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Effects of OH− activity and temperature on the dissolution rate of compacted montmorillonite under highly alkaline conditions

Published online by Cambridge University Press:  02 January 2018

Takuma Sawaguchi ,
Manabu Tsukada ,
Tetsuji Yamaguchi  and
Masayuki Mukai
Takuma Sawaguchi*
Affiliation:
Waste Safety Research Group, Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
Manabu Tsukada
Affiliation:
Waste Safety Research Group, Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
Tetsuji Yamaguchi
Affiliation:
Waste Safety Research Group, Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
Masayuki Mukai
Affiliation:
Waste Safety Research Group, Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
*
*E-mail: sawaguchi.takuma@jaea.go.jp
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Abstract

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The highly alkaline environment induced by cementitious materials in a deep geological disposal system of high-level radioactive waste is likely to alter montmorillonite, the main constituent of bentonite buffer materials. Over long time periods, the alteration may cause the physical and/or chemical barrier functions of the buffer materials to deteriorate. In order to evaluate the long-term alteration behaviour, the dissolution rate, RA (kgm−3 s−1), of compacted pure montmorillonite (Kunipia-F) was investigated experimentally under conditions of hydroxide ion concentration of 0.10—1.0 mol dm−3 at temperatures of 50—90°C. The dissolution rate data, including those from a previous study at 130°C, were formulated as a function of the activity of hydroxide ions, aOH− (mol dm−3), and temperature, T (K), and expressed as RA = 104.5·(aOH−)1.3·e−55000/RT by multiple regression analysis, where R is the gas constant. The dissolution rate of montmorillonite was greater in the compacted montmorillonite than in the compacted sand-bentonite mixtures. The difference can be explained by considering the decrease in aOH− in the mixtures accompanied by dissolution of accessory minerals such as quartz and chalcedony. The dissolution rate model developed for pure montmorillonite is expected to be applied to bentonite mixtures if quantification of the decrease in aOH− is achieved somehow.

Keywords

compacted montmorillonitehighly alkaline conditionsdissolution rateactivity of hydroxide ionstemperatureaccessory minerals
Type
Research Article
Information
Clay Minerals , Volume 51 , Issue 2 , May 2016 , pp. 267 - 278
Creative Commons
Creative Common License - CCCreative Common License - BY
Copyright © The Mineralogical Society of Great Britain and Ireland 2016 This is an Open Access article, distributed under the terms of the Creative Commons Attribution license. (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2016

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