspar. Investigations explore the relationship between initial (0-2 s), integral (0-100 s), net initial (0-2 s less background over 2 s), net integral (0-100 s less background over 100 s) and last 2 s of the orange-red IRSL signals obtained for 100 s versus stimulation temperature (20-460 degree sign C) on both unpreheated and preheated samples. In the potassium feldspar sample examined, competition effects, including thermal enhancement, depletion and possibly quenching affect the orange-red IRSL signals measured. Observed effects (e.g., thermal enhancement, thermal activation energy and the decay rate) over the temperature range 20-120 degree sign C may be explained by tunnelling luminescence processes, IR transitions to the conduction band following excitations from ground state of electron trap by acquiring thermal energy from the lattice and or the random-walk band-tail model. Preheating prior to orange-red IRSL and Thermoluminescence (TL) measurements provides evidence that there are both shallow and deep traps responsible for low- and high-temperature orange-red IRSL and TL peaks. The effects of both preheating and IR bleaching on the orange-red thermally stimulated luminescence (red emission during thermoluminescence, RTL) provide evidence that bleached RTL traps have no significant contribution in the production of orange-red IRSL signals

  13. Fabrication and characterization of low temperature co-fired cordierite glass–ceramics from potassium feldspar

    Wu, Jianfang; Li, Zhen; Huang, Yanqiu; Li, Fei; Yang, Qiuran

    2014-01-01

    Highlights: • Low cost cordierite glass–ceramics were fabricated from potassium feldspar. • The glass–ceramics could be highly densified below 950 °C. • The glass–ceramics exhibit extraordinary properties. • The glass–ceramics can be used as LTCC substrates. • The excess SiO 2 improved the microstructure and properties of the glass–ceramics. -- Abstract: Cordierite glass–ceramics for low temperature co-fired ceramic (LTCC) substrates were fabricated successfully using potassium feldspar as the main raw material. The sintering and crystallization behaviors of the glass–ceramics were investigated by the differential scanning calorimetry (DSC), X-ray diffraction (XRD), and field emission scanning electron microscope (FESEM). The results indicated that the glass–ceramics could be highly densified at 850 °C and the cordierite was the main crystalline phase precipitated from the glasses in the temperature range between 900 and 925 °C. The study also evaluated the physical properties including dielectric properties, thermal expansion and flexural strength of the glass–ceramics. The glass–ceramics showed low dielectric constants in the range of 6–8 and low dielectric losses in the range of 0.0025–0.01. The coefficients of thermal expansion (CTEs) are between 4.32 and 5.48 × 10 −6 K −1 and flexural strength of the glass–ceramics are 90–130 MPa. All of those qualify the glass–ceramics for further research to be used as potential LTCC substrates in the multilayer electronic substrate field. Additionally, the excess SiO 2 acted as a great role in improving the sinterability of the glasses, and the microstructure and dielectric properties of the relevant glass–ceramics

  14. Yellow stimulated luminescence from potassium feldspar: Observations on its suitability for dating

    Lauer, T.; Krbetschek, M.; Mauz, B.; Frechen, M.

    2012-01-01

    Yellow stimulated luminescence (Y-OSL) is the light detected from potassium-rich feldspars at 410 nm under stimulation by a yellow light source emitting 590 nm. The investigation of this study aimed at understanding basic luminescence physics of Y-OSL in order to assess the suitability of the technique for dating. The Y-OSL signal properties tested were signal intensity, thermal assistance, thermal stability, sensitivity to daylight and the suitability of a single aliquot regenerative (SAR) protocol to be employed for equivalent dose (D e ) estimation. D e measurements were conducted on samples of Holocene, last glacial and Tertiary age. The tests were undertaken on sedimentary feldspar separates extracted from aeolian, fluvial and coastal deposits. Results from experiments show that the signal intensity increases by measuring Y-OSL at elevated temperature suggesting thermal assistance characteristics similar to infrared stimulated luminescence (IRSL). The yellow stimulated signal remains unaffected by preheat temperatures up to ∼200 °C suggesting higher thermal stability than the IRSL signal. The Y-OSL signal is less light sensitive than the IRSL signal and D e residuals obtained from modern samples are up to 7 Gy indicating suitability of the technique for ‘older’ and well-bleached sediments. The dose recovery tests successfully recovered the given dose if the specific light sensitivity of Y-OSL is taken into account. For every sample Y-OSL D e values obtained by a single aliquot regenerative dose protocol (SAR) are higher than those obtained by an IRSL SAR approach. From these results we infer high thermal stability and a minimal anomalous fading of the Y-OSL signal. We conclude that Y-OSL has a high potential to date Quaternary sediments that were sufficiently bleached in nature.

  15. DISSOLUTION OF LANTHANUM FLUORIDE PRECIPITATES

    Fries, B.A.

    1959-11-10

    A plutonium separatory ore concentration procedure involving the use of a fluoride type of carrier is presented. An improvement is given in the derivation step in the process for plutonium recovery by carrier precipitation of plutonium values from solution with a lanthanum fluoride carrier precipitate and subsequent derivation from the resulting plutonium bearing carrier precipitate of an aqueous acidic plutonium-containing solution. The carrier precipitate is contacted with a concentrated aqueous solution of potassium carbonate to effect dissolution therein of at least a part of the precipitate, including the plutonium values. Any remaining precipitate is separated from the resulting solution and dissolves in an aqueous solution containing at least 20% by weight of potassium carbonate. The reacting solutions are combined, and an alkali metal hydroxide added to a concentration of at least 2N to precipitate lanthanum hydroxide concomitantly carrying plutonium values.

  16. Aqueous dissolution of sodium aluminosilicate geopolymers derived from metakaolin

    Aly, Z., E-mail: zaynab.aly@ansto.gov.au [Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232 (Australia); Vance, E.R. [Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232 (Australia); Perera, D.S. [School of Materials Science, University of NSW, Kensington, NSW 2052 (Australia)

    2012-05-15

    Highlights: Black-Right-Pointing-Pointer In dilute solutions, Na, Al and Si releases were not sensitive to pH in range 4-10. Black-Right-Pointing-Pointer On heating from 18 to 90 Degree-Sign C in DIW, Na dissolution rate increased by a factor of {approx}4. Black-Right-Pointing-Pointer Elemental extractions in DIW at 18 Degree-Sign C increased linearly with time over 1-7 days. Black-Right-Pointing-Pointer Na release kinetics in DIW followed a pseudo-second-order kinetic model. Black-Right-Pointing-Pointer Contact with KCl, KHCO{sub 3} and phthalate buffers (pH6 and 10) resulted in Na{sup +} {r_reversible} K{sup +} exchange. - Abstract: In dilute aqueous solutions, the elemental releases of Na, Al and Si from a metakaolin-based sodium aluminosilicate geopolymer were not very sensitive to pH in the range of 4-10 but increased outside this range, particularly on the acidic side. To minimise pH drifts, experiments were carried out using small amounts of graded powders in relatively large volumes of water. In deionised water, the Na dissolution rate in 7 days was dominant and increased by at least a factor of {approx}4 on heating from 18 to 90 Degree-Sign C, with greater increases in the extractions of Al and Si. At 18 Degree-Sign C the elemental extractions in deionised water increased approximately linearly with time over the 1-7 days period. Further exposure led to a slower extraction into solution for Na and Si, with a decrease in extraction of Al. It was deduced that framework dissolution was important in significantly acidic or alkaline solutions, but that contributions from water transfer from pores to elemental extractions were present, even at low temperatures in neutral solutions. It was also deduced from the Na release data that the Na leaching kinetics of geopolymer in deionised water (dilute solutions) followed the pseudo-second-order kinetic model and the pseudo-second-order rate constant evaluated. Contact with KCl, KHCO{sub 3}, and pH {approx}6 and 10

  17. Predicting dissolution patterns in variable aperture fractures: 1. Development and evaluation of an enhanced depth-averaged computational model

    Detwiler, R L; Rajaram, H

    2006-04-21

    Water-rock interactions within variable-aperture fractures can lead to dissolution of fracture surfaces and local alteration of fracture apertures, potentially transforming the transport properties of the fracture over time. Because fractures often provide dominant pathways for subsurface flow and transport, developing models that effectively quantify the role of dissolution on changing transport properties over a range of scales is critical to understanding potential impacts of natural and anthropogenic processes. Dissolution of fracture surfaces is controlled by surface-reaction kinetics and transport of reactants and products to and from the fracture surfaces. We present development and evaluation of a depth-averaged model of fracture flow and reactive transport that explicitly calculates local dissolution-induced alterations in fracture apertures. The model incorporates an effective mass transfer relationship that implicitly represents the transition from reaction-limited dissolution to transport-limited dissolution. We evaluate the model through direct comparison to previously reported physical experiments in transparent analog fractures fabricated by mating an inert, transparent rough surface with a smooth single crystal of potassium dihydrogen phosphate (KDP), which allowed direct measurement of fracture aperture during dissolution experiments using well-established light transmission techniques [Detwiler, et al., 2003]. Comparison of experiments and simulations at different flow rates demonstrate the relative impact of the dimensionless Peclet and Damkohler numbers on fracture dissolution and the ability of the computational model to simulate dissolution. Despite some discrepancies in the small-scale details of dissolution patterns, the simulations predict the evolution of large-scale features quite well for the different experimental conditions. This suggests that our depth-averaged approach to simulating fracture dissolution provides a useful approach for

  18. Emotional and Cognitive Coping in Relationship Dissolution

    Wrape, Elizabeth R.; Jenkins, Sharon Rae; Callahan, Jennifer L.; Nowlin, Rachel B.

    2016-01-01

    Dissolution of a romantic relationship can adversely affect functioning among college students and represents one primary reason for seeking campus counseling. This study examined the associations among common coping strategies and distress following relationship dissolution. Avoidance and repetitive negative thinking (RNT) were significantly…

  19. Dissolution Dominating Calcification Process in Polar Pteropods Close to the Point of Aragonite Undersaturation

    Bednaršek, Nina; Tarling, Geraint A.; Bakker, Dorothee C. E.; Fielding, Sophie; Feely, Richard A.

    2014-01-01

    Thecosome pteropods are abundant upper-ocean zooplankton that build aragonite shells. Ocean acidification results in the lowering of aragonite saturation levels in the surface layers, and several incubation studies have shown that rates of calcification in these organisms decrease as a result. This study provides a weight-specific net calcification rate function for thecosome pteropods that includes both rates of dissolution and calcification over a range of plausible future aragonite saturation states (Ωar). We measured gross dissolution in the pteropod Limacina helicina antarctica in the Scotia Sea (Southern Ocean) by incubating living specimens across a range of aragonite saturation states for a maximum of 14 days. Specimens started dissolving almost immediately upon exposure to undersaturated conditions (Ωar∼0.8), losing 1.4% of shell mass per day. The observed rate of gross dissolution was different from that predicted by rate law kinetics of aragonite dissolution, in being higher at Ωar levels slightly above 1 and lower at Ωar levels of between 1 and 0.8. This indicates that shell mass is affected by even transitional levels of saturation, but there is, nevertheless, some partial means of protection for shells when in undersaturated conditions. A function for gross dissolution against Ωar derived from the present observations was compared to a function for gross calcification derived by a different study, and showed that dissolution became the dominating process even at Ωar levels close to 1, with net shell growth ceasing at an Ωar of 1.03. Gross dissolution increasingly dominated net change in shell mass as saturation levels decreased below 1. As well as influencing their viability, such dissolution of pteropod shells in the surface layers will result in slower sinking velocities and decreased carbon and carbonate fluxes to the deep ocean. PMID:25285916

  20. Study of the dissolution of (U,P)O2 mixed oxides with a high plutonium content

    Fournier, S.

    2001-01-01

    Plutonium from nuclear reactors is partially integrated in the fuel cycle as Mixed OXide (U,Pu)O 2 (MOX). Their dissolution in nitric acid is needed to reprocess them in present reprocessing plants. The main difficulty of this study is that dissolution is a phenomenon depending on solution characteristics as well as the structural properties of the pellets, which depend themselves on the material fabrication process. After showing kinetic and thermodynamic dissolution data of mixed oxides in nitric media, an inventory of the parameters which affect the dissolution process has been made. A separable variable concept was introduced in order to describe the process by studying separately the role of chemical parameters of the solution and geometric parameters of the material. The first part of the study estimates the effect of nitric solution chemical parameters (concentrations, acidity, temperature) on the dissolution and underlines the role of the oxide surface protonation step. The second part of this work deals with the study of surface area evolution for materials with controlled plutonium rich heterogeneities. Experimental results show that the pellet surface undergoes erosion and is progressively weakened by the formation of fault lines in the bulk of the material followed by the dispersion of sub-millimeter fragments in the solution. An heterogeneous kinetic model derived from study of solid-gas interface systems has been applied to fuel pellets dissolution, allowing a mechanism to be proposed, based on surface dissolution of the oxide as well as fault creation in the volume. The dissolution kinetics are therefore dependant on the microstructure and mechanical strength and cohesion of the pellets. (author)

  1. Magnesite dissolution and precipitation rates at hydrothermal conditions

    Saldi, Giuseppe

    2009-01-01

    complexation model originally developed at 25 deg. C. The decrease of dissolution rates observed from 150 to 200 deg. C can be explained by the increasing carbonation and hydrolysis of the rate controlling >MgOH 2 + sites. As a result of the decreasing rates of dissolution, the achievement of alkaline conditions and temperatures higher than 100 deg. C by CO 2 -rich fluids represents a favorable condition for CO 2 sequestration as dissolved alkalinity in deep aquifers where carbonate minerals are major constituting phases. The use of a hydrogen electrode concentration cell (HECC) corroborates the kinetic data obtained at close to equilibrium conditions by the precise determination of magnesite solubility product as a function of temperature (50-200 deg. C). These measurements allowed generating the thermodynamic properties of this phase and comparing them with those obtained from calorimetric measurements and phase equilibria experiments. The results of this study significantly improve our understanding of the kinetic behaviour of carbonate minerals in hydrothermal systems and provide an essential database for the future study of dissolution/precipitation reactions of carbonate minerals in complex systems. This work also provides important kinetic constraints for the geochemical modeling of CO 2 sequestration processes and will help the evaluation of impact and risks connected to a long-term storage. (author) [fr

  2. Study of sensitivity change of OSL signals from quartz and feldspars as a function of preheat temperature

    Jungner, H.; Bøtter-Jensen, L.

    1994-01-01

    and as a result, the equivalent dose (ED) would be underestimated. A study of sensitivity changes in feldspars and quartz was carried out with emphasis on the effect of preheat and annealing on the OSL signal. Measurement results obtained are presented, and possible elimination of errors in dating caused...

  3. Infrared stimulated luminescence dating of an Eemian (MIS 5e) site in Denmark using K-feldspar

    Buylaert, Jan-Pieter; Huot, Sebastian; Murray, Andrew S.

    2011-01-01

    Infrared stimulated luminescence (IRSL) dating of K-feldspars may be an alternative to quartz optically stimulated luminescence (OSL) dating when the quartz OSL signal is too close to saturation or when the quartz luminescence characteristics are unsuitable. In this paper, Eemian (MIS 5e) coastal...

  4. Electrons in feldspar II: A consideration of the influence of conduction band-tail states on luminescence processes

    Poolton, H.R.J.; Ozanyan, K.B.; Wallinga, J.

    2002-01-01

    consider what influence the band tails have on the luminescence properties of feldspar, where electrons travel through the sample prior to recombination. The work highlights the dominant role that 0.04-0.05-eV phonons play in both the luminescence excitation and emission processes of these materials...

  5. Exchange of Na+ and K+ between water vapor and feldspar phases at high temperature and low vapor pressure

    Fournier, R.O.

    1976-01-01

    In order to determine whether gas (steam) containing a small amount of dissolved alkali chloride is effective in promoting base exchange of Na+ and K+ among alkali feldspars and coexisting brine or brine plus solid salt, experiments were carried out at 400-700??C and steam densities ranging down to less than 0.05. For bulk compositions rich in potassium, the low pressure results are close to previous high-pressure results in composition of the fluid and coexisting solid phase. However, when the bulk composition is more sodic, alkali feldspars are relatively richer in potassium at low pressure than at high pressure. This behaviour corresponds to enrichment of potassium in the gas phase relative to coexisting brine and precipitation of solid NaCl when the brine plus gas composition becomes moderately sodic. The gas phase is very effective in promoting base exchange between coexisting alkali feldspars at high temperature and low water pressure. This suggests that those igneous rocks which contain coexisting alkali feldspars out of chemical equilibrium either remained very dry during the high-temperature part of their cooling history or that the pore fluid was a gas containing very little potassium relative to sodium. ?? 1976.

  6. Accelerated dissolution of iron oxides in ice

    D. Jeong

    2012-11-01

    Full Text Available Iron dissolution from mineral dusts and soil particles is vital as a source of bioavailable iron in various environmental media. In this work, the dissolution of iron oxide particles trapped in ice was investigated as a new pathway of iron supply. The dissolution experiments were carried out in the absence and presence of various organic complexing ligands under dark condition. In acidic pH conditions (pH 2, 3, and 4, the dissolution of iron oxides was greatly enhanced in the ice phase compared to that in water. The dissolved iron was mainly in the ferric form, which indicates that the dissolution is not a reductive process. The extent of dissolved iron was greatly affected by the kind of organic complexing ligands and the surface area of iron oxides. The iron dissolution was most pronounced with high surface area iron oxides and in the presence of strong iron binding ligands. The enhanced dissolution of iron oxides in ice is mainly ascribed to the "freeze concentration effect", which concentrates iron oxide particles, organic ligands, and protons in the liquid like ice grain boundary region and accelerates the dissolution of iron oxides. The ice-enhanced dissolution effect gradually decreased when decreasing the freezing temperature from −10 to −196 °C, which implies that the presence and formation of the liquid-like ice grain boundary region play a critical role. The proposed phenomenon of enhanced dissolution of iron oxides in ice may provide a new pathway of bioavailable iron production. The frozen atmospheric ice with iron-containing dust particles in the upper atmosphere thaws upon descending and may provide bioavailable iron upon deposition onto the ocean surface.

  7. Effect of the size of nanoparticles on their dissolution within metal-glass nanocomposites under sustained irradiation

    Vu, T. H. Y., E-mail: thi-hai-yen.vu@polytechnique.edu; Ramjauny, Y.; Rizza, G.; Hayoun, M. [Laboratoire des Solides Irradiés, École Polytechnique, CNRS, CEA, Université Paris-Saclay, F-91128 Palaiseau (France)

    2016-01-21

    We investigate the dissolution law of metallic nanoparticles (NPs) under sustained irradiation. The system is composed of isolated spherical gold NPs (4–100 nm) embedded in an amorphous silica host matrix. Samples are irradiated at room temperature in the nuclear stopping power regime with 4 MeV Au ions for fluences up to 8 × 10{sup 16 }cm{sup −2}. Experimentally, the dependence of the dissolution kinetics on the irradiation fluence is linear for large NPs (45–100 nm) and exponential for small NPs (4–25 nm). A lattice-based kinetic Monte Carlo (KMC) code, which includes atomic diffusion and ballistic displacement events, is used to simulate the dynamical competition between irradiation effects and thermal healing. The KMC simulations allow for a qualitative description of the NP dissolution in two main stages, in good agreement with the experiment. Moreover, the perfect correlation obtained between the evolution of the simulated flux of ejected atoms and the dissolution rate in two stages implies that there exists an effect of the size of NPs on their dissolution and a critical size for the transition between the two stages. The Frost-Russell model providing an analytical solution for the dissolution rate, accounts well for the first dissolution stage but fails in reproducing the data for the second stage. An improved model obtained by including a size-dependent recoil generation rate permits fully describing the dissolution for any NP size. This proves, in particular, that the size effect on the generation rate is the principal reason for the existence of two regimes. Finally, our results also demonstrate that it is justified to use a unidirectional approximation to describe the dissolution of the NP under irradiation, because the solute concentration is particularly low in metal-glass nanocomposites.

  8. Luminescence characteristics of quartz and feldspar from tectonically uplifted terraces in Kashmir Basin, Jammu and Kashmir, India

    Jaiswal, Manoj K.; Bhat, M.I.; Bali, B.S.; Ahmad, Shabir; Chen, Y.G.

    2009-01-01

    The Kashmir Valley or the Jhelum basin is an intermontane-basin in NW Himalaya bounded by the Pir Panjal Range in the south and southwest and the Great Himalayan Range in the north and northeast. The valley is marked by active major thrust boundaries in its south and southwestern parts. Remote sensing studies and morphometric analysis suggest neo-tectonic activities and the formation of tectonic terraces due to uplift on the major thrust boundaries in NW Himalayas. The quartz from freshly eroded mountain belts is usually found to show very poor luminescence sensitivity and thus not suitable for optical dating. Similar problems occurred with the quartz from the Srinagar Basin. Due to this, feldspar was selected as a natural dose meter for dating tectonically uplifted terraces in an active and dynamic belt of the NW Himalayas. We report here for the first time the luminescence characteristics of quartz and feldspar minerals from the study area. However, feldspar also shows poor luminescence sensitivity, although enough to perform optical dating. Athermal fading was observed in all the feldspar samples, which was corrected using 'g' values; a large scatter was found in the g values, probably due to intermixing of feldspar grains from varying source rock types and also due to poor luminescence sensitivity. An average g value correction to the mean paleodose was found to agree if compared with the thermo-luminescence date of loess deposit dated earlier. The ages show that the terrace formation started taking place at ∼100 ka in the southwestern part of the Jhelum basin and continued with pulses at 50 ka and 11 ka towards the northwestern part.

  9. Kinetic Typography

    van Leeuwen, Theo; Djonov, Emilia

    2014-01-01

    After discussing broad cultural drivers behind the development of kinetic typography, the chapter outlines an approach to analysing kinetic typography which is based on Halliday's theory of transitivity, as applied by Kress and Van Leeuwen to visual images.......After discussing broad cultural drivers behind the development of kinetic typography, the chapter outlines an approach to analysing kinetic typography which is based on Halliday's theory of transitivity, as applied by Kress and Van Leeuwen to visual images....

  10. Preparation of chromous complexes and their effect on the dissolution of ferrites and chromites

    Sathyaseelan, V.S.; Rufus, A.L.; Velmurugan, S.; Pavithra, E.

