Nanoscale mineral particle characteristics of Gaomiaozi bentonite

Abstract

Gaomiaozi (GMZ) bentonite as a back-filling (buffer) material for repositories of high-level nuclear waste (HLW) has an obvious multiple-pore structure. The particle characteristics of its constituent minerals have significant impacts on its macroscopic physical and mechanical properties. After purification, the nanoscale montmorillonite mineral particle morphology of GMZ bentonite in suspension was observed by atomic force microscope (AFM). The particle size, particle shape and stacking characteristics of particles were statistically analysed. The effects of the hydration process, ambient temperature, and interlayer cation types on its particle characteristics are explored. The particle gradation of GMZ bentonite particles is discontinuous. The large particles have a long stripe shape with an equivalent particle size of 1200 ~ 2500 nm; the small particles have an elliptical shape with an equivalent particle size of 5 ~ 600 nm. Larger the particles particle size, more irregular the particle shape. The complete hydrated bentonite particles contain generally less than 20 layers. The layer thickness is about 0.98 nm, and the layer basal distance is about 1.15 ~ 1.55 nm. The particles with more layers would have a smaller layer basal distance. Low ambient temperature could increase the layer basal distance. Calcium ion exchange increases the layer basal distance, and the opposite is true for sodium ions. The research would be facilitating the understanding of the evolution of multiple pore structures during the bentonite hydration process.