Speciation of Uranium in Fernald Soils by Molecular Spectroscopic Methods:  Characterization of Untreated Soils

A combination of X-ray absorption, optical luminescence, and Raman vibrational spectroscopies along with ancillary techniques such as energy dispersive scanning electron microscopy and powder X-ray diffraction have been used to determine the chemical form of uranium in contaminated soils from the United States Department of Energy's (DOE) former uranium production facility located at Fernald, OH (30 km NW of Cincinnati). The analyses described here have been carried out on soil samples prior to the application of various decontamination technologies under development within the DOE's Uranium in Soils Integrated Demonstration Project. X-ray absorption studies have shown that ∼75−95% of the uranium in bulk samples from the site are in the hexavalent oxidation state. Because of the variety of source terms having several initial oxidation states, this consistency in oxidation state indicates that weathering has had an important role in determining the chemical form of the uranium in the soil. The application of complementary spectroscopic techniques has enabled us to identify specific chemical forms of much of this uranium, namely, autunite-like and schoepite-like phases. Additional uranium minerals were also noted, and their photodecomposition and spatial correlation with source term suggest that they may be uranium species complexed by photochemically degradable organic ligands.