Physicochemical and mineralogical characterization of uranium-contaminatedsoils

Physicochemical and mineralogical properties of the contaminants should be taken into account to decide a remediation strategy for a given radionuclid e because development and optimization of soil remedial technologies are ba sed on physicochemical and mineralogical separation techniques. The objecti ves of this study are to (1) demonstrate how a priori physicochemical and m ineralogical characterization of soil contaminants can direct the developme nt of remediation strategies and their performance evaluation for soil trea tments and (2) understand the nature of uranium contamination and its assoc iation with the soil matrix by chemical extractions. This study examined tw o U-contaminated sites (K311 and K1300) at the DOE K-25 site, presently loc ated at East Tennessee Technology Park, Oak Ridge, Tennessee. Uranium conce ntrations 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 K130 0 site soils. Sodium carbonate/bicarbonate leaching was effective on the K1 300 site soils, whereas citric acid leaching is effective on the K311 site soils. Sequential leaching showed that the majority of the uranium in the c ontaminated soils was contained in carbonate minerals (45%) and iron oxides (40%). Conventional leaching showed that citric acid treatment was most ef fective on the K311 site soils, whereas the sodium carbonate/ bicarbonate t reatment was most effective on the K1300 site soils.