Kinetic study of silica dissolution in aqueous solutions of aromatic organic electrolytes

To evaluate the effect of organic compounds on the dissolution rate of amorphous silica, the dissolution of amorphous silica in pure water and in organic electrolyte solutions were investigated at room temperature at pH 6. Based on the kinetic analyses, the dissolution rate constants of amorphous silica in the organic electrolyte solutions were 18-30 times larger than in pure water but less than those in the NaCl solution, which contained the same Na⁺ concentration as the organic electrolyte solution. The order of dissolution rate constants was N_NaCl>N_tiron>N_phthalate>N_salicylate>N_water. In these experiments, the dried samples were analyzed by FT-IR, and the results indicated that all of the organic composition was adsorbed on the surface of the silica. Compared with pure water, the cations in the organic electrolyte solution were a dominant factor in increasing the dissolution rate of silica. However, compared with NaCl, the dissolution rate of silica decreased in the aromatic organic electrolyte solution due to the adsorption of the organic electrolytes on the surface of the silica as well as to a decrease in the exposed surface. In fact, organic anions containing in the organic electrolytes are retarding the dissolution rate of silica.