Thermochemical effects on the smectite alteration of GMZ bentonite for deep geological repository

International audienceGaomiaozi (GMZ) bentonite has been recognized as the first choice for using as buffer/backfill material in deep geological repository for the disposal of high-level nuclear waste in China. High salinity high pH of the pore solutions may cause changes in the mineralogical composition, the swelling capacity of the bentonite results in affecting the long-term performance of the engineering barrier system. In the present work, a series of hydrothermal reactivity experiments were performed using batch reactors at 20, 35 80 degrees C for evaluating the chemical mineralogical responses of GMZ bentonites. The results show that the dissolution of smectite releases Si Al under the conditions of 1 M KOH at 35 80 degrees C the released Si Al may work as a cementing agent in GMZ bentonite. XRD pattern results show that alteration of the GMZ bentonite is expected to be insignificant for reaction with NaCl, KCl NaOH solutions under low temperatures. However, it is obviously reacted with KOH solutions especially at 80 degrees C, during which cementitious material was produced leading to kaolinitization. When contacted with KOH solutions, the basal spacing (d(001)) of the main primary diffraction peaks (001) value of GMZ bentonite increases with increasing temperature. Salinity also can influence the smectite stability accordingly loss of swelling capacity. This conclusion could be explained by the diffusing double-layer effects induced by salt solutions ion exchange