Impact of 14–140 kGy gamma irradiation on the surface characteristics and adsorption properties of bentonite: Verification study with strontium and selenite

Bentonite is extensively investigated for its critical role in radioactive waste repositories. This study evaluated the impact of gamma irradiation on the structural and sorption properties of FEBEX bentonite to assess its long-term performance under cumulative doses of 14 and 140 kGy, representing conservative exposure scenarios over repository lifetime. Comprehensive analyses were conducted to investigate potential radiation-induced changes in the clay, including Fourier transform infrared spectroscopy, potentiometric titration, cation exchange capacity, zeta potential and external specific surface area measurements. Sorption experiments targeted two representative radionuclides: Sr 2+ (retained through cation exchange) and SeO₃ 2− (retained through surface complexation). To further examine potential effects on surface reactivity, selenite adsorption was also studied on irradiated and non-irradiated alumina as a model for clay aluminol edge sites behaviour. Results showed that gamma irradiation up to 140 kGy did not significantly alter the structure and adsorption mechanisms of bentonite. Retention of both radionuclides remained unchanged in irradiated samples, indicating the preservation of cation exchange and surface complexation mechanisms. Alumina sorption tests additionally confirmed that tested irradiation doses did not compromise the sorption functionality of aluminol sites. These results demonstrate the long-term stability of bentonite and support its suitability as a barrier material for radioactive waste isolation. • Gamma irradiation doses up to 140 kGy did not alter FEBEX bentonite structure. • Cation exchange capacity and N 2 -BET surface area are preserved. • Sorption of Sr 2+ and SeO 3 2− remains unaffected after irradiation. • Experiments with alumina confirm stability of aluminol sited under gamma exposure. • The stability of bentonite under early-stage repository-relevant gamma irradiation is assessed.