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Sample records for cerianite

  1. Alteration of rhyolitic (volcanic) glasses in natural Bolivian salt lakes. - Natural analogue for the behavior of radioactive waste glasses in rock salt repositories

    International Nuclear Information System (INIS)

    Alteration experiments with the R7T7 glass in three salt brines, saturated respectively in MgCl2, MgCl2-CaCl2 and NaCl, showed that the solubilities of most radionuclides are controlled by the secondary phases. Nd, La, and Pr are trapped in powellite, Ce in cerianite, U in coffinite, and Sr is partially immobilized in barite. There is a good similarity between the secondary phases formed experimentally on volcanic glasses and the R7T7 glass altered in MgCl2CaCl2-saturated brine (formation of hydrotalcite and chlorite-serpentine at short-term and saponite at long-term). These results support the use of volcanic glasses alteration patterns in Mg-rich solutions (seawater, brines) to understand the long-term behavior of nuclear waste glasses and to evaluate the stability of the secondary phases. The study of the sediments of Uyuni (Bolivia) showed that the corrosion rate of the rhyolitic glass in brines at 10 C is 12 to 30 time lower than those of rhyolitic glasses altered in high dilute conditions. The neoformed phases in the sediments are: Smectite, alunite, pyrite, barite, celestite and cerianite. The low alteration rate of rhyolitic glasses in brines and the formation of secondary phases such as smectite, barite and cerianite (also formed during the experimental alteration of the R7T7 glass), permit us to expect the low alteration of nuclear waste glasses at long-term in brines and the trapping of certain radionuclides in secondary phases. (orig.)

  2. Mineralogical aspects of Morro de Seis Lagos deposit (Amazonas, Brazil).

    Science.gov (United States)

    Takehara, Lucy; Almeida, Marcelo; Silveira, Francisco

    2014-05-01

    The alkaline body Morro dos Seis Lagos, situated in the northwest Amazonian region, is a Nb bearing deposit formed by thick lateritic regolith as circular geological feature about 5 km in diameter. The host rock of this deposit is an intensely weathered siderite carbonatite. The alkaline intrusion body was formed during the late Mesozoic and enriched during the Cenozoic by process of denudation of the surrounding rocks and formation of lateritic cover with thickness in the order of hundreds of meters. In this process, enrichment of Nb, Fe, Ti, Mn, P and rare earth elements (REE) occurred where the lateritic regolith represents the major Nb mineralization, with estimated inferred reserves of 2.9 billion ton@ 2.8 % Nb2O5, one of the largest deposits of Nb in the world. The mineralogical composition of the lateritic regolith has the predominance of the goethite and hematite, followed by oxy - hydroxides of Mn, Ti - Nb oxides, pyrochlore, cerianite and phosphates. The lateritic regolith samples showed high contents of Fe2O3 40 %, and is followed by elevated Th concentration, which locally has concentration higher than (18%). Another REE mineral is the cerianite. The main manganese minerals are hollandite, romanechite (BaMn9O16[OH4] - mixtures of manganese oxides) and amorphous Mn oxy - hydroxides. The higher concentration of MnO2 (about 40 %) is restricted to manganesiferous range, where manganese minerals occur as layers and filling voids, indicating strong remobilization by later process.

  3. Oxochloroalkoxide of the Cerium (IV and Titanium (IV as oxides precursor

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    Machado Luiz Carlos

    2002-01-01

    Full Text Available The Cerium (IV and Titanium (IV oxides mixture (CeO2-3TiO2 was prepared by thermal treatment of the oxochloroisopropoxide of Cerium (IV and Titanium (IV. The chemical route utilizing the Cerium (III chloride alcoholic complex and Titanium (IV isopropoxide is presented. The compound Ce5Ti15Cl16O30 (iOPr4(OH-Et15 was characterized by elemental analysis, FTIR and TG/DTG. The X-ray diffraction patterns of the oxides resulting from the thermal decomposition of the precursor at 1000 degreesC for 36 h indicated the formation of cubic cerianite (a = 5.417Å and tetragonal rutile (a = 4.592Å and (c = 2.962 Å, with apparent crystallite sizes around 38 and 55nm, respectively.

  4. Synthesis by Sol-gel and characterization of catalysts Ag/Al2O3-CeO2

    International Nuclear Information System (INIS)

    Aluminia, cerium and mixed oxides Al2O3-CeO2 with different relationship Al/Ce (0.75, 0.50 and 0.25) were prepared by sol-gel and used as support for the Ag. The samples were characterized by XRD, DRIFT, TPR and adsorption of N2 to temperature of liquid nitrogen. The surface area BET showed that the materials that contain aluminia present near values among them. XRD allowed to identify to the cerianite in the oxides that whose support contains cerium and to the α-aluminia. A mixture of phases was observed in the aluminia. Vibration bands attributed to the bond Al-O and Ce-O were observed by DRIFT in the catalytic materials. TPR showed differences in the reducibility of the Ag precursor in the indicative catalysts of a different interaction with the support. (Author)

  5. Mineralogy, morphology and crystal-chemistry of the monazite from Catalao 1 (Goias, Brazil); Mineralogia, morfologia e cristaloquimica da monazita de Catalao 1 (Goias, Brazil)

    Energy Technology Data Exchange (ETDEWEB)

