Silica

Silica

The dissolved mineral forms of silica are found in all natural waters. Although silica is only slightly soluble in water and it can be found as ionic silica, silicates, and colloidal or suspended particles. The solubility of silica is highly dependent on pH, temperature, and pressure. Silica’s presence in industrial applications, particularly in high-pressure turbines, is undesirable because of scaling caused as silica precipitates out of solution at the elevated temperatures and pressures. Heating systems and reverse osmosis plants also require monitoring of silica to ensure process efficiency. Silica can be measured photometrically with reagents. Photometric analysis is based on the Beer-Lambert principle of absorbance in which the intensity of the color produced is proportional to the concentration of silica in the sample. Photometric analysis products include handheld colorimeters, portable and benchtop photometers, and spectrophotometers. The low-range method uses an adaptation of the ASTM Method D859 (Heteropoly Molybdenum Blue Method) to measure silica concentrations below 2.00 mg/L (ppm). A high range meter uses an adaptation of the USEPA Method 370.1 and Standard Method 4500-SiO2 C to measure silica concentrations up to 200 mg/L (ppm).