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

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Title: Effect of exchangeable cations on apparent diffusion of Ca2+ ions in Na- and Ca-montmorillonite mixtures
Authors: Kozaki, T. Browse this author →KAKEN DB
Sawaguchi, T. Browse this author
Fujishima, A. Browse this author
Sato, S. Browse this author
Keywords: bentonite
exchangeable cation
geological disposal
radioactive waste
Issue Date: 2010
Publisher: Elsevier
Journal Title: Physics and Chemistry of the Earth, Parts A/B/C
Volume: 35
Issue: 6-8
Start Page: 254
End Page: 258
Publisher DOI: 10.1016/j.pce.2010.04.006
Abstract: 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+ with Ca2+. The Ca2+ cations could be released from cementitious materials and diffuse into the buffer material in the repository. In this study, to evaluate the alteration that could reduce the performance of the bentonite buffer, the apparent diffusion coefficients of HTO and Ca2+ ions were determined from non-steady, one-dimensional diffusion experiments using Na- and Ca-montmorillonite mixtures with different ionic equivalent fractions of Ca2+ ions. The apparent diffusion coefficient of HTO at a dry density of 1.0 Mg m^[-3] slightly increased with an increase in the ionic equivalent fraction of Ca2+ ions. However, the apparent diffusion coefficient of Ca2+ and the activation energy for diffusion at the same dry density were independent of the ionic equivalent fraction of Ca2+ ions. These findings suggest that unlike HTO, which can be postulated to diffuse mainly in pore water, Ca2+ ion diffusion could occur predominantly in interlayer spaces, of which the basal spacing was determined to be constant by the XRD technique.
Type: article (author version)
Appears in Collections:工学院・工学研究院 (Graduate School of Engineering / Faculty of Engineering) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 小崎 完

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