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Dissolution of compacted montmorillonite at hyperalkaline pH and 70°C: in situ VSI and ex situ AFM measurements

Published online by Cambridge University Press:  09 July 2018

H. Satoh ,
T. Ishii  and
H. Owada
H. Satoh*
Affiliation:
Mitsubishi Materials Corporation, Ibaraki, Japan
T. Ishii
Affiliation:
Radioactive Waste Management Funding and Research Center, Tokyo, Japan
H. Owada
Affiliation:
Radioactive Waste Management Funding and Research Center, Tokyo, Japan
*
*E-mail: hsatoh@mmc.co.jp
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Abstract

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In situ measurements were carried out to quantify montmorillonite dissolution rates at a compaction pressure ranging from 0.04 to 10.00 MPa and temperature of 70°C in 0.3 M NaOH solution (pH 12.1 at 70°C) using vertical scanning interferometry (VSI) and an auto-compaction cell. Ex situ measurements of the reacted samples using atomic force microscopy (AFM) were performed to quantify the ratio of edge surface area (ESA) to total surface area (TSA) (XESA = ESA/TSA). Accordingly, the actual ESA for the montmorillonite examined by in situ VSI could be estimated. The XESA value increases as a function of run duration or compaction pressure. At atmospheric pressure, XESA is approximately 0.0054 and converges to ∼0.0107 at 10 MPa, An expression that relates reactive surface area and montmorillonite compaction (XESA/XESA initial = kXESA, k: variable factor) is kXESA = 1.0 + 0.64628 P0.1527 where P is in MPa. Using the calculated XESA, dissolution rates from the in situ VSI measurements are obtained. The early dissolution (<1500 min) at less compaction pressure tends to show faster rates (>1.0 × 10-11 mol/m2/s) than that at higher compaction pressure. The rates after >1500 min are slower, with values of less than 3×6 10-12 mol/m2/s, but there is no significant dependency on the density in the range from 1.0 to 1.7 Mg/m3. These observed rates for compacted montmorillonite are two-orders of magnitude slower (2.63×10-13 mol/m2/s) than dissolution rates in the suspended state.

Keywords

montmorillonitedissolutioncompactionVSIAFMsurface areabentonite bufferalteration
Type
Research Article
Information
Clay Minerals , Volume 48 , Issue 2 , May 2013 , pp. 285 - 294
Creative Commons
Creative Common License - CCCreative Common License - BY
Copyright © The Mineralogical Society of Great Britain and Ireland 2013 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 2013

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