Enhanced cesium retention through zeolitization of bentonite under elevated temperature and potassium-rich alkaline environment

초록

This study investigated the hydrothermal transformation of montmorillonite in bentonite into zeolite under alkaline conditions using KOH solutions (0.02-1 M) at 150 degrees C, simulating the alkaline and thermal environments of high-level radioactive waste geological repositories. The Cs retention increased with increasing KOH concentrations. In the samples reacted with KOH solutions, the Cs retention capacity was approximately 1.3-1.8 times higher than that in the raw bentonite sample. At KOH solutions, the montmorillonite in bentonite underwent substantial structural and chemical alterations, forming K-zeolite (merlinoite) with a stable aluminosilicate framework and enhanced cation exchange capacity (CEC). The eight-membered ring (8-MR) channels (3.3-4.4 and 5.1 & Aring;) in merlinoite provide an ideal environment for Cs retention due to ionic size compatibility and the low hydration energy of Cs+. Thermal and chemical analyses further confirmed the improved thermal and structural stability of merlinoite under high pH conditions. The results indicate that merlinoite formation in bentonite effectively immobilizes Cs+ ions under high temperatures and K-rich alkaline conditions, relevant to radioactive waste disposal.

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