    Toledo, Maria Cristina Motta de; Oliveira, Sonia Maria Barros de; Ferrari, Viviane Carillo [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias]. E-mails: mcristol@usp.br; vferrari@usp.br; Fontan, Francois; Parseval, Philippe de [Universite Paul Sabatier, Toulouse (France). Lab. Mineralogie et Cristallographie]. E-mails: fontan@cict.fr; parseval@insatlse.fr

    2004-03-15

    The Catalao alkaline carbonatite complex hosts a number of mineral resources including monazite. This mineral is a common accessory phase in two lithological units: carbonatite and silexite. Textural evidence suggest that monazite replaced carbonates in the carbonatite and crystallized simultaneously with quartz in the silexite. Monazite was resistant to the strong laterization that affected the massif, except for the incipient transformation into gorceixite or cerianite. In both carbonatite and silexite, monazite occurs as a complex aggregate of sub-micrometric crystals, showing unusual morphological and chemical characteristics. It contains Ca, Sr, and Ba in the A-site, and shows a certain degree of hydration indicated by ATD and IV data. Structural formulae calculated on the basis of sum of cations=1 show a moderate ionic deficiency in the anionic site. Rietveld refinement indicated poor crystallinity. Notwithstanding these peculiar characteristics, cell dimensions are similar to those of standard monazite. (author)

  6. Synthesis by Sol-gel and characterization of catalysts Ag/Al{sub 2}O{sub 3}-CeO{sub 2}; Sintesis por Sol-gel y caracterizacion de catalizadores Ag/Al{sub 2}O{sub 3}-CeO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Zayas, M.L.; Perez H, R. [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico); Rubio, E. [BUAP, Centro de Vinculacion, 72000 Puebla (Mexico); Velasco, A. [BUAP, Facultad de Quimica, 72000 Puebla (Mexico)

    2004-07-01

    Aluminia, cerium and mixed oxides Al{sub 2}O{sub 3}-CeO{sub 2} with different relationship Al/Ce (0.75, 0.50 and 0.25) were prepared by sol-gel and used as support for the Ag. The samples were characterized by XRD, DRIFT, TPR and adsorption of N{sub 2} to temperature of liquid nitrogen. The surface area BET showed that the materials that contain aluminia present near values among them. XRD allowed to identify to the cerianite in the oxides that whose support contains cerium and to the {alpha}-aluminia. A mixture of phases was observed in the aluminia. Vibration bands attributed to the bond Al-O and Ce-O were observed by DRIFT in the catalytic materials. TPR showed differences in the reducibility of the Ag precursor in the indicative catalysts of a different interaction with the support. (Author)

  7. Multi-phase glass-ceramics as a waste form for combined fission products: alkalis, alkaline earths, lanthanides, and transition metals

    International Nuclear Information System (INIS)

    In this study, multi-phase silicate-based glass-ceramics were investigated as an alternate waste form for immobilizing non-fissionable products from used nuclear fuel. Currently, borosilicate glass is the waste form selected for immobilization of this waste stream, however, the low thermal stability and solubility of MoO3 in borosilicate glass translates into a maximum waste loading in the range of 15-20 mass%. Glass-ceramics provide the opportunity to target durable crystalline phases, e.g., powellite, oxyapatite, celsian, and pollucite, that will incorporate MoO3 as well as other waste components such as lanthanides, alkalis, and alkaline earths at levels 2X the solubility limits of a single-phase glass. In addition a glass-ceramic could provide higher thermal stability, depending upon the properties of the crystalline and amorphous phases. Glass-ceramics were successfully synthesized at waste loadings of 42, 45, and 50 mass% with the following glass additives: B2O3, Al2O3, CaO and SiO2 by slow cooling form from a glass melt. Glass-ceramics were characterized in terms of phase assemblage, morphology, and thermal stability. The targeted phases: powellite and oxyapatite were observed in all of the compositions along with a lanthanide borosilicate, and cerianite. Results of this initial investigation of glass-ceramics show promise as a potential waste form to replace single-phase borosilicate glass.

  8. Fluid inclusion study of radioactive granite and cherty cataclasite in the Southeastern part of Nanded district, Maharashtra: implications for the uranium mineralisation

    International Nuclear Information System (INIS)

    Southeastern part of Nanded district, Maharashtra exposes Palaeoproterozoic granitoids, representing the younger phase of Peninsular Gneissic Complex (PGC), mark the northeastern extension of Eastern Dharwar Craton. These granitoids are predominantly pink/grey granites, which are traversed by younger phosphatic cherty cataclasites close to the Deccan Trap capping. They are also affected by profuse pegmatitic/quartzo-feldspathic, quartz and epidote venations, especially close to fault/shear zones. A number of N-S to NNE-SSW, NE-SW, NW-SE and E-W trending lineaments marked by faults/fractures/shear zones and dykes are delineated in this granitic terrain. Among these, NE-SW and NNE-SSW faults/shear zones affecting granitoids and cherty cataclasites in Shahpur-Sujayatpur and Thadisaoli area have recorded significant uranium anomalies (Granitoids: upto 1% U3O8 and 0.20% ThO2; Cherty cataclasites upto 0.11% U3O8 and <0.005% ThO2) and enrichment in rare metal and rare earth element content (Nb-77ppm, Y-111 ppm, Zr-432ppm; n=9 and total REE-1167ppm; n=3). Presence of discrete uranium/thorium minerals (uraninite, b-uranophane and thorite) and high content of resistates viz., apatite, zircon, allanite, sphene, cerianite, monazite and ilmenite are responsible for radioactivity in granitoids while phosphatic material accounts for radioactivity in cherty cataclasites

