EXPERIMENTAL AND THERMODYNAMIC STUDY OF SILVER SOLUBILITY IN WATER-CHLORIDE-CARBON DIOXIDE FLUID

Abstract

In order to elucidate the influence of carbon dioxide on the solvent capacity of water-cat-bun dioxide fluids with respect to noble metals, a combined experimental and thermodynamic study was carried out on the solubility of Ag(met) at 350 degreesC in aqueous 1 m NaCI solutions containing 0.0018-0.025 m HCl under CO2-present and CO2-free conditions in the region of fluid homogeneity at pressures 500 and 700 bar (up to 5.2 and 6.3 mole of dissolved CO2 per one kilogram of H2O, respectively). Silver solubility was modeled using the electrostatic approach accounting for changes in the dielectric constant of a mixed solvent of the water-low polar gas type. The results of experiments in aqueous chloride solutions without CO2 were compared with the data of Ag(met) solubility modeling considering the occurrence of four possible silver chloride complexes: AgCl0, AgCl2-, AgCl32-, and AgCl43-. This provided additional support to the reliability of G values recommended in the literature for AgCl2- the major dissolved silver species in chloride solutions. According to the experimental results, at high acidity of the solutions (0.018 m HCl), the influence of CO2 is manifested in a progressive decrease (by 15-20%) in silver solubility with increasing CO2 content. This effect was not observed in lower acidity solutions (0.0018 m HCl). The obtained experimental and theoretical dependencies of CO2 influence on silver solubility allowed us to estimate the Born coefficient for HCl0, omega = 0.7 x 10(5) cal/mol.