    2012-09-01

    Decontamination of reactor coolant circuits is inevitable in minimising radiation exposure hazard especially during maintenance. Dilute chemical decontamination processes involving organic complexing agents viz., EDTA or NTA along with reducing agents such as ascorbic acid or oxalic acid are quite effective in dissolving magnetite, the predominant corrosion product oxide in carbon steel systems viz., PHWRs. However, dissolution of hematite, mixed ferrites and chromites found in stainless steel systems of BWRs and PWRs are not that easy to dissolve. A two-step process involving oxidation and reduction processes is required to dissolve these oxides. Studies were carried out to develop a single step process. Our earlier studies on high temperature decontamination at 160 deg. C have showed improved dissolution of magnetite, nickel ferrite and other oxides. In the present study, attempt has been made to carry out the oxide dissolution in formulations containing strong reducing agents such as chromous complexes. Dissolution of hematite is very effective under reducing conditions. Addition of ascorbic acid to the formulation containing EDTA and citric acid (EC) enhanced the kinetics 20 folds, while the addition of Cr (II)-EDTA to EC formulation increased the rate 100 folds. In the case of formulation containing NTA and citric acid (NC), the addition of chromous-NTA increased the rate 14 folds. NiFe 2 O 4 showed hardly any dissolution in EC formulation. However, in EAC (formulation containing EDTA, citric acid and ascorbic acid), the rate constant for the dissolution was 1.2x10 -3 min -1 , while it was 8.5x10 -3 min -1 in the case of ECCr (EDTA, citric acid containing chromous ions) formulation. In NTA based formulations also, dissolution rate was found to be enhanced in the presence of chromous ions. Further, there was no preferential dissolution of either Fe or Ni by both EDTA and NTA based formulations and also the rate of dissolution was found to depend linearly on the

  11. Study of anodic dissolution of Fe-Ru alloy with the aid of mossbauer spectroscopy

    Khlystov, A.S.; Fasman, A.B.; Kil'dibekova, G.A.

    1986-01-01

    This paper uses Fe 57 Mossbauer spectroscopy, whereby iron compounds may be identified quantitatively and their composition and structure can be determined, for the study of the relationships of slime formation from Fe-Ru binary alloys. Both the products of dissolution and the composition and state of intermediate phases formed at various stages of anodic dissolution were studied simultaneously. It was found that the slimes formed both during chemical and during electrochemical destruction of ruthenium-iron alloys are finely dispersed systems of complex composition, analogous to those formed in the course of electrochemical dissolution of Ni-Ru alloys, which were found to contain oxide phases of ruthenium (by x-ray spectroscopy and ESCA) and of nickel (by x-ray phase analysis). The difference between the slime compositions is determined mainly by kinetic factors

  12. Radiolytic modelling of spent fuel oxidative dissolution mechanism. Calibration against UO2 dynamic leaching experiments

    Merino, J.; Cera, E.; Bruno, J.; Quinones, J.; Casas, I.; Clarens, F.; Gimenez, J.; Pablo, J. de; Rovira, M.; Martinez-Esparza, A.

    2005-01-01

    Calibration and testing are inherent aspects of any modelling exercise and consequently they are key issues in developing a model for the oxidative dissolution of spent fuel. In the present work we present the outcome of the calibration process for the kinetic constants of a UO 2 oxidative dissolution mechanism developed for using in a radiolytic model. Experimental data obtained in dynamic leaching experiments of unirradiated UO 2 has been used for this purpose. The iterative calibration process has provided some insight into the detailed mechanism taking place in the alteration of UO 2 , particularly the role of · OH radicals and their interaction with the carbonate system. The results show that, although more simulations are needed for testing in different experimental systems, the calibrated oxidative dissolution mechanism could be included in radiolytic models to gain confidence in the prediction of the long-term alteration rate of the spent fuel under repository conditions

  13. Mechanistic Basis of Cocrystal Dissolution Advantage.

    Cao, Fengjuan; Amidon, Gordon L; Rodríguez-Hornedo, Naír; Amidon, Gregory E

    2018-01-01

    Current interest in cocrystal development resides in the advantages that the cocrystal may have in solubility and dissolution compared with the parent drug. This work provides a mechanistic analysis and comparison of the dissolution behavior of carbamazepine (CBZ) and its 2 cocrystals, carbamazepine-saccharin (CBZ-SAC) and carbamazepine-salicylic acid (CBZ-SLC) under the influence of pH and micellar solubilization. A simple mathematical equation is derived based on the mass transport analyses to describe the dissolution advantage of cocrystals. The dissolution advantage is the ratio of the cocrystal flux to drug flux and is defined as the solubility advantage (cocrystal to drug solubility ratio) times the diffusivity advantage (cocrystal to drug diffusivity ratio). In this work, the effective diffusivity of CBZ in the presence of surfactant was determined to be different and less than those of the cocrystals. The higher effective diffusivity of drug from the dissolved cocrystals, the diffusivity advantage, can impart a dissolution advantage to cocrystals with lower solubility than the parent drug while still maintaining thermodynamic stability. Dissolution conditions where cocrystals can display both thermodynamic stability and a dissolution advantage can be obtained from the mass transport models, and this information is useful for both cocrystal selection and formulation development. Copyright © 2018 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

  14. Dissolution rate of BTEX contaminants in water

    Njobuenwu, D.O.; Amadi, S.A.; Ukpaka, P.C.

    2005-01-01

    Benzene, toluene, ethylbenzene and xylenes (BTEX) and substituted benzenes are the most common aromatic compounds in petroleum. BTEX components are the most soluble and mobile fraction of crude oil and many petroleum products, and frequently enter soil, sediments and aquatic environments because of accidental spills, leaks and improper oil waste disposal practices. The mass transfer process of hydrocarbons in aquatic mediums has received considerable attention in the literature. This paper focused on the molecular mass transfer rate of BTEX in water, with the aim of understanding and predicting contaminant fate and transport. A comprehensive model was developed to simulate the molecular dissolution rate of BTEX in a natural water stream. The model considered the physicochemical properties of the BTEX compounds and physical processes relevant to the spreading of contaminants in the sea. The dissolution rate was a function of oil slick area, dissolution mass transferability and oil solubility in water. The total dissolution rate N was calculated and the dissolution mass transfer coefficient K was given as the point value of mass transfer coefficient. Results for the dissolution rate based on the solubility of the components in the water were compared with analytical solutions from previous studies and showed good agreement. The model showed that benzene had the largest dissolution rate, while o-xylene had the lowest rate because of its lower fraction. Benzene dissolution rate was approximately 2.6, which was 20.6 times that of toluene and ethylbenzene. It was concluded that the model is useful in predicting and monitoring the dissolution rate of BTEX contaminants in soil and water systems. 22 refs., 2 tabs., 3 figs

  15. Development of a Unified Dissolution and Precipitation Model and Its Use for the Prediction of Oral Drug Absorption.

    Jakubiak, Paulina; Wagner, Björn; Grimm, Hans Peter; Petrig-Schaffland, Jeannine; Schuler, Franz; Alvarez-Sánchez, Rubén

    2016-02-01

    Drug absorption is a complex process involving dissolution and precipitation, along with other kinetic processes. The purpose of this work was to (1) establish an in vitro methodology to study dissolution and precipitation in early stages of drug development where low compound consumption and high throughput are necessary, (2) develop a mathematical model for a mechanistic explanation of generated in vitro dissolution and precipitation data, and (3) extrapolate in vitro data to in vivo situations using physiologically based models to predict oral drug absorption. Small-scale pH-shift studies were performed in biorelevant media to monitor the precipitation of a set of poorly soluble weak bases. After developing a dissolution-precipitation model from this data, it was integrated into a simplified, physiologically based absorption model to predict clinical pharmacokinetic profiles. The model helped explain the consequences of supersaturation behavior of compounds. The predicted human pharmacokinetic profiles closely aligned with the observed clinical data. In summary, we describe a novel approach combining experimental dissolution/precipitation methodology with a mechanistic model for the prediction of human drug absorption kinetics. The approach unifies the dissolution and precipitation theories and enables accurate predictions of in vivo oral absorption by means of physiologically based modeling.

  16. Chemical dissolution of sulfide minerals

    Chao, T.T.; Sanzolone, R.F.

    1977-01-01

    Chemical dissolution treatments involving the use of aqua regia, 4 N HNO3, H2O2-ascorbic acid, oxalic acid, KClO3+HCl, and KClO3+HCl followed by 4 N HNO3 were applied to specimens of nine common sulfide minerals (galena, chalcopyrite, cinnabar, molybdenite, orpiment, pyrite, stibnite, sphalerite, and tetrahedrite) mixed individually with a clay loam soil. The resultant decrease in the total sulfur content of the mixture, as determined by using the Leco induction furnace, was used to evaluate the effectiveness of each chemical treatment. A combination of KClO3+HCl followed by 4 N HNO3 boiling gently for 20 min has been shown to be very effective in dissolving all the sulfide minerals. This treatment is recommended to dissolve metals residing in sulfide minerals admixed with secondary weathering products, as one step in a fractionation scheme whereby metals in soluble and adsorbed forms, and those associated with organic materials and secondary oxides, are first removed by other chemical extractants.

  17. Dissolution of metallic uranium in alkalis

    Mondino, Angel V.; Wilkinson, Maria V.; Manzini, Alberto C.

    1999-01-01

    The dissolution of U metallic foils has been studied in the framework of the development of an improved 99 Mo-production process. The best conditions for the dissolution of uranium foils of approximately 150 μm are the following: a) NaClO concentrations of 0.20 and 0.23 M with NaOH of 0.27 and 0.31 M respectively; b) temperature of the solution, 70 C degrees; c) volume of the solution, 15 ml / cm 2 of uranium foil; d) dissolution time, 30 minutes. (author)

  18. Dissolution studies of spent nuclear fuels

    1991-02-01

    To obtain quantitative data on the dissolution of high burnup spent nuclear fuel, dissolution study have been carried out at the Department of Chemistry, JAERI, from 1984 under the contract with STA entitled 'Reprocessing Test Study of High Burnup Fuel'. In this study PWR spent fuels of 8,400 to 36,100 MWd/t in averaged burnup were dissolved and the chemical composition and distribution of radioactive nuclides were measured for insoluble residue, cladding material (hull), off-gas and dissolved solution. With these analyses basic data concerning the dissolution and clarification process in the reprocessing plant were accumulated. (author)

  19. From laboratory experiments to a geological disposal vault: calculation of used nuclear fuel dissolution rates

    Sunder, S.; Shoesmith, D.W.; Kolar, M.; Leneveu, D.M.

    1998-01-01

    Calculation of used nuclear fuel dissolution rates in a geological disposal vault requires a knowledge of the redox conditions in the vault. For redox conditions less oxidizing than those causing UO 2 oxidation to the U 3 O 7 , stage, a thermodynamically-based model is appropriate. For more oxidizing redox conditions a kinetic or an electrochemical model is needed to calculate these rates. The redox conditions in a disposal vault will be affected by the radiolysis of groundwater by the ionizing radiation associated with the fuel. Therefore, we have calculated the alpha-, beta- and gamma-dose rates in water in contact with the reference used fuel in the Canadian Nuclear Fuel Waste Management Program (CNFWMP) as a function of cooling time. Also, we have determined dissolution rates of UO 2 fuel as a function of alpha and gamma dose rates from our electrochemical measurements. These room-temperature rates are used to calculate the dissolution rates of used fuel at 100 o C, the highest temperature expected in a container in the CNFWMP, as a function of time since emplacement. It is shown that beta radiolysis of water will be the main cause of oxidation of used CANDU fuel in a failed container. The use of a kinetic or an electrochemical corrosion model, to calculate fuel dissolution rates, is required for a period of ∼1000 a following emplacement of copper containers in the geologic disposal vault envisaged in the CNFWMP. Beyond this time period a thermodynamically-based model adequately predicts the fuel dissolution rates. The results presented in this paper can be adopted to calculate used fuel dissolution rates for other used UO 2 fuels in other waste management programs. (author)

  20. [Phytobezoar dissolution with Coca-Cola].

    Martínez de Juan, F; Martínez-Lapiedra, C; Picazo, V

    2006-05-01

    The treatment of phytobezoar is empiric. The various therapeutic choices include dietary modifications, prokinetic drugs, gastric lavage, enzymatic dissolution, endoscopic treatment, and surgery. We present two cases of phytobezoar with successful outcome after Coca-Cola administration.

  1. Improvement of database on glass dissolution

    Hayashi, Maki; Sasamoto, Hiroshi; Yoshikawa, Hideki

    2008-03-01

    In geological disposal system, high-level radioactive waste (HLW) glass is expected to retain radionuclide for the long term as the first barrier to prevent radionuclide release. The advancement of its performance assessment technology leads to the reliability improvement of the safety assessment of entire geological disposal system. For this purpose, phenomenological studies for improvement of scientific understanding of dissolution/alteration mechanisms, and development of robust dissolution/alteration model based on the study outcomes are indispensable. The database on glass dissolution has been developed for supporting these studies. This report describes improvement of the prototype glass database. Also, this report gives an example of the application of the database for reliability assessment of glass dissolution model. (author)

  2. Low temperature dissolution flowsheet for plutonium metal

    Daniel, W. E. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Almond, P. M. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Rudisill, T. S. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

    2016-05-01

    The H-Canyon flowsheet used to dissolve Pu metal for PuO2 production utilizes boiling HNO3. SRNL was requested to develop a complementary dissolution flowsheet at two reduced temperature ranges. The dissolution and H2 generation rates of Pu metal were investigated using a dissolving solution at ambient temperature (20-30 °C) and for an intermediate temperature of 50-60 °C. Additionally, the testing included an investigation of the dissolution rates and characterization of the off-gas generated from the ambient temperature dissolution of carbon steel cans and the nylon bags that contain the Pu metal when charged to the dissolver.

  3. Investigation of the dissolution of uranium dioxide in nitric media: a new approach aiming at understanding interface mechanisms

    Delwaulle, Celine

    2011-01-01

    This research thesis deals with the back-end cycle of the nuclear fuel by improving, modernizing and optimizing the processes used for all types of fuels which are to be re-processed. After a presentation of the industrial context and of the state of the art concerning dissolution kinetic data for uranium dioxide and mixed oxide, the author proposes a model which couples dissolution kinetics and hydrodynamics of a solid in presence of auto-catalytic species, in order to better understand phenomena occurring at the solid-liquid-gas interface. The next part reports dissolution experiments on a non-radioactive material (copper) and out of a nuclear environment. Then, the author identifies steps which are required to transpose this experiment within a nuclear environment. The first results obtained on uranium dioxide are discussed. Recommendations for further studies conclude the report

  4. Testing the potential of an elevated temperature IRSL signal from K-feldspar

    Buylaert, Jan-Pieter; Murray, A.S.; Thomsen, Kristina Jørkov

    2009-01-01

    on laboratory tests (recycling ratio, recuperation, dose recovery) we show that our SAR protocol is suitable for these samples. The observed post-IR IR fading rates (mean g2days = 1.62 ± 0.06%/decade, n = 24; assuming logarithmic fading) are significantly lower than those measured at 50 °C (mean g2days = 3...... the conventional IRSL signal stimulated at 50 °C and detected in the blue–violet region of the spectrum. One of these was the post-IR IR signal in which first an IR bleach is carried out at a low temperature (e.g. 100 s at 50 °C) and a remaining IRSL signal is measured at an elevated temperature (100 s at 225 °C......; detection in the blue–violet region). It is the latter signal that is of interest in this paper. We test such a post-IR IR dating protocol on K-feldspar extracts from a variety of locations and depositional environments and compare the results with those from the conventional IR at 50 °C protocol. Based...

  5. Influence of feldspar containing lithium in the sintering of triaxial ceramics

    Oliveira, Camila Felippe de; Strecker, Kurt

    2011-01-01

    In this work, the properties of a ceramic material based on a triaxial mass composed of clay, quartz and 15 to 30% feldspar, albite or spodumene, has been investigated. Specimen were prepared by uniaxial pressing under 28.5MPa and sintering at temperatures of 1000, 1100 and 1200 deg C, for 1h. The samples were characterized by their linear shrinkage, apparent porosity, apparent density and flexural strength, as well as analysis of the microstructure. The best results were obtained for samples prepared with 30% spodumene and sintered at 1200 deg C, with a shrinkage of 6.4%, density of 2.01g/cm 3 , porosity of 14.3% and flexural strength of 13.4MPa, while samples prepared with albite exhibited shrinkage of 5.8%, density of 1.9g/cm 3 , porosity of 18.9% and strength of 9.8MPa. Therefore, by the substitution of albite by spodumene in the ceramic triaxial mass, lower sintering temperatures may be employed, thus reducing production costs by the lesser energy consumption. (author)(

  6. IR-RF dating of sand-sized K-feldspar extracts: A test of accuracy

    Buylaert, J.-P.; Jain, M.; Murray, A.S.; Thomsen, K.J.; Lapp, T.

    2012-01-01

    In this paper we use a recently developed radioluminescence (RL) attachment to the Risø TL/OSL reader to test the InfraRed-RadioFluorescence (IR-RF) dating method applied to K-feldspar rich extracts from our known-age archive samples. We present experiments to characterise the instrument performance and to test the reproducibility of IR-RF measurements. These experiments illustrate the high sensitivity and dose rate of our RL system, the negligible influence of the turntable movement on IR-RF signals and the effectiveness of the built in 395 nm LED at bleaching IR-RF signals. We measure IR-RF ages on a set of samples with independent age control using a robust analytical method, which is able to detect any possible sensitivity change. Our IR-RF ages do not agree well with the independent age control; the ages of the younger samples (20–45 ka) are significantly over-estimated while the ages of the older samples (∼130 ka) are significantly under-estimated. Experiments are undertaken to investigate this disagreement and our results indicate that they can most likely be explained by 1) the difficulty of defining the correct bleaching level prior to regeneration measurements, 2) signal instability, 3) sensitivity changes between the additive dose and regenerative dose measurements, or a combination of these three factors.

  7. In Silico Modeling Approach for the Evaluation of Gastrointestinal Dissolution, Supersaturation, and Precipitation of Posaconazole.

    Hens, Bart; Pathak, Shriram M; Mitra, Amitava; Patel, Nikunjkumar; Liu, Bo; Patel, Sanjaykumar; Jamei, Masoud; Brouwers, Joachim; Augustijns, Patrick; Turner, David B

    2017-12-04

    The aim of this study was to evaluate gastrointestinal (GI) dissolution, supersaturation, and precipitation of posaconazole, formulated as an acidified (pH 1.6) and neutral (pH 7.1) suspension. A physiologically based pharmacokinetic (PBPK) modeling and simulation tool was applied to simulate GI and systemic concentration-time profiles of posaconazole, which were directly compared with intraluminal and systemic data measured in humans. The Advanced Dissolution Absorption and Metabolism (ADAM) model of the Simcyp Simulator correctly simulated incomplete gastric dissolution and saturated duodenal concentrations of posaconazole in the duodenal fluids following administration of the neutral suspension. In contrast, gastric dissolution was approximately 2-fold higher after administration of the acidified suspension, which resulted in supersaturated concentrations of posaconazole upon transfer to the upper small intestine. The precipitation kinetics of posaconazole were described by two precipitation rate constants, extracted by semimechanistic modeling of a two-stage medium change in vitro dissolution test. The 2-fold difference in exposure in the duodenal compartment for the two formulations corresponded with a 2-fold difference in systemic exposure. This study demonstrated for the first time predictive in silico simulations of GI dissolution, supersaturation, and precipitation for a weakly basic compound in part informed by modeling of in vitro dissolution experiments and validated via clinical measurements in both GI fluids and plasma. Sensitivity analysis with the PBPK model indicated that the critical supersaturation ratio (CSR) and second precipitation rate constant (sPRC) are important parameters of the model. Due to the limitations of the two-stage medium change experiment the CSR was extracted directly from the clinical data. However, in vitro experiments with the BioGIT transfer system performed after completion of the in silico modeling provided an almost

  8. Dissolution of various metal oxides in different forms in dilute organic complexants

    Srinivasan, M.P.; Chandramohan, P.; Velmurugan, S.; Narasimhan, S.V.; Ranganathan, S.

    2002-01-01

    The dissolution of iron containing metal oxides is of importance in various power plant industries from the point of crud and scale removal for efficient operation and better performance of plant. The removal of these oxides has to be accomplished with minimum corrosion to the structural material, with minimum cost and removal duration and also with minimum waste generation for easy disposal. Activity build-up due to pick up of 60 Co and fission products occurs on PHT system surfaces of nuclear power plants. The dissolution kinetics of these oxides are influenced by pH, redox potential, chelating strength, concentration and temperature of the solution, constitution of oxides, and the physical form of existence of oxides. In this paper the influence of the existence of different forms of iron oxides on the ability of the dissolution characteristics of the different formulations have been brought out. How the change in dissolution characteristics can be ingenuously used to characterize both qualitatively and quantitatively the mixtures of oxides have been brought out. How the magnetite dissolution behaviour varies for base metal unaided condition in different formulation in static condition, in regenerative mode is also brought out. The OCP values and iron release behaviour for magnetite coated CS surface and magnetite pellet were also described. (authors)

  9. Dissolution of various metal oxides in different forms in dilute organic complexants

    Srinivasan, M.P.; Chandramohan, P.; Velmurugan, S.; Narasimhan, S.V. [Water and Steam Chemistry Lab., BARC Facilities, Tamilnadu (India); Ranganathan, S. [Madras Univ. (India). Research Scholar

    2002-07-01

    The dissolution of iron containing metal oxides is of importance in various power plant industries from the point of crud and scale removal for efficient operation and better performance of plant. The removal of these oxides has to be accomplished with minimum corrosion to the structural material, with minimum cost and removal duration and also with minimum waste generation for easy disposal. Activity build-up due to pick up of {sup 60}Co and fission products occurs on PHT system surfaces of nuclear power plants. The dissolution kinetics of these oxides are influenced by pH, redox potential, chelating strength, concentration and temperature of the solution, constitution of oxides, and the physical form of existence of oxides. In this paper the influence of the existence of different forms of iron oxides on the ability of the dissolution characteristics of the different formulations have been brought out. How the change in dissolution characteristics can be ingenuously used to characterize both qualitatively and quantitatively the mixtures of oxides have been brought out. How the magnetite dissolution behaviour varies for base metal unaided condition in different formulation in static condition, in regenerative mode is also brought out. The OCP values and iron release behaviour for magnetite coated CS surface and magnetite pellet were also described. (authors)

  10. Status report on dissolution model development

    Jackson, D.D.

