Solubility model for amorphous silica in concentrated electrolytes

摘要

Silica is one of the major constituents of the earth's crust and is ubiquitously present in most natural materials. The solubility of silica and other silica-containing compounds is, therefore, of primary concern in geochemistry and in chemical processing applications where silica scale formation, resulting from changes in temperature and electrolyte composition, can cause problems in process design and operation. This paper describes the development of an aqueous thermodynamic model for accurately predicting the solubility of amorphous silica and other silica-containing compounds in the system Na(sup +)-H(sup +)-Mg(sup 2+)-NO(sub 3)(sup (minus))-SO(sub 4)(sup 2(minus))-Cl(sup (minus))-H(sub 2)O to high concentration and across the temperature range 25--100 C. This model, which utilizes the aqueous thermodynamic model of Pitzer, includes only one dissolved silica species, H(sub 4)SiO(sub 4)(aq), and is valid in neutral to very acidic solutions. The model is parameterized from the extensive set of solubility data in the literature as well as from new experimental data on amorphous silica solubility in HNO(sub 3) and HCl developed as part of this study. The accuracy of the model is tested on solutions more complex than those used in model parameterization.