Activation energy for diffusion of chloride ions in compacted sodium montmorillonite

Multicomponent diffusion of a suite of tracers (HTO, Cl, Br, I, Na, Sr, Cs) in a single sample of Opalinus Clay

“…In Opalinus Clay, diffusion of cations is enhanced, and that of anions diminished, relative to a neutral tracer such as tritiated water (HTO). This is in line with results from many other diffusion experiments with clayrock, bentonite or pure montmorillonite (Shackelford and Daniel, 1991;Sato et al, 1992;Sato, 2005;Kozaki et al, 1998Kozaki et al, , 2005Kozaki et al, , 2008; Molera and Eriksen, 2002;Van Loon et al, 2003a,b;2004a,b;Melkior et al, 2007;Wersin et al, 2007;Descostes et al, 2008). The increased diffusion of cations is explained either by interlayer or surface diffusion of sorbed cations (Ohlsson and Neretnieks, 1998;Eriksen et al, 1999;Bourg, 2004;Bourg et al, 2007;Glaus et al, 2007), or by diffusion in the diffuse double layer (DDL) that surrounds the negatively charged clay surface and contains an excess of cations (Van Schaik et al, 1966;Kemper and Quirk, 1972;Ochs et al, 1998Ochs et al, , 2001Lehikoinen et al, 1999;Leroy and Revil, 2004;Leroy et al, 2006;Appelo and Wersin, 2007;Jougnot et al, 2009).…”

Modelling approaches for anion-exclusion in compacted Na-bentonite

“…Bentonite has a high proportion of Na-montmorillonite, a clay mineral that swells in water and endows bentonite with a very low hydraulic conductivity. As a result, transport of water and solutes in bentonite is mainly diffusive, with diffusion coefficients that are much smaller than in bulk water, in particular for anions (Kozaki et al, 1998(Kozaki et al, , 2001Madsen, 1998a;Ochs et al, 2001;Bourg et al, 2007;Van Loon et al, 2007). Natural clay formations that are currently under investigation for waste repository exhibit similar diffusion properties due to their low porosity and significant content in swelling clay minerals (Descostes et al, 2008).…”

Diffusion of Helium in Water-Saturated, Compacted Sodium Montmorillonite

“…Therefore, comparison of the literature values 2,3) and the present values is not pursued further. Figure 3 shows plots of the apparent helium diffusion coefficients obtained in the present work with those of tritium 9) in the form of HTO, and chloride ions 10) in compacted sodium montmorillonite. Like those of HTO and Cl − , the diffusion coefficients of helium decrease monotonously as a function of dry density, although the values of the helium diffusion coefficients are somewhat larger than those of HTO and Cl − .…”