Solid-liquid phase equilibria of the quaternary system Na+//Cl−, NO3−, SO42−-H2O at 358.15 K

Abstract

The stable (solid + liquid) phase equilibrium and the solution density of the quaternary system Na+//Cl−, NO3−, SO42−-H2O and its subsystems at 358.15 K were determined by the isothermal solution saturation method and moist residues. All phase diagrams of ternary systems for Na+//Cl−, SO42−-H2O, Na+//Cl−, NO3−-H2O, Na+// NO3−, SO42−-H2O at 358.15 K contain one invariant point, two invariant curves, and three crystallization regions. Neither double salt nor solid solution is found in the three ternary systems at 358.15 K. When NaCl, NaNO3, and Na2SO4 are analyzed as (7.02, 48.62, 1.58) wt %, respectively, the quaternary system Na+//Cl−, NO3−, SO42−-H2O reach saturation at 358.15 K. The phase diagram of the quaternary system at 358.15 K includes one invariant point, three invariant curves, and three crystallization regions. The three crystallization regions correspond to NaCl, NaNO3, and Na2SO4 and the Na2SO4 crystallization region is much bigger than that of the other two salts. Moreover, using the “translation technology”, the phase diagram of Na+//Cl−, SO42−, NO3−-H2O system can be predicted and constructed. All experimental data, especially the crystalline regions, can provide the fundamental basis for the design and optimization of the crystallization process of NaCl, NaNO3, and Na2SO4 in coal chemical high salinity wastewater.