Diffusion behavior of Se(IV) and Re(VII) in GMZ bentonite

Abstract The diffusion behavior of HSeO 3 − and ReO 4 − was investigated in Gaomiaozi (GMZ) bentonite by the through-diffusion method. The effective diffusion coefficient D e , porosity e and rock capacity factor α were measured in order to evaluate the impact of porosity on anion diffusion in compacted bentonite. The D e values of HSeO 3 − and ReO 4 − were (4.5–54) × 10 − 12 and (3.0–53) × 10 − 12 m 2 /s at dry densities from 1300 to 1800 kg/m 3 , respectively. HSeO 3 − sorbed on GMZ bentonite with a distribution coefficient K d in the range of (1.4–1.8) × 10 − 4 m 3 /kg, whereas ReO 4 − showed little sorption. Moreover, the diffusion behavior of HSeO 3 - and ReO 4 - was similar to that of SeO 3 2- and 99 TcO 4 - . Since the minimum average pore diameter at a bulk dry density below 1800 kg/m 3 is much larger than that of anions, the constrictivity δ could be neglected. The D e or the apparent diffusion coefficient D a was related to porosity e by Archie's law and by a pore diffusion model with linear and logarithmic relations between τ and e. The best fit was obtained by Archie's relation.