    1983-07-01

    The computer program PROTOCOL models the dissolution reactions of chemical species in water. It is being developed particularly to study the dissolution of proposed nuclear waste forms and related phases. Experimentally derived leaching rate functions are coupled to thermochemical equilibrium calculations and water flow rates. The program has been developed over a period of years. This report describes improvements that have been done in the past year

  11. Dissolution of the Mors salt dome

    Lindstroem Jensen, K.E.

    1982-01-01

    Regardless of the interpretation of the measured salinity profiles above the Mors salt dome, they can at most be the result of dissolution rates of about 0.004 mm per year. This means that it would take more than 2.5 mill. years to dissolve 10 m of salt. Variations in groun water velocity and cap rock porosity will not significantly change this condition. The stability of the Mors salt dome is therefore not affected by dissolution of the dome. (EG)

  12. Effect of particle size on solubility, dissolution rate, and oral bioavailability: evaluation using coenzyme Q10 as naked nanocrystals

    Sun J

    2012-11-01

    Full Text Available Jiao Sun,1 Fan Wang,1,2 Yue Sui,1 Zhennan She,1 Wenjun Zhai,1 Chunling Wang,1 Yihui Deng11College of Pharmacy, Shenyang Pharmaceutical University, Shenyang, China; 2Beijing Zhijianjinrui Applied Pharmaceutical Science Inc, Beijing, ChinaAbstract: In this paper work, four naked nanocrystals (size range 80–700 nm were prepared without any surfactant or polymer using the solvent/nonsolvent method. The effects of particle size on their solubility, dissolution, and oral bioavailability were investigated. Solubility and dissolution testing were performed in three types of dissolution medium, and the studies demonstrated that the equilibrium solubilities of coenzyme Q10 nanocrystals and bulk drugs were not affected by the dissolution media but the kinetic solubilities were. Kinetic solubility curves and changes in particle size distribution were determined and well explained by the proposed solubilization model for the nanocrystals and bulk drugs. The particle size effect on dissolution was clearly influenced by the diffusion coefficients of the various dissolution media, and the dissolution velocity of coenzyme Q10 increased as particle size decreased. The bioavailability of coenzyme Q10 after oral administration in beagle dogs was improved by reducing the particle size. For 700 nm nanocrystals, the AUC0–48 was 4.4-fold greater than that for the coarse suspensions, but a further decrease in particle size from 700 nm to 120 nm did not contribute to improvement in bioavailability until the particle size was reduced to 80 nm, when bioavailability was increased by 7.3-fold.Keywords: particle size, solubility, dissolution, nanocrystal, bioavailability, coenzyme Q10

  13. Evaluation of a three compartment in vitro gastrointestinal simulator dissolution apparatus to predict in vivo dissolution.

    Takeuchi, Susumu; Tsume, Yasuhiro; Amidon, Gregory E; Amidon, Gordon L

    2014-11-01

    In vitro dissolution tests are performed for new formulations to evaluate in vivo performance, which is affected by the change of gastrointestinal (GI) physiology, in the GI tract. Thus, those environmental changes should be introduced to an in vitro dissolution test. Many studies have successfully shown the improvement of in vitro-in vivo correlations (IVIVC) by introducing those physiological changes into dissolution tests. The gastrointestinal simulator (GIS), a multicompartment in vitro dissolution apparatus, was developed to evaluate in vivo drug dissolution. A gastric-emptying rate along with transit rate are key factors to evaluate in vivo drug dissolution and, hence, drug absorption. Dissolution tests with the GIS were performed with Biopharmaceutical Classification System class I drugs at five different gastric-emptying rates in the fasted state. Computational models were used to determine in vivo gastric-emptying time for propranolol and metoprolol based on the GIS dissolution results. Those were compared with published clinical data to determine the gastric half-emptying time. In conclusion, the GIS is a practical tool to assess dissolution properties and can improve IVIVC. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.

  14. Dissolution process for advanced-PWR-type fuels

    Black, D.E.; Decker, L.A.; Pearson, L.G.

    1979-01-01

    The new Fluorinel Dissolution Process and Fuel Storage (FAST) Facility at ICPP will provide underwater storage of spent PWR fuel and a new head-end process for fuel dissolution. The dissolution will be two-stage, using HF and HNO 3 , with an intermittent H 2 SO 4 dissolution for removing stainless steel components. Equipment operation is described

  15. Development and Validation of a Dissolution Test Method for ...

    Purpose: To develop and validate a dissolution test method for dissolution release of artemether and lumefantrine from tablets. Methods: A single dissolution method for evaluating the in vitro release of artemether and lumefantrine from tablets was developed and validated. The method comprised of a dissolution medium of ...

  16. A kinetics database and scripts for PHREEQC

    Hu, B.; Zhang, Y.; Teng, Y.; Zhu, C.

    2017-12-01

    Kinetics of geochemical reactions has been increasingly used in numerical models to simulate coupled flow, mass transport, and chemical reactions. However, the kinetic data are scattered in the literature. To assemble a kinetic dataset for a modeling project is an intimidating task for most. In order to facilitate the application of kinetics in geochemical modeling, we assembled kinetics parameters into a database for the geochemical simulation program, PHREEQC (version 3.0). Kinetics data were collected from the literature. Our database includes kinetic data for over 70 minerals. The rate equations are also programmed into scripts with the Basic language. Using the new kinetic database, we simulated reaction path during the albite dissolution process using various rate equations in the literature. The simulation results with three different rate equations gave difference reaction paths at different time scale. Another application involves a coupled reactive transport model simulating the advancement of an acid plume in an acid mine drainage site associated with Bear Creek Uranium tailings pond. Geochemical reactions including calcite, gypsum, and illite were simulated with PHREEQC using the new kinetic database. The simulation results successfully demonstrated the utility of new kinetic database.

  17. Development of cataclastic foliation in deformation bands in feldspar-rich conglomerates of the Rio do Peixe Basin, NE Brazil

    Nicchio, Matheus A.; Nogueira, Francisco C. C.; Balsamo, Fabrizio; Souza, Jorge A. B.; Carvalho, Bruno R. B. M.; Bezerra, Francisco H. R.

    2018-02-01

    In this work we describe the deformation mechanisms and processes that occurred during the evolution of cataclastic deformation bands developed in the feldspar-rich conglomerates of the Rio do Peixe Basin, NE Brazil. We studied bands with different deformation intensities, ranging from single cm-thick tabular bands to more evolved clustering zones. The chemical identification of cataclastic material within deformation bands was performed using compositional mapping in SEM images, EDX and XRD analyses. Deformation processes were identified by microstructural analysis and by the quantification of comminution intensity, performed using digital image processing. The deformation bands are internally non homogeneous and developed during five evolutionary stages: (1) moderate grain size reduction, grain rotation and grain border comminution; (2) intense grain size reduction with preferential feldspar fragmentation; (3) formation of subparallel C-type slip zones; (4) formation of S-type structures, generating S-C-like fabric; and (5) formation of C‧-type slip zones, generating well-developed foliation that resembles S-C-C‧-type structures in a ductile environment. Such deformation fabric is mostly imparted by the preferential alignment of intensely comminuted feldspar fragments along thin slip zones developed within deformation bands. These processes were purely mechanical (i.e., grain crushing and reorientation). No clays or fluids were involved in such processes.

  18. Jarosite dissolution rates in perchlorate brine

    Legett, Carey; Pritchett, Brittany N.; Elwood Madden, Andrew S.; Phillips-Lander, Charity M.; Elwood Madden, Megan E.

    2018-02-01

    Perchlorate salts and the ferric sulfate mineral jarosite have been detected at multiple locations on Mars by both landed instruments and orbiting spectrometers. Many perchlorate brines have eutectic temperatures bearing rocks and sediments may have been altered by perchlorate brines. Here we measured jarosite dissolution rates in 2 M sodium perchlorate brine as well as dilute water at 298 K to determine the effects of perchlorate anions on jarosite dissolution rates and potential reaction products. We developed a simple method for determining aqueous iron concentrations in high salinity perchlorate solutions using ultraviolet-visible spectrophotometry that eliminates the risk of rapid oxidation reactions during analyses. Jarosite dissolution rates in 2 M perchlorate brine determined by iron release rate (2.87 × 10-12 ±0.85 × 10-12 mol m-2 s-1) were slightly slower than the jarosite dissolution rate measured in ultrapure (18.2 MΩ cm-1) water (5.06 × 10-12 mol m-2 s-1) using identical methods. No additional secondary phases were observed in XRD analyses of the reaction products. The observed decrease in dissolution rate may be due to lower activity of water (ɑH2O = 0.9) in the 2 M NaClO4 brine compared with ultrapure water (ɑH2O = 1). This suggests that the perchlorate anion does not facilitate iron release, unlike chloride anions which accelerated Fe release rates in previously reported jarosite and hematite dissolution experiments. Since dissolution rates are slower in perchlorate-rich solutions, jarosite is expected to persist longer in perchlorate brines than in dilute waters or chloride-rich brines. Therefore, if perchlorate brines dominate aqueous fluids on the surface of Mars, jarosite may remain preserved over extended periods of time, despite active aqueous processes.

  19. Report on the intercomparison run F-1 U and K(Th) in feldspar

    1990-01-01

    The present report deals with a recent intercomparison on the determination of uranium, thorium and potassium in potassium feldspar, carried out in 1976-77 and involving the participation of 20 institutes who returned a total of 196 individual results on three elements. Analytical techniques employed by the participating institutes included gamma spectrometry, emission spectroscopy, atomic absorption, X-ray fluorescence, fluorimetry and neutron activation. Each of these techniques has its own particular weakness: The basic principles of gamma-spectrometric technique for the determination of U, Th and K are well known. It is, however, difficult to determine the low concentrations of radioactive nuclides which can be found in geological materials due to systematic errors arising from non-equilibration of decay chains in the samples and from other sources including calibration. Determination of uranium in geological materials by non-destructive neutron activation analysis also has some problems. Elements such as Th, Ta, Pt, Ru, Zn and Ba when irradiated in a nuclear reactor with thermal and epithermal neutrons yield radioactive isotopes, the gamma rays of which interfere with those used in uranium determination. Detection limits for three elements U, Th and K for thermal neutron activation have been reported as 0.7, 1.0 and 10 ppb respectively, however, this seems over-optimistic to expect in real-life situations. Measurement of delayed neutrons and fission track methods for uranium and thorium also have interference problems. Fluorimetry is a suitable method for uranium at low concentrations (down to 0.1 ppm) but one has to take care to overcome quenching by removing, or at least diluting, interfering elements. The determination of some important elements in geochemical samples is often difficult because of their small concentration as well as of the presence of interfering matrix elements in the samples. Some systematic differences seem to exist between the methods

  20. Chemical Zoning of Feldspars in Lunar Granitoids: Implications for the Origins of Lunar Silicic Magmas

    Mills, R. D; Simon, J. I.; Alexander, C.M. O'D.; Wang, J.; Christoffersen, R.; Rahman, Z..

    2014-01-01

    Fine-scale chemical and textural measurements of alkali and plagioclase feldspars in the Apollo granitoids (ex. Fig. 1) can be used to address their petrologic origin(s). Recent findings suggest that these granitoids may hold clues of global importance, rather than of only local significance for small-scale fractionation. Observations of morphological features that resemble silicic domes on the unsampled portion of the Moon suggest that local, sizable net-works of high-silica melt (>65 wt % SiO2) were present during crust-formation. Remote sensing data from these regions suggest high concentrations of Si and heat-producing elements (K, U, and Th). To help under-stand the role of high-silica melts in the chemical differentiation of the Moon, three questions must be answered: (1) when were these magmas generated?, (2) what was the source material?, and (3) were these magmas produced from internal differentiation. or impact melting and crystallization? Here we focus on #3. It is difficult to produce high-silica melts solely by fractional crystallization. Partial melting of preexisting crust may therefore also have been important and pos-sibly the primary mechanism that produced the silicic magmas on the Moon. Experimental studies demonstrate that partial melting of gabbroic rock under mildly hydrated conditions can produce high-silica compositions and it has been suggested by that partial melting by basaltic underplating is the mechanism by which high-silica melts were produced on the Moon. TEM and SIMS analyses, coordinated with isotopic dating and tracer studies, can help test whether the minerals in the Apollo granitoids formed in a plutonic setting or were the result of impact-induced partial melting. We analyzed granitoid clasts from 3 Apollo samples: polymict breccia 12013,141, crystalline-matrix breccia 14303,353, and breccia 15405,78

  1. Effect of infiltrated water on rheology of plagioclase feldspar under lower crustal condition

    Kido, M.; Muto, J.; Koizumi, S.; Nagahama, H.

    2016-12-01

    Fluids in the deep crust have an important role in deformation of lithosphere and seismicity. In this study, we performed deformation experiments to reveal rheological properties of plagioclase feldspars as a main constituent of crustal materials with infilitrated water. Axial compression tests on synthetic polycrystalline anorthite (An) were performed in a Griggs-type deformation apparatus at temparature of 900 °C, strain rates of roughly about 10-5 s-1 and various confining pressures of 0.8-1.4 GPa. Distilled water was added on samples before tests. Times for infiltration of water into samples were changed to investigate the variation of strength associated with diffusion of water. Strengths of wet An tended to decrease with infiltration time or strain magnitude. If other conditions such as temperature, time and strain being the same, strengths increase with confining pressures. Recovered samples show that deformation was concentrated in the lower part of samples. Differential stresses were significantly lower than predicted values by a previous flow law for wet An obtained by low pressure gas apparatus ( 0.4 GPa, Rybacki et al., 2006). This implies that the effect of water on mechanical behavior in higher pressure might be larger than those predicted by lower pressure experiments. Ideal water concentration and strength profile of internal of samples were estimated by one-dimensional model of grain boundary diffusion. Estimated strength of internal part of samples was significant higher than measured stresses. There is possibility that cataclastic flow partially occurred in samples. In addition, deformation-enhanced fluid flow probably occurred. In conclusion, strength of wet An depends on water infiltration time, strain magnitude and confining pressure. The results suggest that the strength of fluid-rich regions in the lower crust becomes lower than that predicted by previous studies.

  2. Geochemical thermodynamic and kinetic modeling that take into account the mass transfer phenomena in saturated porous medium

    Gerard, Frederic

    1996-01-01

    The mass transport mechanisms (advection. mechanical dispersion and molecular diffusion) have been introduced into the thermodynamic and kinetic geochemical code KINDIS. This innovative approach to couple chemical and transport mass transfers has allowed us to develop a reactive transport or hydrochemical code named KIRMAT, which naturally preserve the comprehensive geochemical functions of KINDIS. Mass transport phenomena through the total connected porosity of a water-saturated porous medium are solved over one spatial dimension (ID). The finite difference method is used. An explicit or forward time scheme is computed. The advective finite difference expression may be either centered or upstream weighted. Thus, ail of the hydrodynamic conditions may be modeled (from the pure advection to pure diffusion). The mass transport and geochemical flux are solved simultaneously (one-step algorithm). Moreover. the code KIRMAT is designed to quantify reactive mass transport through a double or dual porosity medium, in which the flow porosity (filled by free water) and the diffusion porosity (containing stagnant water) are viewed as two distinct sub mediums or Systems. Under some given conditions, the need to solve one or the other mass transport equation is a function of the water-rock System size. The accuracy of the kinetic constraint has been improved in KIRMAT. Two new kinetic rate laws have been introduced for the dissolution of the most abundant silicates (alkali feldspars, silica. etc.). These rate laws integrate the quantitatively important inhibitor and catalytic effects involved with some dissolved chemical elements that are ubiquitous in natural aqueous solutions. The basic step. the numerical verification of the code, has been tackled with two complementary approaches. The numerical results from KIRMAT have been compared to those calculated from an exact solution and a new method has been developed and used. We have compared the numerical results of KIRMAT in

  3. Physical kinetics

    Lifschitz, E.M.; Pitajewski, L.P.

    1983-01-01

    The textbook covers the subject under the following headings: kinetic gas theory, diffusion approximation, collisionless plasma, collisions within the plasma, plasma in the magnetic field, theory of instabilities, dielectrics, quantum fluids, metals, diagram technique for nonequilibrium systems, superconductors, and kinetics of phase transformations

  4. Heparin kinetics

    Swart, C.A.M. de.

    1983-01-01

    The author has studied the kinetics of heparin and heparin fractions after intravenous administration in humans and in this thesis the results of this study are reported. Basic knowledge about the physico-chemical properties of heparin and its interactions with proteins resulting in anticoagulant and lipolytic effects are discussed in a review (chapter II), which also comprises some clinical aspects of heparin therapy. In chapter III the kinetics of the anticoagulant effect are described after intravenous administration of five commercial heparin preparations. A mathematical model is presented that fits best to these kinetics. The kinetics of the anticoagulant and lipolytic effects after intravenous injection of various 35 S-radiolabelled heparin fractions and their relationship with the disappearance of the radiolabel are described in chapter IV. Chapter V gives a description of the kinetics of two radiolabels after injection of in vitro formed complexes consisting of purified, 125 I-radiolabelled antithrombin III and various 35 S-radiolabelled heparin fractions. (Auth.)

  5. Dissolution testing of orally disintegrating tablets.

    Kraemer, Johannes; Gajendran, Jayachandar; Guillot, Alexis; Schichtel, Julian; Tuereli, Akif

    2012-07-01

    For industrially manufactured pharmaceutical dosage forms, product quality tests and performance tests are required to ascertain the quality of the final product. Current compendial requirements specify a disintegration and/or a dissolution test to check the quality of oral solid dosage forms. These requirements led to a number of compendial monographs for individual products and, at times, the results obtained may not be reflective of the dosage form performance. Although a general product performance test is desirable for orally disintegrating tablets (ODTs), the complexity of the release controlling mechanisms and short time-frame of release make such tests difficult to establish. For conventional oral solid dosage forms (COSDFs), disintegration is often considered to be the prerequisite for subsequent dissolution. Hence, disintegration testing is usually insufficient to judge product performance of COSDFs. Given the very fast disintegration of ODTs, the relationship between disintegration and dissolution is worthy of closer scrutiny. This article reviews the current status of dissolution testing of ODTs to establish the product quality standards. Based on experimental results, it appears that it may be feasible to rely on the dissolution test without a need for disintegration studies for selected ODTs on the market. © 2012 The Authors. JPP © 2012 Royal Pharmaceutical Society.

  6. Crystal modifications and dissolution rate of piroxicam.

    Lyn, Lim Yee; Sze, Huan Wen; Rajendran, Adhiyaman; Adinarayana, Gorajana; Dua, Kamal; Garg, Sanjay

    2011-12-01

    Piroxicam is a nonsteroidal anti-inflammatory drug with low aqueous solubility which exhibits polymorphism. The present study was carried out to develop polymorphs of piroxicam with enhanced solubility and dissolution rate by the crystal modification technique using different solvent mixtures prepared with PEG 4000 and PVP K30. Physicochemical characteristics of the modified crystal forms of piroxicam were investigated by X-ray powder diffractometry, FT-IR spectrophotometry and differential scanning calorimetry. Dissolution and solubility profiles of each modified crystal form were studied and compared with pure piroxicam. Solvent evaporation method (method I) produced both needle and cubic shaped crystals. Slow crystallization from ethanol with addition of PEG 4000 or PVP K30 at room temperature (method II) produced cubic crystal forms. Needle forms produced by method I improved dissolution but not solubility. Cubic crystals produced by method I had a dissolution profile similar to that of untreated piroxicam but showed better solubility than untreated piroxicam. Cubic shaped crystals produced by method II showed improved dissolution, without a significant change in solubility. Based on the XRPD results, modified piroxicam crystals obtained by method I from acetone/benzene were cube shaped, which correlates well with the FTIR spectrum; modified needle forms obtained from ethanol/methanol and ethanol/acetone showed a slight shift of FTIR peak that may be attributed to differences in the internal structure or conformation.

  7. Aqueous dissolution rates of uranium oxides

    Steward, S.A.; Mones, E.T.

    1994-10-01

    An understanding of the long-term dissolution of waste forms in groundwater is required for the safe disposal of high level nuclear waste in an underground repository. The main routes by which radionuclides could be released from a geological repository are the dissolution and transport processes in groundwater flow. Because uranium dioxide is the primary constituent of spent nuclear fuel, the dissolution of its matrix in spent fuel is considered the rate-limiting step for release of radioactive fission products. The purpose of our work has been to measure the intrinsic dissolution rates of uranium oxides under a variety of well-controlled conditions that are relevant to a repository and allow for modeling. The intermediate oxide phase U 3 O 8 , triuranium octaoxide, is quite stable and known to be present in oxidized spent fuel. The trioxide, UO 3 , has been shown to exist in drip tests on spent fuel. Here we compare the results of essentially identical dissolution experiments performed on depleted U 3 O 8 and dehyrated schoepite or uranium trioxide monohydrate (UO 3 ·H 2 O). These are compared with earlier work on spent fuel and UO 2 under similar conditions

  8. Catalysed electrolytic metal oxide dissolution processes

    Machuron-Mandard, X.

