Inhibition and Growth Control of Colloidal Silica: Designed Chemical Approaches

G roundwaters in areas such as Texas, New Mexico, Arizona, California, parts of southern Europe, the Pacific Rim, and Latin America contain high silica concentrations (50 to 100 ppm, as colloidal silica [SiO 2 ]). These levels arise from dissolution of various silicate-containing minerals into the groundwater. Silica precipitation and deposition occur mostly in evaporative cooling systems, where cation/anion levels gradually increase from partial water evaporation. Silica solubility, which depends on water chemistry and temperature, generally is accepted to be 150 to 180 ppm. Operators must maintain silica at an acceptable level to avoid silica deposits. This requires operation at very low cycles of concentration (which consumes large amounts of water) or use of chemical water treatments that prevent silica scale formation and deposition. Silica and silicate deposits are particularly difficult to remove once they form. Harsh chemical cleaning or mechanical removal is usually required.