Mean Activity Coefficients and Phase Equilibria of the LiCl-KCl-CH ₃ OH ( <i>w</i> )-H ₂ O(1- <i>w</i> ), <i>w</i> = 20% Mixed Solvent at 273.15 K

The oilfield brines are rich in mineral resources, such as potassium and lithium, and have important development and utilization values. This work employs a combined experimental and modeling method to systematically investigate the thermodynamic properties and solid–liquid phase equilibria of the LiCl-KCl-CH3OH(w = 20%)-H2O mixed solvent system at 273.15 K. First, the activity coefficients of KCl in the KCl-CH3OH(w = 20%)-H2O mixed solvent were determined using the cell potential method. Subsequently, the Pitzer model and programming solver were utilized to determine the single salt parameters βLiCl(0), βLiCl(1), and CLiClΦ of LiCl and the mixed ion interaction parameters θK,Li and ψK,Li,Cl in mixed solvent. The other thermodynamic properties of the LiCl-KCl-CH3OH(w = 20%)-H2O mixed solvent were calculated by Pitzer equations. Furthermore, solid–liquid phase equilibria for this LiCl-KCl-CH3OH(w = 20%)-H2O mixed solvent system at 273.15 K were measured by using the isothermal dissolution equilibrium method. The results demonstrate good agreement between the experimental data and the modeling, validating the reliability of the fitted parameters. The results also indicate that the addition of methanol can inhibit salt solubility, providing a theoretical basis for the separation of LiCl and KCl from brine.