Aggregation of silica dispersions by iron(III)

Abstract

Abstract The coagulation and restabilization of silica dispersions by iron(III) has been studied as a function of pH, applied metal ion concentration (Ct), and the surface area of the dispersed phase (S). Understanding and interpretation of these phenomena in the iron(III)-silica system requires a knowledge of the interrelationships among Ct, pH, and S. Results are presented graphically as log Ct-pH and log Ct-log S domains of coagulation and restabilization. Hydrolyzed iron(III) is observed to be a better coagulant than nonhydrolyzed ferric ions and is also able to restabilize silica dispersions. Adsorption of hydrolyzed iron(III) species is responsible for the influence of the surface area of the solid silica phase on coagulation and restabilization. The observed dependence on surface area is in agreement with that predicted by a Langmuir model. Light scattering and refiltration rate measurements are shown to provide complementary quantitative measures of coagulation and restabilization, permitting these phenomena to be studied over a wide range of solid phase concentrations.