Structure and thermodynamics of uranium-containing iron garnets
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of California, Davis, CA (United States)
- Univ. of California, Davis, CA (United States)
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Univ. of Chicago, Chicago, IL (United States)
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Use of crystalline garnet as a waste form phase appears to be advantageous for accommodating actinides from nuclear waste. Previous studies show that large amounts of uranium (U) and its analogues such as cerium (Ce) and thorium (Th) can be incorporated into the garnet structure. In this study, we synthesized U loaded garnet phases, Ca3UxZr2–xFe3O12 (x = 0.5–0.7), along with the endmember phase, Ca3(Zr2)SiFe3+2O12, for comparison. The oxidation states of U were determined by X-ray photoelectron and absorption spectroscopies, revealing the presence of mixed pentavalent and hexavalent uranium in the phases with x = 0.6 and 0.7. The oxidation states and coordination environments of Fe were measured using transmission 57Fe-Mössbauer spectroscopy, which shows that all iron is tetrahedrally coordinated Fe3+. U substitution had a significant effect on local environments, the extent of U substitution within this range had a minimal effect on the structure, and unlike in the x = 0 sample, Fe exists in two different environments in the substituted garnets. The enthalpies of formation of garnet phases from constituent oxides and elements were first time determined by high temperature oxide melt solution calorimetry. The results indicate that these substituted garnets are thermodynamically stable under reducing conditions. Furthermore, our structural and thermodynamic analysis further provides explanation for the formation of natural uranium garnet, elbrusite-(Zr), and supports the potential use of Ca3UxZr2–xFe3O12 as viable waste form phases for U and other actinides.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Biological and Environmental Research (BER)
- Grant/Contract Number:
- AC52-06NA25396; SC0001089; AC06-76RLO1930; FG02-94ER14466; AC02-06CH11357
- OSTI ID:
- 1296668
- Alternate ID(s):
- OSTI ID: 1435357
- Report Number(s):
- LA-UR-15-27116
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 189; ISSN 0016-7037
- Publisher:
- The Geochemical Society; The Meteoritical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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journal | April 2019 |
Effect of calcium oxide doping on the microstructure and optical properties of YAG transparent ceramics
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journal | December 2018 |
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