  9. Catalysts with Cerium in a Membrane Reactor for the Removal of Formaldehyde Pollutant from Water Effluents

    Directory of Open Access Journals (Sweden)

    Mirella Gutiérrez-Arzaluz

    2016-05-01

    Full Text Available We report the synthesis of cerium oxide, cobalt oxide, mixed cerium, and cobalt oxides and a Ce–Co/Al2O3 membrane, which are employed as catalysts for the catalytic wet oxidation (CWO reaction process and the removal of formaldehyde from industrial effluents. Formaldehyde is present in numerous waste streams from the chemical industry in a concentration low enough to make its recovery not economically justified but high enough to create an environmental hazard. Common biological degradation methods do not work for formaldehyde, a highly toxic but refractory, low biodegradability substance. The CWO reaction is a recent, promising alternative that also permits much lower temperature and pressure conditions than other oxidation processes, resulting in economic benefits. The CWO reaction employing Ce- and Co-containing catalysts was carried out inside a slurry batch reactor and a membrane reactor. Experimental results are reported. Next, a mixed Ce–Co oxide film was supported on an γ-alumina membrane used in a catalytic membrane reactor to compare formaldehyde removal between both types of systems. Catalytic materials with cerium and with a relatively large amount of cerium favored the transformation of formaldehyde. Cerium was present as cerianite in the catalytic materials, as indicated by X-ray diffraction patterns.

  10. Catalysts with Cerium in a Membrane Reactor for the Removal of Formaldehyde Pollutant from Water Effluents.

    Science.gov (United States)

    Gutiérrez-Arzaluz, Mirella; Noreña-Franco, Luis; Ángel-Cuevas, Saúl; Mugica-Álvarez, Violeta; Torres-Rodríguez, Miguel

    2016-01-01

    We report the synthesis of cerium oxide, cobalt oxide, mixed cerium, and cobalt oxides and a Ce-Co/Al₂O₃ membrane, which are employed as catalysts for the catalytic wet oxidation (CWO) reaction process and the removal of formaldehyde from industrial effluents. Formaldehyde is present in numerous waste streams from the chemical industry in a concentration low enough to make its recovery not economically justified but high enough to create an environmental hazard. Common biological degradation methods do not work for formaldehyde, a highly toxic but refractory, low biodegradability substance. The CWO reaction is a recent, promising alternative that also permits much lower temperature and pressure conditions than other oxidation processes, resulting in economic benefits. The CWO reaction employing Ce- and Co-containing catalysts was carried out inside a slurry batch reactor and a membrane reactor. Experimental results are reported. Next, a mixed Ce-Co oxide film was supported on an γ-alumina membrane used in a catalytic membrane reactor to compare formaldehyde removal between both types of systems. Catalytic materials with cerium and with a relatively large amount of cerium favored the transformation of formaldehyde. Cerium was present as cerianite in the catalytic materials, as indicated by X-ray diffraction patterns. PMID:27231888

  11. Cu O-CeO2 catalysts for the CO preferential oxidation (CO PROX)

    International Nuclear Information System (INIS)

    The aim of this work is to synthesize and characterize Cu-Ce catalysts prepared by homogeneous precipitation with urea and, also, to evaluate their catalytic activity for the preferential oxidation of CO.Cu-Ce precursors with different copper content were prepared (the atomic ratio of copper to total metal was varied between 0 and 60%). Upon mild thermal treatment under air atmosphere (T = 723 K) powders are readily converted into nano-CeO2 with high superficial area.The catalysts were characterized by X-ray diffraction, it was found that all of them contained CeO2 (cerianite), and only the sample with the highest copper content contained Cu O (tenorite).The samples were evaluated in the catalytic reaction of preferential oxidation of CO in the temperature range between 373 and 523 K.It was found that they are very active and selective.The best catalytic performance was shown by the catalysts with a copper to total metal ratio of 10 to 20%

  12. Optical properties and electrochromic characterization of sol-gel deposited ceria films

    Energy Technology Data Exchange (ETDEWEB)

    Oezer, N. [Department of Materials Science and Mineral Engineering, University of California, 94720-1760 Berkeley, CA (United States)

    2001-06-01

    Ceria (CeO{sub 2}) films were deposited by the sol-gel spin coating process and optical and electrochromic properties have been investigated. Ceria coating solutions were prepared using cerium ammonium nitrate and ethanol. The films were characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV-visible (UV-Vis) spectroscopy and cyclic voltammetry. XRD analysis of the films showed that they had a cerianite structure for heat treatment temperatures at or above 450C. XPS examinations show that the film stoichiometry was CeO{sub 2}. The SEM examinations showed that the surface texture was very uniform and homogeneous. Optical constants of the films were calculated from transmittance (T) spectra using optical spectrometer in the wavelength range of 300-900nm. The refractive index (n), and extinction coefficient (k) values were n=1.82{+-}0.01 and k=0.02{+-}0.002 at 550nm, respectively. The optical bandgap (E{sub g}) of crystalline cerium oxide film was 3.1{+-}0.003eV. The electrochemical behavior investigated in 0.5M LiClO{sub 4} propylene carbonate (PC) electrolyte. Cyclic voltammetry showed a reversible electrochemical insertion or extraction of the Li{sup +} ions maintaining a high optical transmissivity. Spectroelectrochemistry showed that these films could be used as optically passive counter-electrode in transmissive electrochromic devices.

