Phase Equilibria for the Aqueous Quinary System Li⁺, Na⁺, K⁺, Mg²⁺//Cl^––H₂O Saturated with NaCl·2H₂O at 258.15 K

The phase diagram can guide the comprehensive utilization of salt lake brine, particularly lithium extraction. In this paper, the study on phase equilibria of the quinary system Li⁺, Na⁺, K⁺, Mg²⁺//Cl^––H₂O saturated with NaCl·2H₂O and its subsystem Li⁺, Na⁺, Mg²⁺//Cl^––H₂O at 258.15 K were carried out using the isothermal dissolution equilibrium method. Based on the experimental data, equilibrium diagrams for stable phases were plotted. For the equilibrium diagram of the quaternary system Li⁺, Na⁺, Mg²⁺//Cl^––H₂O at 258.15 K, there are two invariant points, five univariant curves, and four crystallization fields. The quinary system Li⁺, Na⁺, K⁺, Mg²⁺//Cl^––H₂O saturated with NaCl·2H₂O at 258.15 K contains three invariant points, seven univariant curves, and five crystallization fields. Comparing the phase diagram of the system at 258.15 K to that at 298.15 K reveals that, except KCl, all crystallization zones have decreased, and LiCl·MgCl₂·7H₂O has the smallest crystallization zone compared to the other salts in the systems. This fundamental research could be valuable for promoting comprehensive utilization of the lithium-containing salt lake brine.