A new interpretation of measured ionic diffusion coefficient in compacted bentonite-based materials

Previous model based on free-water properties to interpret the measured diffusion coefficient in compacted bentonite-based materials is demonstrated to be inadequate. A model considering ionic diffusion in clay surface (bound) and interstitial (free) water is presented to interpret the measured diffusion coefficients and to explain the possible reasons for the discrepancies in the data. The measured diffusion coefficient is determined by the predominant diffusion pathway, which depends on the charge of diffusing species, soil fabric, diffusion time and by the starting concentration condition of the method used.