Influence of heating and water-exposure on the liquid limits of GMZ01 and MX80 bentonites

Bentonite has been considered as a buffer material for embedding canisters with high-level radioactive waste (HLW) in deep geological repositories. GMZ bentonite deposit, located in Xinghe County, Inner Mongolia Autonomous Region, China was proposed as a buffer/backfill material for HLW repository in China. The liquid limits of natural Na-bentonite GMZ01 and commercial Na-bentonite MX80, which are previously heated at 80 degrees C and 95 degrees C, respectively, and exposed to water for different times are measured. It is observed that the liquid limit of GMZ01 increases slightly at the beginning, and then decreases as the heating time increases, while the liquid limit of MX80 decreases with the heating time. The liquid limits of both GMZ01 and MX80 decrease with increasing water-exposure time. After the samples are heated at 80 degrees C and 95 degrees C for several months, the mineralogical composition of GMZ01 does not exhibit evident change, whereas MX80 experiences some changes. In addition, the chemical composition, cation exchange capacity (CEC) and exchangeable cation of all the samples do not change significantly.