Effect of polysilicic acid on the precipitation of calcium carbonate

The precipitations of calcium carbonate (CaCO3) from supersaturated solutions were investigated in the absence and presence of polysilicic acid under the condition of pH 9 at room temperature. The turbidity of the CaCO3 solution in the presence of polysilicic acid was lower than that in the absence of polysilicic acid, suggesting that the polysilicic acid inhibits the precipitation of CaCO3. The turbidity of solutions was distinctly decreased with increasing the polysilicic acid concentration. SEM images of the precipitates provide visual evidence that colloidal silica adhered to active growth sites of CaCO3 nucleus through electrostatic attraction to inhibit the growth of CaCO3 crystals.