Montmorillonite alteration in KOH solutions at 35C and 60C

Ueda, Mai*; Nakabayashi, Ryo*; Kijima, Tatsuya*; Sato, Tsutomu*; Yoneda, Tetsuro*; Otake, Tsubasa*; Oda, Chie  

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.