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Report No.

X-ray CT observations of altered bentonite by hyperalkaline-fluids; Dissolution kinetics of montmorillonite in compacted bentonite

Nakabayashi, Ryo*; Elakneswaran, Y.*; Sato, Tsutomu*; Otake, Tsubasa*; Oda, Chie  ; Yoneda, Tetsuro*; Kaneko, Katsuhiko*

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$$^{3}$$) with a 0.3M NaOH solution at 80$$^{circ}$$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.



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