Prediction of the Thermodynamic Behavior of Aqueous Silica in Aqueous Complex Solutions at Various Temperatures

Abstract

Experimental solubilities of amorphous silica in several aqueous electrolyte solutions and in aqueous solutions of organic compounds, and theoretical considerations of cavity formation, electrostriction collapse, ion solvation and long- and short-range interaction of the solvated ions with one another permit the calculation of the partial excess free energy and the activity coefficient of aqueous silica. It is shown that in the case of non-dissociated organic compoundwater solutions, the variation of log \( {m_{Si{O_2}}} \) with the reciprocal of the dielectric constant of the solution is described by a single linear equation whatever the nature of the organic compound. For aqueous electrolyte solutions, a specific linear relationship between log \( {m_{Si{O_2}}} \) and the reciprocal of the dielectric constant occurs for each electrolyte. The success of the theoretical equation in reproducing the experimental solubilities of amorphous silica in aqueous solutions of electrolytes and organic compounds supports previous evidence indicating a polar charge distribution in the solvated SiO2 molecule. Our data afford the calculation of the effective local charge of dissolved SiO2 molecules and of the short-range interaction parameters between SiO2 and various ions at temperatures up to 350°C.