The surface properties of clay minerals modified by intensive dry milling — revisited

The present study broadened the research on the effect of the intensive physical disintegration of clay minerals (kaolinite and “Otay” montmorillonite) and mica (ripidolite), carried out by high-energy ball milling (HEBM), on their surface physico-chemical characteristics, i.e., the specific surface area (SSA), the cation exchange capacity (CEC), and the electrokinetic properties. The mechanical disintegration of clay minerals occurred in two consecutive processes. Significant changes of the size, morphology and structure were followed by the change of the physico-chemical properties. The decrease of the particle size of the clay minerals resulted in significant increases in the SSA and CEC values, and in the exposure of new, amphoteric surfaces, significantly changing the electrophoretic mobility (EPM). Prolonged milling produced amorphous alumina–silicate aggregates. These solids exhibited the same morphological properties, SSA and CEC, despite the fact that they were formed from initially different clay minerals. In contrast, the electrophoretic mobility of these samples was significantly changed, exemplifying the significance of the initial chemical composition and the formation of different types of surface structures on the physico-chemical processes at amorphous solid-surface–liquid interfaces.