Influence of flow regime on U(VI) sorption kinetics in fine sediments at the Hanford site, Washington, USA

The effect of flow rate on U(VI) sorption kinetics was investigated by a series of column tests using the reactive mass fraction (<2mm) of sediments from the 300 Area in Hanford, WA. Three sets of constant flow rates subject to multiple stop flow events were employed to obtain U(VI) breakthrough curves at the column outlet. A lognormal distributed multi-rate surface complexation model was used to match the experimental breakthrough curves and calibrate the parameters of the multi-rate distribution. The results from the column tests clearly show that the mean of the lognormal distributed sorption rate constants increase with the flow rate, while the standard deviation of the lognormal distributions decreases with the flow rate. This finding is the first empirical evidence for the flow rate dependence of the multi-rate sorption kinetics and is thus of fundamental importance for future efforts to further improve the predictive modeling and remediation of U contamination.