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

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