Electrokinetic Study of Migration of Anions, Cations, and Water in Water-Saturated Compacted Sodium Montmorillonite

Abstract

Electromigration studies of 36 Cl À ions and 22 Na þ ions, and electro-osmosis of water traced with HTO and H 2 18 O were conducted with water-saturated compacted sodium montmorillonite having dry densities from 0.8 to 1.6 Mg/m 3 . The mobilities and dispersivities for each species were obtained from the apparent electromigration velocities and hydrodynamic dispersion coefficients, respectively. When corrected by water flow, the apparent diffusion coefficients of Cl À ions obtained from the Einstein relation are in good agreement with the coefficients obtained from an earlier conventional diffusion experiment in the high dry densities (above 1.3 Mg/m 3 ). This result suggests that the migration pathways of Cl À ions are nearly identical to those of water above 1.3 Mg/m 3 . The former diffusion coefficient is smaller than the latter in the low dry densities (below 1.3 Mg/m 3 ), suggesting that Cl À ions migrate in the region distant from the montmorillonite sheets. In contrast, for Na þ ions, the obtained D a values without water flow correction are in good agreement with conventional values at all dry densities. This suggests that Na þ ions migrate mainly in the interlayer and the vicinity of montmorillonite sheets. The dispersivities increase with increasing dry densities for all species. This corresponds to a geometrical complexity that increases with increasing dry density.

Self-Diffusion of Water and Ions in Clay Barriers

“…Two alternative methodologies have contributed to the database on a and D a discussed in the present chapter. The first consists in electromigration experiments whereby a clay sample enriched with a uniform planar source of the species of interest is exposed to an electric field E in the direction normal to the planar source (Maes et al, 1999;Higashihara et al, 2004;Tanaka et al, 2011). Information on D a is obtained by carrying out such experiments at several values of E and, then, extrapolating either the electromigration velocity or the dispersion coefficient to E ¼ 0.…”

Donnan-ion hydration model to estimate the electroosmotic permeability of clays

“…However, electrokinetic phenomena have been scarcely studied in these materials, although there is a growing interest among the scientific community since a broader knowledge of these materials is required [29][30][31][32][33]. Nevertheless, few data on electro-…”

Investigation of Reactive Transport and Coupled THMC Processes in the EBS

“…The diffusion of water and ions in water-saturated compacted clay barriers has, therefore, been extensively characterized, though mostly at ambient temperatures (Molera and Eriksen, 2002;Molera et al, 2003;Nakashima, 2003;Wang et al, 2005;Melkior et al, 2009;Tachi et al, 2010;Glaus et al, 2011;Tanaka et al, 2011;Holmboe et al, 2011).…”