Structure and stability of uranium(VI) compounds formed in carbonate containing solution
- Los Alamos National Lab., NM (United States)
Structural and thermodynamic properties of actinide(VI) compounds in aquatic systems are of particular importance to understand and predict their geochemical behavior. We investigated the system U(VI)/H{sub 2}O/NaCl/Na{sub 2}CO{sub 3} by a multi-method approach to determine the structure of U(VI) solution species and solid phases. Monomeric and polymeric carbonate complexes, UO{sub 2}(CO{sub 3}){sub n}{sup 2-2n} and (UO{sub 2}){sub 3}(CO{sub 3}){sub 6}{sup 6-}, and chloro complexes, UO{sub 2}Cl{sub n}{sup 2-n}, have been found to be the major soluble complexes in carbonate containing solution, and their stability has been investigated as a function of carbonate, chloride, and other electrolyte concentrations. We have applied spectroscopic techniques, including Raman, UV-Vis, laser-induced fluorescence, and EXAFS, and powder and single crystal X-ray diffraction to investigate the structure of U(VI) chloride and carbonate complexes and to determine significant species` formation constants. Single crystals of (K-18-Crown-6)UO{sub 2}Cl{sub 4} and (18-Crown-6)UO{sub 2}Cl{sub 2}(H{sub 2}O){sub 2} have been obtained from aqueous solution and characterized. Three major types of U(VI) carbonates structures have been found: monomeric UO{sub 2}(CO{sub 3}){sub n}{sup 2-2n} solution species with n = 1-3, planar D{sub 3h} trimetallic anion (UO{sub 2}){sub 3}(CO{sub 3}){sub 6}{sup 6-} formed at U(VI) : CO{sub 3}{sup 2-} concentration ratios of 1 : 3 in solution and solid state, and polymeric UO{sub 2}(CO{sub 3}){sub n} layers found in the solid state of rutherfordine, UO{sub 2}CO{sub 3}. Na{sub 4}AnO{sub 2}(CO{sub 3}){sup 3{sm_bullet}x}H{sub 2}O(s) has been found to form at high carbonate concentrations and its structure will be presented.
- OSTI ID:
- 560212
- Report Number(s):
- CONF-970443-; TRN: 97:005895-0195
- Resource Relation:
- Conference: 213. national meeting of the American Chemical Society, San Francisco, CA (United States), 13-17 Apr 1997; Other Information: PBD: 1997; Related Information: Is Part Of 213th ACS national meeting; PB: 2904 p.
- Country of Publication:
- United States
- Language:
- English
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