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Title: Structure and thermodynamics of uranium-containing iron garnets

Abstract

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, Ca 3U xZr 2–xFe 3O 12 (x = 0.5–0.7), along with the endmember phase, Ca 3(Zr 2)SiFe 3+ 2O 12, 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 Fe 3+. 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 thatmore » 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 Ca 3U xZr 2–xFe 3O 12 as viable waste form phases for U and other actinides.« less

Authors:
 [1];  [2];  [3];  [3];  [4];  [4];  [3];  [4];  [5]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of California, Davis, CA (United States)
  2. Univ. of California, Davis, CA (United States)
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  4. Univ. of Chicago, Chicago, IL (United States)
  5. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1296668
Alternate Identifier(s):
OSTI ID: 1435357
Report Number(s):
LA-UR-15-27116
Journal ID: ISSN 0016-7037
Grant/Contract Number:  
AC52-06NA25396; AC06-76RLO1930; FG02-94ER14466
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 189; Journal ID: ISSN 0016-7037
Publisher:
The Geochemical Society; The Meteoritical Society
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; 36 MATERIALS SCIENCE; Inorganic and Physical Chemistry

Citation Formats

Guo, Xiaofeng, Navrotsky, Alexandra, Kukkadapu, Ravi K., Engelhard, Mark H., Lanzirotti, Antonio, Newville, Matthew, Ilton, Eugene S., Sutton, Stephen R., and Xu, Hongwu. Structure and thermodynamics of uranium-containing iron garnets. United States: N. p., 2016. Web. doi:10.1016/j.gca.2016.05.043.
Guo, Xiaofeng, Navrotsky, Alexandra, Kukkadapu, Ravi K., Engelhard, Mark H., Lanzirotti, Antonio, Newville, Matthew, Ilton, Eugene S., Sutton, Stephen R., & Xu, Hongwu. Structure and thermodynamics of uranium-containing iron garnets. United States. doi:10.1016/j.gca.2016.05.043.
Guo, Xiaofeng, Navrotsky, Alexandra, Kukkadapu, Ravi K., Engelhard, Mark H., Lanzirotti, Antonio, Newville, Matthew, Ilton, Eugene S., Sutton, Stephen R., and Xu, Hongwu. Thu . "Structure and thermodynamics of uranium-containing iron garnets". United States. doi:10.1016/j.gca.2016.05.043. https://www.osti.gov/servlets/purl/1296668.
@article{osti_1296668,
title = {Structure and thermodynamics of uranium-containing iron garnets},
author = {Guo, Xiaofeng and Navrotsky, Alexandra and Kukkadapu, Ravi K. and Engelhard, Mark H. and Lanzirotti, Antonio and Newville, Matthew and Ilton, Eugene S. and Sutton, Stephen R. and Xu, Hongwu},
abstractNote = {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.},
doi = {10.1016/j.gca.2016.05.043},
journal = {Geochimica et Cosmochimica Acta},
number = ,
volume = 189,
place = {United States},
year = {Thu Sep 15 00:00:00 EDT 2016},
month = {Thu Sep 15 00:00:00 EDT 2016}
}

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