Migration of Uranium (IV)/(VI) in the Presence of Humic Acids in Quartz Sand: A Laboratory Column Study

The migration behavior of U(IV)/U(VI) in the presence of humic acids was studied in a laboratory quartz sand system by column experiments. It was found that humic acid influences the transport of U(IV) and U(VI). In presence of humic acid both redox species migrate nearly as fast as the groundwater flow. Retardation factors of 1.11 ± 0.03 and 1.14 ± 0.03 as well as eluate recoveries of 0.83 ± 0.09 and 0.65 ± 0.07 were determined for U(VI) and U(IV), respectively. In case of U(VI) humic acid exhibits a clear mobilizing effect compared to the humic acid-free system. There are also strong indications for a similar effect on the U(IV) transport.
The present study demonstrates that humic acids can play an important role in the migration of tetravalent actinides. Consequently, the humic colloid-borne transport of actinides has to be taken into account in performance assessment.