    1994-01-01

    The hydrometallurgical processes designed for recovering valuable metals from mineral ores as well as industrial wastes usually require preliminary dissolution of inorganic compounds in aqueous media before extraction and purification steps. Unfortunately, most of the minerals concerned hardly or slowly dissolve in acidic or basic solutions. Metallic oxides, sulfides and silicates are among the materials most difficult to dissolve in aqueous solutions. They are also among the main minerals containing valuable metals. The redox properties of such materials sometimes permit to improve their dissolution by adding oxidizing or reducing species to the leaching solution, which leads to an increase in the dissolution rate. Moreover, limited amounts of redox promoters are required if the redox agent is regenerated continuously thanks to an electrochemical device. Nuclear applications of such concepts have been suggested since the dissolution of many actinide compounds (e.g., UO 2 , AmO 2 , PuC, PuN,...) is mainly based on redox reactions. In the 1980s, improvements of the plutonium dioxide dissolution process have been proposed on the basis of oxidation-reduction principles, which led a few years later to the design of industrial facilities (e.g., at Marcoule or at the french reprocessing plant of La Hague). General concepts and well-established results obtained in France at the Atomic Energy Commission (''Commissariat a l'Energie Atomique'') will be presented and will illustrate applications to industrial as well as analytical problems. (author)

  9. Dissolution profiles of perindopril and indapamide in their fixed-dose formulations by a new HPLC method and different mathematical approaches

    Gumieniczek Anna

    2015-09-01

    Full Text Available A new HPLC method was introduced and validated for simultaneous determination of perindopril and indapamide. Validation procedure included specificity, sensitivity, robustness, stability, linearity, precision and accuracy. The method was used for the dissolution test of perindopril and indapamide in three fixed-dose formulations. The dissolution procedure was optimized using different media, different pH of the buffer, surfactants, paddle speed and temperature. Similarity of dissolution profiles was estimated using different model-independent and model-dependent methods and, additionally, by principal component analysis (PCA. Also, some kinetic models were checked for dissolved amounts of drugs as a function of time.

  10. Dissolution Coupled Biodegradation of Pce by Inducing In-Situ Biosurfactant Production Under Anaerobic Conditions

    Dominic, J.; Nambi, I. M.

    2013-12-01

    Biosurfactants have proven to enhance the bioavailability and thereby elevate the rate of degradation of Light Non Aqueous Phase Liquids (LNAPLs) such as crude oil and petroleum derivatives. In spite of their superior characteristics, use of these biomolecules for remediation of Dense Non Aqueous Phase Liquids (DNAPLs) such as chlorinated solvents is still not clearly understood. In this present study, we have investigated the fate of tetrachloroethylene (PCE) by inducing in-situ biosurfactants production, a sustainable option which hypothesizes increase in bioavailability of LNAPLs. In order to understand the effect of biosurfactants on dissolution and biodegradation under the inducement of in-situ biosurfactant production, batch experiments were conducted in pure liquid media. The individual influence of each process such as biosurfactant production, dissolution of PCE and biodegradation of PCE were studied separately for getting insights on the synergistic effect of each process on the fate of PCE. Finally the dissolution coupled biodegradation of non aqueous phase PCE was studied in conditions where biosurfactant production was induced by nitrate limitation. The effect of biosurfactants was differentiated by repeating the same experiments were the biosurfactant production was retarded. The overall effect of in-situ biosurfactant production process was evaluated by use of a mathematical model. The process of microbial growth, biosurfactant production, dissolution and biodegradation of PCE were translated as ordinary differential equations. The modelling exercise was mainly performed to get insight on the combined effects of various processes that determine the concentration of PCE in its aqueous and non-aqueous phases. Model simulated profiles of PCE with the kinetic coefficients evaluated earlier from individual experiments were compared with parameters fitted for observations in experiments with dissolution coupled biodegradation process using optimization

  11. Dissolution mechanism of austenitic stainless steels in lead-bismuth eutectic at 500 deg. C

    Roy, M.

    2012-01-01

    In the framework of the future nuclear power plants studies, lead-bismuth eutectic (LBE) is foreseen as a coolant in the primary or the secondary circuit in three nuclear systems. The use of this liquid alloy induces corrosion issues for structural steels. In liquid lead alloys, steels can undergo two corrosion phenomena: dissolution or oxidation depending on the temperature and the dissolved oxygen content in LBE. The goal of this study is to identify the dissolution mechanisms of austenitic steels in LBE at 500 deg. C. Four Fe-Cr-Ni model austenitic steels, the 316L steel and five other industrial steels were corroded in LBE up to, respectively, 3000, 6000 and 200 h. The dissolution mechanism is identical for all steels: it starts by a preferential dissolution of chromium and nickel. This dissolution leads to the formation of a ferritic corrosion layer penetrated by LBE and containing between 5 and 10 at% of chromium and almost no nickel. This study demonstrates that dissolutions of nickel and chromium are linked. Otherwise, the corrosion kinetics is linear whatever the tested austenitic steel. The controlling steps of the austenitic steels' corrosion rates have been identified. Natural convection in the LBE bath leads to the formation of a diffusion boundary layer at the steel surface. Chromium diffusion in this diffusion boundary layer seems to control the corrosion rates of the model and industrial austenitic steels except the 316L steel. Indeed, the corrosion rate of the 316L steel is controlled by an interfacial reaction which is either the simultaneous dissolution of nickel and chromium in Ni, Cr compounds or the nickel and chromium dissolution catalyzed by the dissolved oxygen in LBE. This study has permitted to highlight the major role of chromium on the corrosion mechanisms and the corrosion rates of austenitic steels: the corrosion rate increases when chromium activity increases. Finally, the impact of the dissolved oxygen and the minor alloying

  12. Sorption of Eu(III) at feldspar/water interface. Effects of pH, organic matter, counter ions, and temperature

    Li, Ping; Liang, Jianjun; Fan, Qiaohui [Chinese Academy of Sciences, Lanzhou (China). Key Lab. of Petroleum Resources Research; Wu, Hanyu [Chinese Academy of Sciences, Lanzhou (China). Key Lab. of Petroleum Resources Research; Lanzhou Univ. (China). Radiochemistry Lab.; Yin, Zhuoxin; Pan, Duoqiang; Wu, Wangsuo [Lanzhou Univ. (China). Radiochemistry Lab.; Xu, Di [Chinese Academy of Sciences, Nanjing (China). State Key Lab. of Lake Science and Environment

    2017-07-01

    The sorption of Eu(III) on potassium feldspar (K-feldspar) was studied under various physicochemical conditions such as pH, temperature, counter ions and organic matter. The results showed that the sorption of Eu(III) on K-feldspar significantly increased with the increase of pH, and high Eu(III) concentration can inhibit such immobility to some extent. The presence of humic acid (HA) can increase the sorption of Eu(III) on K-feldspar in low pH range; while inhibit to a large extent under alkaline conditions. It is very interesting that at pH ∝6.5, high ionic strength can promote the sorption of Eu(III) on K-feldspar in the presence of HA. In contrast, Eu(III) sorption was restricted obviously by NaCl in the absence of HA. The sorption procedure was involved with ion exchange and/or outer-sphere complexation as well as inner-sphere complexation. The presence of F{sup -} and PO{sub 4}{sup 3-} dramatically enhanced Eu(III) sorption on K-feldspar, whereas both SO{sub 4}{sup 2-} and CO{sub 3}{sup 2-} had negative effects on Eu(III) sorption. X-ray photoelectron spectroscopy analysis indicated that Eu(III) tended to form hydrolysates at high initial concentration (3 x 10{sup -4} mol/L) and high temperature (338 K).

  13. Enhancement of the glass corrosion in the presence of clay minerals: testing experimental results with an integrated glass dissolution model

    Godon, N.; Vernaz, E.Y.

    1992-01-01

    Recent glass dissolution experiments, conducted at 90 deg C in the presence of potential backfill materials, indicate remarkably faster glass corrosion in the presence of clay, compared to tests where the glass is leached either alone or with alternative backfill materials. This effect correlates with the clay content in the backfill, and may be attributed to the removal of silica from solution. Scorpion, or dissolution with reprecipitation of a silica-rich clay, have been proposed as possible mechanisms for the silica consumption. The results of some experiments have been tested against a glass dissolution model, in which a widely used kinetic equation for glass corrosion is coupled with diffusive silica transport through a single porosity, linearly sorbing medium, which represents the backfilling. Because the glass corrosion rates imposed by the kinetic equation are inversely proportional to the silicic acid concentration of the leachant contacting the glass, the model predicts enhanced glass dissolution if silica is sorbed by the porous medium. The experimental data proved to be consistent with the predicted enhancement of the glass dissolution. Moreover, the model-estimated distribution coefficients for silica sorption (K d ) fall within the range of values extracted from available literature data, thus supporting the hypothesis that the observed high corrosion rates are due to sorption of silica on the clay mineral surfaces. (author)

  14. Criticality safety in high explosives dissolution

    Troyer, S.D.

    1997-01-01

    In 1992, an incident occurred at the Pantex Plant in which the cladding around a fissile material component (pit) cracked during dismantlement of the high explosives portion of a nuclear weapon. Although the event did not result in any significant contamination or personnel exposures, concerns about the incident led to the conclusion that the current dismantlement process was unacceptable. Options considered for redesign, dissolution tooling design considerations, dissolution tooling design features, and the analysis of the new dissolution tooling are summarized. The final tooling design developed incorporated a number of safety features and provides a simple, self-contained, low-maintenance method of high explosives removal for nuclear explosive dismantlement. Analyses demonstrate that the tooling design will remain subcritical under normal, abnormal, and credible accident scenarios. 1 fig

  15. Dissolution experiments of unirradiated uranium dioxide pellets

    Ollila, K.

    1985-01-01

    The purpose of this study was to measure the dissolution rate of uranium from unirradiated uranium dioxide pellets in deionized water and natural groundwater. Moreover, the solubility limit of uranium in natural groundwater was measured. Two different temperatures, 25 and 60 deg C were used. The low oxygen content of deep groundwater was simulated. The dissolution rate of uranium varied from 10 -7 to 10 -8 g cm -2 d -1 . The rate in reionized water was one order of magnitude lower than in groundwater. No great difference was observed between the natural groundwaters with different composition. Temperature seems to have effect on the dissolution rate. The solubility limit of uranium in natural groundwater in reducing conditions, at 25 deg C, varied from 20 to 600 μg/l and in oxidizing conditions, at 60 deg C, from 4 to 17 mg/l

  16. Waste form dissolution in bedded salt

    Kaufman, A.M.

    1980-01-01

    A model was devised for waste dissolution in bedded salt, a hydrologically tight medium. For a typical Spent UnReprocessed Fuel (SURF) emplacement, the dissolution rate wll be diffusion limited and will rise to a steady state value after t/sub eq/ approx. = 250 (1+(1-epsilon 0 ) K/sub D//epsilon 0 ) (years) epsilon 0 is the overpack porosity and K/sub d/ is the overpack sorption coefficient. The steady state dissolution rate itself is dominated by the solubility of UO 2 . Steady state rates between 5 x 10 -5 and .5 (g/year) are achievable by SURF emplacements in bedded salt without overpack, and rates between 5 x 10 -7 and 5 x 10 -3 (g/year) with an overpack having porosity of 10 -2

  17. Magnetic resonance imaging of tablet dissolution.

    Nott, Kevin P

    2010-01-01

    Magnetic resonance imaging (MRI) is the technique of choice for measuring hydration, and its effects, during dissolution of tablets since it non-invasively maps (1)H nuclei associated with 'mobile' water. Although most studies have used MRI systems with high-field superconducting magnets, low-field laboratory-based instruments based on permanent magnet technology are being developed that provide key data for the formulation scientist. Incorporation of dissolution hardware, in particular the United States Pharmacopeia (USP) apparatus 4 flow-through cell, allows measurements under controlled conditions for comparison against other dissolution methods. Furthermore, simultaneous image acquisition and measurement of drug concentration allow direct comparison of the drug release throughout the hydration process. The combination of low-field MRI with USP-4 apparatus provides another tool to aid tablet formulation. Copyright 2009 Elsevier B.V. All rights reserved.

  18. DISSOLUTION OF IRRADIATED MURR FUEL ASSEMBLIES

    Kyser, E.

    2010-06-17

    A literature survey on the dissolution of spent nuclear fuel from the University of Missouri Research Reactor (MURR) has been performed. This survey encompassed both internal and external literature sources for the dissolution of aluminum-clad uranium alloy fuels. The most limiting aspect of dissolution in the current facility configuration involves issues related to the control of the flammability of the off-gas from this process. The primary conclusion of this work is that based on past dissolution of this fuel in H-Canyon, four bundles of this fuel (initial charge) may be safely dissolved in a nitric acid flowsheet catalyzed with 0.002 M mercuric nitrate using a 40 scfm purge to control off-gas flammability. The initial charge may be followed by a second charge of up to five bundles to the same dissolver batch depending on volume and concentration constraints. The safety of this flowsheet relies on composite lower flammability limits (LFL) estimated from prior literature, pilot-scale work on the dissolution of site fuels, and the proposed processing flowsheet. Equipment modifications or improved LFL data offer the potential for improved processing rates. The fuel charging sequence, as well as the acid and catalyst concentrations, will control the dissolution rate during the initial portion of the cycle. These parameters directly impact the hydrogen and off-gas generation and, along with the purge flowrate determine the number of bundles that may be charged. The calculation approach within provides Engineering a means to determine optimal charging patterns. Downstream processing of this material should be similar to that of recent processing of site fuels requiring only minor adjustments of the existing flowsheet parameters.

  19. Quartz dissolution and silica deposition in hot-dry-rock geothermal systems

    Robinson, B.A.

    1982-07-01

    The kinetics of quartz dissolution control the produced fluid dissolved silica concentration in geothermal systems in which the downhole residence time is finite. The produced fluid of the Phase I, Run Segment 5 experimental Hot Dry Rock (HDR) geothermal system at Fenton Hill, NM, was undersaturated with respect to quartz in one pass through the reservoir, suggesting that the rate of granite dissolution governed the outlet dissolved silica concentration in this system. The literature data for the rate of quartz dissolution in water from 65 to 625/sup 0/C is correlated using an empirical rate law which is first order in quartz surface area and degree of undersaturation of the fluid. The Arrhenius plot (ln k vs T/sup -1/) is linear over eight orders of magnitude of the rate constant, verifying the validity of the proposed rate expression. Carefully performed quartz dissolution experiments in the present study duplicated the literature data and completed the data base in the temperature range from 150 to 250/sup 0/C. Identical experiments using crushed granite indicate that the rate of quartz dissolution in the presence of granite could be as much as 1 to 2 orders of magnitude faster than the rates observed in the pure quartz experiments. A temperature dependent HDR reservoir model incorporates the quartz dissolution rate law to simulate the dissolved silica behavior during the Fenton Hill Run Segment 5 experiment. For this low-permeability, fracture-dominated reservoir, the assumptions of one-dimensional plug flow through a vertically-inclined rectangular fracture and one-dimensional rock heat conduction perpendicular to the direction of flow are employed. These simplifications lead to an analytical solution for the temperature field in the reservoir.

  20. Formation, transformation and dissolution of phases formed on surfaces

    Shoesmith, D.W.

    1983-03-01

    The basic mechanisms of film growth, transformation, and dissolution of phases formed on surfaces are discussed. Film growth can occur via solid-state processes or via substrate (usally metal or alloy) dissolution, followed by local supersaturation and precipitation of an insoluble phase. The phase(s) formed may be metastable and transform to a more stable phase, via either solid-state or dissolution-reprecipitation processes. Film dissolution reactions can also occur via a variety of mechanisms, including: (i) direct chemical dissolution when no oxidation state change occurs; (ii) redox dissolution when the film dissolves via a redox reaction involving a reducing or oxidizing agent in solution; and (iii) autoreduction, where film dissolution is coupled to metal dissolution. Such film-growth and dissolution processes, which often produce complex multilayer films, are common in the nuclear industry. A number of examples are discussed

  1. Microbially mediated barite dissolution in anoxic brines

    Ouyang, Bingjie; Akob, Denise M.; Dunlap, Darren; Renock, Devon

    2017-01-01

    Fluids injected into shale formations during hydraulic fracturing of black shale return with extraordinarily high total-dissolved-solids (TDS) and high concentrations of barium (Ba) and radium (Ra). Barite, BaSO_4, has been implicated as a possible source of Ba as well as a problematic mineral scale that forms on internal well surfaces, often in close association with radiobarite, (Ba,Ra)SO_4. The dissolution of barite by abiotic processes is well quantified. However, the identification of microbial communities in flowback and produced water necessitates the need to understand barite dissolution in the presence of bacteria. Therefore, we evaluated the rates and mechanisms of abiotic and microbially-mediated barite dissolution under anoxic and hypersaline conditions in the laboratory. Barite dissolution experiments were conducted with bacterial enrichment cultures established from produced water from Marcellus Shale wells located in northcentral Pennsylvania. These cultures were dominated by anaerobic halophilic bacteria from the genus Halanaerobium. Dissolved Ba was determined by ICP-OES and barite surfaces were investigated by SEM and AFM. Our results reveal that: 1) higher amounts of barium (up to ∼5 × ) are released from barite in the presence of Halanaerobium cultures compared to brine controls after 30 days of reaction, 2) etch pits that develop on the barite (001) surface in the presence of Halanaerobium exhibit a morphology that is distinct from those that form during control experiments without bacteria, 3) etch pits that develop in the presence of Halanaerobium exhibit a morphology that is similar to the morphology of etch pits formed in the presence of strong organic chelators, EDTA and DTPA, and 4) experiments using dialysis membranes to separate barite from bacteria suggest that direct contact between the two is not required in order to promote dissolution. These results suggest that Halanaerobium increase the rate of barite dissolution in anoxic

  2. Saltcake dissolution FY 1998 status report

    HERTING, D.L.

    1999-01-01

    A laboratory scouting study was completed on the dissolution characteristics of Hanford waste from three single-shell waste tanks: 241-BY-102, 241-BY-106, and 241-B-106. Gross dissolution behavior (percent undissolved solids as a function of dilution) is explained in terms of characteristics of individual salts in the waste. The percentage of the sodium inventory retrievable from the tanks by dissolving saltcake at reasonable dilution levels is estimated at 86% of the total sodium for tank BY-102, 98% for BY-106, and 79% for B-106

  3. Effect of sodium lauryl sulfate in dissolution media on dissolution of hard gelatin capsule shells.

    Zhao, Fang; Malayev, Vyacheslav; Rao, Venkatramana; Hussain, Munir

    2004-01-01

    Sodium lauryl sulfate (SLS) is a commonly used surfactant in dissolution media for poorly water soluble drugs. However, it has occasionally been observed that SLS negatively impacts the dissolution of drug products formulated in gelatin capsules. This study investigated the effect of SLS on the dissolution of hard gelatin capsule shells. The USP paddle method was used with online UV monitoring at 214 nm (peptide bond). Empty size #0 capsule shells were held to the bottom of the dissolution vessel by magnetic three-prong sinkers. SLS significantly slowed down the dissolution of gelatin shells at pH < 5. Visually, the gelatin shells transformed into some less-soluble precipitate under these conditions. This precipitate was found to contain a higher sulfur content than the gelatin control sample by elemental analysis, indicating that SLS is part of the precipitate. Additionally, the slowdown of capsule shell dissolution was shown to be dependent on the SLS concentration and the ionic strength of the media. SLS interacts with gelatin to form a less-soluble precipitate at pH < 5. The use of SLS in dissolution media at acidic pH should be carefully evaluated for gelatin capsule products.

  4. Assessing the effect of dissolved organic ligands on mineral dissolution rates: An example from calcite dissolution

    DeMaio, T.; Grandstaff, D.E.

    1997-01-01

    Experiments suggest that dissolved organic ligands may primarily modify mineral dissolution rates by three mechanisms: (1) metal-ligand (M-L) complex formation in solution, which increases the degree of undersaturation, (2) formation of surface M-L complexes that attack the surface, and (3) formation of surface complexes which passivate or protect the surface. Mechanisms (1) and (2) increase the dissolution rate and the third decreases it compared with organic-free solutions. The types and importance of these mechanisms may be assessed from plots of dissolution rate versus degree of undersaturation. To illustrate this technique, calcite, a common repository cementing and vein-filling mineral, was dissolved at pH 7.8 and 22 C in Na-Ca-HCO 3 -Cl solutions with low concentrations of three organic ligands. Low citrate concentrations (50 microM) increased the dissolution rate consistent with mechanism (1). Oxalate decreased the rate, consistent with mechanism (3). Low phthalate concentration (<50 microM) decreased calcite dissolution rates; however, higher concentrations increased the dissolution rates, which became faster than in inorganic solutions. Thus, phthalate exhibits both mechanisms (2) and (3) at different concentrations. In such cases linear extrapolations of dissolution rates from high organic ligand concentrations may not be valid

  5. Field Exploration and Life Detection Sampling for Planetary Analogue Research (FELDSPAR)

    Gentry, D.; Stockton, A. M.; Amador, E. S.; Cable, M. L.; Cantrell, T.; Chaudry, N.; Cullen, T.; Duca, Z. A.; Jacobsen, M. B.; Kirby, J.; McCaig, H. C.; Murukesan, G.; Rennie, V.; Rader, E.; Schwieterman, E. W.; Stevens, A. H.; Sutton, S. A.; Tan, G.; Yin, C.; Cullen, D.; Geppert, W.

    2017-12-01

    Extraterrestrial studies are typically conducted on mg samples from cm-scale features, while landing sites are selected based on m to km-scale features. It is therefore critical to understand spatial distribution of organic molecules over scales from cm to the km, particularly in geological features that appear homogenous at m to km scales. This is addressed by FELDSPAR, a NASA-funded project that conducts field operations analogous to Mars sample return in its science, operations, and technology [1]. Here, we present recent findings from a 2016 and a 2017 campaign to multiple Martian analogue sites in Iceland. Icelandic volcanic regions are Mars analogues due to desiccation, low nutrient availability, temperature extremes [2], and are relatively young and isolated from anthropogenic contamination [3]. Operationally, many Icelandic analogue sites are remote enough to require that field expeditions address several sampling constraints that are also faced by robotic exploration [1, 2]. Four field sites were evaluated in this study. The Fimmvörðuháls lava field was formed by a basaltic effusive eruption associated with the 2010 Eyjafjallajökull eruption. Mælifellssandur is a recently deglaciated plain to the north of the Myrdalsjökull glacier. Holuhraun is a basaltic spatter and cinder cone formed by 2014 fissure eruptions just north of the Vatnajökull glacier. Dyngjusandur is a plain kept barren by repeated aeolian mechanical weathering. Samples were collected in nested triangular grids from 10 cm to the 1 km scale. We obtained overhead imagery at 1 m to 200 m elevation to create digital elevation models. In-field reflectance spectroscopy was obtained with an ASD spectrometer and chemical composition was measured by a Bruker handheld XRF. All sites chosen were homogeneous in apparent color, morphology, moisture, grain size, and reflectance spectra at all scales greater than 10 cm. Field lab ATP assays were conducted to monitor microbial habitation, and home

  6. Tibetan tectonics from 40Ar/39Ar analysis of a single K-feldspar sample

    Richter, F.M.; Lovera, O.M.; Harrison, T.M.; Copeland, P.

