Measurements and calculations of solid-liquid equilibria in the quaternary system NaBr-KBr-Na2SO4-K2SO4-H2O at 298Â K

Solid-liquid equilibria in the quaternary system NaBr-KBr-Na2SO4-K2SO4-H2O at 298 K were measured by isothermal solution saturation method. The equilibrium solid phase and solubilities of salts in the system were determined. The experimental data are used to plot the solubility diagram and water content diagram of the quaternary system. It was found that quaternary system NaBr-KBr-Na2SO4-K2SO4-H2O at 298 K contains the double salt Na2SO4·3K2SO4 (Gla), and its solubility diagram has four invariant points, nine univariant curves, and six crystallization fields. The solids are NaBr·2H2O, Na2SO4, Na2SO4·10H2O, K2SO4, KBr and Na2SO4·3K2SO4 (Gla). The values of binary and mixing interaction parameters, the Debye-Hückel parameter Aϕ and the standard chemical potentials of the salts in the quaternary system at 298 K were obtained from the literature and adapted to standard temperature. Based on the Pitzer approach, the solubilities in the system NaBr-KBr-Na2SO4-K2SO4-H2O at 298 K have been calculated using the parameters. The calculated and measured phase diagram of the quaternary system was plotted. The results show that the calculated solubilities agree well with the experimental data.