Metastable Phase Equilibrium In The System Li⁺, K⁺, Mg²⁺//Cl^--H₂Oat323K

In order to explore and comprehendive utilize the resource of underground brinesin the west of Sichuan Basin, the solubility, density and pH value of the equilibratedsolution in the quateranry system Li⁺，K⁺，Mg²⁺//Cl^--H₂O and the ternary system Li⁺，K⁺//Cl^--H₂O were studied at323K using an isothermal evaporation method. Based onthe experimental data, the metastable phase diagram, the density vs compositiondiagram, and pH vs composition diagram were plotted.Results show that the ternary system is of a simple eutectic type, no double saltor solid solution formed at323K. The phase diagram consists of one invariant point,two uninvariant curves, and two crystallization regions. The crystallization regionscorrespond to single salts potassium chloride （KCl） and lithium chloride monohydrate（LiCl·H₂O）, respectively. Salt LiCl has strong salting-out effect on salt KCl. Thedensity increases with the increase of the mass fraction of LiCl, while the pH valuedecreases with the increase of the mass fraction of LiCl. Comparisons between themetastable phase diagrams at298K and at323K show that the crystallization formshave not changed, whereas the crystallization zones have slight changes. Thecrystallization field of salt LiCl is larger at323K, while the crystallization region ofsalt KCl is smaller at323K.Two incommensurate double salts potassium carnallite （KCl·MgCl₂·6H₂O，K-Car）and lithium carnallite （LiCl·MgCl₂·7H₂O，Li-Car） are formed in quaternary systemLi⁺，K⁺，Mg²⁺//Cl-H₂O at323K. The metastable phase diagram of this system underinvestigated temperature contains three invariant points, seven univariant curves andfive crystallization fields. The composition of the three invariant points is E1LiCl4.36%, MgCl₂95.29%, KCl0.35%; E2LiCl56.00%, MgCl₂43.49%, KCl0.51%;E3LiCl74.38%, MgCl₂20.59%, KCl0.53%, respectively. The univariant curves are e1E1, E1E2, e2E2, e3E2, E2E3, p1E3and p2E3. The crystallization fields correspond tothree single salts LiCl·H₂O, KCl, Bis and two double salts K-Car, and Li-Car,respectively. The solubility of potassium carnallite is less than that of lithiumcarnallite by comparing the crystallization areas of them. The two carnallites didn’tconvert into solid solution.