  13. Surface morphology, optical and electrochemical properties of undoped and Ni-doped CeO2 thin films prepared by polymeric precursor method

    Science.gov (United States)

    Khosousi Sani, Zara; Esmaeli Ghodsi, Farhad; Mazloom, Jamal

    2016-04-01

    In this study, undoped and Ni-doped CeO2 thin films were deposited onto glass and ITO substrates by polymeric precursor (Pechini) method. Grazing incidence X-ray diffraction analysis revealed that the ceria thin film has a cerianite structure with the average crystallite size of 14 nm while the doped samples are amorphous. X-ray photoelectron spectroscopy (XPS) confirmed the presence of predominant Ce4+ oxidation state of ceria and Ni2+ in the films. Scanning electron microscopy (SEM) micrographs showed that the surface texture is crack free and the CeO2 grains regularly distributed on the surface. Optical constant (refractive index and extinction coefficient) and thickness of films were calculated using pointwise unconstraint minimization approach. The optical transmittance increases and the absorption edge has a blue shift by Ni incorporation. The highest band gap value (i.e., 3.43 eV) was obtained for 2.5 mol.% Ni doping sample. The refractive index and extinction coefficient of ceria films were decreased by Ni doping. The evaluated thicknesses are in the range of 150-170 nm. The strength of interband transition was appraised as a function of nickel content by using dielectric function. Luminescent emission intensity of the ceria film was enhanced by Ni doping. Cyclic voltammetry (CV) measurement revealed that the total charge density and ion storage capacitance of ceria thin film were increased by Ni doping.

  14. Studies of mineralogy and geochemistry of Rare Earth Elements in permo-Triassic Bauxite deposit, Northeast of Bukan, North West of Iran

    International Nuclear Information System (INIS)

    Bauxite deposit of Permo-Triassic age in northeast of Bukan was developed stratiformly along the boundary between Ruteh and Elika formations, and includes four distinct rock units. This deposit was affected by tectonic and morphological processes. Mineralogical and geochemical investigations showed that during weathering processes, two mechanisms of ferrugenization and deferrugenization played crucial role in formation of minerals such as Diaspora, boehmite, hematite, goethite, kaolinite, pyrophyllite, clinochlore, illite, montmorillonite, anatase, rutile, albite, sanidine, quartz, and calcite in this deposit. By taking notice of field evidence and of mineralogical and geochemical data, the basalts (whose remnants are still present along the contact of this deposit with carbonate bedrock) are the potential parent rock of this deposit. The distribution pattern of rare earth elements (normalized to chondrite and basaltic parent rock) along with anomaly variations of Eu, Ce, and (La/Yb)N indicates differentiation of LREEs from HREEs during bauxitization processes. Further geochemical considerations indicate that the concentrations of LREEs were occurred by hematite, goethite, manganese oxides, cerianite, and secondary phosphates (rhabdophane, vitusite, gorceixite, monazite) and of HREEs by clay minerals; rutile, anatase, zircon, euxenite, and fergusonite. Incorporation of the results obtained from mineralogical and geochemical investigations suggests that in addition to factors such as p H of weathering solutions, ionic potential, composition of the parent rock, and fixation by residual minerals, adsorption processes also played crucial role in enrichment of rare earth elements during moderate to intense lateritization in the study area

  15. Rare earth element mineralogy and geochemistry in a laterite profile from Madagascar

    International Nuclear Information System (INIS)

    Highlights: • Secondary REE-mineralogy depend on redox conditions inside a laterite. • Detailed mineralogy in different layers of a laterite is given. • A Gd-sulfate is described. • Change in bulk rock chemistry control REE mineralogy. - Abstract: In this study, rare earth element (REE) distribution has been investigated in a weathering profile from central Madagascar. Combination of bulk rock geochemical data (elements and isotopes) with mineral characterization reveals a remarkable evolution of the REE abundances and REE-minerals in the vertical weathering profile. In the fresh tonalite (bedrock), REE + Y concentrations are typical of granitoids (299–363 ppm) and the main REE-minerals are allanite and chevkinite. In the C-horizon (saprolite), primary REE-minerals disappear and REEs are transported via fluid to precipitate rhabdophane group minerals in cracks and pores. The presence of sulfate ligands, produced by sulfide oxidation, may be responsible for the REE speciation, as suggested by the composition of the secondary REE-minerals. Rhabdophane group minerals contain up to 9 wt% SO3 and 7 wt% CaO, indicating a mixture between rhabdophane sensu stricto, (REE)PO4·H2O, and tristamite, (Ca,U,Fe(III))(PO4,SO4)·2H2O. Due to intense Ca-leaching, rhabdophane disappears and Al-phosphates (alunite–jarosite group) are found in the soil. Cerianite (Ce(IV)O2) also precipitates in the B-horizon of the soil. Mass transfer calculations based on immobile Ti indicate significant REE leaching in A-horizon with preferential leaching of the heavy REE. REEs accumulate partly in the B-horizon. The uniform Nd isotope compositions and the constant proportion of immobile elements do not reveal external input. In the B-horizon, total REE + Y reach 2194 ppm with high Ce concentrations (1638 ppm; 9*Cebedrock) compared to other REE (3–4*REEbedrock). Tetravalent Ce state is dominant in the B-horizon and requires oxidizing conditions that likely account for the accumulation

