Development of a thermodynamic model for the Li2CO3-NaCl-Na2SO4-H2O system and its application

The study of the solid-liquid phase equilibrium for the Li2CO3-NaCl-Na2SO4-H2O system is of significance to separate lithium from the mother liquor obtained by the reaction of lithium chloride/lithium sulfate and sodium carbonate. The phase equilibrium data for the binary system of Li2CO3-H2O, the ternary systems of Li2CO3-NaCl-H2O and Li2CO3-Na2SO4-H2O, and the quaternary system of Li2CO3-NaCl-Na2SO4-H2O over the temperature range from 283.15 K to 363.15 K were measured. Based on the Pitzer's model embedded in the Aspen Plus™, the phase equilibrium data for the systems of NaCl-H2O, Na2SO4-H2O and NaCl-Na2SO4-H2O taken from literatures were firstly predicted to verify the applicability of parameters from the default database and literatures. Subsequently, besides the solubility of Li2CO3 in water at different temperatures, the values for the systems of Li2CO3-NaCl-H2O and Li2CO3-Na2SO4-H2O at 298.15 K and 343.15 K were correlated, and then the obtained parameters can well predict the phase equilibrium data for the systems of Li2CO3-NaCl-H2O, Li2CO3-Na2SO4-H2O Li2CO3-NaCl-Na2SO4-H2O at T = (313.15, 323.15 or 363.15) K. Through the rigorous thermodynamic model representing the Li2CO3-NaCl-Na2SO4-H2O system developed, the phase diagram of the ternary Li2CO3-NaCl-H2O system at T = (298.15, 343.15 or 363.15) K visualized with lucidity, and the course of crystallization to produce Li2CO3 from the mother liquor was illustrated. All of these will provide a thermodynamic basis for the separation of lithium from mother liquor and optimization of Li2CO3 production process.