Experimental determination and thermodynamic modeling of solid–liquid equilibria in the system NaCl–Na2SO4–H3BO3–H2O at 323.15 K and its application in industry

The solubilities and refractive indices in the systems NaCl–Na 2 SO 4 –H 3 BO 3 –H 2 O and NaCl–H 3 BO 3 –H 2 O at 323.15 K were investigated with the isothermal dissolution equilibrium method. The phase diagram of the ternary system consists of two single-salt crystallization fields of NaCl and H 3 BO 3 , two solubility univariant curves, and one invariant point. The dry-salt diagram of the quaternary system is composed of three single-salt crystallization fields corresponding to NaCl, Na 2 SO 4 and H 3 BO 3 , three solubility univariant curves, and one invariant point. A comparison of the diagrams of the quaternary system at (298.15, 323.15 and 373.15) K shows that areas of sodium chloride and sodium sulfate salts region increases whereas the area of H 3 BO 3 region decreases distinctly with temperature increasing. Combining the Pitzer parameters and solubilities in the ternary systems in this study and literatures, the lacking Pitzer parameters for H 3 BO 3 were fitted on the basis of Pitzer model. The calculated solubilities with the model agree well with the experimental data. The phase diagrams and Pitzer model for the quaternary system at 298.15 and 323.15 K were then used to conduct a computer simulation of brine separation. All H 3 BO 3 and most of Na 2 SO 4 can be separated from the solution with segmental evaporation method.