Porosity investigation of compacted bentonite using through-diffusion method and multi-porosity model

The diffusion behavior of ReO4- and HSeO3- in low-grade bentonites was firstly investigated under different compacted dry densities. The effective diffusion coefficient, the accessible porosity, and the rock capacity factor were measured by a through-diffusion method. The effective diffusion coefficient was approximately three times in Zhisin bentonite with 36.8 wt% of montmorillonite than that in GMZ bentonite with 74.5 wt% of montmorillonite. The porosity distribution of the compacted bentonite was analyzed by a multi-porosity model. The effects of the compacted dry density, the ionic strength, and the stacking number on porosities were discussed. The compacted dry density had obvious influence on the accessible porosity, the diffuse double layer porosity, and the interlayer porosity. The effects of ionic strength and stacking number were mainly on the diffuse double layer porosity, leading to the alteration of the accessible porosity and the effective diffusion coefficient. Moreover, the multi-porosity model could successfully predict the trend of effective diffusion coefficient in compacted bentonite combined with Archie law, which provides a useful tool to understand the relationship between the microstructure of montmorillonite and the diffusion of radionuclide anions.