Silica scale formation is one of the potential problems for the practical operation of geothermal plants. In this study, we examined optimal pH (3, 6 and 9) and temperature (298–353 K) conditions for the treatment process of waste geothermal fluids using a silica polymerization kinetics calculation. The kinetic model of Fleming was applied to nuclear growth and rate-limiting steps. The polymerization rate at pH 9 was about 3 times higher than that at pH 6 during the nucleus growth process, whereas these speeds did not change due to the difference in temperature. The pseudo-equilibrium concentration at pH 6 followed Van’t Hoff theory, but that at pH 9 was higher at 298 K than that at 313 K. Our results, therefore, suggest neutral pH conditions are the most suitable to suppress the silica scale, and then the optimal temperature for the treatment could be estimated from the initial silica concentration according to this kinetic model.