    1991-01-01

    40 Ar/ 39 Ar data on an alkali feldspar sample from the Quxu pluton, Gangdese batholith, southern Tibet, allow a detailed assessment of unroofing and uplift history between 35 and 18 Ma. The 39 Ar Arrhenius plot for this sample shows departures from a linear relationship between the effective diffusion parameter, log(D/r 2 ), and reciprocal temperature, which we interpret to be the result of a distribution of distinct diffusion-domain sizes. We use an alternative way of plotting the Arrhenius data that exhibits domain size versus cumulative % 39 Ar released during step heating. The 40 Ar/ 39 Ar age spectrum of the sample has features, such as local age plateaus, that are most easily explained in terms of the distinctive closure age of particular domains. The fact that the same distribution of diffusion-domain sizes explains both the Arrhenius data and the age spectrum is an indication that the diffusion properties operating in the laboratory are those of the sample while it was in its natural environment. Modelling of the age spectrum with a distribution of domain sizes results in the recovery of a continuous cooling-history segment rather than a single time-temperature datum. We demonstrate the robustness of the cooling-curve determination by showing the large misfits to the age spectrum that arise from relatively small changes in the cooling history. The best-fit cooling curve for the Quxu sample shows a decreasing rate of cooling in the time interval 35-18 Ma, followed by a very rapid cooling beginning at about 18 Ma. We have used a thermal model for the conductive cooling of an unroofing pluton to estimate the rate of unroofing required to explain the Quxu cooling curve, and find that in the 35-20 Ma time interval, the primary control of the thermal evolution is the conductive loss of magmatic heat with little or no unroofing (unroofing rates of approximately 0.05 mm/yr) followed by a brief period (<5 Ma) of very rapid unroofing with rates of order 2 mm

  7. Deformation-Induced Dissolution and Precipitation of Nitrides in Austenite and Ferrite of a High-Nitrogen Stainless Steel

    Shabashov, V. A.; Makarov, A. V.; Kozlov, K. A.; Sagaradze, V. V.; Zamatovskii, A. E.; Volkova, E. G.; Luchko, S. N.

    2018-02-01

    Methods of Mössbauer spectroscopy and electron microscopy have been used to study the effect of the severe plastic deformation by high pressure torsion in Bridgman anvils on the dissolution and precipitation of chromium nitrides in the austenitic and ferritic structure of an Fe71.2Cr22.7Mn1.3N4.8 high-nitrogen steel. It has been found that an alternative process of dynamic aging with the formation of secondary nitrides affects the kinetics of the dissolution of chromium nitrides. The dynamic aging of ferrite is activated with an increase in the deformation temperature from 80 to 573 K.

  8. The dissolution behavior of borosilicate glasses in far-from equilibrium conditions

    Neeway, James J.; Rieke, Peter C.; Parruzot, Benjamin P.; Ryan, Joseph V.; Asmussen, R. Matthew

    2018-04-01

    An area of agreement in the waste glass corrosion community is that, at far-from-equilibrium conditions, the dissolution of borosilicate glasses used to immobilize nuclear waste is known to be a function of both temperature and pH. The aim of this work is to study the effects of temperature and pH on the dissolution rate of three model nuclear waste glasses (SON68, ISG, AFCI). The dissolution rate data are then used to parameterize a kinetic rate model based on Transition State Theory that has been developed to model glass corrosion behavior in dilute conditions. To do this, experiments were conducted at temperatures of 23, 40, 70, and 90 °C and pH (22 °C) values of 9, 10, 11, and 12 with the single-pass flow-through (SPFT) test method. Both the absolute dissolution rates and the rate model parameters are compared with previous results. Rate model parameters for the three glasses studied here are nearly equivalent within error and in relative agreement with previous studies though quantifiable differences exist. The glass dissolution rates were analyzed with a linear multivariate regression (LMR) and a nonlinear multivariate regression performed with the use of the Glass Corrosion Modeling Tool (GCMT), with which a robust uncertainty analysis is performed. This robust analysis highlights the high degree of correlation of various parameters in the kinetic rate model. As more data are obtained on borosilicate glasses with varying compositions, a mathematical description of the effect of glass composition on the rate parameter values should be possible. This would allow for the possibility of calculating the forward dissolution rate of glass based solely on composition. In addition, the method of determination of parameter uncertainty and correlation provides a framework for other rate models that describe the dissolution rates of other amorphous and crystalline materials in a wide range of chemical conditions. The higher level of uncertainty analysis would provide

  9. Kinetic Interface

    2009-01-01

    A kinetic interface for orientation detection in a video training system is disclosed. The interface includes a balance platform instrumented with inertial motion sensors. The interface engages a participant's sense of balance in training exercises.......A kinetic interface for orientation detection in a video training system is disclosed. The interface includes a balance platform instrumented with inertial motion sensors. The interface engages a participant's sense of balance in training exercises....

  10. Deformation of quartz and feldspar at mid-crustal depths in an extensional normal fault (Viveiro Fault, NW Spain)

    López-Sánchez, M. A.; Llana-Fúnez, S.; Marcos, A.; Martínez, F. J.

    2012-04-01

    Metamorphic reactions, deformation mechanism and chemical changes during mylonitization and ultramylonitization of granite affected by a crustal-scale shear zone are investigated using microstructural observations and quantitative analysis. The Vivero Fault (VF) is a large extensional shear zone (>140Km) in NW of Iberia that follows the main Variscan trend dipping 60° toward the West. The movement accumulated during its tectonic history affects the major lithostratigraphic sequence of Palaeozoic and Neoproterozoic rocks and the metamorphic facies developed during Variscan orogenesis. Staurolite, and locally, andalucite plus biotite grew in the hangingwall during the development of VF, overprinted the previous regional Variscan greenschist facies metamorphism. Andalusite growth took place during the intrusion of syntectonic granitic bodies, such as the deformed granite studied here. The Penedo Gordo granite is coarse-grained two-mica biotite-rich granite intruding the VF and its hangingwall. This granite developed a localized deformation consisting of a set of narrow zones (mm to metric scales) heterogeneously distributed subsequently to its intrusion. Based on pseudosections for representative hangingwall pelites hosting the granite and the inferred metamorphic evolution, the shear zone that outcrops at present-day erosion surface was previously active at 14,7-17 km depth (390-450 MPa). Temperature estimates during deformation reach at least the range 500-600° C, implying a local gradient of 35±6°C/km. Microstructures in the mylonites are characterized by bulging (BLG) to subgrain rotation (SGR) recristallization in quartz with the increasing of deformation. Albitisation, flame-perthite and tartan twining are common in K-feldspar at the early stage of deformation. The inferred dominant deformation mechanisms are: i) intracrystalline plasticity in quartz, ii) cataclasis with syntectonic crystallisation of very fine albite-oligoclase and micas in K-feldspar, and

  11. Influence of pH and temperature on alunite dissolution rates and products

    Acero, Patricia; Hudson-Edwards, Karen

    2015-04-01

    , leading to dissolved Al/K ratios between 0.5 and 2.5. This depletion of Al in the solution is especially clear for the experiments at pH 4.5-4.8 and 8 and it is consistent with the results of elemental quantifications of the same proportions in the reacted alunite surfaces using X-ray Photoelectron Spectroscopy (XPS). REFERENCES Flaten, T.P. (2001): Aluminium as a risk factor in Alzheimzer's disease, with emphasis on drinking water. Brain Research Bulletin 55: 187-196. Nordstrom, D.K. (2011): Hydrogeochemical processes governing the origin, transport and fate of major and trace elements from mine wastes and mineralized rock to surface waters. Applied Geochemistry 26: 1777-1791. Prietzel, J., & Hirsch, C. (1998). Extractability and dissolution kinetics of pure and soil-added synthesized aluminium hydroxy sulphate minerals. European journal of soil science, 49(4), 669-681. Swayze, G.A., Ehlmann, B.L., Milliken, R.E., Poulet, F., Wray, J.J., Rye, R.O., Clark, R.N., Desborough, G.A., Crowley, J.K., Gondet, B., Mustard, J.F., Seelos, K.D. and Murchie, S.L., 2008. Discovery of the Acid-Sulfate Mineral Alunite in Terra Sirenum, Mars, Using MRO CRISM: Possible Evidence for Acid-Saline Lacustrine Deposits?, American Geophysical Union, Fall Meeting 2008, abstract #P44A-04. Welch, S. A., Kirste, D., Christy, A. G., Beavis, F. R., & Beavis, S. G. (2008): Jarosite dissolution II'Reaction kinetics, stoichiometry and acid flux. Chemical Geology, 254(1), 73-86.

  12. Mechanism of the transpassive dissolution and secondary passivation of chromium in sulphuric acid solutions

    Bojinov, M.; Betova, I.; Raicheff, R.; Fabricius, G.; Laitinen, T.; Saario, T.

    1998-01-01

    The transpassive dissolution and secondary passivation of Cr in 1..10 M H 2 SO 4 solutions were studied by a combination of different electrochemical methods. The steady-state polarization curves for transpassive dissolution exhibited a Tafel behaviour with a slope being independent on the acid concentration. Lower dissolution rates were measured for higher acid concentrations. Ring-disk measurements showed a release of both soluble Cr(VI) and Cr(III) during transpassivity. Impedance spectra were qualititatively similar in all acid concentrations, comprising one capacitive and two inductive semicircles. A kinetic model comprising two parallel transpassive dissolution paths was consistent with the experimental results. Typical passivation diagrams were observed for Cr in 10 M H 2 SO 4 , and a secondary passive state was established at higher potentials. The formation of the secondary passive film was confirmed by contact electric resistance (CER) measurements. A renewed version of the surface charge approach was consistent with the experimental results in the region of the secondary passivation. (orig.)

  13. Electrochemical and dissolution studies on coated film and magnetite pellet in PDCA and NTA based formulations

    Srinivasan, M.P.; Sumathi, S.; Rangarajan, S.; Narasimhan, S.V.

    2000-01-01

    In water cooled nuclear reactors magnetite often exists as both mobile particulate protective film on the inner surface of the PHT system. To determine the mechanism and kinetics of dissolution from a film coated on carbon steel (CS) and magnetite pellet electrochemical measurements were carried out in 2,6-pyridine dicarboxylic acid (PDCA) and nitrilo-triacetic acid (NTA) based formulations containing ascorbic acid (AA) and citric acid (CA) at 28 degC and 60 degC. The solution redox potential arises based on the release of relative amounts of Fe 2+ and Fe 3+ . Complexation, adsorption and reduction affect the concentration of these species in solutions. On coated specimen, the pore size and rate of formation via auto reduction contribute to the observed potential. In PDCA based formulation higher percentage of magnetite dissolution with lower base metal corrosion was observed as compared to that in NTA based formulation. The base metal aided dissolution due to the pores and microcracks in the film (Auto reduction) was observed for coated film. The dominant role of surface adsorption characteristics of PDCA, AA and CA were evident in magnetite pellet dissolution studies. (author)

  14. Development and validation of a dissolution test for lodenafil carbonate based on in vivo data.

    Codevilla, Cristiane Franco; Castilhos, Tamara dos Santos; Cirne, Carolina Araújo; Froehlich, Pedro Eduardo; Bergold, Ana Maria

    2014-04-01

    Lodenafil carbonate is a phosphodiesterase type 5 inhibitor used for the treatment of erectile dysfunction. Currently, there is no dissolution test reported for lodenafil carbonate and this drug is not listed in any pharmacopoeia. The present study focused on the development and validation of a dissolution test for lodenafil carbonate tablets, using a simulated absorption profile based on in vivo data. The appropriate conditions were determined after testing sink conditions. Different conditions as medium, surfactant concentration and rotation speed were evaluated. The percentage of dose absorbed was calculated by deconvolution, using the Wagner-Nelson method. According to the obtained results, the use of 0.1 M HCl + 1.5% SLS (900 mL, at 37 + 0.5 °C) as the dissolution medium, paddles at 25 rpm were considered adequate. The samples were quantified by UV spectroscopy at 295 nm and the validation was performed according to international guidelines. The method showed specificity, linearity, accuracy and precision, within the acceptable range. Kinetics of drug release was better described by the first-order model. The proposed dissolution test can be used for the routine quality control of lodenafil carbonate in tablets.

  15. Filling material for a buried cavity in a collapse area using light-weighted foam and active feldspar

    Cho, Jin Woo; Lee, Ju-hyoung; Kim, Sung-Wook; Choi, Eun-Kyeong

    2017-04-01

    Concrete which is generally used as filling material for a buried cavity has very high strength but significantly high self-load is considered its disadvantage. If it is used as filling material, the second collapse due to additional load, causing irreversible damage. If light-weighted foam and active feldspar are used to solve this problem, the second collapse can be prevented by reducing of self-load of filling material. In this study, the specimen was produced by mixing light-weighted foam, active feldspar and cement, and changes in the density, unconfined compressive strength and hydraulic conductivity were analyzed. Using the light-weighted foam could enable the adjustment of density of specimen between 0.5 g/cm3 and 1.7 g/cm3, and if the mixing ratio of the light-weighted foam increases, the specimen has more pores and smaller range of cross-sectional area. It is confirmed that it has direct correlation with the density, and if the specimen has more pores, the density of the specimen is lowered. The density of the specimen influences the unconfined compressive strength and the hydraulic conductivity, and it was also confirmed that the unconfined compressive strength could be adjusted between 0.6 MPa and 8 MPa and the hydraulic conductivity could be adjusted between 10-9cm/sec and 10-3cm/sec. These results indicated that we can adjust unconfined compressive strength and hydraulic conductivity of filling materials by changing the mixing amount of lightweight-weighted foam according to the requirements of the field condition. Keywords: filling material, buried cavity, light-weighted foam, feldspar Acknowledgement This research was supported by a Grant from a Strategic Research Project (Horizontal Drilling and Stabilization Technologies for Urban Search and Rescue (US&R) Operation) funded by the Korea Institute of Civil Engineering and Building Technology.

  16. Physicochemical characterization and dissolution properties of ...

    calorimetry (DSC), powder x-ray diffractometry (PXRD) and Fourier transform infrared (FT-IR) spectroscopy. Phase solubility studies revealed an AL-type diagram indicating a 1:1 stoichiometric inclusion complex and a stability constant value of 914 M-1. Solubility and dissolution rates of PYR and the binary systems were ...

  17. Dissolution enhancement of Tibolone by micronization technique

    Kailash Bansal

    2012-01-01

    Conclusion: Micronization technique has a significant impact on the dissolution of Tibolone. The experimental findings suggest that micronization can be used for the preparation of rapidly dissolving formulations of Tibolone, and could potentially lead to improvement in the in-vivo bioavailability of Tibolone oral tablets.

  18. Sodium tetraphenylborate solubility and dissolution rates

    Barnes, M.J.; Peterson, R.A.; Swingle, R.F.; Reeves, C.T.

    1995-01-01

    The rate of solid sodium tetraphenylborate (NaTPB) dissolution in In-Tank Precipitation salt solutions has been experimentally determined. The data indicates that the dissolution rate of solid NaTPB is a minor contributor the lag time experienced in the 1983 Salt Decontamination Demonstration Test and should not be considered as the rate determining step. Current analytical models for predicting the time to reach the composite lower flammability limit assume that the lag time is not more than 6 hours, and the data supports this assumption (i.e., dissolution by itself requires much less than 6 hours). The data suggests that another step--such as mass transport, the reaction of a benzene precursor or the mixing behavior--is the rate determining factor for benzene release to the vapor space in Tank 48H. In addition, preliminary results from this program show that the degree of agitation employed is not a significant parameter in determining the rate of NaTPB dissolution. As a result of this study, an improved equation for predicting equilibrium tetraphenylborate solubility with respect to temperature and sodium ion concentration has been determined

  19. Efavirenz Dissolution Enhancement I: Co-Micronization

    Helvécio Vinícius Antunes Rocha

    2012-12-01

    Full Text Available AIDS constitutes one of the most serious infectious diseases, representing a major public health priority. Efavirenz (EFV, one of the most widely used drugs for this pathology, belongs to the Class II of the Biopharmaceutics Classification System for drugs with very poor water solubility. To improve EFV’s dissolution profile, changes can be made to the physical properties of the drug that do not lead to any accompanying molecular modifications. Therefore, the study objective was to develop and characterize systems with efavirenz able to improve its dissolution, which were co-processed with sodium lauryl sulfate (SLS and polyvinylpyrrolidone (PVP. The technique used was co-micronization. Three different drug:excipient ratios were tested for each of the two carriers. The drug dispersion dissolution results showed significant improvement for all the co-processed samples in comparison to non-processed material and corresponding physical mixtures. The dissolution profiles obtained for dispersion with co-micronized SLS samples proved superior to those of co-micronized PVP, with the proportion (1:0.25 proving the optimal mixture. The improvements may be explained by the hypothesis that formation of a hydrophilic layer on the surface of the micronized drug increases the wettability of the system formed, corroborated by characterization results indicating no loss of crystallinity and an absence of interaction at the molecular level.

  20. Modeling of Dissolution Effects on Waterflooding

    Alexeev, Artem; Shapiro, Alexander; Thomsen, Kaj

    2015-01-01

    reaction rates) may exhibit rapid increase of porosity and permeability near the inlet probably indicating a formation of high permeable channels (wormholes). Water saturation in the zone of dissolution increases due to an increase in the bulk volume accessible for the injected fluid. Volumetric non...

  1. 25 CFR 11.605 - Dissolution.

    2010-04-01

    ... Domestic Relations § 11.605 Dissolution. (a) The Court of Indian Offenses shall enter a decree of... supported by evidence that (i) the parties have lived separate and apart for a period of more than 180 days..., or provided for child custody, the support of any child entitled to support, the maintenance of...

  2. Dilution physics modeling: Dissolution/precipitation chemistry

    Onishi, Y.; Reid, H.C.; Trent, D.S.

    1995-09-01

    This report documents progress made to date on integrating dilution/precipitation chemistry and new physical models into the TEMPEST thermal-hydraulics computer code. Implementation of dissolution/precipitation chemistry models is necessary for predicting nonhomogeneous, time-dependent, physical/chemical behavior of tank wastes with and without a variety of possible engineered remediation and mitigation activities. Such behavior includes chemical reactions, gas retention, solids resuspension, solids dissolution and generation, solids settling/rising, and convective motion of physical and chemical species. Thus this model development is important from the standpoint of predicting the consequences of various engineered activities, such as mitigation by dilution, retrieval, or pretreatment, that can affect safe operations. The integration of a dissolution/precipitation chemistry module allows the various phase species concentrations to enter into the physical calculations that affect the TEMPEST hydrodynamic flow calculations. The yield strength model of non-Newtonian sludge correlates yield to a power function of solids concentration. Likewise, shear stress is concentration-dependent, and the dissolution/precipitation chemistry calculations develop the species concentration evolution that produces fluid flow resistance changes. Dilution of waste with pure water, molar concentrations of sodium hydroxide, and other chemical streams can be analyzed for the reactive species changes and hydrodynamic flow characteristics

  3. Physicochemical characterization and dissolution properties of ...

    STORAGESEVER

    2009-04-20

    Apr 20, 2009 ... 1Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Obafemi Awolowo University, Ile-Ife, Nigeria. .... were carefully and homogenously blended in a mortar, to prepare ... different binary systems with HP-β-CD were carried out by adding an excess ..... Overall, the rank order of dissolution rates of.

  4. Toward a consistent model for glass dissolution

    Strachan, D.M.; McGrail, B.P.; Bourcier, W.L.

    1994-01-01

    Understanding the process of glass dissolution in aqueous media has advanced significantly over the last 10 years through the efforts of many scientists around the world. Mathematical models describing the glass dissolution process have also advanced from simple empirical functions to structured models based on fundamental principles of physics, chemistry, and thermodynamics. Although borosilicate glass has been selected as the waste form for disposal of high-level wastes in at least 5 countries, there is no international consensus on the fundamental methodology for modeling glass dissolution that could be used in assessing the long term performance of waste glasses in a geologic repository setting. Each repository program is developing their own model and supporting experimental data. In this paper, we critically evaluate a selected set of these structured models and show that a consistent methodology for modeling glass dissolution processes is available. We also propose a strategy for a future coordinated effort to obtain the model input parameters that are needed for long-term performance assessments of glass in a geologic repository. (author) 4 figs., tabs., 75 refs

  5. Oxidative dissolution of ruthenium deposits onto stainless steel by permanganate ions in alkaline medium

    Floquet, S.; Eysseric, C.; Maurel, D. [Commissariat a l' Energie Atomique (CEA/Valrho), Bagnols-sur-Ceze (France)

    2008-07-01

    During spent nuclear fuel reprocessing ruthenium is liable to form black ruthenium deposits on the stainless steel walls of process equipments. These deposits promote corrosion and can eventually obstruct the off-gas lines. The results of decontamination of 304L stainless steel test specimens covered with RuO(OH){sub 2} . xH{sub 2}O deposits by permanganate ions in alkaline medium are described. The ruthenium deposits were dissolved by oxidation of RuO(OH){sub 2} to RuO{sub 4}{sup 2-} ions, while the permanganate ions were reduced to MnO{sub 4}{sup 2-} ions and then to manganese dioxide MnO{sub 2}. The parameters affecting the kinetics of oxidative dissolution of these deposits were examined. The results indicate that the oxidative dissolution kinetics depends on the instantaneous surface area of the deposit, and that the dissolution rate increases with the concentrations of MnO{sub 4}{sup -} and OH{sup -} ions. (orig.)

  6. Combining infrared- and green-laser stimulation sources in single-grain luminescence measurements of feldspar and quartz

    Duller, G.A.T.; Bøtter-Jensen, L.; Murray, A.S.

