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

The diffusion behavior of HSeO3- and ReO4- was investigated in Gaomiaozi (GMZ) bentonite by the through diffusion method. The effective diffusion coefficient De, porosity epsilon and rock capacity factor a were measured in order to evaluate the impact of porosity on anion diffusion in compacted bentonite. The D-e values of HSeO3- and ReO4- were (4.5-54) x 10(-12) and (3.0-53) x 10(-12) m(2)/S at dry densities from 1300 to 1800 kg/m(3), respectively. HSeO3- sorbed on GMZ bentonite with a distribution coefficient K-d in the range of (1.4-1.8) x 10(-4) m(3)/kg, whereas ReO4- showed little sorption. Moreover, the diffusion behavior of HSeO3- and ReO4- was similar to that of SeO(3)(2)(-)and (TcO4-)-Tc-99 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 delta could be neglected. The D-e or the apparent diffusion coefficient D-a was related to porosity epsilon by Archie's law and by a pore diffusion model with linear and logarithmic relations between T and epsilon. The best fit was obtained by Archie's relation. (C) 2014 Elsevier B.V. All rights reserved.