Montmorillonite plays a key role in engineered barrier systems in the high-level radioactive waste repository because of its large sorption capacity and high swelling pressure. However, the sorption capacity of montmorillonite can be largely varied dependent on the surrounding environments. This study conducted the batch simulation for U(VI) sorption on Na-montmorillonite by utilizing the cation exchange and surface complexation coupled (2SP-NE-SC/CE) model and evaluated the effects of physicochemical properties (i.e., pH, temperature, competing cations, U(VI) concentration, and carbonate species) on U(VI) sorption. The simulation demonstrated that the U(VI) sorption was affected by physicochemical properties: the pH and temperature relate to aqueous U(VI) speciation, the competing cations relate to the cation exchange process and selectivity, the U(VI) concentration relates to saturation at sorption sites. For example, the Kd (L kg−1) of Na-montmorillonite represented the largest values of 2.7×105 L kg−1 at neutral pH condition and had significantly decreased at acidic pH<3, showing non-linear and diverse U(VI) sorption at the ranged pH from 2 to 11. Additionally, the U(VI) sorption on montmorillonite significantly decreased in presence of carbonate species. The U(VI) sorption for long-term in actual porewater chemistry and temperature of high-level radioactive waste repository represented that the sorption capacity of Na-montmorillonite was affected by various external properties such as concentration of competing cation, temperature, pH, and carbonate species. These results indicate that geochemical sorption capacity of bentonite should be evaluated by considering both geological and aquifer environments in the high-level radioactive waste repository.

• Jeonghwan Hwang(Korea Atomic Energy Research Institute (KAERI))
• Weon Shik Han(Yonsei University) Corresponding author
• Jung-Woo Kim(Korea Atomic Energy Research Institute (KAERI))
• Won Woo Yoon(Yonsei University)