Silica in alkaline brines.

Analysis of sodium carbonate-bicarbonate brines from closed basins in volcanic terranes of Oregon and Kenya reveals silica contents of up to 2700 parts per million at pH's higher than 10. These high concentrations of SiO(2) can be attributed to reaction of waters with silicates, and subsequent evaporative concentration accompanied by a rise in pH. Supersaturation with respect to amorphous silica may occur and persist for brines that are out of contact with silicate muds and undersaturated with respect to trona; correlation of SiO(2) with concentration of Na and total CO(2) support this interpretation. Addition of more-dilute waters to alkaline brines may lower the pH and cause inorganic precipitation of substantial amounts of silica.