Equilibrium, kinetic, and thermodynamic studies of adsorption of Sr(II) from aqueous solution onto GMZ bentonite

Due to low hydraulic conductivity, high swelling capacity, and good adsorption properties, the Gaomiaozi (GMZ) bentonite has been proposed as one of the most suitable buffer/backfill materials for the construction of engineering barriers in geological repository for high-level nuclear waste disposal in China. In this study, the adsorption of Sr(II) on the GMZ bentonite was studied using the batch technique, and the effects of contact time, pH, ionic strength, temperature, and concentration were analyzed. The results obtained from the tests show that the adsorption process achieved equilibrium within 60 min, and the adsorption capacity for Sr(II) by the GMZ bentonite was about 9.72 mg/g under the given experimental conditions. The equilibrium adsorption data were fitted to the second-order kinetic equation. The adsorption capacity for Sr(II) onto the GMZ bentonite increases with increasing pH from 3 to 13 but decreases with increasing ionic strength from 0 to 1.0-M NaCl. Maximum adsorption at a temperature of 298.15 K was determined to be achieved at pH >= 7. The adsorption reaction was exothermic, and the process of adsorption was favored at low temperature. The adsorption of Sr(II) was dominated by ion exchange. Furthermore, the D-R adsorption isotherm model was used for the description of the adsorption process.