  16. Multi-phase glass-ceramics as a waste form for combined fission products: alkalis, alkaline earths, lanthanides, and transition metals

    Energy Technology Data Exchange (ETDEWEB)

    Crum, Jarrod V.; Turo, Laura A.; Riley, Brian J.; Tang, Ming; Kossoy, Anna

    2012-04-01

    In this study, multi-phase silicate-based glass-ceramics were investigated as an alternate waste form for immobilizing non-fissionable products from used nuclear fuel. Currently, borosilicate glass is the waste form selected for immobilization of this waste stream, however, the low thermal stability and solubility of MoO{sub 3} in borosilicate glass translates into a maximum waste loading in the range of 15-20 mass%. Glass-ceramics provide the opportunity to target durable crystalline phases, e.g., powellite, oxyapatite, celsian, and pollucite, that will incorporate MoO{sub 3} as well as other waste components such as lanthanides, alkalis, and alkaline earths at levels 2X the solubility limits of a single-phase glass. In addition a glass-ceramic could provide higher thermal stability, depending upon the properties of the crystalline and amorphous phases. Glass-ceramics were successfully synthesized at waste loadings of 42, 45, and 50 mass% with the following glass additives: B{sub 2}O{sub 3}, Al{sub 2}O{sub 3}, CaO and SiO{sub 2} by slow cooling form from a glass melt. Glass-ceramics were characterized in terms of phase assemblage, morphology, and thermal stability. The targeted phases: powellite and oxyapatite were observed in all of the compositions along with a lanthanide borosilicate, and cerianite. Results of this initial investigation of glass-ceramics show promise as a potential waste form to replace single-phase borosilicate glass.

  17. Behaviour of major, minor and trace elements (including REEs during kaolinization processes at Zonouz deposit, northeast of Marand, East Azarbaidjan province

    Directory of Open Access Journals (Sweden)

    Vahideh Alipour

    2011-11-01

    Full Text Available The Zonouz kaolin deposit is located ~15 km northeast of Marand, East-Azarbaidjan province. Based on physical features in field investigations, such as color, five distinct kaolin types including (1 white, (2 lemon, (3 gray, (4 brown, and (5 yellow are distinguished in the deposit. Field evidence and petrographic studies indicate that the deposit is genetically close to trachy-andesite rocks. According to mineralogical data, the deposit contains quartz, kaolinite, montmorillonite, calcite, pyrophyllite, chlorite, muscovite-illite, dolomite, hematite, and anatase minerals. Geochemical data indicate that function of alteration processes on trachy-andesite rocks during development of Zonouz ore deposit was accompanied by leaching of elements such as Al, Na, K, Rb, Ba, V, Hf, Cu, Zr, Tm, Yb, and Lu, enrichment of elements such as U, Nb, and Ta, and leaching-fixation of elements such as Si, Fe, Ca, Mg, Ti, Mn, P, Cs, Sr, Th, Co, Cr, Ni, Y, Ga, LREE, Tb, Dy, Ho, and Er. Incorporation of obtained results from mineralogical and geochemical studies show that physico-chemical conditions of alteration environment, the relative stability of primary minerals, surface adsorption, preferential sorption by metallic oxides, existing of organic matters, scavenging and concentration processes, and fixation in neomorphic mineralogical phases played important role in distribution of elements in the deposit. Geochemical studies show that development of the deposit is relative to two types of processes, (1 hypogene and (2 supergene. The distribution pattern of REEs indicates that differentiation degree of LREEs from HREEs in supergene kaolins is more than hypogene kaolins. Geochemical studies indicate that minerals such as Mn-oxides, zircon, anatase, hematite, cerianite, and secondary phosphates (monazite, rhabdophane, churchite, and zenotime are the potential hosts for rare earth elements in this deposit.

  18. Microstructure and Composition of a Ce-pyrochlore: A Chemical Analog for Pu-pyrochlore

    Science.gov (United States)

    Xu, Huifang; Wang, Yifeng; Garvie, Laurence A. J.; Putnam, Robert L.; Navrotsky, Alexandra

    2003-07-01

    Ce-pyrochlore (CaCeTi2O7), is a chemical analogue for CaPuTi2O7, which is a proposed ceramic waste form for deposition of excess weapon-usable Pu in geological repositories. Ce-pyrochlore was synthesized by firing and annealing a mixture of Ce(NO3)4, TiO2, and Ca(OH)2 with a stoichiometry of CaCeTi2O7 at 1,300°C for 50 hours. The annealed product contains Ce-pyrochlore, Ce-bearing perovskite, CeO2 (cerianite), and minor CaO. Electron energy-loss spectroscopy (EELS) was used to determine the valence of Ce in the synthesized materials using the shape of the Ce M4,5 edge. Cerium in the perovskite is dominated by Ce3+. The Ce4+/ΣCe in the pyrochlore is 0.8, giving (Ca0.87Ce0.203+Ce0.864+Ti0.05)Ti2O7. High-resolution TEM images show that the boundary between pyrochlore and perovskite is semicoherently bonded. The orientational relationship between the neighboring pyrochlore and perovskite is not random. There are no glassy phases observed at the grain boundaries between pyrochlore and perovskite, and between CeO2 and pyrochlore. It is postulated, based on the presence of trivalent Ce in the Ce-pyrochlore, that the neutron poisons such as Gd can be incorporated into the CaPuTi2O7 phase.

