CARBONATE LEACHING OF URANIUM FROM CONTAMINATED SOILS

Uranium(U)was successfully removed from contaminated soils from the Fe rnald Environmental Management Project (FEMP) site near Fernald, Ohio. The laboratory column leach process, referred to as the simulated hea p leach process, using 0.5 M sodium bicarbonate as the dominant reagen t, was able to achieve uranium removals of 75-90%, corresponding appro ximately to the percentage of uranium in the oxidized state. Parametri c optimization studies are reported. The dissolution of uranium took p lace in two stages: a rapid desorption associated with soil surfaces a nd a slow step associated with diffusion of uranium toward solid surfa ces. In addition, use of the oxidizing agent, sodium peroxide, improve d uranium removal due to oxidation of U(IV), enhancing the solubility of the uranium. The results suggest that the process will be effective for field scale remediation of uranium-contaminated soils because of the efficiency, mild complexing agent employed, lack of prescreening o f the sail and the simple equipment necessary. Two relevant companion studies have recently been completed. The first, a scale-up demonstrat ion [Turney, W. R. J. R.; Mason, C. F. V.; Lu, N.; Duff, M. C.; Dry, D . Pilot Treatment Project for the Remediation of Uranium-Contaminated Soil at a Former Nuclear Weapons Development Site at the LANL; Waste M anagement '97, Tucson, 1997], using a Los Alamos site, confirms the ap proach to be effective up to 1 ton of soil and the second, a cost stud y, suggests this method is economically competitive for large soil vol umes (> 1000 cu yd) when combined with a radionuclide presort [Cumming s, M.; Booth, S. R. Remediation of Uranium-Contaminated Soil using the Segmented Gate System and Containerized Vat Leaching Techniques: A Co st Effectiveness Study.