Physicochemical behaviors of kaolin slurries with and without cations—Contributions of alumina and silica sheets

Numerous studies on the surface charge-pH and yield stress-pH behaviors of kaolin slurries with respect to the pH-dependency of alumina (Al) sheets, silica (Si) sheets and edges in kaolin particles have been carried out. There is, however, still a paucity of studies that explain if the alumina sheets or the silica sheets in kaolin particles contribute in greater extents to the surface charges of kaolin particles that will consequently affect the kaolin particle interactions and yield stresses. In this study, the contributions of the alumina and the silica sheets to the zeta potential-pH and yield stress-pH behaviors of Riedel kaolin particles, which display no isoelectric points (IEPs), are analyzed by comparing these behaviors of Riedel kaolin slurries to that of alumina and silica slurries with and without Mg2+ and Ca2+ cations. With and without cations, the behaviors of Riedel kaolin slurries were more similar to the behaviors of silica compared to alumina slurries. The principal reason for this similarity is due to the high concentrations of negative charges on both silica and Riedel kaolin particles at all pH compared to the lower concentrations of negative charges on alumina particles. This explains that the permanently negatively charged silica sheets contribute in greater extents to the surface charge-pH and yield stress-pH behaviors of Riedel kaolin slurries compared to the alumina sheets.