(299f) Impact of Silica in Water Treatment Technology

In many parts of the world the use of water in reverse osmosis (RO), cooling, boiler, and geothermal applications is limited by the poor solubility of silica. Silica, the second most abundant element, is found in all natural water supplies. Silica solution chemistry is very complex and difficult to predict. In RO feedwaters, silica can exist in three different forms as follows: Monomer silica or silicic acid, polymeric silica that results from polymerization of silicic acid, and filterable silica. Ca²⁺ and Mg²⁺ ions have a strong influence on the formation of filterable silicate. It has been proved that the polymeric silica is mainly responsible for the membrane scaling. The challenge is how to exceed the range of silica solubility to facilitate the use of RO systems in areas where the available feedwaters have high silica concentrations. Silica solubility is well known to be influenced by both pH-value and temperature. This paper is a review on silica fouling problems and the use of various products for extending silica solubility.