Carbonate leaching of uranium from contaminated soils

Uranium(U)was successfully removed from contaminated soils from the Fernald Environmental Management Project (FEMP) site near Fernald, Ohio. The laboratory column leach process, referred to as the simulated heap leach process, using 0.5 M sodium bicarbonate as the dominant reagent, was able to achieve uranium removals of 75-90%, corresponding approximately to the percentage of uranium in the oxidized state. Parametric optimization studies are reported. The dissolution of uranium took place in two stages: a rapid desorption associated with soil surfaces and a slow step associated with diffusion of uranium toward solid surfaces. In addition, use of the oxidizing agent, sodium peroxide, improved 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 of the sail and the simple equipment necessary. Two relevant companion studies have recently been completed. The first, a scale-up demonstration [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 Management '97, Tucson, 1997], using a Los Alamos site, confirms the approach to be effective up to 1 ton of soil and the second, a cost study, suggests this method is economically competitive for large soil volumes (> 1000 cu yd) when combined with a radionuclide presort [Cummings, M.; Booth, S. R. Remediation of Uranium-Contaminated Soil using the Segmented Gate System and Containerized Vat Leaching Techniques: A Cost Effectiveness Study.