Measurement and\nTheoretical Calculation of Phase Equilibrium\nin the Quaternary System KCl-NaCl-MgCl<sub>2</sub>‑H<sub>2</sub>O at 303.15 and 308.15 K

The\nphase equilibrium of the quaternary system KCl-NaCl-MgCl<sub>2</sub>-H<sub>2</sub>O and its subsystems was measured at 303.15\nand 308.15 K by the isothermal dissolution equilibrium method. The\npresence of KCl·MgCl<sub>2</sub>·6H<sub>2</sub>O, a type\nof double salt, was observed in this quaternary system. The phase\ndiagrams at both temperatures include two invariant points, five univariant\ncurves, and four crystallization regions. Due to the strong salting-out\neffect of MgCl<sub>2</sub>, both KCl and NaCl exhibit lower solubilities.\nIn addition, the solubility of KCl increases with temperature rising\nfrom 273.15 to 323.15 K. High MgCl<sub>2</sub> concentration and low\ntemperature are advantageous for enhancing KCl yield. The determination\nof solubility data for the quaternary system KCl-NaCl-MgCl<sub>2</sub>-H<sub>2</sub>O at 303.15 and 308.15 K contributes to the completion\nof the thermodynamic database and facilitates its application in real\nindustrial processes at temperatures close to those studied. Moreover,\nthe applicability of the Pitzer model and relevant parameters in solubility\nprediction of this quaternary system at 303.15 and 308.15 K were systematically\nverified. No significant discrepancies were detected with increasing\nionic strength in concentrated solutions. The Pitzer model and existing\nparameters are suitable for the rapid solubility prediction in this\nsystem and demonstrate high prediction accuracy.