Diffusive transport through compacted Na- and Ca-bentonite

Effect of exchangeable cations on apparent diffusion of Ca2+ ions in Na- and Ca-montmorillonite mixtures

“…This change in HTO diffusivity agrees with the experimental results described in a previous paper by Choi and Oscarson (1996), in which a higher apparent diffusivity of HTO in Ca-bentonite than in Na-bentonite was reported. They also reported that a greater proportion of large pores in Ca-bentonite than in Na-bentonite was determined by Hg intrusion porosimetry, and concluded that higher diffusivity of HTO in Ca-bentonite can be attributed to the different microstructure of the compared bentonite.…”

“…Thus, the smaller specific surface area measured by the BET method for Ca-montmorillonite suggests a larger aggregate size in the Ca-montmorillonite than in the Na-montmorillonite. Since there is no difference in the basal spacing between Na-and Ca-montmorillonite, the difference of the aggregate size can be attributed to the number of unit layers making up the montmorillonite aggregate, as pointed out by Choi and Oscarson (1996). That implies that the change in the apparent diffusion coefficient of HTO could be caused by the structural changes in the pore spaces rather than in the interlayer spaces where the basal spacing was found to remain constant.…”

“…These predictions should be based on studies of the diffusivities of Ca 2+ ions in both the Na-bentonite and the altered bentonite. Although extensive studies have been performed for the diffusion of radionuclides in bentonite (Bourg et al, 2008, Glaus et al, 2007, Gonzalez-Sanchez et al, 2008, Kozaki et al, 2008, Melkior et al, 2009, there are few studies on the diffusivities of Ca 2+ ions in compacted bentonite (Kozaki et al, 2001a) and the effects of exchangeable cations on diffusion of radionuclides (Choi and Oscarson, 1996, Kozaki et al, 1999a, 2005 The diffusion mechanism of Ca 2+ ions in compacted montmorillonite discussed in this paper is based on these experimental data.…”

Modeling Cation Diffusion in Compacted Water-Saturated Sodium Bentonite at Low Ionic Strength

“…The unknown G // -value, considered to vary with 74 bentonite dry bulk density, is routinely estimated by fitting a diffusion model to experimental 75 data on the diffusion of water tracers in bentonite in the x // direction (5,14,(19)(20)(21)(22) …”

Laboratory Experiments on Bentonite Samples: FY15 Progress

“…with regard to cationic, anionic and neutral species, in a given system). ) (Muurinen et al, 1986;Sato et al, 1992;Kozaki et al, 1996Kozaki et al, , 1998aChoi and Oscarson, 1996;Kozaki et al, 1999a;b, 2001, 2008Lee et al, 1996;Nakajima et al, 1997;Nakashima, 2000Nakashima, , 2002Nakashima, , 2003Nakashima, , 2006Molera, 2002;Molera and Eriksen, 2002;Molera et al, 2003;Sato and Suzuki, 2003;Van Loon et al, 2003a;b, 2004a;b, 2005a;b, 2007;Wang, 2003;Jansson and Eriksen, 2004;García-Gutiérrez et al, 2004;Sato and Miyamoto, 2004;Suzuki et al, 2004;García-Gutiérrez et al, 2009;Wang and Liu, 2004;Wang and Tao, 2004;Melkior et al, 2005Melkior et al, , 2007Melkior et al, , 2009Nakashima and Mitsumori, 2005;Wang et al, 2005;Appelo and Wersin, 2007;Glaus et al, 2011Glaus et al, , 2013Motellier et al, 2007;Glaus et al, 2007Glaus et al, , 2008Glaus et al, , 2010…”