Physicochemical and Mineralogical Characterization of Uranium-Contaminated Soils

Physicochemical and mineralogical properties of the contaminants should be taken into account to decide a remediation strategy for a given radionuclide because development and optimization of soil remedial technologies are based on physicochemical and mineralogical separation techniques. The objectives of this study are to (1) demonstrate how a priori physicochemical and mineralogical characterization of soil contaminants can direct the development of remediation strategies and their performance evaluation for soil treatments and (2) understand the nature of uranium contamination and its association with the soil matrix by chemical extractions. This study examined two U-contaminated sites (K311 and K1300) at the DOE K-25 site, presently located at East Tennessee Technology Park, Oak Ridge, Tennessee. Uranium concentrations of the soils ranged from 1499 to 216,413 Bq kg^?1 at both sites. Scanning electron microscopy with backscattered electron spectroscopy and X-ray diffraction analysis showed that the dominant U phases are U oxides (schoepite), U-Ca-silicate (uranophane) and U silicate (coffinite) from the K311 site soils, whereas U-Ca-oxide and U-Ca-phosphate dominate in the K1300 site soils. Sodium carbonate/bicarbonate leaching was effective on the K1300 site soils, whereas citric acid leaching is effective on the K311 site soils. Sequential leaching showed that the majority of the uranium in the contaminated soils was contained in carbonate minerals (45%) and iron oxides (40%). Conventional leaching showed that citric acid treatment was most effective on the K311 site soils, whereas the sodium carbonate/ bicarbonate treatment was most effective on the K1300 site soils.