Two types (aril and ester) of nitrogen bearing cationic surfactants were applied to recover silica from fluids supersaturated with respect to silica at the Sumikawa geothermal plant, northeast Japan. The reagents were mixed with two kinds of fluids ; one was fluids immediately after flashing under an atmospheric pressure (no retaining time ; NRT) and the other was fluids keeping in teflon bottles for 15 minutes at 90°C (15 minutes retaining time ; 15RT) after flashing. Total silica concentrations in both decreased with increasing the reagent concentration independent of the cohesion types and the molecular weight except for a starting material for the aril type one. Total silica concentrations in fluids with 15RT were lower than those in fluids with NRT and reached a nearly constant value of 380 mg/l (more than 50 mg/l reagent concentration), the solubility of amorphous silica at 90°C estimated in this study. Zeta potentials of silica slurries were increased with increasing the reagent concentration and crossovered the zero potentials around 75 mg/l reagent concentration for fluids with 15RT and around 100 mg/1 for fluids with NRT. From these results, the following model is demonstrated as a deposition mechanism ; in fluids with 15RT, 20 monomer silicas became one polymer silica by polymerization after flashing and reacted with one nitrogen ion in one cation cohesion.
