Solubilities at 15癈 for KCl-NaCl-MgCl2-H2O quaternary system were measured systematically and tabulated. The crystallization regions of KCl, NaCl, MgCl2.6 H2O and KCl.MgCl2.6H2O were found in the quaternary phase diagram. The Pitzer's equations for electrolyte solns. was used to predict the system. All parameters used for calculation were evaluated by the method of least squares. Also, the solubilities at 15癈 for the system KCl-NaCl-MgCl2-H2O were calculated by means of the parameters. The calculated values agree with that measured within experimental error.

Key words: PHASE EQUILIBRIUM, WATER, SOLUBILITY, QUATERNARY SYSTEM, SODIUM CHLORIDE, POTASSIUM CHLORIDE, MAGNESIUM CHLORIDE, OPTIMIZATION, LEAST SQUARE METHODS, MATHEMATICAL STATISTICS