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

摘要: 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 Sr2+ 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 Sr2+ 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 Sr2+
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 Sr2+
adsorption, and the inhibition efficacy decreases in the order Fe3+>Ca2+>Mg2+>K+ . The presence of bentonite
colloids in a granite column slightly influences the retention of Sr2+ in the column while markedly reducing
the Sr2+ penetration time from 70 h to 18 h. However, the coexistence of Co2+, Ni2+, and Cs+ in a multinuclide
system weakens the ability of the colloids to promote Sr2+ 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 Sr2+>Cs+ >Ni2+>Co2+. This study provides insights into Sr2+ migration in cave repositories for low- and
medium-level radioactive waste.