Metastable Phase Equilibria in the Aqueous Ternary Systems KCl + MgCl2 + H2O and KCl + RbCl + H2O at 298.15 K

摘要

The solubilities and physicochemical properties such as density and refractive index of the solution in the ternary systems KCl + MgCl2 + H2O and KCl + RbCI + H2O were investigated at 298.15 K using an isothermal evaporation method. The crystalloid forms of the solid phase were determined using chemical analysis and an X-ray diffraction method. On the basis of experimental data, the metastable equilibrium phase diagrams and the physicochemical properties vs composition in the ternary systems at 298.15 Kwere constructed. In the metastable phase diagram of the ternary system KCl + MgCl2 + H2O at 298.15 K, there are two invariant points, three univariant curves, and three crystallization fields corresponding to potassium chloride (KCl), magnesium chloride hexahydrate (MgCl2·6H2O), and a double salt carnallite (KCl·MgCl2·6H2O). In the metastable phase diagram of the ternary system KCl + RbCl + H2O, there are two invariant points and three crystallization fields corresponding to the single salts potassium chloride (KCl), rubidium chloride (RbCl), and a solid solution of potassium and rubidium chloride [(K, Rb)Cl]. Comparisons between the metastable phase diagrams at 298.15 K and at 323.15 K show that the crystallization forms have not changed, while the crystallization zones have slight changes. The calculated densities and refractive indices using an empirical equation have the maximum relative error < 0.016.