Release of contaminant U(VI) from soils

The retention, mobility, and bio-availability of U(VI) in contaminated soils depend strongly on release of U(VI). Laboratory batch experiments were performed to evaluate the factors (ionic strength of the extraction solution and solution volume to solid mass ratio) controlling the release of U(VI) from contaminated soil at Oak Ridge, Tennessee. Increase in ionic strength shows an evident effect on U(VI) release as indicated by the increase in release rates and associated release mass of U(VI). The ratio of solution volume to solid mass (V/M) has a significant impact on the release of U(VI). Increase in the V/M ratio shows a negligible effect on the U(VI) release over a 4-day period. However, at Day 30 and Day 120, larger V/M ratios cause greater U(VI) release. The maximum U(VI) concentrations observed in the release experiments are in the range of schoepite solubility estimated under conditions relevant to the experiments, suggesting that schoepite solubility primarily controls the U(VI) release, but that solubilization and desorption effects cannot be distinguished using macroscopic methods. (orig.)