Effects of dry density and exchangeable cations on the diffusion process of sodium ions in compacted montmorillonite

Kozaki, Tamotsu; Fujishima, Atsushi; Saitô, Nobuhiko; Sato, Shunsuke; Ôhashi, Hiroshi

doi:10.1016/j.enggeo.2005.06.010

Cited by 43 publications

(49 citation statements)

References 18 publications

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“…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. Table 2, and the dependency of these values on the Ca 2+ ionic equivalent fractions is shown in Figure 4, along with those of the activation energies for Na + diffusion (Kozaki et al, 2005) and Cs + diffusion (Kozaki et al, 1999a). The activation energy for Ca 2+ diffusion is found to be independent of the ionic equivalent fractions of Ca 2+ , although the activation energies for Na + and Cs + diffusion vary as a function of the Ca 2+ ionic equivalent fraction.…”

Section: Resultsmentioning

confidence: 96%

“…In this study the Na + /Ca 2+ ratio of exchangeable cations in the mixtures is expressed by the ionic equivalent fraction of Ca 2+ (-). The detailed procedure for preparation of homoionized montmorillonite was described in a previous paper (Kozaki et al, 2005).…”

Section: Methodsmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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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: Resultsmentioning

confidence: 96%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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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“…These materials are 41 under consideration for a similar use as barriers in the subsurface storage of high-level 42 radioactive waste, where their low saturated hydraulic conductivity would ensure that molecular 43 diffusion is one of the main transport processes resulting in passage through the barrier (3,4). 44 Efforts to predict the performance of bentonite barriers have motivated numerous 45 experiments on solute diffusion in compacted water-saturated Na-bentonite (5)(6)(7)(8)(9)(10)(11)(12)(13). and 'macropores' (all other pores), with weighting by the molar fractions of the species of 56 interest in these two compartments (α macropore and α interlayer , with α macropore + α interlayer = 1): 57…”

Section: Introductionmentioning

confidence: 99%

“…Kozaki and coworkers used purified Kunipia-F bentonite (11,(25)(26)(27)(28)(29) or mixtures of purified 112…”

Section: Introductionmentioning

confidence: 99%

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

Bourg

Sposito

Bourg

2007

Environ. Sci. Technol.

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23Sodium bentonites are used as barrier materials for the isolation of landfills and are under 24 consideration for a similar use in the subsurface storage of high-level radioactive waste. The 25 performance of these barriers is determined in large part by molecular diffusion in the bentonite 26 pore space. We tested two current models of cation diffusion in bentonite against experimental 27 data on the relative apparent diffusion coefficients of two representative cations, sodium and 28 strontium. On the 'macropore/nanopore' model, solute molecules are divided into two categories, 29 with unequal pore-scale diffusion coefficients, based on location: in macropores or in interlayer 30 nanopores. On the 'surface diffusion' model, solute molecules are divided into categories based 31 on chemical speciation: dissolved or adsorbed. The macropore/nanopore model agrees with all 32 experimental data at partial montmorillonite dry densities ranging from 0.2 (a dilute bentonite 33 gel) to 1.7 kg dm -3 (a highly compacted bentonite with most of its pore space located in 34 interlayer nanopores), whereas the surface diffusion model fails at partial montmorillonite dry 35 densities greater than about 1.2 kg dm -3 . 36 37

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Diffusion of La3+ in Compacted GMZ Bentonite Used as Buffer Material in HLW Disposal

Chen

Niu

et al. 2014

Engineering Geology for Society and Territory - Volume 6

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It has been studied that the GMZ bentonite which has a chemical barrier property can play an important role in retarding the migration of radioactive nuclide. In order to understand the diffusion properties of nuclide in GMZ bentonite, a series of experiments were conducted to obtain the apparent diffusion coefficient of La 3+ in GMZ bentonite under different dry density and pH value conditions using a autonomous ion diffusion instrument. The results show that the apparent diffusion coefficient of La 3+ decreases significantly with the increasing dry density or pH value. The influence of dry density on the diffusion is very apparent for a low dry density, and the influence gradually slow down with the increase of dry density. At last the influence mechanism of the dry density and pH value on diffusion coefficient was also analyzed. KeywordsGMZ bentonite Á Diffusion property Á Lanthanum ion IntroductionThe deep geological disposal which based on a multi-barrier system is the most appropriate means for safe disposal of high-level radioactive waste (HLW). Bentonite has been chosen as the buffer/backfill material for this disposal because of good mechanical buffer resistance, low permeability, better swelling property and adsorption property (Wen 2006).The chemical barrier properties of bentonite are mainly manifested in retarding the migration of radioactive nuclide. Considering most of the nuclide uranium, thorium, plutonium in disposal repository are actinide elements, and lanthanide and actinide elements have similar electronic configuration inside and outside layer which determine their similar physical and chemical properties. Therefore the lanthanide ions are always selected instead of radionuclide in the study. In this work, effects of the dry density and pH value on the diffusion property of La 3+ in GMZ bentonite were studied. Experimental MaterialsThe GMZ bentonite derived from inner mongolia China was used in this experiment. Its major mineral is (Wang and Su 2006): montmorillonite 75.4 %, quartz 11.7 %, crystaballite 7 %, feldspar 4.3 %, calcite 0.5 %, kaolinite 0.8 %. It has been studied that GMZ bentonite has strong cation exchange capacity, hydration ability and strong adsorption ability.

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Effects of dry density and exchangeable cations on the diffusion process of sodium ions in compacted montmorillonite

Cited by 43 publications

References 18 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

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

Diffusion of La3+ in Compacted GMZ Bentonite Used as Buffer Material in HLW Disposal

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