Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

The stable (solid + liquid) phase equilibria and physico-chemical properties of the solution in the ternary systems (K2SO4 + KH2PO4 + H2O) and (K2SO4 + KCl + H2O) at T = 313.15 K were determined by using an isothermal solution saturation method. According to the experimental data, the phase diagrams and the diagrams of physico-chemical properties versus composition were plotted. It was found that there were one invariant point, two univariant curves and three fields of crystallization in the ternary systems (K2SO4 + KH2PO4 + H2O) and (K2SO4 + KCl + H2O) at T = 313.15 K. On the basis of the phase diagrams obtained, we analyzed each invariant point. When K2SO4 and KH2PO4 were analyzed as (7.71, 20.99) wt%, respectively, the ternary system (K2SO4 + KH2PO4 + H2O) reached saturation at T = 313.15 K. When K2SO4 and KCl were analyzed as (1.15, 27.08) wt%, respectively, the ternary system (K2SO4 + KCl + H2O) reached saturation at T = 313.15 K. The solubility of K2SO4 is the lowest among the three salts, and the crystalline fields of K2SO4 in the two ternary systems are larger than that of KH2PO4 and KCl, which shows that K2SO4 can be easily separated from the mixed aqueous solution. Thus, knowledge of (solid + liquid) equilibrium, especially the crystalline fields at T = 313.15 K, would be extremely valuable to design and optimize solvent extraction process of KH2PO4 and other crystallization processes involving the two ternary systems in the industrial production.