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Ueda, Mai*; Nakabayashi, Ryo*; Kijima, Tatsuya*; Sato, Tsutomu*; Yoneda, Tetsuro*; Otake, Tsubasa*; Oda, Chie
no journal, ,
In the current study, the promoted illitization of montmorillonite in KOH solutions was investigated. Montmorillonite was added to 0, 0.1, 0.5, 1.0, and 3.0 M KOH solutions, which were then sealed and kept at 35 or 60 
C for up to 270 days. Reaction products were analyzed by XRD to check the expandability, an empirical determination of layer charge and observation by AFM. 10 and 35% of illite layer in randomly interstratified illite/smectite minerals were estimated by XRD for 0.1 M and 3.0 M solutions, respectively. Changes in the peak intensities obtained from the XRD patterns could be assigned to the dissolution of montmorillonite, but with some uncertainty affected the reliability of the quantification of illite. No significant illitization was observed based on the results of layer charge and AFM observation. Consequently, there is no direct evidence for significant illitization of montmorillonite in KOH solutions under the experimental conditions of the current study.
Suzuki, Shinichi; Yaita, Tsuyoshi; Matsumura, Daiju; Okajima, Yuka*; Kobayashi, Toru; Nishihata, Yasuo
no journal, ,
Nakabayashi, Ryo*; Elakneswaran, Y.*; Sato, Tsutomu*; Otake, Tsubasa*; Oda, Chie; Yoneda, Tetsuro*; Kaneko, Katsuhiko*
no journal, ,
The current study developed developed an in situ microstructural analysis method using X-ray CT to track bentonite/hyperalkaline fluid interactions. An advective alteration experiment was conducted by reacting a compacted bentonite (0.3 Mg/m
) with a 0.3M NaOH solution at 80C for 180 days. No significant dissolution of montmorillonite in the bentonite was observed using X-ray CT, although the formation of secondary minerals could be quantified by X-ray CT. A geochemical modeling using the dissolution rate of montmorillonite obtained in a dispersed system did not fit the experimental data, but could provide a satisfactory match to that by changes to the reactive surface area and the inclusion of an empirical term to account for the saturation state of montmorillonite. This implies that there is difference in effective reactive surface area and effect of the saturation state on the dissolution rate between dispersed and compacted systems.