Self-Diffusion of Sodium Ions in Compacted Sodium Montmorillonite

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

doi:10.13182/nt98-a2819

Cited by 106 publications

(83 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Diffusion experiments were conducted for montmorillonite samples with different ionic equivalent fractions of Ca 2+ at a constant temperature, which ranged from 288 to 323 K. The detailed procedures of XRD measurement and the diffusion experiment are described elsewhere (Kozaki et al, 1998).…”

Section: Methodsmentioning

confidence: 99%

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

View full text Add to dashboard Cite

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.

show abstract

Section: Methodsmentioning

confidence: 99%

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

View full text Add to dashboard Cite

show abstract

“…Three and two layers associated with the interlayer ions Na + ,Ca 2+ and Mg 2+ , respectively for SM and MX-80 (Kozaki et al, 1998;Van Loon et al, 2007;Cases et al, 1997, Ferrage et al, 2007Melkior et al, 2009). Since Na/Ca-smectites tend to segregate into a mixture of Na-smectite and Ca-smectite (Iwasaki and Takashi, 1988), the mean coverage in the interlayers was calculated according to the following relation:…”

Section: Characteristics Of the Water-saturated Compacted Clay Mediamentioning

confidence: 98%

“…Sato et al, 1992) or modelled by molecular dynamic approaches (Tambach et al, 2004;Chavez-Paez et al, 2001). The number of water layers in the interlayer depends on the nature of the interlayer cations and on the compaction degree (Kozaki et al, 1998;Ferrage et al, 2005). The external surface water structure and properties can be probed by a molecular dynamics study showing significant density oscillations up to three water layers at phyllosilicate mineral surfaces (Greathouse and Cygan, 2006;Wang et al, 2006;Marry et al, 2008;Tournassat et al, 2009b).…”

Section: Introductionmentioning

confidence: 99%

Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study

Montavon

Guo

Tournassat

et al. 2009

Geochimica et Cosmochimica Acta

View full text Add to dashboard Cite

. Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study. Geochimica et Cosmochimica Acta, Elsevier, 2009, 73 (24) AbstractThe aim of the present work was to quantify accessible porosities for iodide and for a water tracer (HTO) on water-saturated compacted clay samples (illite, montmorillonite and MX-80 bentonite) and to relate these macroscopic values to the forms of water in these porosities (surface/bulk water, external/internal water). Low field proton NMR was used to characterize and quantify the forms of water. This enabled the three different populations (structural OH, external surface and internal surface water) to be differentiated on hydrated clays by considering the difference in proton mobility. An accurate description of the water forms within the different populations did not appear possible when water molecules of these populations were in contact because of the occurrence of rapid exchange reactions. For this 2 reason, it was not possible to use the low resolution NMR method to quantify external surface and bulk water in fully water-saturated compacted clay media at room temperature. This latter information could however be estimated when analyzing the samples at -25°C. At this temperature, a distinction based on the difference in mobility could be made since surface water remained in a semi-liquid state whereas bulk water froze. In parallel, accessible porosities for anions and HTO were determined by an isotopic dilution method using capillaries to confine the materials. HTO was shown to probe the whole pore volume (i.e. the space made of surface and bulk water). When the surface water volume was mainly composed of interlayer water (case of montmorillonite and bentonite), iodide was shown to be located in the pore space made of bulk water. When the interlayer water was not present (case of illite), the results showed that iodide could access a small fraction of the surface water volume localized at the external surface of the clay particles.

show abstract

“…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.

View full text Add to dashboard Cite

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

show abstract

Self-Diffusion of Sodium Ions in Compacted Sodium Montmorillonite

Cited by 106 publications

References 11 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

Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study

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

Contact Info

Product

Resources

About