Liquid-solid metastable phase equilibria for the quaternary system (NaCl-KCl-CaCl₂-H₂O) at 308.15 K

Abstract

The solubility and the physicochemical properties (densities, viscosities, refractive indices, conductivities and pH) in the liquid-solid metastable system (NaCl-KCl-CaCl₂-H₂O) at 308.15 K have been investigated using the isothermal evaporation method, and the dry-salt phase diagram, water-phase diagram, and the diagram of physicochemical properties vs. composition in the system were plotted. One three-salt cosaturated point, three metastable solubility isotherm curves, and three crystallization regions corresponding to sodium chloride, potassium chloride and calcium chloride tetrahydrate were formed, and neither solid solution nor double salts were found. On the basis of the extended Harvie-Weare (HW) model and its temperature-dependent equation, the values of the Pitzer parameters β⁽⁰⁾, β⁽¹⁾, C ^ϕ for NaCl, KCl and CaCl₂, the mixing ion-interaction parameters θ_Na,K, θ_Na,Ca, θ_K,Ca, Ψ_Na,K,Cl, Ψ_Na,Ca,Cl, Ψ_K,Ca,Cl, and the Debye-Hückel parameter A ^ϕ and the chemical potentials of the minerals in the quaternary system at 308.15 K were fitted, and the predictive solubility based on the temperature-dependent equation and the chemical potentials of the minerals agrees well with the experimental data.