In a geothermal power station, silica scale often causes serious problems, such as a decline of the heat exchanger's performance, and plugging of pipelines and permeable layers. Polymerization of silicic acid dissolved in geothermal water plays an important role in silica scale formation, and this reaction is affected by many factors, such as temperature, pH, silica concentration and coexisting elements. In this study, the effect of residence time, temperature, aluminum concentration, and pH on silica precipitation was investigated to resolve silica scale troubles. The experimental results were as follows : Polymerization of silicic acid supersaturated in geothermal water progressed by decreasing temperature and increasing residence time. The aggregation through the formation of Si-O ···Al 3+ ···O-Si bonds occurred in the narrow pH range between 4 and 5. A large quantity of silica precipitation formed by adding trace amounts of aluminum. We present a new process of silica removal from geothermal water based on the optimum conditions obtained by experiments.
