Phase equilibrium and phase diagram for 2-2-the quaternary system (Li+, K+//Cl-, SO4 -H2O) at 288.15 K

The phase and physicochemical properties diagrams of the quaternary system (Li+, K+//Cl-, SO4 -H2O) at 288.15 K were constructed using the solubilities, densities, and refractive indices measured. In the phase diagrams of the system there are three invariant points, seven univariant isotherm dissolution curves, and five crystallization regions corresponding to3lithium chloride monohydrate (LiCl∙H2O), lithium sulfate monohydrate (Li2SO4∙H2O), potassium chloride (KCl), potassium sulfate (K2SO4), and double salt lithium potassium sulfate (Li2SO4∙K2SO4), where the double salt lithium potassium sulfate (Li2SO4∙K2SO4) is an incongruent double salt. The crystallization area of potassium sulfate (K2SO4) is the largest, and the crystallized zone of lithium chloride monohydrate (LiCl∙H2O) is the smallest. These results indicate that potassium sulfate is easy to saturate and crystallize from solution and that lithium chloride has a high solubility during isothermal evaporation. The solution density and refractive index of the quaternary system change regularly with the increase of K+ concentration.