Investigation of Solid-Liquid Equilibria on the Mg2+//Cl-,SO42--H2O System and the Na+,Mg2+//Cl-,SO42--H2O System at T=313.15 K and P=88.35 kPa

In this study, the isothermal solution equilibrium method was used to determine the liquid-phase composition of the ternary system Mg2+//Cl-, SO42-H2O at 313.15 K. The wet residue method of Scherinemakers combined with X-ray powder diffraction determined the corresponding solid-phase composition. Based on this, the phase equilibrium data of the quaternary system Na+, Mg2+//Cl-, SO42-H2O were determined and the phase diagram was drawn. The ternary system Mg2+// Cl-, SO42--H2O has four invariance points, five univariate curves, and five single-salt crystallization regions, which confirms that the existence of magnesium sulfate at 313.15 K is in the form of MgSO4 center dot nH(2)O (s) (n = 7, 6, 5, 4). The quaternary system Na+, Mg2+//Cl-, SO42--H2O contains four ternary systems, which are interactive quaternary systems. The system has six invariance points and eight crystallization regions (Na2SO4, Na2SO4 center dot MgSO4 center dot 4H(2)O, MgSO4 center dot 7H(2)O, MgSO4 center dot 6H(2)O, MgSO4 center dot 5H(2)O, MgSO4 center dot 4H(2)O, MgCl2 center dot 6H(2)O, NaCl). The physical properties (density and viscosity) of the equilibrium liquid phase were measured, and the corresponding physical property-composition diagram was drawn.