Study On Metastable Phase Equilibria In Quinary System Li⁺, K⁺,Rb⁺, Mg²⁺//Cl^--H₂O At323K

The underground brine in Pingluoba is famous for its high concentrations of potassium, lithium, borate, magnesium, and the rare alkali elements rubidium and cesium. In this paper, the metastable phase equilibria of the quinary system Li+, K+Rb+, Mg2+//Cl--H2O and its two subsystems Li+, Rb+, Mg2+//Cl--H2O and K+, Rb+, Mg2+//Cl--H2O were studied at323K using an isothermal evaporation method. The solubilities, densities, and refractive indices of the equilibrated solution were measured. On the basis of the experimental data, the metastable equilibrium phase diagrams and the physicochemical properties vs composition diagrams in the quaternary systems at323K were plotted. The stereo-diagram and projected phase diagrams of the quinary systems (saturated with KC1and RbCl), corresponding water content diagrams, physicochemical properties vs composition diagrams, potassium (rubidium) content diagrams of the quinary systems were constructed.Quarternary system Li+, Rb+, Mg2+//Cl--H2O is of a complex type, with two double salts LiCl·MgCl2·7H2O and RbCl·MgCl2·6H2O formed. The metastable phase diagram of the system consists of three invariant point, seven univariant curves and five crystallization fields corresponding to single salts LiCl·H2O, RbCl, MgCl2·6H2O, and double salts LiCl·MgCl2·7H2O and RbCl·MgCl2·6H2O, respectively.The quarternary system K+,Rb+, Mg2+//Cl--H2O is of a complex type with double salts KCl·MgCl2·6H2O, RbCl·MgCl2·6H2O and solid solution (K,Rb)Cl formed.The metastable phase diagram of the system consists of four invariant point, nine univariant curves and six crystallization fields corresponding to three single salts KCl, RbCl, MgCl2·6H2O, two double salts KCl·MgCl2·6H2O and RbCl·MgCl2·6H2O, and one solid solution (K,Rb)Cl, respectively.The quinary system Li+, K+, Rb+, Mg2+//Cl--H2O is of a complex type, with double salts LiCl·MgCl2·7H2O, KCl·MgCl2·6H2O, RbCl·MgCl2·6H2O and solid solution (K, Rb)Cl formed.The metastable phase diagram of the system consists of six invariant point, seventeen univariant curves and eight crystallization fields corresponding to four single salts LiCl·H2O, KCl, RbCl, MgCl2·6H2O, one solid solution,(K,Rb)Cl, and three LiCl·MgCl2·7H2O, RbCl·MgCl2·6H2O and KCl·MgCl2·6H2O, respectively.