Silica precipitation kinetics: the role of solid surface complexation mechanism integrating the magnesium effects from 25 to 300°C

Abstract : The results presented in this paper allow identifying and integrating the role of magnesium in the kinetic rate of silica precipitation. The basic thermodynamic and kinetic approaches are not sufficient to comprehensively describe the kinetic rate of silica precipitation as well as the simultaneous changes of the solution properties such as pH variations. Trial-error modelling tests reveal that it is necessary to take into account the silica solid surface complexation reactions, in particular the protonation reactions of the silanol sites outcropping of silica surface, in the kinetic law to reproduce measured properties (pH, dissolved silica concentrations, etc.). This newly developed kinetic law is able to correctly describe silica precipitation in presence of magnesium as well as chemical changes in the aqueous phase up to high temperatures (300°C).