Effect of inorganic salts on Se(IV) and Re(VII) diffusions in bentonite

iffusion behaviors of Se(IV) and Re(VII) in bentonite were investigated by a through-diffusion method in nitrate, sulfate, carbonate and silicate solutions. SEM-EDS analysis showed that Se(IV) was reduced to red precipitate Se(0) by sulfite. Se(IV) was sorbed on bentonite with distribution coefficient Kd of (2.6–5.3)×10-4 m3/kg in sulfite, nitrate and sulfate solutions, whereas it was hardly sorbed in carbonate and silicate solutions. The effective diffusion coefficients were De= (0.81–7.0)×10-11 m2/s for Se(IV) and De= (1.4–4.4)×10-11 m2/s for Re(VII). The De value of Se(IV) exhibited a dependence on the inorganic salts in the order of sulfite ≈ nitrate ≈ sulfate > silicate > carbonate, whereas the salts had insignificant effect on Re(VII) diffusion. The results suggest that the discrepancy in diffusion mechanism may lead to the different impact of the salts on the diffusion of Se(IV) and Re(VII) in GMZ bentonite.