The uranium weathering rate as an indicator of uranium mobility in contaminated soil

The goals of this study were to determine the rate of uranium weathering in contaminated soil from the Fernald Environmental Project (FEMP) site near Cincinnati Ohio and to estimate from this rate the maximum solution-phase U concentrations expected during typical leaching events at the site. Uranium release rates were measured in four experiments with different soil-to-solution ratios and flow rates using a mixed-flow reactor and a pH 7.4 1.67 mM CaCl{dollar}sb2{dollar} influent solution. The experimental uranium weathering rate, {dollar}rm0.20pm0.01 mu g U hsp{lcub}-1{rcub} gsp{lcub}-1{rcub}sb{lcub}soil{rcub},{dollar} was independent of the steady-state uranium concentration over the range in these experiments, 0.038 to 0.235 ppm U, and applied to a relatively small labile fraction of the total soil uranium. Qualitative calculations based on this rate predict that the uranium concentrations of the soil solution should be about 1 ppm during leaching events, far above that typical of natural waters.