Solid–Liquid Equilibria in Reciprocal Quinary System Li⁺, Na⁺, K⁺/Br^–, and SO₄^2––H₂O at 298.15 K

In addition to the common sodium salt, potassium salt, magnesium salt, and sulfate, salt lake brine is also rich in trace components in varying degrees, such as lithium, bromine, rubidium, cesium, and so forth, which is of great industrial value. These trace components are further concentrated and enriched in old brine during the process of evaporation and concentration of brine resources. In view of the coexistence characteristics of lithium, potassium, bromine, and other ions in old halide, the phase equilibria of quinary system Li+, Na+, K+/Br–, and SO42––H2O were studied by the isothermal dissolution equilibrium method at 298.15 K. The solubility data of the equilibrium liquid phase were measured, and the compositions of the solid phase as well as the crystal forms of the equilibrium solid phase were identified when the equilibrium was achieved. The corresponding 3D and dry-base phase diagrams (Na2SO4·10H2O, K2SO4, LiBr·2H2O, Li2SO4·H2O, KBr, and NaBr·2H2O saturated) were drawn based on the phase equilibrium experimental data. The research results of phase equilibria and phase diagrams reveal that the phase relations and crystallization–dissolution law of each component in solution lay a certain foundation for further research on multi-temperature phase equilibrium and thermodynamic properties of the high-component brine system and to provide basic thermodynamic data for guiding the rational development and comprehensive utilization of brine resources.