Phase Equilibrium of the Ternary System Na2SO3–Na2SO4–H2O at 293.15, 313.15, and 353.15 K

Abstract

The phase equilibrium data of the ternary system Na2SO3–Na2SO4–H2O at 293.15, 313.15, and 353.15 K were determined by the isothermal dissolution method. There are one invariant point, two univariant isothermal dissolution curves, and three crystallization regions at each temperature. As the temperature increases from 293.15 to 313.15 K, the solubilities of both Na2SO4 and Na2SO3 increase. The single crystallization region of Na2SO4 decreases, while the single crystallization region of Na2SO3 increases. When the temperature increases from 313.15 to 353.15 K, the solubilities of both Na2SO4 and Na2SO3 decrease. The single crystallization region of Na2SO4 decreases, and the single crystallization region of Na2SO3 is basically unchanged. Furthermore, based on the solubility data, the Pitzer ion interaction model was used to calculate the relevant Pitzer parameters and then to calculate the solubilities of Na2SO3 and Na2SO4 theoretically. The calculated Na2SO3 and Na2SO4 solubilities basically agree with the experimental values. The data obtained in this work have important implications for the design and optimization of the Na2SO3 crystallization process from resorcinol production wastewater.