Removal and Recovery of Silica Source from Geothermal Water Recycling System by Calcium Nitrate and Sodium Hydroxide

摘要

In order to elucidate the possibility of removal of silicic acid from geothermal water, the calcium nitrate and sodium hydroxide as removing agent was investigated under various conditions. The initial concentration of silicic acid in geothermal water was 412 ppm as Si. The concentration of silicic acid decreased rapidly when the removing agent was added. Precipitation reaction for silicic acid reached equilibrium within 30 minutes and was independent of pH. The removing rate of silicic acid increased with increasing the pH of solution. The high concentration of silicic acid in geothermal water was perfectly removed by addition of calcium nitrate with molar ratio of Ca/Si over 2.1 at pH12. XRD pattern showed that the component of precipitation was calcium silicate hydrate Ca_2SiO_4·nH_2O (CSH).