The effect of dissolved silica on the action of hydrolysing metal coagulants

Using a simple continuous optical technique, coupled with measurements of electrophoretic mobility, the effect of silicic acid or dissolved silica on the coagulation of kaolin suspensions has been examined. The results show that the presence of dissolved silica greatly affects the coagulation process at both low and high coagulant concentrations. The effect depends on the silica concentration and solution pH. Dissolved silica can improve, suppress or even prevent coagulation, and these effects may be due to the modification of hydrolysis species and precipitates due to the interaction between the metal ions and dissolved silica. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.