Diffusion mechanism of chloride ions in sodium montmorillonite

Kozaki, Tamotsu; Inada, K.; Sato, Shunsuke; Ôhashi, Hiroshi

doi:10.1016/s0169-7722(00)00146-7

Cited by 83 publications

(46 citation statements)

References 16 publications

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“…Considering high porosity of the montmorillonite (0.65 at dry density of 1.0 Mg m -3 ) and high diffusivity of HTO in the pore water, the same as that in free water, it can be supposed that HTO predominantly diffuses in the pore water at the dry density of 1.0 Mg m -3 . This can be supported by the fact that almost the same diffusion coefficients were reported for HTO and Cl -in Na-montmorillonite at this dry density (Kozaki et al, 2001b). corresponding to the three-water-hydrate state of the basal spacing) was found when the exchangeable cations of Na + were replaced with Ca 2+ .…”

Section: Resultssupporting

confidence: 78%

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

Kozaki

Sawaguchi

Fujishima

et al. 2010

Physics and Chemistry of the Earth, Parts A/B/C

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Compacted Na-bentonite, of which the major mineral is montmorillonite, is a candidate buffer material for the geological disposal of high-level radioactive waste. A potential alteration of the bentonite in a repository is the partial replacement of the exchangeable cations of Na However, the apparent diffusion coefficient of Ca 2+ and the activation energy for diffusion at the same dry density were independent of the ionic equivalent fraction of Ca 2+ ions. These findings suggest that unlike HTO, which can be postulated to diffuse mainly in pore water, Ca 2+ ion diffusion could occur predominantly in interlayer spaces, of which the basal spacing was determined to be constant by the XRD technique.

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Section: Resultssupporting

confidence: 78%

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

Kozaki

Sawaguchi

Fujishima

et al. 2010

Physics and Chemistry of the Earth, Parts A/B/C

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“…The rationale for using bentonite is its dense microstructure and swelling capacity in compacted form, rendering diffusion as the only way of transport from or to the canister holding the nuclear waste, as well as the high sorption capacity for many radionuclides. Previous studies have shown that the diffusive transport of radionuclides in water saturated compacted bentonite under ambient conditions is governed by several different parameters, such as compaction, smectite content, ionic strength and the specific interactions between the diffusants and montmorillonite, the main component of bentonite (Eriksen et al, 1999;Kozaki et al, 1998;2001;Molera and Eriksen, 2002;Van Loon et al, 2007). Under repository conditions however, the bentonite barrier will inevitably be exposed to ionizing radiation (mainly γ from Cs-137) under anoxic conditions.…”

Section: Introductionmentioning

confidence: 99%

Effect of γ-radiation on radionuclide retention in compacted bentonite

Holmboe

Norrfors

Jönsson

et al. 2011

Radiation Physics and Chemistry

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Compacted bentonite is proposed as an engineered barrier in many concepts for disposal of high level nuclear waste. After the initial deposition however, the bentonite barrier will inevitably be exposed to ionizing radiation (mainly γ) under anoxic conditions. Because of this, the effects of γ-radiation on the apparent diffusivity values and sorption coefficients in bentonite for Cs + and Co 2+ were tested under different experimental conditions. Radiation induced effects on sorption were in general more noticeable for Co 2+ than for Cs + , which generally showed no significant differences between irradiated and unirradiated clay samples. For Co 2+ however, the sorption to irradiated MX80 was significantly lower than to the unirradiated clay samples regardless of the experimental conditions. This implies that γ-radiation may alter the surface characteristics contributing to surface complexation of Co 2+ . With the experimental conditions used however, the effect of decreasing sorption was not large enough to be reflected on the obtained Da values.

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“…Diffusion coefficients of Na [31] and Cl [8], in particular, were adopted from other studies where the system was similar to a compacted Na-bentonite. Based on Kozaki et al [8], Cl -diffusivity decreases with increasing bentonite density. This can be explained by salt sieving due to anion exclusion from the diffuse double layers.…”

Section: Methodsmentioning

confidence: 99%

“…Several studies have been carried out to understand the behaviour of particular species in compacted bentonite plug, where double-layers (DL) are overlapping since they are so thick. Kozaki et al [8] and Bourg et al [9,10] are some examples of studies of diffusivity of ions in compacted sodium bentonites. Electrical conductivity of colloids and clay-rich porous materials is a pertinent parameter when studying electrokinetic applications.…”

Section: Introductionmentioning

confidence: 99%

Bentonite electrical conductivity: a model based on series–parallel transport

2010

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Bentonite has significant applications nowadays, among them as landfill liners, in concrete industry as a repairing material, and as drilling mud in oil well construction. The application of an electric field to such perimeters is under wide discussion, and subject of many studies. However, to understand the behaviour of such an expansive and plastic material under the influence of an electric field, the perception of its electrical properties is essential. This work serves to compare existing data of such electrical behaviour with new laboratorial results. Electrical conductivity is a pertinent parameter since it indicates how much a material is prone to conduct electricity. In the current study, total conductivity of a compacted porous medium was established to be dependent upon density of the bentonite plug. Therefore, surface conductivity was addressed and a series-parallel transport model used to quantify/predict the total conductivity of the system.

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Diffusion mechanism of chloride ions in sodium montmorillonite

Cited by 83 publications

References 16 publications

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

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

Effect of γ-radiation on radionuclide retention in compacted bentonite

Bentonite electrical conductivity: a model based on series–parallel transport

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