Solid–Liquid Phase Equilibria and Solubility Modeling of the Quaternary System LiBr–KBr–Li2SO4–K2SO4–H2O at 288.2 K

The solid–liquid phase equilibria of the quaternary system LiBr–KBr–Li₂SO₄–K₂SO₄–H₂O at 288.2 K were investigated in detail by the isothermal dissolution equilibrium method. The dry salt phase diagram and the three-dimensional phase diagram of the quaternary system were plotted. The phase diagrams show three invariant points, seven univariate curves, and five solid phase crystallization regions corresponding to K₂SO₄, Li₂SO₄·H₂O, Li₂SO₄·K₂SO₄, KBr, and LiBr·2H₂O. Lithium bromide exhibited the highest solubility, which increased significantly with rising temperature and showed a strong salting-out effect on KBr, K₂SO₄, and Li₂SO₄. Solubility data at different temperatures were compared and discussed. Furthermore, the ion interaction parameters of the Pitzer model for this system were fitted using solubility data, and a solubility model for the quaternary system at 288.2 K was established. The solubility results from the model are in high agreement with the experimental results. This research provides solid–liquid phase equilibrium data for the development of underground brine rich in lithium, potassium, and bromine.