Solid–Liquid Metastable Phase Equilibria in the Five-Component System (Li + Na + K + Cl + SO4 + H2O) at 308.15 K

Abstract

The metastable equilibrium solubilities and the physicochemical properties including refractive index, density, viscosity, conductivity, and pH for the aqueous reciprocal five-component system (Li + Na + K + Cl + SO4 + H2O) at 308.15 K were studied using the isothermal evaporation method. According to the experimental data, the dry-salt-phase diagram, sodium-phase diagram, water-phase diagram, and the diagrams of physicochemical properties versus composition were plotted. The dry-salt-phase diagram of the five-component system includes seven four-salt cosaturated points, fourteen univariant solubility curves, and eight crystallization zones all saturated with sodium chloride. Three kinds of double salts of lithium salts (Db1, Li2SO4·3Na2SO4·12H2O; Db2, Li2SO4·Na2SO4; Db3, 2Li2SO4·Na2SO4·K2SO4) were found, and no solid solution was formed in the metastable five-component system. Because the Pitzer mixing ion-interaction parameters containing lithium and sodium such as θLi,Na, ΨLi,Na,Cl, and ΨLi,Na,SO4 at 308.15 K are scarce, the solubilities of the five-component system at 298.15 K were calculated on the basis of Pitzer’s ion-interaction theory and the chemical equilibrium Harvie–Møller–Weare model (HMW model). A comparison of the calculated phase diagram at 298.15 K and the experimental phase diagram at 308.15 K was also carried out.