Solubility Phase Diagram of the Quaternary System Li+, Mg2+//Cl–, SO42––H2O at 298.15 K: Experimental Redetermination and Model Simulation

Abstract

Solubility isotherms for the ternary system MgCl2–MgSO4–H2O and the quaternary reciprocal system Li+, Mg2+//Cl–, SO42––H2O were determined at 298.15 K by an isothermal dissolution method. In the ternary phase diagram, there are six solubility branches corresponding to the solid phases MgSO4·nH2O(s) (n = 7, 6, 5, 4, 1) and MgCl2·6H2O(s). In the quaternary equilibrium phase diagram, there are 16 solubility co-saturated lines corresponding to the solid phases MgSO4·nH2O(s) (n = 7, 6, 5, 4, 1), MgCl2·6H2O(s), Li2SO4·H2O(s), LiCl·MgCl2·7H2O(s), and LiCl·H2O(s). This report describes for the first time that the equilibrium solid phases MgSO4·H2O(s) and MgSO4·4H2O(s) have been found to exist in this quaternary system. However, the phase field of MgSO4·H2O(s) overlaps with the phase fields of MgSO4·4H2O(s) and MgSO4·5H2O(s), which indicates that MgSO4·4H2O(s) and MgSO4·5H2O(s) are metastable phases; MgSO4·H2O(s) is a relatively more stable phase in both the ternary and quaternary systems. A Pitzer–Simonson–Clegg ...