Anion diffusion pathways in bentonite clay compacted to different dry densities

Diffusion of the anions Cl ⁻ and I ⁻ in MX-80 compacted bentonite has been studied at different ionic strengths (0.01, 0.1 M NaClO ₄) and clay density (0.4, 0.8, 1.2, 1.8 g cm ⁻³ ) at the buffered pH of bentonite 8.2 using a through-diffusion technique with measurement of breakthrough curves and concentration profiles in the bentonite. Apparent diffusivities and capacity factors ( α= ε+ ρK _d) are obtained from diffusion simulations using the computer code ANADIFF. Two diffusion processes, both with density and ionic strength dependent apparent diffusivities and capacity factors, were observed. The diffusion processes observed are ascribed to diffusion in intralayer and interparticle water. The experimental data indicate that intralayer water constitutes the dominating part of water in bentonite compacted to dry the densities 0.4–1.8 g cm ⁻³ studied in this work.