The solubility of amorphous silica was determined in sodium chloride,potassium chloride, magnesium chloride and calium chloride solutions from 0.01 to 1moI/I and at temperatures of 21,36,50 and 65℃. The Setchenow equation was applied to the results, which enabled us to estimate the equilibrium concentration of "dissoloved silica" (molybdate-reactive silica) in the studied chloride solutions.
Next, the effects of pH, supersaturation of silica and salt concentration on the polymerization rate of silica were investigated at 35℃. In the pH range from 6.4 to 7.9, the maximum polymerization rate increased with increasing pH. The maxima occurred when dissoloved silica decreased by 25% of the initial supersaturation concentrations irrespective of pH. The polymerization rate was found to be dependent on the supersaturation degree rather than on the supersaturation concentration of silica. The results in magnesium chloride solutions suggest that magnesium ions may act as nuclei in the formation of colloidal silica in geothermal waters.