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Saito, Yuki*; Ishiwata, Tobimaru*; Horiuchi, Misato*; Nishiki, Yuto*; Kikuchi, Ryosuke*; Otake, Tsubasa*; Kawakita, Ryohei; Takayama, Yusuke; Mitsui, Seiichiro; Sato, Tsutomu*
Shigen, Sozai Koenshu (Internet), 11(1), 7 Pages, 2024/03
no abstracts in English
- and K-montmorilloniteKawakita, Ryohei; Saito, Akito*; Sakuma, Hiroshi*; Anraku, Sohtaro; Kikuchi, Ryosuke*; Otake, Tsubasa*; Sato, Tsutomu*
Applied Clay Science, 231, p.106722_1 - 106722_7, 2023/01
Times Cited Count：2 Percentile：20.84(Chemistry, Physical)Ishiwata, Tobimaru*; Kikuchi, Ryosuke*; Otake, Tsubasa*; Sato, Tsutomu*; Kawakita, Ryohei; Takayama, Yusuke; Mitsui, Seiichiro
no journal, ,
It is known that the cementation of bentontie may cause the reduction of swelling pressure. However, fundamental mechanism of this reducing swelling pressure has not been well understood. To understand the mechanism, it is essential to identify the cementitious materials and observe the changes in microstructure associated with cementation. In this study, the microstructural observation and swelling tests were conducted on several bentonite ores collected from Tsukinuno Mine in Yamagata Prefecture, Japan, as natural analog of cementation, and the relationship between petrographic texture and swelling pressure was discussed. Thin sections of bentonite ores were prepared by dry polishing technique to observe flat surfaces in micro scales. Scanning electron microscopy (SEM) demonstrated the widespread distribution of authigenic, a few micron silica in the matrix of montmorillonite. Transmission electron microscopy (TEM) revealed that the micro silica minerals (commonly quartz and less commonly amorphous silica) adhered to the edge of montmorillonite grains. These observations suggest that the adherence of these cementitious materials to montmorillonite prevents water access to the interlayer of montmorillonite and swelling, resulting in a decrease in swelling pressure. While these microstructures were observed commonly in all samples collected from several bentonite beds, the relative abundance of montmorillonite and micro silica minerals varied among different beds. It is possible that the swelling pressure in the cemented bentonite is affected by the relative abundance of montmorillonite and cementitious materials.
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 80
C 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.
C and 60CUeda, Mai*; Nakabayashi, Ryo*; Kijima, Tatsuya*; Sato, Tsutomu*; Yoneda, Tetsuro*; Otake, Tsubasa*; Oda, Chie
no journal, ,
Montmorillonite-rich bentonite is expected to be used as a buffer material in the geological disposal of radioactive wastes. Cement used for the construction of the disposal facility will generate highly alkaline leachates dominated by KOH and NaOH, which may act to cause the alteration of montmorillonite and the loss of the properties of bentonite suitable for the buffer material. In the current study, the illitization of montmorillonite in KOH solutions, which is considered as one of possible alteration processes, was investigated by conducting batch-type reaction experiments at 35 and 60C for up to 270 days. Based on XRD analyses and AFM observations for the reaction products, the formation of illite/smectite interstratified minerals, the increase in the layer charge, and the increase in hight and the decrease in basal area of the dispersed flat particles were recognised. These results indicate that illitization proceeded simultaneously with dissolution of montmorillonite.
Kikuchi, Ryosuke*; Fujimura, Tatsuya*; Sato, Tsutomu*; Otake, Tsubasa*; Otomo, Yoko*; Goto, Takahiro*; Suzuki, Satoru*; Taniguchi, Naoki; Suzuki, Hiroyuki*
no journal, ,
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.
Ishiwata, Tobimaru*; Kikuchi, Ryosuke*; Otake, Tsubasa*; Sato, Tsutomu*; Kawakita, Ryohei; Takayama, Yusuke; Mitsui, Seiichiro
no journal, ,
Bentonite clay is planned to be used as a buffer material in the geological disposal of high-level radioactive wastes. The swelling property of bentonite is expected to keep low permeability and control the migration of radionuclides thereby ensuring the safety of geological disposal. In the long-term, however, cementation of bentonite may degrade the swelling property where secondary minerals precipitate and adhere to the montmorillonite component of bentonite. In the present study, natural bentonite ores were investigated as analogues to cementation of bentonite in geological disposal. The images of SEM and EPMA were integrated into "mineral map", which could visually illustrate the distributions of individual mineral grains including fine cementitious minerals. Finally, multi regression analysis (MRA) was used to investigate correlation between petrographic parameters and swelling pressure. MRA showed swelling pressure of bentonite increases with the content of montmorillonite, and decreases with the total perimeter of accessary minerals. This suggests that the presence of secondary minerals can inhibit the swelling of montmorillonite and the area of contact between montmorillonite and secondary minerals might be a key parameter.
solution; The Effect of pH and C-S-H precipitationKijima, Tatsuya*; Nakabayashi, Ryo*; Elakneswaran, Y.*; Oda, Chie; Otake, Tsubasa*; Sato, Tsutomu*; Yoneda, Tetsuro*
no journal, ,
pH dependency of Montmorillonite dissolution rate in Ca-Cl-OH aqueous solution system was confirmed by conducting a flow-through type dissolution experiment. C-S-H formed depending on the experimental pH and concentration of Ca. The dissolution rate determined in the condition where C-S-H formed differed from the rates obtained in NaOH solutions.