    2003-01-01

    A system designed for measurement of the optically stimulated luminescence (OSL) from individual sand-sized mineral grains has been constructed. Previously, this system was equipped only with a green laser emitting at 532 run, but now an infrared (IR) laser at 830 run has been added. It is now...... possible to interchangeably use the two laser sources for optical stimulation. This is especially valuable for the measurement of feldspars. The power density using the IR laser at the grain is similar to500 W cm(-2), and stimulation for 1 s reduces the OSL signal to near background level. Initial results...

  7. Increase in Ice Nucleation Efficiency of Feldspars, Kaolinite and Mica in Dilute NH3 and NH4+-containing Solutions

    Kumar, A.; Marcolli, C.; Luo, B.; Krieger, U. K.; Peter, T.

    2017-12-01

    Semivolatile species present in the atmosphere are prone to adhere to mineral dust particle surfaces during long range transport, and could potentially change the particle surface properties and its ice nucleation (IN) efficiency. Immersion freezing experiments were performed with microcline (K-feldspar), known to be highly IN active, suspended in aqueous solutions of ammonia, (NH4)2SO4, NH4HSO4, NH4NO3, NH4Cl, Na2SO4, H2SO4, K2SO4 and KCl to investigate the effect of solutes on the IN efficiency. Freezing of emulsified droplets investigated with a differential scanning calorimeter (DSC) showed that the heterogeneous ice nucleation temperatures deviate from the water activity-based IN theory, describing heterogeneous ice nucleation temperatures as a function of solution water activity by a constant offset with respect to the ice melting point curve (Zobrist et al. 2008). IN temperatures enhanced up to 4.5 K were observed for very dilute NH3 and NH4+-containing solutions while a decrease was observed as the concentration was further increased. For all solutes with cations other than NH4+, the IN efficiency decreased. An increase of the IN efficiency in very dilute NH3 and NH4+-containing solutions followed by a decrease with increasing concentration was also observed for sanidine (K-feldspar) and andesine (Na/Ca-feldspar). This is an important indication towards specific chemical interactions between solutes and the feldspar surface which is not captured by the water activity-based IN theory. A similar trend is present but less pronounced in case of kaolinite and mica, while quartz is barely affected. We hypothesize that the hydrogen bonding of NH3 molecules with surface -OH groups could be the reason for the enhanced freezing temperatures in dilute ammonia and ammonium containing solutions as they could form an ice-like overlayer providing hydrogen bonding groups for ice to nucleate on top of it. This implies to possibilities of enhanced IN efficiency, especially

  8. Investigations of the post-IR IRSL protocol applied to single K-feldspar grains from fluvial sediment samples

    Nian, Xiaomei; Bailey, Richard M.; Zhou, Liping

    2012-01-01

    The post-IR IRSL protocol with single K-feldspar grains was applied to three samples taken from a fluvial sedimentary sequence at the archaeological site of the Dali Man, Shaanxi Province, China. K-feldspar coarse grains were extracted for measurement. Approximately 30–40% of the grains were sufficiently bright to measure, and after application of rejection criteria based on signal strength, recuperation, recycling ratio and saturation dose, ∼10–15% of the grains were used for D e calculation. The relationship of signal decay rate and form of D e (t) with the recovery dose were investigated. The dose recovery ratios of the samples after initial bleaching with the four different light sources were within uncertainties of unity. No anomalous fading was observed. The over-dispersion of the recovered dose and D e values were similar, suggesting neither incomplete resetting of the post-IR IRSL signals nor spatially heterogeneous dose rates significantly affected the natural dose estimates. The values of D e obtained with the single K-feldspar grain post-IR IRSL protocol were in the range ∼400–490 Gy. Combining all of the measured single-grain signals for each of the individual samples (into a ‘synthetic single aliquot’) increased the D e estimates to the range ∼700–900 Gy, suggesting that the grains screened-out by the rejection criteria may have the potential to cause palaeodose over-estimation, although this finding requires a more extensive investigation. Thermally transferred signals were found in the single K-feldspar grains post-IR IRSL protocol, and the proportion of thermally transferred signal to test-dose OSL signal (stimulation at 290 °C) from the natural dose was higher than from regenerative doses, and the proportion was grain- and dose-dependent. As such, TT-post-IR IRSL signals at 290 °C have the potential to cause dose underestimation, although this may be reduced by using larger test-dose irradiations. Our study demonstrates

  9. Reductive Dissolution of Goethite and Hematite by Reduced Flavins

    Shi, Zhi; Zachara, John M.; Wang, Zheming; Shi, Liang; Fredrickson, Jim K.

    2013-10-02

    The abiotic reductive dissolution of goethite and hematite by the reduced forms of flavin mononucleotide (FMNH2) and riboflavin (RBFH2), electron transfer mediators (ETM) secreted by the dissimilatory iron-reducing bacterium Shewanella, was investigated under stringent anaerobic conditions. In contrast to the rapid redox reaction rate observed for ferrihydrite and lepidocrocite (Shi et al., 2012), the reductive dissolution of crystalline goethite and hematite was slower, with the extent of reaction limited by the thermodynamic driving force at circumneutral pH. Both the initial reaction rate and reaction extent increased with decreasing pH. On a unit surface area basis, goethite was less reactive than hematite between pH 4.0 and 7.0. AH2DS, the reduced form of the well-studied synthetic ETM anthraquinone-2,6-disulfonate (AQDS), yielded higher rates than FMNH2 under most reaction conditions, despite the fact that FMNH2 was a more effective reductant than AH2DS for ferryhydrite and lepidocrocite. Two additional model compounds, methyl viologen and benzyl viologen, were investigated under similar reaction conditions to explore the relationship between reaction rate and thermodynamic properties. Relevant kinetic data from the literature were also included in the analysis to span a broad range of half-cell potentials. Other conditions being equal, the surface area normalized initial reaction rate (ra) increased as the redox potential of the reductant became more negative. A non-linear, parabolic relationship was observed between log ra and the redox potential for eight reducants at pH 7.0, as predicted by Marcus theory for electron transfer. When pH and reductant concentration were fixed, log ra was positively correlated to the redox potential of four Fe(III) oxides over a wide pH range, following a non-linear parabolic relationship as well.

  10. Solutal convection induced by dissolution. Influence on erosion dynamics and interface shaping.

    Berhanu, Michael; Philippi, Julien; Cohen, Caroline; Derr, Julien; Courrech du Pont, Sylvain

    2017-04-01

    Rock fractures invaded by a water flow, are often subjected to dissolution, which let grow and evolve the initial fracture network, by evacuating the eroded minerals under a solute form. In the case of fast kinetic of dissolution, local erosion rate is set by the advection of the solute. The erosion velocity decreases indeed with the solute concentration at the interface and vanishes when this concentration reaches the saturation value. Even in absence of an imposed or external flow, advection can drive the dissolution, when buoyancy effects due to gravity induce a solutal convection flow, which controls the erosive dynamics and modifies the shape of the dissolving interface. Here, we investigate using model experiments with fast dissolving materials and numerical simulations in simplified situations, solutal convection induced by dissolution. Results are interpreted regarding a linear stability analysis of the corresponding solutal Rayleigh-Benard instability. A dissolving surface is suspended above a water height, initially at rest. In a first step, solute flux is transported through a growing diffusion layer. Then after an onset time, once the layer exceeds critical width, convection flow starts under the form of falling plumes. A dynamic equilibrium results in average from births and deaths of intermittent plumes, setting the size of the solute concentration boundary layer at the interface and thus the erosion velocity. Solutal convection can also induce a pattern on the dissolving interface. We show experimentally with suspended and inclined blocks of salt and sugar, that in a linear stage, the first wavelength of the dissolution pattern corresponds to the wavelength of the convection instability. Then pattern evolves to more complex shapes due to non-linear interactions between the flow and the eroded interface. More generally, we inquire what are the conditions to observe a such solutal convection instability in geological situations and if the properties of

  11. Dissolution of two NWCF calcines: Extent of dissolution and characterization of undissolved solids

    Brewer, K.N.; Herbst, R.S.; Tranter, T.J.

    1995-01-01

    A study was undertaken to determine the dissolution characteristics of two NWCF calcine types. A two-way blended calcine made from 4 parts nonradioactive aluminum nitrate and one part WM-102 was studied to determine the extent of dissolution for aluminum-type calcines. A two-way blend of 3.5 parts fluorinel waste from WM-187 and 1 part sodium waste from WM-185 was used to determine the extent of dissolution for zirconium-type calcines. This study was necessary to develop suitable aqueous separation flowsheets for the partitioning of actinides and fission products from ICPP calcines and to determine the disposition of the resulting undissolved solids (UDS). The dissolution flowsheet developed by Herbst was used to dissolve these two NWCF calcine types. Results show that greater than 95 wt% of aluminum and zirconium calcine types were dissolved after a single batch contact with 5 M HNO 3 . A characterization of the UDS indicates that the weight percent of TRU elements in the UDS resulting from both calcine type dissolutions increases by approximately an order of magnitude from their concentrations prior to dissolution. Substantial activities of cesium and strontium are also present in the UDS resulting from the dissolution of both calcine types. Multiple TRU, Cs, and Sr analyses of both UDS types show that these solids are relatively homogeneous. From this study, it is estimated that between 63.5 and 635 cubic meters of UDS will be generated from the dissolution of 3800 M 3 of calcine. The significant actinide and fission product activities in these UDS will preclude their disposal as low-level waste. If the actinide and fission activity resulting from the UDS is the only considered source in the dissolved calcine solutions, an estimated 99.9 to 99.99 percent of the solids must be removed from this solution for it to meet non-TRU Class A low-level waste

  12. In vitro Dissolution Studies on Solid Dispersions of Mefenamic Acid.

    Rao, K R S Sambasiva; Nagabhushanam, M V; Chowdary, K P R

    2011-03-01

    Solid dispersions of mefanamic acid with a water-soluble polymer polyvinyl pyrrolidine and a super disintegrant, primojel were prepared by common solvent and solvent evaporation methods employing methanol as the solvent. The dissolution rate and dissolution efficiency of the prepared solid dispersions were evaluated in comparison to the corresponding pure drug. Solid dispersions of mefenamic acid showed a marked enhancement in dissolution rate and dissolution efficiency. At 1:4 ratio of mefenamic acid-primojel a 2.61 fold increase in the dissolution rate of mefenamic acid was observed with solid dispersion. The solid dispersions in combined carriers gave much higher rates of dissolution than super disintegrants alone. Mefanamic acid-primojel-polyvinyl pyrrolidine (1:3.2:0.8) solid dispersion gave a 4.11 fold increase in the dissolution rate of mefenamic acid. Super disintegrants alone or in combination with polyvinyl pyrrolidine could be used to enhance the dissolution rate of mefenamic acid.

  13. Subdiffusion kinetics of nanoprecipitate growth and destruction in solid solutions

    Sibatov, R. T.; Svetukhin, V. V.

    2015-06-01

    Based on fractional differential generalizations of the Ham and Aaron-Kotler precipitation models, we study the kinetics of subdiffusion-limited growth and dissolution of new-phase precipitates. We obtain the time dependence of the number of impurities and dimensions of new-phase precipitates. The solutions agree with the Monte Carlo simulation results.

  14. High temperature dissolution of ferrites, chromites and bonaccordite in chelating media

    Sathyaseelan, V.S.; Subramanian, H.; Anupkumar, B.; Rufus, A.L.; Velmurugan, S.; Narasimhan, S.V., E-mail: snv@igcar.gov.in [BARC Facilities, Water and Steam Chemistry Div., Tamilnadu (India)

    2010-07-01

    Different methods have been employed world wide for the decontamination of reactor coolant system surfaces. The success of a decontamination process mainly depends on the oxide dissolution efficiency of the decontamination formulation. Among the oxides, Fe{sub 3}O{sub 4} undergoes easy dissolution in organic acid media at normal temperatures. However, dissolution of chromites and mixed ferrites is not that easy in organic chelant media at normal temperatures even in the presence of redox reagents. Hence, a high temperature process was attempted for the dissolution of ferrites and chromites. A re-circulation system consisting of an autoclave, pump, heat exchanger etc. all lined with teflon was used for carrying out high temperature dissolution experiments. This study describes the high temperature dissolution kinetics of Fe{sub 3}O{sub 4}, NiFe{sub 2}O{sub 4}, and Cr{sub 2}O{sub 3}. Nitrilotriacetic acid (NTA), a well known solvent for metal oxides, was applied at temperatures ranging from 80 to 180{sup o}C. About six fold increase in dissolution rate was observed for Fe{sub 3}O{sub 4} in this temperature range. Effect of N{sub 2}H{sub 4} on oxide dissolution was studied. Lower dissolution rates were observed for Fe{sub 3}O{sub 4} and NiFe{sub 2}O{sub 4} in the presence of hydrazine. Oxide dissolution efficiency of other chelating agents like EDTA, PDCA etc. and the effect of reducing agents like oxalic acid and ascorbic acid on high temperature dissolution also has been studied. The effect of incorporation of boron and zinc in the iron and chromium oxides has also been studied. Bonaccordite (Ni{sub 2}FeBO{sub 5}) has been observed in the fuel deposits of pressurized Water Reactors especially in the AOA affected plants. Zinc ferrite/chromite are formed in reactors adopting zinc injection passivation technique to control radiation field. Bonaccordite and zinc ferrite/chromite formed over the reactor coolant system structural materials are also difficult to dissolve

  15. Self irradiation effects on the thorium phosphate diphosphate dissolution (TPD): simulation by external irradiations

    Tamain, C.; Ozgumus, A.; Dacheux, N.; Garrido, F.; Thome, L.; Corbel, C.; Genet, M.

    2004-01-01

    The Thorium Phosphate Diphosphate (TPD), proposed as a ceramic for the long term immobilization of actinides, was externally irradiated with several ions and energies (but also with gamma rays) in order to simulate the self-irradiation. The influence of the electronic energy loss was first investigated. Thus, the XRD measurements have shown a complete amorphization of the material under 10 13 ions of Kr.cm -2 , while no significant structural change occurred after 5.10 13 S.cm -2 , 2.10 16 He.cm -2 or 320 kGy of dose of gamma rays. The dissolution of the raw and irradiated pellets was studied versus several parameters such as amorphized fraction, energy loss of incident ions, radiolytic species produced in situ in the leachate during irradiation (such as H 2 O 2 ), temperature and acidity. The results reveal an important increase of the dissolution kinetics for amorphized pellets compared to raw ceramic. (authors)

  16. Interaction Between Second-Phase Particle Dissolution and Abnormal Grain Growth in an Austenitic Stainless Steel

    Dutra J.C.

    2002-01-01

    Full Text Available The continuing development of stainless steels has resulted in complex steel compositions with substantial amounts of alloying elements. The benefits of such additions invariably come attached to unavoidable disadvantages. One of the most critical item is the potential microstructural instability of the material. Alloying elements may be in a supersaturated solid solution, in which the precipitation of carbides, nitrides, borides and intermetallic phases occurs in a wide range of temperatures. In order to dissolve the mentioned precipitates, solution annealing is commonly performed. However, at the temperature range in which this treatment is carried out, the onset of abnormal grain growth can occur. The interaction between the dissolution of these second-phase particles and the occurrence of abnormal grain growth is investigated in this work. This study also shows that the thermodynamics and the kinetics of dissolution of precipitates may be used to predict whether abnormal grain growth takes place.

  17. Dissolution testing of intermediary products in uranium dioxide production by the sol-gel method

    Melichar, F.; Landspersky, H.; Urbanek, V.

    1979-01-01

    A method was developed of dissolving polyuranates and uranium dioxides in sulphuric acid and in carbonate solutions for testing intermediate products in the sol-gel process preparation of uranium dioxide. A detailed granulometric analysis of spherical particle dispersion was included as part of the tests. Two different production methods were used for the two types of studied materials. The test results show that the test method is suitable for determining temperature sensitivity of the materials to dissolution reaction. The geometrical distribution of impurities in the spherical particles can be determined from the dissolution kinetics. The method allows the determination of the effect of carbon from impurities on the process of uranium dioxide leaching and is thus applicable for testing materials prepared by the sol-gel method. (Z.M.)

  18. Studies of dissolution solutions of ruthenium metal, oxide and mixed compounds in nitric acid

    Mousset, F.; Eysseric, C.; Bedioui, F.

    2004-01-01

    Ruthenium is one of the fission products generated by irradiated nuclear fuel. It is present throughout all the steps of nuclear fuel reprocessing-particularly during extraction-and requires special attention due to its complex chemistry and high βγ activity. An innovative electro-volatilization process is now being developed to take advantage of the volatility of RuO 4 in order to eliminate it at the head end of the Purex process and thus reduce the number of extraction cycles. Although the process operates successfully with synthetic nitrato-RuNO 3+ solutions, difficulties have been encountered in extrapolating it to real-like dissolution solutions. In order to better approximate the chemical forms of ruthenium found in fuel dissolution solutions, kinetic and speciation studies on dissolved species were undertaken with RuO 2 ,xH 2 O and Ru 0 in nitric acid media. (authors)

  19. Kinetics and

    Mojtaba Ahmadi

    2016-11-01

    Full Text Available The aqueous degradation of Reactive Yellow 84 (RY84 by potassium peroxydisulfate (K2S2O8 has been studied in laboratory scale experiments. The effect of the initial concentrations of potassium peroxydisulfate and RY84, pH and temperature on RY84 degradation were also examined. Experimental data were analyzed using first and second-order kinetics. The degradation kinetics of RY84 of the potassium peroxydisulfate process followed the second-order reaction kinetics. These rate constants have an extreme values similar to of 9.493 mM−1min−1 at a peroxydisulfate dose of 4 mmol/L. Thermodynamic parameters such as activation (Ea and Gibbs free energy (ΔG° were also evaluated. The negative value of ΔGo and Ea shows the spontaneous reaction natural conditions and exothermic nature.

  20. A comparative study of the luminescence characteristics of polymineral fine grains and coarse-grained K-, and Na-rich feldspars

    Tsukamoto, Sumiko; Jain, Mayank; Murray, Andrew S.

    2012-01-01

    for K-feldspar samples, when a preheat temperature of 250 °C for 60 s is used. After preheating to a higher temperature (320 °C for 60 s) all samples show a TL reduction around 410 °C in the blue detection window. Pulse annealing experiments for IRSL and pIRIR signals for preheats between 320 °C and 500...... °C indicate that the signal stabilities are similar among the different feldspar types, when a higher preheat temperature (>320 °C) is used. Thermal activation energies for IRSL and pIRIR signals are largest in K-feldspar and smallest in polymineral fine grains, in both blue and UV detection windows...... for both fast time-resolved (TR) and continuous wave (CW) signals. These results suggest that IRSL and pIRIR signals in polymineral fine grains originate mainly from Na-feldspar grains; these signals are less thermally stable than those from K-feldspar, but a more stable signal (presumably from K...

  1. Rare earth element geochemistry of feldspars: examples from Fe-oxide Cu-Au systems in the Olympic Cu-Au Province, South Australia

    Kontonikas-Charos, Alkis; Ciobanu, Cristiana L.; Cook, Nigel J.; Ehrig, Kathy; Krneta, Sasha; Kamenetsky, Vadim S.

    2018-04-01

    Rare earth element (REE) fractionation trends in feldspars are reported from Olympic Dam (including Wirrda Well and Phillip's Ridge) and Cape Donington (Port Lincoln), for comparison with two other igneous-hydrothermal terranes within the eastern Gawler Craton: Moonta-Wallaroo and Hillside. The case studies were selected as they represent 1590 Ma Hiltaba Suite and/or 1845 - 1810 Ma Donington Suite granites, and, aside from Cape Donington, are associated with Mesoproterozoic iron-oxide copper gold (IOCG)-type mineralization. Both plagioclase and alkali feldspar were analyzed within selected samples with the purpose of constraining and linking changes in REE concentrations and fractionation trends in feldspars to local and whole-rock textures and geochemistry. Two unique, reproducible fractionation trends were obtained for igneous plagioclase and alkali feldspars, distinguished from one another by light rare earth element enrichment, Eu-anomalies and degrees of fractionation (e.g. La/Lu slopes). Results for hydrothermal albite and K-feldspar indicate that REE concentrations and fractionation trends are generally inherited from igneous predecessors, however in some instances, significant amounts of REE appear to have been lost to the fluid. These results may have critical implications for the formation of world-class IOCG systems, in which widespread alkali metasomatism plays a key role by altering the physical and chemical properties of the host rocks during early stages of IOCG formation, as well as trapping trace elements (including REE).

  2. Use of rice straw ash as substitute of feldspar in triaxial porcelain; Cenizas del tamo de arroz como substituto del feldespato en la fabricacion de ceramica blanca

    Alvaro Guzman, A.; Silverio Delvasto, A.; Enrique Sanchez, V.; Vicente Amigo, B.

    2013-02-01

    The substitution of raw materials for processing high energy consumption materials by agricultural and agro-industrial wastes causes a positive impacts on the environment preservation. One of these residues is rice straw, which according to FAO estimation, its annual production is about 600 million tons. In this research was studied the use of rice straw ash as substitute of the use of feldspar in the white ware production. Clay-feldspar-quartz porcelains are referred to as triaxial white ware. Specimens of semidry triaxial mixtures, where feldspar was substituted for different percentages of CTA, were prepared by uniaxial pressing, followed by drying and sintering. Physical and mechanical properties of sintered bodies were evaluated. The porosity and the compressive strength of the fired pieces do increase with additions of up to 75% of CTA in substitution of feldspar. Their mineralogical phases were determined by DRX and SEM; grains of quartz, and needles of primary and secondary mullite were identified in a vitreous phase. It was concluded that feldspar can be substituted positively by CTA in white ware pastes. (Author) 22 refs.

  3. Development and validation of dissolution test for Metoprolol ...

    The dissolution method which uses USP apparatus I (Basket) with rotating at 100 rpm, 900 ml of different dissolution medium, ultra violet spectroscopy for quantification was demonstrated to be robust, discriminating and transferable. Dissolution tests conditions were selected after it was demonstrated that the Metoprolol ...

  4. Influence of diopside: feldspar ratio in ceramic reactions assessed by quantitative phase analysis (X-ray diffraction - Rietveld method)

    Kuzmickas, L.; Andrade, F.R.D.; Szabo, G.A.J.; Motta, J.F.M.; Cabral Junior, M.

