Adsorption characteristics of strontium by bentonite colloids acting on claystone of candidate high-level radioactive waste geological disposal sites

The bentonite colloid produced in the deep geological repository of high-level radioactive waste can directly affect the migration of radionuclide strontium when it acts on claystone. The adsorption characteristics of strontium were investigated on claystone with the presence or absence of bentonite colloids from the Suhongtu area of China. The effects of different influencing factors, such as pH and solid content, on the adsorption process were investigated by batch adsorption experiments, and spectroscopic techniques were used to characterize the samples before and after adsorption of strontium. The results show that the presence of bentonite colloids can promote the adsorption of strontium on claystone under alkaline conditions. and the general order kinetic model provided the best fit to the experimental data. Strontium is adsorbed on the surface of claystone and bentonite colloid by ion exchange and surface complexation. Most of the Sr²⁺ formed SrCO₃ with CO₃^2- after ion exchange with Ca²⁺ and Mg²⁺ in plagioclase and dolomite, and a small amount of Sr²⁺ was adsorbed by complexation with -OH, Al-O and Si-O. These results provide a scientific basis for predicting the migration of strontium in subsurface porous media and the siting of high-level radioactive waste repositories.