Degradation of GMZ bentonite by diffusion of alkaline solutions with various pH

This study delves into the degradation of GMZ bentonite, a critical material in the deep geological disposal of high-level radioactive waste, when exposed to alkaline solutions with varying pH levels. Through a year-long diffusion test, the research examines changes in mineral composition, chemical elements, and microstructure, using advanced techniques like X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), and scanning electron microscope-energy dispersive spectrometry (SEM–EDS). The findings reveal that higher pH levels and the presence of K+ ions significantly accelerate the dissolution of montmorillonite, the primary component of bentonite, leading to a decrease in its swelling properties and an increase in permeability. The study also identifies the formation of illite in bentonite reacted with KOH solutions, highlighting the role of cation exchange in mineral transformation. Moreover, the research underscores the importance of using low-alkali cement with reduced K+ content to mitigate bentonite degradation in engineering applications. The conclusions drawn from this study provide valuable insights into the long-term stability of bentonite in alkaline environments, which is crucial for the safe and effective disposal of high-level radioactive waste.