Study on the diffusion behavior of rhenium in CTAB-modified bentonite

Abstract The use of cationic surfactant CTAB (cetyltrimethylammonium bromide) to modify bentonite has the advantages of convenience, speed, and large loading capacity. Due to the chemical similarity between rhenium and technetium, many hydrogeological studies on technetium use rhenium as a substitute for cold testing. Therefore, in this study, CTAB was used as a modifier for organic modification of bentonite by cation exchange method to change its properties and better adsorb Re(VII). The feasibility of using CTAB-modified bentonite as an additive in backfill materials was discussed through a series of experiments. The research results indicate that the addition of modified bentonite significantly inhibits the diffusion of Re(VII) in bentonite, manifested as a decrease in total diffusion amount, diffusion flux, apparent diffusion coefficient, and effective diffusion coefficient, while increasing the rock capacity factor. When the mass ratio of modified bentonite in the diffusion medium increases from 0 % to 20 %, the effective diffusion coefficient of Re decreases from 19.56 × 10−11 cm 2 /s to 0.046 × 10−11 cm 2 /s, the rock capacity factor of the diffusion medium increases from 0.995 to 29.43. In addition, the increase in pH value and ionic strength affects the surface sites of bentonite, thereby increasing the surface diffusion coefficient and effective diffusion coefficient of rhenium, while the rock bearing capacity decreases. These findings suggest that the adsorption capacity of TcO 4 − can be enhanced by doping modified bentonite in backfill materials, reducing the migration of TcO 4 − within the backfill material, potentially providing benefits for the safe storage of high-level radioactive waste.