  19. Synthesis and characterization of thermoluminescent glass-ceramics Li{sub 2}O-Al{sub 2}O{sub 3}-SiO{sub 2}:CeO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Gutierrez, Omar. D., E-mail: omargutierrez@itm.edu.c [Grupo Mytec, Instituto Tecnologico Metropolitano, Calle 73 No 76A-354 Via al Volador, Medellin (Colombia); Osorio, Edison [Grupo de Quimica-Fisica Teorica, Instituto de Quimica, Universidad de Antioquia, A A. 1226, Medellin (Colombia); Departamento de Ciencias Quimicas, Universidad Andres Bello, Av. Republica 275, Santiago (Chile); Paucar, Carlos. G. [Grupo de Ceramicos y Vitreos, Facultad de Ciencias, Universidad Nacional de Colombia, A A. 568, Medellin (Colombia); Cogollo, Rafael [Grupo de Materiales y Fisica Aplicada, Universidad de Cordoba, Codigo Postal 354, Monteria (Colombia); Hadad, C.Z. [Grupo de Quimica-Fisica Teorica, Instituto de Quimica, Universidad de Antioquia, A A. 1226, Medellin (Colombia)

    2009-08-15

    Vitroceramic powders of Li{sub 2}O-Al{sub 2}O{sub 3}-SiO{sub 2} systems (LAS), doped with 1% (LAS:1Ce) and 10% (LAS:10Ce) molar of cerianite (CeO{sub 2}) were synthesized by means of the gelification technique of metal formates of aluminum and lithium, in the presence of tetraethoxy silane and CeO{sub 2}. The gels obtained were dried (120 deg. C, 2.5 h), calcined (480 deg. C, 5 h) and sinterized (1250 deg. C, 30 min). The sinterized samples were characterized by X-ray difraction (XRD), scanning electron microscopy (SEM) and microchemical analysis (EDS). There is evidence for a mixture of two phases of 64% beta-spodumene (Li{sub 2}O-Al{sub 2}O{sub 3}-4SiO{sub 2}) and 36% beta-eucryptite (Li{sub 2}O-Al{sub 2}O{sub 3}-2SiO{sub 2}). The LAS:1Ce system was enriched in aluminum, the LAS:10Ce system showed areas of heterogeneous composition; some regions with a shortage of CeO{sub 2}, while others zones with cerium cumulus. From the microscopy images it was found that CeO{sub 2} acts as a densificant agent in LAS system, favoring the sintering in the host. The chemical route and the sintering processes utilized allow the production of samples exhibiting an acceptable linear correlation between total thermoluminescent emission intensity and the irradiation dose when the CeO{sub 2} concentration is low (less than 1%), opening the possibility of using this kind of glass-ceramic in dosimetry.

  20. The solvent extraction of cerium from sulphate solution - mini plant trials

    International Nuclear Information System (INIS)

    Full text: The Mt. Weld deposit in Western Australia has a complex rare earth mineralisation. The rare earth phosphate minerals, which include monazite, are amenable to conventional caustic cracking followed by hydrochloric acid dissolution of the trivalent rare earths. The presence of the mineral cerianite in the ore, which is unaffected by the alkali attack, results in rejection of a considerable proportion of the cerium to the acid leach residue. The recovery of cerium from a sulphate solution, resulting from the processing of such a residue, is the subject of the current paper. The liquor treated by solvent extraction contained 63 g L-1 rare earths and the cerium to total rare earth ratio was 75%. Other impurities, including Fe and Th, totalled 2000 ppm. A solvent mixture of commercially available extractants in a low aromatic content diluent was used to extract Ce4+ selectively over the trivalent rare earths. Partial co-extraction of Fe and Th occurred but it was found that these elements were not easily stripped and therefore selective back extraction of cerium was possible. The cerium was stripped from the organic phase by hydrochloric acid and hydrogen peroxide. In continuous counter-current trials two extraction stages and three strip stages were used. In order to produce two grades of strip liquor, stripping was divided into two circuits. The first strip circuit consisting of a single stage, contained proportionally more of the trivalent rare earths. The second strip circuit, consisting of two stages, removed the remaining cerium with proportionally less of the rare earths. A bleed solvent stream was treated for removal of impurities to prevent build-up in the solvent. In the continuous counter current trials, 95% Ce4+ extraction was achieved and the Ce to total rare earth ratio was upgraded to > 99%

  1. Geochemistry and mineralogy of the radioactive minerals associated with some pegmatite veins of the Ukma-Nawahatu Hursi sector, Purulia district, W.B., in the Precambrian Chhotanagpur Gneissic complex

    International Nuclear Information System (INIS)

