Bacterially mediated and abiotic heterogeneous reduction of aqueous uranyl are of great interest due to the threat posed by uranium in the environment and the strong influence that oxidation state has on uranium solubility. In most such studies the oxidation state of uranium was identified as U(IV) and/or U(VI). The exception for the abiotic case is the study of Ilton et al. (2005) which showed that reduction of U(VI) on a ferrous silicate surface produced both sorbed U(V) and U(IV) over a broad range of pH. The primary method used to identify the distribution of U oxidation states was X-ray photoelectron spectroscopy (XPS). In particular, the satellite structure of the U4f line was a very important tool for unraveling oxidation states because the binding energy separations between the U(V) and U(IV) primary core lines were often too small to easily resolve individual peaks in the composite spectra. Although the satellite structures reflect the bonding environment as well as oxidation states, recent work (Ilton et al. 2007) indicates that the U4f satellite structures appear to be particularly robust indicators of the oxidation state of U in oxides and oxyhydroxides. This has strong implications for interpreting the XPS of mixed valence U oxides but is not with out controversy. For example, although XPS studies of corroding UO2 have recorded the appearance of U4f satellites that are consistent with near-surface U(V), most such work has hypothesized that the satellites result from bonding environment effects in U(IV)-U(VI) mixed valence UO2+x. In this regard, we are beginning to use ab initio many-body theory to better distinguish the effects of oxidation state and bonding environment on the core-level XPS and XANES of actinide minerals and compounds. .

Ilton E.S. et al. (2005) Inorg. Chem. 44, 2986-2988; Ilton E.S. et al. (2007) Surf. Sci. 601, 908-916.