INHIBITION OF SILICA-SILICATE DEPOSIT IN INDUSTRIAL WATERS

The potential for silica scaling exists when the concentration of dissolved silica exceeds the solubility equilibrium limit for amorphous silica at the temperature and pH of the solution. The key to the formation of amorphous silica deposits seems to be in the polymerization of monomeric silica; it is catalyzed by hydroxide ion at pH >4 and the rate becomes fastest in the pH range 6-8. Above this pH range, silicate species become important. Polymerization of silica requires a balance of unionized and ionized silicate species. At higher pH, this balance is shifted towards the ionization of silicic acid and so the polymerization of silica tends to slow down; however, the potential for the formation of calcium-magnesium silicates increases. Commonly employed precipitation inhibitors are not very effective for inhibiting silica polymerization but can prevent calcium-magnesium silicate formation. This paper presents the results of the study to inhibit silica/silicate deposits by shifting the silica/silicate equilibrium in favor of silicate formation and employing commonly used precipitation inhibitors.