Quantitative Study of Surface Deprotonation Induced Settling Mode Transition of Silica Colloidal Particles

摘要

References(15) The effect of surface deprotonation of colloidal silica particles on settling mode transition has been studied quantitatively. We observed the settling mode transitions of silica aqueous suspensions by adding a pH controlled CaCl2 electrolyte solution as a coagulant. Depending on the solution pH, three types of settling modes were observed, i.e. “no settling mode”, “free settling mode” and “hindered settling mode”. In these observations, a large pH drop occurred immediately after mixing of the coagulant. To describe the pH drop, we developed a simple mathematical model consisting of a 1-pK Stern model and a mass balance equation of protons on silica particles. The model shows excellent agreement with experiments in the number of dissociated protons from a silica surface (np). Furthermore, the boundaries of the three setting modes in the pH-φ phase diagram are also well explained by the value of np. Our results clarify that the extent of colloidal instability is quantitatively described by np.