A recent study examined in unprecedented detail the structural and thermodynamic properties of uranium (U(v)) containing compounds called metal monouranates. Metal monouranates are of considerable interest due to their relevance to nuclear technology.
The new findings on this understudied form of uranium help complete the picture of uranium solid-state chemistry and could improve models of and strategies for minimizing the environmental impact of uranium contamination.
Uranium poses a serious risk to groundwater contamination at the Hanford Site and other locations worldwide. Its chemistry is complex because uranium can exist in several different oxidation states, each having different properties. Remediation strategies have focused on developing approaches for converting the highly soluble U(VI) form of uranium into the less soluble U(IV) form, which poses less risk of contamination due to its lower mobility in groundwater and soil. While much research has focused on these two forms of uranium, remediation efforts have been limited by the lack of knowledge about the intermediate U(v) form of uranium. To address this question, a team of researchers recently examined in unprecedented detail the structural and thermodynamic properties of U(v)-containing compounds called metal monouranates. U(v) containing monouranates allow in-depth structural and stability investigations. The research team used a variety of advanced structural and spectroscopic techniques combined with calorimetric measurements and computational modeling. Mossbauer and X-ray photoelectron spectroscopy (XPS) analyses were performed at the RadEMSL radiochemistry facility at EMSL, the Environmental Molecular Sciences Laboratory, a Department of Energy (DOE) national scientific user facility. This project, receiving major support from the DOE Energy Frontier Research Center, “Materials Science of Actinides,” and led by the University of California, Davis, included participation by a team of scientists from Pacific Northwest National Laboratory; Los Alamos National Laboratory; Argonne National Laboratory; and Lawrence Berkeley National Laboratory; as well as the Nuclear Energy Center of the Negev, Israel; University of California, Berkeley; University of Michigan; and University of Chicago. The research team confirmed the presence of U(v)in the thermodynamically stable metal monouranates CrUO4 and FeUO4. The structural and thermodynamic behavior of U5+ elucidated in this work is relevant to applications in the nuclear industry and radioactive waste disposal. For example, the thermodynamic studies suggest these compounds are highly stable, making them potentially useful in precipitating uranium from oxidizing aqueous environments.
This work was supported by DOE’s Office of Science (Office of Biological and Environmental Research), including support of EMSL, a DOE Office of Science User Facility. Major funding was provided by the DOE Energy Frontier Research Center, Materials Science of Actinides, Office of Basic Energy Sciences. This work was also supported by the National Science Foundation, DOE GeoSciences and the Laboratory-Directed Research and Development Program at Los Alamos National Laboratory.
X. Guo, E. Tiferet, L. Qi, J. M. Soloman, A. Lanzirotti, M. Newville, M. H. Engelhard, R. K. Kukkadapu, D. Wu, E. S. Ilton, M. Asta, S. R. Sutton, H. Xu, and A. Navrotsky, “U(v) in metal urinates: a combined experimental and theoretical study of MgUO4, CrUO4 and FeUO4”,Dalton Transactions (2016) 45,4622-4632DOI: 10.1039/c6dt00066e