TWO VIEWPOINTS FOR REMOVAL OF SILICIC ACID FROM GEOTHERMAL WATER TO PREVENT SILICA SCALING

Abstract

As a prevention method of silica scales at geothermal power plants, removal of silicic acid from geothermal water was studied from two chemical viewpoints: removal of supersaturated polysilicic acid and removal of all monosilicic acid by the addition of cethyltrimethylammonium bromide (CTAB) and calcium chloride accompanying pH adjustment, respectively. As the polymerization of silicic acid proceeds and polysilicic acid grows, the removal efficiency of polysilicic acid is higher. At the addition of 10-4 M CTAB, most of the polysilicic acid was removed. For removal of monosilicic acid, the addition of the same amount of Ca2+ as monosilicic acid and the following adjustment to pH 12 around 90? is the best condition to precipitate all of silicic acid as a calcium silicate hydrate from geothermal water. In addition, aluminum, which affects the formation of silica scale, is also removed by the both methods.