Solid-liquid stable phase equilibria of the quaternary system Na+ //Cl−, SO42−, CO32−-H2O and its subsystems Na+ //Cl−, CO32−-H2O and Na+ //SO42−, CO32−-H2O at 353.15 K

Abstract

The solid-liquid phase equilibria of the solution in the quaternary system Na+ //Cl−, SO42−, CO32−-H2O and its subsystems Na+ //Cl−, CO32−-H2O and Na+ //SO42−, CO32−-H2O at 353.15 K were measured by isothermal solution saturation method. The equilibrium solids were determined by the Schreinemaker's method of wet residues and X-ray diffraction (XRD). Based on the experimental data, the phase diagrams were plotted and analysed. There is one monohydrate in the ternary system Na+ //CO32−, Cl−-H2O at T = 353.15 K, and the phase diagram contains one invariant point, two univariant curves and four crystallization regions. The ternary system Na+ //SO42−, CO32−−H2O at T = 353.15 K is more complex than the previous system since one monohydrate and one anhydrous double salt are found; the phase diagram contains two invariant points, three univariant curves and six crystallization regions. The phase diagram of the quaternary system Na+ //Cl−, SO42−, CO32−-H2O at 353.15 K includes two invariant points, five univariant curves, and four crystallization fields of single salts corresponding to NaCl, Na2SO4, Na2CO2·H2O and 2Na2SO4·Na2CO2. The results obtained in this study can help identify the solutions from which fractional crystallization of Na2SO4 and NaCl will be more effective.