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A Thermodynamic Analysis on the Effect of Salinity on Interlayer Space of Na-Montmorillonite

Published online by Cambridge University Press:  20 February 2017

Haruo SATO
Haruo SATO*
Affiliation:
Graduate School of Natural Science and Technology, Okayama University, 3−1−1, Tsushima-naka, Kita-ku, Okayama-shi, Okayama 700-8530, Japan
*
*(Email: ph3c5tsu@okayama-u.ac.jp)
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Abstract

Bentonite is used as one of the materials for engineered barrier systems in a radioactive waste repository. Since the major clay mineral constituent of bentonite is montmorillonite, its physico-chemical properties are important. Basal spacing of water-saturated Na-montmorillonite is reported to decrease with increasing Na-montmorillonite density. This paper presents a thermodynamic model to calculate change in the interlayer space of Na-montmorillonite based on the relative partial molar Gibbs free energy (dG) of interlayer water as contacted with a solution of an arbitrary salinity (NaCl concentration). Directly change in montmorillonite density (ρdm) against salinity was calculated by the thermodynamic model. The dG of interlayer water as contacted with a solution of an arbitrary salinity can be calculated by dG = dGH2O+ dGS (dGH2O: relative partial molar Gibbs free energy of interlayer water, dGS: that of water in a solution of an arbitrary salinity). The author previously reported an empirical correlation of dGH2O vs. water content for Na-montmorillonite. The dependence of ρdm on salinity was calculated by replacing dGH2O in the empirical correlation with dG. ρdm increased with salinity. Concretely, initially the ρdm-values of 0.5 and 1.0 Mg/m3 increased to 1.05 and 1.16 Mg/m3 under 0.5 m-NaCl, respectively. Interlayer space vs. salinity was estimated based on the measured results of basal spacing vs. ρdm by XRD and the average density of montmorillonite vs. salinity calculated by this model.

Keywords

layeredenvironmentwaste management
Type
Articles
Information
MRS Advances , Volume 1 , Issue 61: Scientific Basis for Nuclear Waste Management XXXIX , 2016 , pp. 4027 - 4033
Copyright
Copyright © Materials Research Society 2017 

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References

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