    Some barite-bearing pegmatites in the Ukma-Nawahatu-Hursi sector (23° 25 min - 26 sec N, 86° 02 min - 04 sec E) in Purulia dist., West Bengal, have association of radioactive minerals in the form of coarse-grained pitchblack lumps and irregular patches. The present author and his associates first reported the occurrence of this radioactive belt along a ENE-WSW shearzone during their fieldwork in November, 1978. Groundborne radiometric survey and isorad mapping has established a radioactive high zone of about 15 km length running through Ukma, Nawahatu and Hursi areas. Mineralogical studies of the radioactive minerals have revealed the occurrence of Chevkinite, Aeschynite, Brannerite, Allanite, Uraninite, Tyuyamunite, Davidite, Euxenite, Samarskite, Thorutite, Autunite, Cerianite, in association with quartz, barite, microcline as the principal minerals and various minor minerals like biotite, vermiculite, hornblende, augite, orthoclase, celsian, muscovite, calcite, epidote, zoisite, ilmenite, sphene, rutile, hematite, magnetite, anatase, galena and sodic plagioclase. The barite-bearing pegmatites occur as lenses or lenticular veins hosted by garnetiferous sillimanite-biotite-quartz-schist or occasionally by migmatite. Near Nawahatu the radioactive barite-pegmatite vein occurs at or near the junction between the footwall amphibolite and hangingwall garnetiferous schist. The pegmatite veins have followed mainly schistosity of the host rock and dip at 70°-80° towards south. Chemical analyses of individual radioactive minerals by SEM-EDX and also of the bulk radioactive lumps by ICP-MS have shown significant concentration of U, Tb and Rare earths. Minor and trace element analyses also record notable contents of Zr, Ga, Sc, Pb, Zn, Nb, Cu, Ni, V, Cr, As, W, Pd, Ag and TI. Details of chemical analytical data are presented here. Chemically active fluids generated during metamorphism, metasomatism and granitic activity appear to have played a significant role in the

  2. Effect of support on iron promoted rhodium nanocatalysts for ethanol synthesis from CO hydrogenation

    Science.gov (United States)

    Carrillo Sanchez, Pamela Carolina

    Depleting fossil fuel sources coupled with the deleterious effects of petroleum-based fuel combustion have led to the development of sustainable ways for energy production. One alternative is the production of biofuels like ethanol. Ethanol's biggest advantages are its high energy density, biodegradability and carbon neutrality. A potential scalable process is the conversion of synthetic gas (syngas: CO, CO2, H 2) produced from gasification of biomass with the use of Rh-based catalysts. The work presented in this thesis aimed to study the effect of the introduction of 1, 5, and 10 wt % CeO2 into a TiO2 support on Fe promoted-Rh catalysts for ethanol production from CO hydrogenation. The mixed-oxide CeO2-TiO2 support was synthesized by a sol-gel method where Rh and Fe nanoparticles were deposited by wet incipient impregnation. Reactivity studies were carried under CO hydrogenation conditions with the use of gas chromatography. Characterization of the bare support and the catalyst that showed the best ethanol selectivity were performed by in-situ X-ray diffraction synchrotron experiments. Ethanol selectivity increases with ceria content with a shift on product distribution and CO conversion rates compared to Rh supported on single TiO2 and CeO2. This could be explained by a synergetic effect between CeO2 and TiO2 and to the to the formation of amorphous and mobile species of CeOx that can act as dispersing agents for the Rh particles increasing catalytic sites for CO insertion and for the stabilization of HCOx species. XRD characterization analysis of 10%CeO2-90%TiO2 identified three crystallographic phases: anatase, TiO2(B), and cerianite. The unpromoted 2%Rh/10%CeO2-90%TiO2 in-situ XRD analysis showed an absence of Rh0 under CO hydrogenation conditions. Conversely, the addition of Fe to the different mixed-oxide compositions showed comparable ethanol selectivity at the expense of methane formation. Therefore, the introduction of ceria into the titania support on

  3. Calcite and dolomite in intrusive carbonatites. II. Trace-element variations

    Science.gov (United States)

    Chakhmouradian, Anton R.; Reguir, Ekaterina P.; Couëslan, Christopher; Yang, Panseok

    2016-04-01

    The composition of calcite and dolomite from several carbonatite complexes (including a large set of petrographically diverse samples from the Aley complex in Canada) was studied by electron-microprobe analysis and laser-ablation inductively-coupled-plasma mass-spectrometry to identify the extent of substitution of rare-earth and other trace elements in these minerals and the effects of different igneous and postmagmatic processes on their composition. Analysis of the newly acquired and published data shows that the contents of rare-earth elements (REE) and certain REE ratios in magmatic calcite and dolomite are controlled by crystal fractionation of fluorapatite, monazite and, possibly, other minerals. Enrichment in REE observed in some samples (up to ~2000 ppm in calcite) cannot be accounted for by coupled substitutions involving Na, P or As. At Aley, the REE abundances and chondrite-normalized (La/Yb)cn ratios in carbonates decrease with progressive fractionation. Sequestration of heavy REE from carbonatitic magma by calcic garnet may be responsible for a steeply sloping "exponential" pattern and lowered Ce/Ce* ratios of calcite from Magnet Cove (USA) and other localities. Alternatively, the low levels of Ce and Mn in these samples could result from preferential removal of these elements by Ce4+- and Mn3+-bearing minerals (such as cerianite and spinels) at increasing f(O2) in the magma. The distribution of large-ion lithophile elements (LILE = Sr, Ba and Pb) in rock-forming carbonates also shows trends indicative of crystal fractionation effects (e.g., concomitant depletion in Ba + Pb at Aley, or Sr + Ba at Kerimasi), although the phases responsible for these variations cannot be identified unambiguously at present. Overall, element ratios sensitive to the redox state of the magma and its complexing characteristics (Eu/Eu*, Ce/Ce* and Y/Ho) are least variable and in both primary calcite and dolomite, approach the average chondritic values. In consanguineous

  4. Batievaite-(Y), Y2Ca2Ti[Si2O7]2(OH)2(H2O)4, a new mineral from nepheline syenite pegmatite in the Sakharjok massif, Kola Peninsula, Russia

    Science.gov (United States)

    Lyalina, L. M.; Zolotarev, A. A.; Selivanova, E. A.; Savchenko, Ye. E.; Krivovichev, S. V.; Mikhailova, Yu. A.; Kadyrova, G. I.; Zozulya, D. R.

