Investigation of co-transport behavior of strontium and bentonite colloids in granite disposal environment

Colloids are prevalent in nuclear waste repositories, with bentonite colloids posing an uncontrollable risk factor for nuclide migration processes. In this study, static adsorption experiments were coupled with dynamic shower experiments to comprehensively investigate the influence of bentonite colloids on \({\hbox {Sr}^{2+}}\) migration in granite, considering adsorption capacity. Bentonite colloids have a considerably greater adsorption capacity than both bentonite and granite, with a maximum adsorption of 30.303 mg/g. The adsorption behavior of bentonite colloids on \({\hbox {Sr}^{2+}}\) is well described by the Langmuir isotherm and pseudo-second-order kinetic models, indicating that a single-layer chemical adsorption process is controlled by the site activation energy. The adsorbed \({\hbox {Sr}^{2+}}\) is unevenly distributed on the colloids, and the adsorption mechanism may involve ion exchange with Ca. Bentonite colloids exhibit superior adsorption in neutral environments. The cations in groundwater inhibit \({\hbox {Sr}^{2+}}\) adsorption, and the inhibition efficacy decreases in the order \({\hbox {Fe}^{3+}}>{\hbox {Ca}^{2+}}>{\hbox {Mg}^{2+}}>{\hbox {K}^+}\) . The presence of bentonite colloids in a granite column slightly influences the retention of \({\hbox {Sr}^{2+}}\) in the column while markedly reducing the \({\hbox {Sr}^{2+}}\) penetration time from 70 h to 18 h. However, the coexistence of \({\hbox {Co}^{2+}}\) , \({\hbox {Ni}^{2+}}\) , and \({\hbox {Cs}^{+}}\) in a multinuclide system weakens the ability of the colloids to promote \({\hbox {Sr}^{2+}}\) migration. In comigration of colloid and multinuclide systems, the adsorption of nuclides by bentonite colloids causes the nuclide migration speed to decrease in the order \({\hbox {Sr}^{2+}}\)  >  \({\hbox {Cs}^{+}}\)  >  \({\hbox {Ni}^{2+}}\)  >  \({\hbox {Co}^{2+}}\) . This study provides insights into \({\hbox {Sr}^{2+}}\) migration in cave repositories for low- and medium-level radioactive waste.