Strontium and cesium adsorption to bentonite colloids in Na–Cl–SO4 type groundwater

The adsorption of Sr 2+ and Cs + onto Gaomiaozi bentonite colloids (GMZC) was investigated to evaluate their role in radionuclide migration. The results show that within a concentration range of 20–100 mg·L⁻ 1 for Sr 2+ and Cs + , the distribution coefficient decreases with increasing ion concentration. The mechanistic study indicates that the adsorption of Sr 2+ is predominantly governed by surface complexation, whereas that of Cs + is mainly driven by ion exchange. Furthermore, Sr 2+ induces structural ordering of GMZC layers and promotes particle aggregation. However, in Na-Cl-SO 4 groundwater, the bentonite suspension showed poor stability and a significantly weakened adsorption capacity for both 90 Sr and 137 Cs, demonstrating the decisive impact of water chemistry on its barrier function.