    2016-05-01

    Batievaite-(Y), Y2Ca2Ti[Si2O7]2(OH)2(H2O)4, is a new mineral found in nepheline syenite pegmatite in the Sakharjok alkaline massif, Western Keivy, Kola Peninsula, Russia. The pegmatite mainly consists of nepheline, albite, alkali pyroxenes, amphiboles, biotite and zeolites. Batievaite-(Y) is a late-pegmatitic or hydrothermal mineral associated with meliphanite, fluorite, calcite, zircon, britholite-group minerals, leucophanite, gadolinite-subgroup minerals, titanite, smectites, pyrochlore-group minerals, zirkelite, cerianite-(Ce), rutile, behoite, ilmenite, apatite-group minerals, mimetite, molybdenite, and nickeline. Batievaite-(Y) is pale-cream coloured with white streak and dull, greasy or pearly luster. Its Mohs hardness is 5-5.5. No cleavage or parting was observed. The measured density is 3.45(5) g/cm3. Batievaite-(Y) is optically biaxial positive, α 1.745(5), β 1.747(5), γ 1.752(5) (λ 589 nm), 2V meas. = 60(5)°, 2V calc. = 65°. Batievaite-(Y) is triclinic, space group P-1, a 9.4024(8), b 5.5623(5), c 7.3784(6) Å, α 89.919(2), β 101.408(2), γ 96.621(2)°, V 375.65(6) Å3 and Z = 1. The eight strongest lines of the X-ray powder diffraction pattern [d(Å)(I)(hkl)] are: 2.991(100)(11-2), 7.238(36)(00-1), 3.061(30)(300), 4.350(23)(0-1-1), 9.145(17)(100), 4.042(16)(11-1), 2.819(16)(3-10), 3.745(13)(2-10). The chemical composition determined by electron probe microanalysis (EPMA) is (wt.%): Nb2O5 2.25, TiO2 8.01, ZrO2 2.72, SiO2 29.96, Al2O3 0.56, Fe2O3 0.43, Y2O3 11.45, La2O3 0.22, Ce2O3 0.33, Nd2O3 0.02, Gd2O3 0.07, Dy2O3 0.47, Er2O3 1.07, Tm2O3 0.25, Yb2O3 2.81, Lu2O3 0.45, CaO 24.98, MnO 1.31, MgO 0.01, Na2O 1.13, K2O 0.02, F 2.88, Cl 0.19, H2O 6.75 (determined on the basis of crystal structure data), O = (F,Cl) -1.25, total 97.09 wt.%. The empirical formula based on the EPMA and single-crystal structure analyses is (Y0.81Ca0.65Mn0.15Zr0.12Yb0.11Er0.04Fe3+ 0.04Ce0.02Dy0.02Lu0.02La0.01Tm0.01)Σ2.00((H2O)0.75Ca0.70□0.55)Σ2.00Ca2.00(□0.61Na0.25( H2O

  5. Methanol reformer with water vapor and oxygen in catalysts of Cu/CeO2-ZrO2 to generate H2

    International Nuclear Information System (INIS)

    to the zirconia having as area in ZrO2 7m2/g and for CeO2 of 60 m2/g and it was modified respectively with a slight decrease of 5 and 56 m2/g. The crystalline phases present in the catalysts are the tetragonal and the monoclinic in the catalyst Cu/ZrO2; tetragonal in the catalyst rich in zirconia (Cu/ZC10). For the catalysts Cu/CeO2 and Cu/ZC90 the cerianite phase is identified (characteristic of the cubic structure of the cerium). In the catalyst Cu/ZC50 a mixture of oxides made up of zirconia-cerium is observed (tetragonal and cubic). The morphology shows semi spheric particles for the materials rich in ZrO2 and planar added in the materials rich in CeO2 that in turn form attaches of greater dimensions. All the TPR profiles was characterized to present consumption peaks of H2 associated with the CuO reduction. The addition of CeO2 to ZrO2 promotes the reduction from the CuO at low temperatures regarding to the catalyst Cu/ZrO2. It is clearly observed that the biggest activity in the transformation of the methanol was in the catalysts rich in cerium in the whole temperature interval studied. As long as for the catalysts rich in zirconia and in the catalyst Cu/ZC50 the increment in the catalytic activity was smaller in function of the temperature. To the maximum reaction temperature (300 C) it was observed the following behavior: Cu/CeO2 ≅ Cu/ZC90 > Cu/ZC50 > Cu/ZC10 > Cu/ZrO2. It is important to mention that the catalysts more active are those that present peaks of copper reduction to smaller 300 C. As for the selectivity toward the H2, in the region of high methanol conversion the rich catalysts in cerium presented bigger selectivity regarding the catalysts rich in zirconia. Due to the methanol conversion increases conforms to it increased the reaction temperature, the decrease in the production of H2 observed in the catalysts with high zirconia content, it can be associated by the oxidation of H2 with O2. The catalytic behavior of the catalysts Cu/ZrO2-CeO2 can