    2013-01-01

    White ceramics were produced with raw mixtures prepared with varying proportions of diopside-rich rock (0 to 20 wt.%) and potassic feldspar (40 to 20 wt.%), and fixed proportions of kaolinite (40 wt.%) and quartz (20 wt.%), fired in a temperature range from 1170 to 1210 deg C. The phases identified in the experimental ceramics were quartz, anorthite, mullite and glass, and their relative mass proportions were determined by X-ray diffraction (Rietveld method). The addition of diopside as a partial substitute for potassic feldspar causes the formation of a calcium silicate, analogous of the natural anorthite (CaSi 2 Al 2 O 8 ) in the ceramics, with proportional reduction in its glass and mullite contents. Water absorption and porosity of the ceramic bodies clearly decrease with increasing firing temperature, while the effect of the raw mixture composition on the physical and mechanical properties of the ceramics is less evident. Diopside-rich rock has low iron content (1.5 wt.% Fe 2 O 3 ) and, therefore, promotes white burning. (author)

  5. Luminescence dating of the PASADO core 5022-1D from Laguna Potrok Aike (Argentina) using IRSL signals from feldspar

    Buylaert, Jan-Pieter; Murray, A.S.; Gebhardt, A.C.

    2013-01-01

    We have measured and tested a luminescence chronology for the PASADO core 5022-1D from the maar lake of Laguna Potrok Aike. Because of unsuitable quartz OSL characteristics, sand-sized K-feldspar extracts were chosen as a dosimeter and the dose was measured using a post-IR IRSL (pIRIR290......) measurement protocol. Using this approach we were able to access a stable signal and thus avoid the ubiquitous problem of feldspar signal instability. Extensive laboratory tests show that the chosen pIRIR290 protocol is applicable to these samples. We also developed a new criterion based on known relative...... or stratigraphy; the resulting age–depth profile is self-consistent, increases smoothly with depth and is in agreement with independent age control based on volcanic ash layers (Reclús, Mt Burney and Hudson tephras) at the top and middle of the core. Our new luminescence chronology suggests that the 5022-1D core...

  6. Influence of diopside: feldspar ratio in ceramic reactions assessed by quantitative phase analysis (X-ray diffraction - Rietveld method)

    Kuzmickas, L.; Andrade, F.R.D.; Szabo, G.A.J. [Universidade de Sao Paulo (IGc/USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotecnia; Motta, J.F.M.; Cabral Junior, M., E-mail: lukuzmickas@gmail.com, E-mail: dias@usp.br, E-mail: gajszabo@usp.b, E-mail: motta.jf@gmail.com, E-mail: marsis@ipt.br [Instituto de Pesquisas Tecnologicas (IPT), Sao Paulo, SP (Brazil). Secao de Recursos Minerais e Tecnologia Ceramica

    2013-04-15

    White ceramics were produced with raw mixtures prepared with varying proportions of diopside-rich rock (0 to 20 wt.%) and potassic feldspar (40 to 20 wt.%), and fixed proportions of kaolinite (40 wt.%) and quartz (20 wt.%), fired in a temperature range from 1170 to 1210 deg C. The phases identified in the experimental ceramics were quartz, anorthite, mullite and glass, and their relative mass proportions were determined by X-ray diffraction (Rietveld method). The addition of diopside as a partial substitute for potassic feldspar causes the formation of a calcium silicate, analogous of the natural anorthite (CaSi{sub 2}Al{sub 2}O{sub 8}) in the ceramics, with proportional reduction in its glass and mullite contents. Water absorption and porosity of the ceramic bodies clearly decrease with increasing firing temperature, while the effect of the raw mixture composition on the physical and mechanical properties of the ceramics is less evident. Diopside-rich rock has low iron content (1.5 wt.% Fe{sub 2}O{sub 3}) and, therefore, promotes white burning. (author)

  7. Origin of K-feldspar megacrystals from Monte das Gameleiras granite, Rio Grande do Norte/Paraiba, Brazil

    Galindo, A.C.

    1988-01-01

    The Monte das Gameleiras granitic batholith is located at the boundary between Rio Grande do Norte and Paraiba States in northeastern Brazil. Two main types of granitic rocks have been identified in this batholith. Dioritic inclusions occur in both of them. The predominating type is an extremely porphyritic syenogranite, which is intruded by a fine-grained monzogranite. K-feldspar megacrysts are found in both porphyritic granite and dioritic inclusions. The megacrysts long axes average around 4 cm, reaching up to 9 or 10 cm. The megacrysts are euhedral, zoned, and, sometimes, they show rapakivi texture. Flow textures and tuillage are common, but irregularly distributed. The K-feldspar megacrysts contain inclusions of plagioclase, biotite, quartz, hornblende, sphene, and apatite. These inclusions are concentrically arranged and parallel to the megacrysts zones. The included minerals are generally smaller than the same minerals in the groundmass. Microprobe analyses and X-ray difraction studies show that the megacrysts of both facies are similar in composition, containing around 90% of orthoclase. Taking into account the textural and compositional aspects, it is concluded that the megacrysts of porphyritic granite and dioritic inclusions are phenocrysts and not porphyroblasts. (author) [pt

  8. Granulocyte kinetics

    Peters, A.M.; Lavender, J.P.; Saverymuttu, S.H.

    1985-01-01

    By using density gradient materials enriched with autologous plasma, the authors have been able to isolate granulocutes from other cellular elements and label them with In-111 without separation from a plasma environment. The kinetic behavior of these cells suggests that phenomena attributed to granulocyte activation are greatly reduced by this labeling. Here, they review their study of granulocyte kinetics in health and disease in hope of quantifying sites of margination and identifying principal sites of destruction. The three principle headings of the paper are distribution, life-span, and destruction

  9. The Dissolution Behavior of Borosilicate Glasses in Far-From Equilibrium Conditions

    Neeway, James J.; Rieke, Peter C.; Parruzot, Benjamin PG; Ryan, Joseph V.; Asmussen, Robert M.

    2018-02-10

    In far-from-equilibrium conditions, the dissolution of borosilicate glasses used to immobilize nuclear waste is known to be a function of both temperature and pH. The aim of this paper is to study effects of these variables on three model waste glasses (SON68, ISG, AFCI). To do this, experiments were conducted at temperatures of 23, 40, 70, and 90 °C and pH(RT) values of 9, 10, 11, and 12 with the single-pass flow-through (SPFT) test method. The results from these tests were then used to parameterize a kinetic rate model based on transition state theory. Both the absolute dissolution rates and the rate model parameters are compared with previous results. Discrepancies in the absolute dissolution rates as compared to those obtained using other test methods are discussed. Rate model parameters for the three glasses studied here are nearly equivalent within error and in relative agreement with previous studies. The results were analyzed with a linear multivariate regression (LMR) and a nonlinear multivariate regression performed with the use of the Glass Corrosion Modeling Tool (GCMT), which is capable of providing a robust uncertainty analysis. This robust analysis highlights the high degree of correlation of various parameters in the kinetic rate model. As more data are obtained on borosilicate glasses with varying compositions, the effect of glass composition on the rate parameter values could possibly be obtained. This would allow for the possibility of predicting the forward dissolution rate of glass based solely on composition

  10. The Dissolution of Double Holliday Junctions

    Bizard, Anna H; Hickson, Ian D

    2014-01-01

    as "double Holliday junction dissolution." This reaction requires the cooperative action of a so-called "dissolvasome" comprising a Holliday junction branch migration enzyme (Sgs1/BLM RecQ helicase) and a type IA topoisomerase (Top3/TopoIIIα) in complex with its OB (oligonucleotide/oligosaccharide binding......Double Holliday junctions (dHJS) are important intermediates of homologous recombination. The separate junctions can each be cleaved by DNA structure-selective endonucleases known as Holliday junction resolvases. Alternatively, double Holliday junctions can be processed by a reaction known......) fold containing accessory factor (Rmi1). This review details our current knowledge of the dissolution process and the players involved in catalyzing this mechanistically complex means of completing homologous recombination reactions....

  11. Study of dissolution process and its modelling

    Juan Carlos Beltran-Prieto

    2017-01-01

    Full Text Available The use of mathematical concepts and language aiming to describe and represent the interactions and dynamics of a system is known as a mathematical model. Mathematical modelling finds a huge number of successful applications in a vast amount of science, social and engineering fields, including biology, chemistry, physics, computer sciences, artificial intelligence, bioengineering, finance, economy and others. In this research, we aim to propose a mathematical model that predicts the dissolution of a solid material immersed in a fluid. The developed model can be used to evaluate the rate of mass transfer and the mass transfer coefficient. Further research is expected to be carried out to use the model as a base to develop useful models for the pharmaceutical industry to gain information about the dissolution of medicaments in the body stream and this could play a key role in formulation of medicaments.

  12. Aggregation, sedimentation, dissolution and bioavailability of ...

    To understand their fate and transport in estuarine systems, the aggregation, sedimentation, and dissolution of CdSe quantum dots (QDs) in seawater were investigated. Hydrodynamic size increased from 40 to 60 nm to >1 mm within 1 h in seawater, and the aggregates were highly polydispersed. Their sedimentation rates in seawater were measured to be 4–10 mm/day. Humic acid (HA), further increased their size and polydispersity, and slowed sedimentation. Light increased their dissolution and release of dissolved Cd. The ZnS shell also slowed release of Cd ions. With sufficient light, HA increased the dissolution of QDs, while with low light, HA alone did not change their dissolution. The benthic zone in estuarine systems is the most probable long-term destination of QDs due to aggregation and sedimentation. The bioavailability of was evaluated using the mysid Americamysis bahia. The 7-day LC50s of particulate and dissolved QDs were 290 and 23 μg (total Cd)/L, respectively. For mysids, the acute toxicity appears to be from Cd ions; however, research on the effects of QDs should be conducted with other organisms where QDs may be lodged in critical tissues such as gills or filtering apparatus and Cd ions may be released and delivered directly to those tissues. Because of their increasing use and value to society, cadmium-based quantum dots (QDs) will inevitably find their way into marine systems. In an effort to understand the fate and transport of CdSe QDs in estuar

  13. DISSOLUTION OF ZIRCONIUM AND ALLOYS THEREFOR

    Swanson, J.L.

    1961-07-11

    The dissolution of zirconium cladding in a water solution of ammonium fluoride and ammonium nitrate is described. The method finds particular utility in processing spent fuel elements for nuclear reactors. The zirconium cladding is first dissolved in a water solution of ammonium fluoride and ammonium nitrate; insoluble uranium and plutonium fiuorides formed by attack of the solvent on the fuel materiai of the fuel element are then separated from the solution, and the fuel materiai is dissolved in another solution.

  14. Saltcake Dissolution FY 2000 Status Report

    HERTING, D.L.

    2000-01-01

    Laboratory tests were completed on the dissolution characteristics of Hanford saltcake waste from single-shell waste tanks 241-TX- 113, 241-BY-102, 241-BY-106, 241-A-101, and 241-S-102 (henceforth referred to as TX-113, BY-102, BY-106, A-101, and S-102, respectively). This work was funded by the Tanks Focus Area (EM-50) under Technical Task Plan Number RL0-8-WT-41, ''PHMC Pretreatment--Saltcake Dissolution''. The tests performed on saltcake from tank TX-113 were similar in scope to those completed in previous years on waste from tanks BY-102, BY-106, B-106, A-101, and S-102 (Herting 1998, 1999). In addition to the ''standard'' dissolution tests, new types of tests were performed this year related to feed stability and radionuclide distribution. The River Protection Project (RPP) is tasked with retrieving waste from double-shell and single-shell tanks to provide feed for vitrification. The RPP organization needs chemical and physical data to evaluate technologies for retrieving the waste. Little significant laboratory testing has been done to evaluate in-tank dissolution parameters for the various types of saltcake wastes that exist in single-shell tanks. A computer modeling program known as the Environmental Simulation Program (ESP), produced by OLI Systems, Inc of Morris Plains, New Jersey, is being used by the RPP organization to predict solubilities during dilution and retrieval of all tank waste types. Data from this task are provided to ESP users to support evaluation, refinement, and validation of the ESP model

  15. Chemical alteration of cement hydrates by dissolution

    Sugiyama, Daisuke; Fujita, Tomonari; Nakanishi, Kiyoshi

    2000-01-01

    Cementitious material is a potential waste packaging and backfilling material for the radioactive waste disposal, and is expected to provide both physical and chemical containment. In particular, the sorption of radionuclides onto cementitious material and the ability to provide a high pH condition are very important parameters when considering the release of radionuclides from radioactive wastes. For the long term, in the geological disposal environment, cement hydrates will be altered by, for example, dissolution, chemical reaction with ions in the groundwater, and hydrothermal reaction. Once the composition or crystallinity of the constituent minerals of a cement hydrate is changed by these processes, the pH of the repository buffered by cementitious material and its sorption ability might be affected. However, the mechanism of cement alteration is not yet fully understood. In this study, leaching experiments of some candidate cements for radioactive waste disposal were carried out. Hydrated Ordinary Portland Cement (OPC), Blast Furnace Slag blended cement (OPC/BFS) and Highly containing Flyash and Silicafume Cement (HFSC) samples were contacted with distilled water at liquid:solid ratios of 10:1, 100:1 and 1000:1 at room temperature for 200 days. In the case of OPC, Ca(OH) 2 dissolved at high liquid:solid ratios. The specific surface area of all cement samples increased by leaching process. This might be caused by further hydration and change of composition of constituent minerals. A model is presented which predicts the leaching of cement hydrates and the mineral composition in the hydrated cement solid phase, including the incongruent dissolution of CSH gel phases and congruent dissolution of Ca(OH) 2 , Ettringite and Hydrotalcite. Experimental results of dissolution of Ca-O-H and Ca-Si-O-H phases were well predicted by this model. (author)

  16. Relationships with former stepgrandparents after remarriage dissolution.

    Sanner, Caroline; Coleman, Marilyn; Ganong, Lawrence

    2018-03-01

    Increases in stepfamily formation and longevity suggest that more children have stepgrandparent relationships than ever before. Because remarriages end in divorce more often than first marriages, many children experience the involuntary dissolution of stepgrandparent ties. Little is known about stepgrandparent relationships in general, and even less is known about how these relationships are affected by remarriage dissolution. Guided by symbolic interaction theory, the purpose of this study was to understand how stepgrandchildren make sense of their relationships with former stepgrandparents. We explored their perceptions of why relationships were or were not maintained and the impact of continued or dissolved ties on their personal well-being. Former stepgrandchildren (N = 29) aged 18 to 37 were interviewed about their former stepgrandparents. The quality and continuity of these relationships were contingent on stepgrandchildren's relationships with former stepparents, biological parents' relationships with former stepgrandparents, and efforts by former stepgrandparents to remain involved. Losing ties with former stepgrandparents was upsetting, especially when relationships with biological grandparents were not close. Individuals who maintained relationships with former stepgrandparents benefitted from continued access to valuable resources (e.g., positive role models, additional sources of love and support). Our findings have important implications for clinicians' and researchers' understanding of the effects of remarriage dissolution on children as well as the intergenerational efforts that may be critical for preserving meaningful stepfamily ties. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

  17. Dissolution of Marriage According to Canon Law

    MSc. Sulejman Ahmedi

    2013-12-01

    Full Text Available In the Canon law, dissolution of marriage is not allowed since it was considered sacred and as such cannot break until the two spouses are alive, except only if one of the spouses passes away. But throughout history we find cases when allowed dissolution of the marriage and causes specific conditions set by the church. Thus, according to the Old Testament, if, a man married to a woman, didn’t like something about his wife, should write a request for divorce and allow her to leave his home. Meanwhile according to the New Testament records, divorce is prohibited. Although most Protestants continue to espouse the view that marriage was sacred and as such should not be divorced, from those who had supported the idea of granting the divorce. One of them was Luther, who in his remarks before his preachers said: "In my opinion, the issue of divorce belongs to the law, are not they to whom called for regulation of parental relationships, why not have they the authority to regulate the relations between spouses". Protestant churches allow the dissolution of marriage: a Because of adultery by the wife; allowed by Jesus, b Unjustified abandonment of the marital community; c If there were other reasons: if one spouse refuses to have sexual marriage, if the husband abuses his wife     repeatedly and without cause, severe illness of one spouse.

  18. Anomalous dissolution of metals and chemical corrosion

    DRAGUTIN M. DRAZIC

    2005-03-01

    Full Text Available An overview is given of the anomalous behavior of some metals, in particular Fe and Cr, in acidic aqueous solutions during anodic dissolution. The anomaly is recognizable by the fact that during anodic dissolutionmore material dissolves than would be expected from the Faraday law with the use of the expected valence of the formed ions. Mechanical disintegration, gas bubble blocking, hydrogen embrittlement, passive layer cracking and other possible reasons for such behavior have been discussed. It was shown, as suggested by Kolotyrkin and coworkers, that the reason can be, also, the chemical reaction in which H2O molecules with the metal form metal ions and gaseous H2 in a potential independent process. It occurs simultaneously with the electrochemical corrosion process, but the electrochemical process controls the corrosion potential. On the example of Cr in acid solution itwas shown that the reason for the anomalous behavior is dominantly chemical dissolution, which is considerably faster than the electrochemical corrosion, and that the increasing temperature favors chemical reaction, while the other possible reasons for the anomalous behavior are of negligible effect. This effect is much smaller in the case of Fe, but exists. The possible role of the chemical dissolution reacton and hydrogen evolution during pitting of steels and Al and stress corrosion cracking or corrosion fatigue are discussed.

  19. Dissolution rates of DWPF glasses from long-term PCT

    Ebert, W.L.; Tam, S.W.

    1996-01-01

    We have characterized the corrosion behavior of several Defense Waste Processing Facility (DWPF) reference waste glasses by conducting static dissolution tests with crushed glasses. Glass dissolution rates were calculated from measured B concentrations in tests conducted for up to five years. The dissolution rates of all glasses increased significantly after certain alteration phases precipitated. Calculation of the dissolution rates was complicated by the decrease in the available surface area as the glass dissolves. We took the loss of surface area into account by modeling the particles to be spheres, then extracting from the short-term test results the dissolution rate corresponding to a linear decrease in the radius of spherical particles. The measured extent of dissolution in tests conducted for longer times was less than predicted with this linear dissolution model. This indicates that advanced stages of corrosion are affected by another process besides dissolution, which we believe to be associated with a decrease in the precipitation rate of the alteration phases. These results show that the dissolution rate measured soon after the formation of certain alteration phases provides an upper limit for the long-term dissolution rate, and can be used to determine a bounding value for the source term for radionuclide release from waste glasses. The long-term dissolution rates measured in tests at 20,000 per m at 90 degrees C in tuff groundwater at pH values near 12 for the Environmental Assessment glass and glasses made with SRL 131 and SRL 202 frits, respectively

  20. Development and validation of spectrophotometric method for assay determination and in vitro dissolution studies of sofosbuvir tablets

    Zaman, B.; Hassan, W.; Noreen, H.

    2017-01-01

    In vitro dissolution of sofosbuvir 400 mg tablets dosage form was performed, using USP dissolution apparatus type-II (paddle type), at 75rpm ± 4 %, and 900mL ± 1%, 0.05 M phosphate buffer pH 6.8 ± 0.05 equilibrated at 37.0 ± 0.5ºC as dissolution medium. Percentage of dissolved sofosbuvir as a function of time was determined using the straight line equation and linear regression using zero order and first order ANOVA based kinetics model. Comparative dissolution studies on two different generic brands A and B was performed comparing the drug release profile with innovator brand Sovaldi 400 mg tablets. The comparison of dissolution profiles was evaluated using model independent approach. The values of similarity factor f2 were (4 and 3) and the difference factor f1 were (64 and 50) for both generic products A and B respectively. A simple and precise spectrophotometric method was developed for estimation of sofosbuvir in dissolution medium based on spectrophotometric detection at wavelength 262 nm. The specific absorbance (A = 1%) of sofosbuvir was 178.5 ± 4% and Beer’s law was obeyed in the concentration ranges 4µg mL−1 to 48µg mL−1. The method was validated appropriately for accuracy, precision, linearity, and specificity, according the guidelines of United State Pharmacopoeia and International Conference on Harmonization. The calibration curve was linear with correlation coefficient (r > 0.9999) and there was no spectral interference from excipients present in the tablets dosage form. This method is precise, rapid and specific for determination of sofosbuvir in tablets dosage form and successfully applied for assay determination and in vitro dissolution studies. (author)

  1. Dissolution characteristics of chalcedony under alkaline condition. Study for changes in mineral composition of engineered barrier composed by bentonite

    Watanabe, Yasutaka; Yokoyama, Shingo

    2016-01-01

    In the engineered barrier of radioactive waste disposal facilities, it is expected that bentonite is exposed to alkaline groundwater which arise from leaching of cementations materials. Minerals contained in the bentonite will be dissolved by reactions of the alkaline groundwater. Some bentonite contains silica such as quartz and chalcedony. Chalcedony is categorized in intermediate silica which is microcrystalline. It is known that dissolution of silica influences to the dissolution of smectite by means of solubility. However, dissolution kinetics of chalcedony in the alkaline condition has not been investigated, which is an uncertainty in geochemical simulations to evaluate a long-term stability of the engineered barrier. Therefore, this study performed flow-through experiments in alkaline conditions using chalcedony in order to obtain the dissolution rate of the chalcedony. The flow-through experiments was performed using NaOH-NaCl solution adjusted to 0.3 mol/L of ionic strength. Initial pH of the solution was from 8.9 to 13.5. As a result, higher pH and higher temperature showed higher Si ion concentrations of reacted solutions. The dissolution rate of the samples was calculated using Si ion concentrations at steady state of the experiment. Note that, the dissolution rate of the chalcedony was almost same as that of quartz at same temperature. After the experiments, SEM observation showed that rough surface of the chalcedony partly changed to smooth surface like quartz. It is supposed that rough surface of chalcedony was rapidly dissolved because of low degree of crystallization. The dissolution rate obtained is supposedly applicable to highly crystalline SiO 2 of chalcedony. (author)

  2. Geoengineering impact of open ocean dissolution of olivine on atmospheric CO2, surface ocean pH and marine biology

    Köhler, Peter; Abrams, Jesse F; Völker, Christoph; Hauck, Judith; Wolf-Gladrow, Dieter A

    2013-01-01

    Ongoing global warming induced by anthropogenic emissions has opened the debate as to whether geoengineering is a ‘quick fix’ option. Here we analyse the intended and unintended effects of one specific geoengineering approach, which is enhanced weathering via the open ocean dissolution of the silicate-containing mineral olivine. This approach would not only reduce atmospheric CO 2 and oppose surface ocean acidification, but would also impact on marine biology. If dissolved in the surface ocean, olivine sequesters 0.28 g carbon per g of olivine dissolved, similar to land-based enhanced weathering. Silicic acid input, a byproduct of the olivine dissolution, alters marine biology because silicate is in certain areas the limiting nutrient for diatoms. As a consequence, our model predicts a shift in phytoplankton species composition towards diatoms, altering the biological carbon pumps. Enhanced olivine dissolution, both on land and in the ocean, therefore needs to be considered as ocean fertilization. From dissolution kinetics we calculate that only olivine particles with a grain size of the order of 1 μm sink slowly enough to enable a nearly complete dissolution. The energy consumption for grinding to this small size might reduce the carbon sequestration efficiency by ∼30%. (letter)

  3. Study of the effect of water radiolysis on zirconolite dissolution

    Tribet, M.

