Surface charge characteristics of Gaomiaozi bentonite in high-level nuclear waste repositories

Gaomiaozi (GMZ) bentonite is an excellent backfill material for high-level nuclear waste repositories. The bentonite minerals possess a laminated structure and carry a negative charge. These surface charge characteristics play a crucial role in the development of the electric double layer at the liquid-solid interface and the adsorption of nuclear elements during the hydration process. Following the purification of GMZ bentonite, the surface electric potential of bentonite mineral colloids in suspension and compacted bentonite blocks was measured using atomic force microscopy (AFM). Additionally, the influence of various factors on its surface charge characteristics was examined, including the types of interlayer cations, ambient temperature, number of layers, and dry density. The findings reveal that at 20 degrees C, the surface electric potential of Na-bentonite quasi- crystals averages around-225.2 mV, while that of Ca-bentonite quasicrystals averages approximately-155.3 mV. Additionally, the surface electric potential increases logarithmically with the number of layers. In the compacted state, its surface potential would decrease. An increase in the dry density of compacted bentonite results in a decrease in the surface electric potential. High ambient temperatures can increase the surface electric potential. The research findings offer valuable data and a theoretical foundation for predicting colloid formation, nuclear element adsorption, and swelling pressure development in bentonites used in high-level nuclear waste repositories.