Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

In this paper, the stable phase equilibria of the quaternary systems LiCl-NaCl-MgCl2-H2O, LiCl-KCl-MgCl2-H2O and Li2SO4-K2SO4-MgSO4-H2O were studied at 288.15 K using an isothermal dissolution equilibrium method and the solubility of each system was measured. Based on experimental solubility data, the dry salt diagrams and the diagrams of water-content vs composition of three quaternary systems were plotted. In addition to the single salts, there is a double salt LiCl*MgCl2*7H2O formation at 288.15 K in quaternary system LiCl-NaCl-MgCl2-H2O. In quaternary system LiCl-KCl-MgCl2-H2O, there are two kinds of double salt LiCl*MgCl2*7H2O and KCl*MgCl2*6H2O. It has been found that LiCl has a strong salting-out effect on both NaCl and KCl, which result in NaCl and KCl having larger crystallization regions in each phase diagram. At 288.15 K, the phase diagram of quaternary system Li2SO4-K2SO4-MgSO4-H2O has phase fields of single salt Li2SO4*H2O, K2SO4 and MgSO4*7H2O, and that of double salts K2SO4*MgSO4*6H2O and Li2SO4*K2SO4. The solubilities of the three quaternary systems at 288.15 K were calculated by using the Pitzer electrolyte solution theory model. The parameters involved but not previously reported were obtained by using the solubility data of ternary subsystems and the method of multivariate linear regression. The results show that the calculated results are in good agreement with the experimental results.