Measuring retardation factors of ¹³³cesium and ⁸⁸strontium cations using column test

A flow-through column test setup was developed to measure the breakthrough curves of ¹³³cesium (Cs) and ⁸⁸strontium (Sr) cations in a natural silty sand. Advantages of this column setup include ensuring full saturation with a back-pressure technique and maintaining a constant hydraulic gradient condition with overflow design. The former eliminates large variations in retardation factor (Rd) from reduced surface sites for contaminant-retarding reactions and increased duration time, both caused by unsaturation. The latter creates a more realistic simulation of the field condition than a constant-flow-rate setup. The retardation factors of Sr and Cs cations were found to be 3.561 and 27.369, which were slightly lower than the range under similar but broader ranges of fines content and pH. This slight difference is attributed to the lower fines content of the soil, high input concentrations of both Cs and Sr, and the competing monovalent and divalent cations in the influent with high ionic strength. Although not significant in this study, particle migration was observed.