Phase equilibria and thermodynamic model of the quinary system (Li+, Na+, Mg2+//Cl-, SO42--H2O) at 273.15 K and 0.1 MPa

Abstract The solubilities of the quinary system (Li+, Na+, Mg2+//Cl−, SO42−-H2O) at 273.15 K were investigated using the isothermal dissolution method. The diagrams of dry-salt-phase, sodium-phase and water-phase were plotted accurately. The dry-salt-phase diagram of this quinary system includes five invariant points, eleven univariant solubility curves, and seven crystallization zones all saturated with sodium chloride. Two double salts of Li2SO4·3Na2SO4·12H2O and LiCl·MgCl2·7H2O were found, and no solid solution was formed. Pitzer model and its extended Harvie-Moller-Weare (HMW) model were used to fit the solubility equilibrium constants of LiCl·2H2O, Li2SO4·H2O and the two double salts, and the mixing ion-interaction parameters of θLi,Na, θLi,Mg, ψLi,Na,Cl, ψLi,Mg,Cl, ψLi,Na,SO4 and ψLi,Mg,SO4 of this system at 273.15 K, which are not reported in the literature. In addition, the calculated solubilities of the quinary system at 273.15 K were demonstrated, and the comparison between the calculated and experimental data shows that the predicted solubilities obtained by the extended HW model are basically consistent with experimental data.