    2007-09-01

    conditions (solid irradiation or not). The behaviour of Ti and Zr is enhanced (about 100 times) in presence of complexing species such as fluoride ions. Nevertheless, the alteration remains very weak, even in presence of complexing species and is sorely observable on the solid surface. Elementary releases are first kinetically controlled: if we base on Nd releases, the dissolution under radiolytic conditions is about 5 orders of magnitude higher than out of radiolysis. However, this kinetic step is shorter, a couple of hours, compared to a couple of days out of radiolysis. When there is only water radiolysis, a thermodynamic step is then observed as soon as the leachate is saturated in respect to the Zr and Ti hydroxides phases: elemental releases then become constant. When the solid is also irradiated, colloids are observed, although the leachate is not saturated in respect with hydroxides phases. The formation of these colloids could arise from chemical equilibriums modification induced by ionizations occurring in the solid during its irradiation. The radiolytic production of H 2 O 2 is lower than predicted by the calculated primary yield, because of the consumption of H 2 O 2 or its precursors by chemical reactions involving others radiolytic species such as H2 or the aqueous electron. (author)

  4. Late Quaternary cooling rate constrained by multiple IRSL thermochronometers of potassium feldspars for granites from Kongur Shan, Chinese Pamir

    Qin, Jintang; Chen, Jie; Valla, Pierre; Herman, Frédéric

    2015-04-01

    The Kongur Shan (East Pamir), located at the northwestern Tibetan Plateau, is one of the most active orogens on Earth, where both tectonic processes along major active faults and climatic forcing (extensive glaciers coverage) are contributing to the regional landscape evolution. The exhumation rates since late Miocene was constrained to be ~6.5 - 4.2 mm/yr. However, it is still debated whether the exhumation rate accelerated since the Quaternary, of which the climate was featured by the cyclic glaciations with periods of 100 ka and 40 ka. In this study, we tried to employ luminescence thermochronology, which is a still in developing method, to resolve the impact of glacial cycles on exhumation rate. Our study site is located ~10 km to the east of the active Kongur normal fault, along the major valley of Gez river. We sampled three granite rocks from a sub-horizontal tunnel across the granite massif; one was from the entrance of the tunnel, and other two samples were from inside of the tunnel, where the measured ambient temperature is as high as 60-70 ° C. The distances of these samples are within 2 km. Four types of IRSL signals extracted from potassium feldspars (K-feldspars) were measured for each individual sample, and the results of isothermal decay experiments indicated these signals were of different thermal stabilities. Therefore, they may serve as four thermochronometers with different closure temperature. We employ these multiple thermochronometers together for each single sample to constrain their cooling rates. Our preliminary results, which are based on the simplified luminescence model of K-feldspars, suggest that the averaged cooling rate of the last 200 ka is as high as 1.4 oC/ka, which corresponds to an exhumation rate of ~ 2.3 to 0.9 cm/yr with the geothermal gradient assumed to be 60 to 150 oC/km. It seems to imply that the glacial cycles during the Quaternary substantially accelerated the exhumation rate of granite massif of Kongur Shan.

  5. The dissolution rate constant of magnetite in water at different temperatures and pH conditions

    Mohajery, Khatereh; Deydier de Pierrefeu, Laurent; Lister, Derek H.

    2012-09-01

    Under the nominal conditions of power system coolants, the corrosion of components made of carbon steel is limited by the magnetite films that develop on surfaces. In some situations, the magnetite film loses much of its protective ability and corrosion and loss of iron to the system are exacerbated. Common examples of such situations occur when the system is non-isothermal so that temperature gradients cause differences in magnetite solubility around the circuit; the resulting areas of under-saturation in iron give rise to dissolution of normally protective films. Condensing steam in two-phase systems may also promote oxide dissolution. When the turbulence in the system is high, oxide degradation is aggravated and flow-accelerated corrosion (FAC) results. The subsequent increased loading of systems with iron leads to fouling of flow passages and heat transfer surfaces and in reactor primary coolants to rising radiation fields, while FAC can have disastrous results in terms of pipe wall thinning and eventual rupture. Magnetite dissolution is clearly a key contributor to these processes. Thus, the conventional mechanistic description of FAC postulates magnetite dissolution in series with mass transfer of iron from the film to the bulk coolant. In the resulting equations, if the dissolution rate constant is considerably less than the mass transfer coefficient for a particular situation, dissolution will control and flow should have no effect. This is clearly untenable for FAC, so it is often assumed that mass transfer controls and the contribution from oxide dissolution is ignored - on occasion when data on dissolution kinetics are available and sometimes when those data show that dissolution should control. In most cases, however, dissolution rate constants for magnetite are not available. At UNB Nuclear we have a research program using a high-temperature loop to measure dissolution rates of magnetite in water under various conditions of flow, temperature and

  6. The study of photo-and thermally-induced diffusion and dissolution of Af in As30S70 amorphous films and its reastion products

    Wágner, T.; Macková, Anna; Peřina, Vratislav; Rauhala, E.; Seppälä, A.; Kasap, S. O.; Frumar, M.; Vlček, M.

    2002-01-01

    Roč. 299, č. 1 (2002), s. 1028-1032 ISSN 0022-3093 R&D Projects: GA ČR GP102/01/D069 Keywords : state chemical-reaction * photoenhanced dissolution * kinetics * backscattering * layers * glass Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.435, year: 2002

  7. Dissolution chemistry and biocompatibility of single-crystalline silicon nanomembranes and associated materials for transient electronics.

    Hwang, Suk-Won; Park, Gayoung; Edwards, Chris; Corbin, Elise A; Kang, Seung-Kyun; Cheng, Huanyu; Song, Jun-Kyul; Kim, Jae-Hwan; Yu, Sooyoun; Ng, Joanne; Lee, Jung Eun; Kim, Jiyoung; Yee, Cassian; Bhaduri, Basanta; Su, Yewang; Omennetto, Fiorenzo G; Huang, Yonggang; Bashir, Rashid; Goddard, Lynford; Popescu, Gabriel; Lee, Kyung-Mi; Rogers, John A

    2014-06-24

    Single-crystalline silicon nanomembranes (Si NMs) represent a critically important class of material for high-performance forms of electronics that are capable of complete, controlled dissolution when immersed in water and/or biofluids, sometimes referred to as a type of "transient" electronics. The results reported here include the kinetics of hydrolysis of Si NMs in biofluids and various aqueous solutions through a range of relevant pH values, ionic concentrations and temperatures, and dependence on dopant types and concentrations. In vitro and in vivo investigations of Si NMs and other transient electronic materials demonstrate biocompatibility and bioresorption, thereby suggesting potential for envisioned applications in active, biodegradable electronic implants.

  8. Mechanisms of oxide dissolution by acid chelating agents

    Blesa, M.A.; Maroto, A.J.G.

    1982-01-01

    In this paper, the different possible rate controlling processes in the dissolution of metallic oxides are examined. In particular, the following situations are assessed: mass-transfer control; coupling of mass-transfer and reactions at the interface; interface equilibration with the solution; various interface disruption and reconstruction phenomena. For each of the above mentioned cases, the influence of variables such as reagent concentration, temperature, pH, fluid hydrodynamics and general and specific catalysts is discussed. Depending upon the particular situation it is found that a more rational basis for the development of reagent is given by these considerations. The influence of chelating agents on both the thermodynamics and kinetics of the process is discussed, and the results of experimental studies in batch on magnetite and various ferrites are presented and discussed. For this purpose, several reagents were studied, including some very effective ones like thioglycolic acid, and others commonly used in actual decontamination, like ethylenediaminetetraacetic acid and oxalic acid. The relation to other (reductive) chemical decontamination procedures is discussed. The relevance of these studies to decontamination of metallic surfaces is discussed

  9. Some considerations referring to mechanisms of iron oxides dissolution

    Radulescu, M.; Stefanescu, D.; Popa, L.; Mogosan, S.

    2010-01-01

    Full text: Under nuclear power plant operational conditions, the carbon steel components in a such nuclear station react with high temperature cooling agent forming several iron oxides and oxyhydroxides. These substances forming some randomly located deposits on the piping walls, can result in some damaging consequences such as: tube constrictions, pitting and intergranular corrosion and finally decreasing of heat transfer and the development of a radiation field around the primary circuit. The decontamination process being in fact a descaling process, involves the chemical dissolution of corrosion deposits in diluted acidic reagents containing usually a complexing carboxylic acid, a reductant and a corrosion inhibitor. A comparative survey of our experimental results with those published in literature on the up-mentioned topics is presented in our paper. To evaluate the removing rates of these superficial films two types of methods were used: gravimetric and potentiodynamic techniques. While the gravimetry supplied us the weight losses data necessary to establish the descaling process kinetics, the potentiodynamic method was used to compare the values of descaling rates obtained from electrochemical data. Correlating our experimental data with those from literature, we adopted two models of mechanisms applicable to our specific conditions. (authors)

  10. water alteration processes and kinetics of basaltic glasses, natural analogue of nuclear glasses

    Techer, I.; Advocat, Th.; Vernaz, E.; Lancelot, J.R.; Liotard, J.M.

    1997-01-01

    Dissolution experiments of a basaltic glass were carried out at 90 deg C for different reaction progresses. The initial dissolution rate was compared with values obtained for rhyolitic glass and the R7T7 nuclear glass. The activation energy was also determined by computing literature data. The results provide similar reactional mechanism for basaltic and nuclear glasses. Dissolution rates measured under saturation conditions were compared to theoretical dissolution rates. These ones were calculated using two kinetic models: the first rate equation is the Grambow's law which only takes into account ortho-silica acid activity; the second rate equation was proposed by Daux et al., where silica and aluminum are combined to formulate the affinity. The comparison between experimental and theoretical results point out that these two models are not appropriate to describe the alteration kinetic of basaltic glasses. (authors)

  11. Physisorption kinetics

    Kreuzer, Hans Jürgen

    1986-01-01

    This monograph deals with the kinetics of adsorption and desorption of molecules physisorbed on solid surfaces. Although frequent and detailed reference is made to experiment, it is mainly concerned with the theory of the subject. In this, we have attempted to present a unified picture based on the master equation approach. Physisorption kinetics is by no means a closed and mature subject; rather, in writing this monograph we intended to survey a field very much in flux, to assess its achievements so far, and to give a reasonable basis from which further developments can take off. For this reason we have included many papers in the bibliography that are not referred to in the text but are of relevance to physisorption. To keep this monograph to a reasonable size, and also to allow for some unity in the presentation of the material, we had to omit a number of topics related to physisorption kinetics. We have not covered to any extent the equilibrium properties of physisorbed layers such as structures, phase tr...

  12. Sorption of environmentally relevant radionuclides (U(VI), Np(V)) and lanthanides (Nd(III)) on feldspar and mica

    Richter, Constanze

    2015-11-05

    A safe storage of radioactive waste in repositories is an important task to protect humans and the environment from radio- and chemotoxicity. Long-term safety assessments predict the behavior of potential environmental contaminants like the actinides plutonium, uranium, or neptunium, in the near and far field of repositories. For such safety assessments, it is necessary to know the migration behavior of the contaminants in the environment, which is mainly dependent on the aquatic speciation, the solubility product of relevant solid phases, and the retardation due to sorption on surrounding minerals. Thus, an investigation of sorption processes of contaminants onto different minerals as well as the derivation of mineral specific surface complexation model (SCM) parameters is of great importance. Feldspar and mica are widely distributed in nature. They occur as components of granite, which is considered as a potential host rock for a repository in Germany, and in numerous other rocks, and thus also in the far field of nearly all repositories. However, their sorption behavior with actinides has only been scarcely investigated until now. In order to better characterize these systems and subsequently to integrate these minerals into the long-term safety assessments, this work focuses on the investigation of the sorption behavior of U(VI), Np(V), and Nd(III) as analogue for An(III) onto the minerals orthoclase and muscovite, representing feldspars and mica, respectively. All investigations were performed under conditions relevant to the far field of a repository. In addition to the extensive characterization of the minerals, batch sorption experiments, spectroscopic investigations, and surface complexation modeling were performed to elucidate the uptake and speciation of actinides on the mineral surfaces. In addition, the influence of microorganisms naturally occurring on the mineral surfaces and the effect of Ca{sup 2+} on U(VI) uptake on the minerals was studied. The

  13. Sorption of environmentally relevant radionuclides (U(VI), Np(V)) and lanthanides (Nd(III)) on feldspar and mica

    Richter, Constanze

    2015-01-01

    A safe storage of radioactive waste in repositories is an important task to protect humans and the environment from radio- and chemotoxicity. Long-term safety assessments predict the behavior of potential environmental contaminants like the actinides plutonium, uranium, or neptunium, in the near and far field of repositories. For such safety assessments, it is necessary to know the migration behavior of the contaminants in the environment, which is mainly dependent on the aquatic speciation, the solubility product of relevant solid phases, and the retardation due to sorption on surrounding minerals. Thus, an investigation of sorption processes of contaminants onto different minerals as well as the derivation of mineral specific surface complexation model (SCM) parameters is of great importance. Feldspar and mica are widely distributed in nature. They occur as components of granite, which is considered as a potential host rock for a repository in Germany, and in numerous other rocks, and thus also in the far field of nearly all repositories. However, their sorption behavior with actinides has only been scarcely investigated until now. In order to better characterize these systems and subsequently to integrate these minerals into the long-term safety assessments, this work focuses on the investigation of the sorption behavior of U(VI), Np(V), and Nd(III) as analogue for An(III) onto the minerals orthoclase and muscovite, representing feldspars and mica, respectively. All investigations were performed under conditions relevant to the far field of a repository. In addition to the extensive characterization of the minerals, batch sorption experiments, spectroscopic investigations, and surface complexation modeling were performed to elucidate the uptake and speciation of actinides on the mineral surfaces. In addition, the influence of microorganisms naturally occurring on the mineral surfaces and the effect of Ca 2+ on U(VI) uptake on the minerals was studied. The

  14. Oxygen mobility in alkali feldspars; Etude de la mobilite de l'oxygene dans les feldspaths alcalins

    Merigoux, H [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1968-03-15

    The oxygen mobility is shown from oxygen atoms exchange between potassic and sodic feldspars and 18 oxygen enriched water. Exchanges are carried out in autoclaves between 400 and 800 deg. C under a water pressure between 300 and 800 bars. The oxygen is extracted from silicate by a ClF{sub 3} attack. Two distinct mechanisms may be found. The first one is auto-diffusion; for adularia we have: D = 9.10{sup -7} exp(-32000/RT) (cm{sup 2}.s{sup -1}), for albite: D 4.5.10{sup -5} exp(-37000/RT) (cm{sup 2}.s{sup -1}). The second one, more rapid, is associated with alkali atoms exchanges. These results are applied to the order-disorder problem in feldspars and to the oxygen geochemistry. (author) [French] La mobilite de l'oxygene est mise en evidence a partir d'echanges d'atomes d'oxygene entre des feldspaths potassiques et sodiques en presence d'une eau enrichie en oxygene 18. Les echanges sont effectues en autoclave entre 400 et 800 deg. C sous des pressions de vapeur d'eau comprises entre 300 et 800 bars. L'oxygene est extrait du silicate par attaque au ClF{sub 3}. Deux mecanismes, bien distincts, peuvent se rencontrer. Le premier correspond a l'autodiffusion de l'oxygene; dans le domaine etudie on trouve pour l'adulaire: D = 9,10{sup -7} exp(-32000/RT) (cm{sup 2}.s{sup -1}), et pour l'albite: D 4,5.10{sup -5} exp(-37000/RT) (cm{sup 2}.s{sup -1}). Le second, beaucoup plus rapide, est associe a l'echange des atomes alcalins avec la solution. Ces resultats sont appliques au probleme du passage ordre-desordre dans les feldspaths et a la geochimie de l'oxygene. (auteur)

  15. Dissolution rate enhancement of piroxicam by ordered mixing.

    Saharan, Vikas Anand; Choudhury, Pratim Kumar

    2012-07-01

    Micronized piroxicam was mixed with lactose, mannitol, sorbitol, maltitol and sodium chloride to produce ordered mixture in a glass vial by manual hand shaking method. The effect of excipients, surfactant, superdisintegrant, drug concentration and carrier particle size on dissolution rate was investigated. Dissolution rate studies of the prepared ordered mixtures revealed that all water soluble excipients increased the dissolution rate of piroxicam when compared to the dissolution rate of piroxicam or its suspension. Ordered mixture formulation PLF4, consisting of lactose as water soluble excipient, SSG (8% w/s) and SLS (1% w/w), released piroxcam at a very fast rate so much so that about 90% of the composition had passed into solution within 2 min. The order of the dissolution rate enhancement for ordered mixtures of various water soluble excipients was: lactose > mannitol > maltitol > sorbitol > sodium chloride. Carrier granules of size 355-710 µm were most effective in increasing the dissolution rate of drug from ordered mixtures. Decreasing the carrier particle size reduced drug dissolution from ordered mixtures. The dissolution rate of ordered mixtures consisting of 1-5% w/w piroxicam was superior to dissolution rate of piroxicam suspension. The dissolution data fitting and the resulting regression parameters indicated Hixson Crowell, cube root law, as the best fit to drug release data of ordered mixtures.

  16. Crystallization kinetics of the borax decahydrate

    Ceyhan, A. A.; Sahin, Ö.; Bulutcu, A. N.

    2007-03-01

    The growth and dissolution rates of borax decahydrate have been measured as a function of supersaturation for various particle sizes at different temperature ranges of 13 and 50 °C in a laboratory-scale fluidized bed crystallizer. The values of mass transfer coefficient, K, reaction rate constant, kr and reaction rate order, r were determined. The relative importances of diffusion and integration resistance were described by new terms named integration and diffusion concentration fraction. It was found that the overall growth rate of borax decahydrate is mainly controlled by integration (reaction) steps. It was also estimated that the dissolution region of borax decahydrate, apart from other materials, is controlled by diffusion and surface reaction. Increasing the temperature and particle size cause an increase in the values of kinetic parameters ( Kg, kr and K). The activation energies of overall, reaction and mass transfer steps were determined as 18.07, 18.79 and 8.26 kJmol -1, respectively.

  17. Dissolution of LMFBR fuel-sodium aerosols

    Allen, M.D.; Moss, O.R.

    1979-01-01

    Plutonium dioxide, normally insoluble in biological fluids, becomes much more soluble when mixed with sodium as the aerosol is formed. Sodium-fuel aerosols are approximately 20 times less soluble in simulated lung fluid than in distilled water. Solubility of sodium-fuel aerosols increases when Na 2 CO 3 are added to the distilled-water dissolution fluid. Mixed-oxide fuel aerosols without sodium present are relatively insoluble in distilled water, simulated lung fluid, and distilled water with Na 2 CO 3 and NaHCO 3 added

  18. System and process for dissolution of solids

    Liezers, Martin; Farmer, III, Orville T.

    2017-10-10

    A system and process are disclosed for dissolution of solids and "difficult-to-dissolve" solids. A solid sample may be ablated in an ablation device to generate nanoscale particles. Nanoparticles may then swept into a coupled plasma device operating at atmospheric pressure where the solid nanoparticles are atomized. The plasma exhaust may be delivered directly into an aqueous fluid to form a solution containing the atomized and dissolved solids. The composition of the resulting solution reflects the composition of the original solid sample.

  19. Dissolution behavior of lithium compounds in ethanol

    Tomohiro Furukawa

    2016-12-01

    Full Text Available In order to exchange the components which received irradiation damage during the operation at the International Fusion Materials Irradiation Facility, the adhered lithium, which is partially converted to lithium compounds such as lithium oxide and lithium hydroxide, should be removed from the components. In this study, the dissolution experiments of lithium compounds (lithium nitride, lithium hydroxide, and lithium oxide were performed in a candidate solvent, allowing the clarification of time and temperature dependence. Based on the results, a cleaning procedure for adhered lithium on the inner surface of the components was proposed.

  20. pH-metric solubility. 3. Dissolution titration template method for solubility determination.

    Avdeef, A; Berger, C M

    2001-12-01

    The main objective of this study was to develop an effective potentiometric saturation titration protocol for determining the aqueous intrinsic solubility and the solubility-pH profile of ionizable molecules, with the specific aim of overcoming incomplete dissolution conditions, while attempting to shorten the data collection time. A modern theory of dissolution kinetics (an extension of the Noyes-Whitney approach) was applied to acid-base titration experiments. A thermodynamic method was developed, based on a three-component model, to calculate interfacial, diffusion-layer, and bulk-water reactant concentrations in saturated solutions of ionizable compounds perturbed by additions of acid/base titrant, leading to partial dissolution of the solid material. Ten commercial drugs (cimetidine, diltiazem hydrochloride, enalapril maleate, metoprolol tartrate, nadolol, propoxyphene hydrochloride, quinine hydrochloride, terfenadine, trovafloxacin mesylate, and benzoic acid) were chosen to illustrate the new titration methodology. It was shown that the new method is about 10 times faster in determining equilibrium solubility constants, compared to the traditional saturation shake-flask methods.