Metastable Phase Equilibrium in the Aqueous Ternary System (KCl−CaCl2−H2O) at (288.15 and 308.15) K

Abstract

The solubility and the physicochemical properties (density and refractive index) in the liquid-solid metastable system (KC1-CaCl 2 -H 2 O) at (288.15 and 308.15) K were determined using the isothermal evaporation method. Based on the experimental data, the metastable phase diagrams and the diagrams of physicochemical properties vs composition in the system at (288.15 and 308.15) K were plotted. In the metastable phase diagrams of the ternary system at (288.15 and 308.15) K, there are in all one invariant point, two univariant curves, and two crystallization zones, corresponding to potassium chloride, antarcticite (CaCl 2 ·6H 2 O) at 288.15 K, and potassium chloride, and calcium chloride tetrahydrate (CaCl 2 ·4H 2 O), at 308.15 K. This system at both temperatures belongs to a simple eutectic type, and neither double salts nor solid solution were found. Based on the extended Harvie-Weare (HW) models and temperature-dependent equations at (288.15 and 308.15) K, respectively, the values of the Pitzer parameters β (0) , β (1) , and C φ for KCl and CaCl 2 , the mixed ion-interaction parameters θ K,Ca and Ψ K,Ca,Cl , the Debye-Hiickel parameter A φ , and the standard chemical potentials of the minerals in the ternary system were obtained by fitting. Using the temperature-dependent equations and the standard chemical potentials of the minerals respectively, the predictive solubilities for the ternary system at both temperatures are presented. A comparison between the calculated and experimental results at each temperature shows that the predicted solubilities obtained with the extended HW model agree well with experimental data.