X-ray spectroscopic studies of microbial transformations of uranium

摘要

Several uranium compounds, U-metal (alpha-phase), UO2, U3O8, gamma-UO3, uranyl acetate, uranyl nitrate, uranyl sulfate, aqueous and solid forms of 1:1 U:citric acid and 1:1:2 U:Fe:citric acid mixed-metal complexes, and a precipitate obtained by photodegradation of the U-citrate complex were characterized by X-ray spectroscopy using XPS, XANES, and EXAFS. XPS and XANES were used to determine U oxidation states. The magnitude of the energy shift with oxidation state, and the ability to detect mixed-valent forms make these ideal techniques for determining uranium speciation in wastes subjected to bacterial action. The structure of 1:1 U:citric acid complex in both the aqueous and solid state was determined by EXAFS analysis of hexavalent uranium at the L(sub M) absorption edge and suggests the presence of a binuclear complex with a (UO2)(2)((mu),(eta)(sup 2) -citrato)(sub 2) core with a U-U distance of 5.2 angstroms.