Activity Coefficients and Phase Equilibria in the LiCl–KCl–CH ₃ OH–H ₂ O Mixed System at 298.2 K

The Qaidam Basin of China abounds in salt lake resources containing lithium, potassium, and boron. Lithium precipitation mother liquor is generated during lithium carbonate production. To investigate solution thermodynamic properties of lithium salts and support its utilization, the thermodynamic activity coefficients and phase equilibria of the LiCl–KCl–CH3OH–H2O mixed solvent system at 298.2 K are studied. The mean activity coefficients of KCl in the KCl−CH3OH−H2O and the LiCl−KCl−CH3OH−H2O mixed solvent system are measured using cell potentials and the Nernst equation. Via multiple linear regression and nonlinear programming fitting, the Pitzer single-salt parameters of LiCl (β(0), β(1), and CΦ) and ion interaction parameters (θK,Li and ψK,Li,Cl) at 298.2 K are obtained, and then mean activity coefficients of LiCl, osmotic coefficients, water activities, and excess Gibbs free energies via the Pitzer model are calculated accordingly. Moreover, the mixed solvent system’s phase equilibria via isothermal dissolution equilibrium are also determined. Solubility data modeling with these parameters agrees well with experimental results, validating the model’s efficacy in predicting lithium–potassium salt phase behavior in methanol-containing mixed solvents.