Stability Analysis of GMZ Bentonite Colloids: Aggregation Mechanism Transition and the Edge Effect in Strongly Alkaline Conditions

Abstract In this study, the basic physicochemical properties (composition, morphology and surface charge) of the colloids obtained from Gaomiaozi (GMZ) bentonite were analyzed and photon correlation spectroscopy (PCS) tests were conducted for looking into the effects of ionic strength and pH on the stability. The results showed that the bentonite colloids were composed primarily of montmorillonite and cristobalite, and remained stable up to at least 8 months in pure water system, and its self-coagulation was negligible. The titration curves of the bentonite colloids showed a typical titration shape of montmorillonite clay, while a common intersection at the point of zero charge (PZC) around 9.5 and a slightly higher net proton sorption capacity compared with bulk form of GMZ bentonite reported in the literature were observed. The stability was strongly PZC dependent, around which the critical coagulation concentration (CCC) value rose rapidly with increasing pH stemming from the transition of different aggregation mechanisms. Further, a more important effect of the edge charge in strongly alkaline conditions was found to exist. This work can be helpful for better understanding the stability characterization of layered clay colloids and provides a valuable reference for safety assessments of the deep geological disposal repository for high-level radioactive wastes.