Actinide Partitioning and Radiation Effects in U(VI)-Solids: Thermodynamic & Mechanistic Study
- Washington State Univ., Pullman, WA (United States). Dept. of Chemistry
- Univ. of Michigan, Ann Arbor, MI (United States)
In most environmental systems, the mobility of a contaminant metal cation depends on its partitioning between the solid and solution phase. At the molecular level, partitioning to the solid phase is controlled by the coordination requirements of the contaminant cation. In this work, we developed linear free energy relationships (LFERs) to describe the partitioning of non-U actinide cations to U(VI) solid phases in a radiation environment; the LFERs are based on knowledge of the actinide coordination environment in or on the surface of the U(VI) solid, and the impact of ionizing radiation on the atomic interactions of the non-U actinide cations. LFERs were established for predicting (1) free energies of formation of pure U(VI) solids and solid solutions with non-U actinide cations, and (2) the adsorption of non-U actinide cations to pure U(VI) solids. We demonstrated the application of LFERs developed from knowledge of molecular structures of U(VI) solid phases to predict the predominance of U(VI) oxide hydrate and silicate solid phases as a function of geochemical conditions. We extended our efforts to define LFERs for U(VI) phosphate solids, and included the impact of actinide self-radiation on all LFERs for free energies of formation for U(VI) solids. We also defined LFERs for the formation of solid solutions between the U(VI) solids and non-U actinide cations such as Th, Np, Pu, Am, and Cm. We demonstrated the importance of nanocrystalline solids in the solid phase partitioning of these non-U actinide cations. For those solid solutions formed, we investigated the impact of ionizing radiation on the stability of those phases, and the release of the non-U actinide cations from the solids. Finally, developed LFERs to predict the adsorption of the non-U actinide cations to the surfaces of U(VI) oxide hydrates and U(VI) phosphates. We determined adsorption constants and coordination requirements for actinide adsorption to U(VI) solid phases. We determined correlations between our measured adsorption constants and published thermodynamic values for their behavior in aqueous systems to develop relevant LFERs for these systems. Such LFERs can now be used to predict non-U actinide adsorption to assemblages of U(VI) solid phases. We also investigated the impact of ballistic interactions from ionizing radiation and subsequent annealing on the overall partitioning of the non-U actinides to the U(VI) solids.
- Research Organization:
- Washington State Univ., Pullman, WA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Contributing Organization:
- Univ. of Michigan, Ann Arbor, MI (United States)
- DOE Contract Number:
- FG02-06ER15782
- OSTI ID:
- 1145182
- Report Number(s):
- DOE-WSU-15782
- Country of Publication:
- United States
- Language:
- English
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