Functionalization of layered double hydroxides on bentonite for cesium and iodine retention in high-level radioactive waste disposal

Bentonite is regarded as an adequate buffer material in deep geological repositories and its swelling properties serve to prevent the penetration of groundwater into the repository and to minimize the release of radionuclides. However, bentonite is rarely effective in removing anionic radionuclides due to its permanent negative surface charge. The aim of this study was to enhance the anion removal ability of bentonite by incorporating layered double hydroxides (LDH) with a high anion exchange capacity. The functionalization of CuAlBi LDH on bentonite (CuAlBi LDH@Ben) revealed an effective approach for removing both cesium and iodine from aqueous solutions. The peak shift of the Si–O stretching band to higher frequencies, the vertically oriented platelet morphology, and the increase in specific surface area provide confirmation that LDH platelets grow on the surface of montmorillonite. The CuAlBi LDH@Ben demonstrates enhanced anion retention performance in bentonite without impacting its retention behavior toward cations, as evidenced by K_d values of 1943.1 mL/g for Cs⁺, 442.4 mL/g for I⁻, and 650.7 mL/g for IO₃⁻, respectively.