Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

The stable phase diagram of the quaternary water-salt system Li+, Na+, Cs+ // SO4 2- - H2O was studied at T = 298.2 K by the isothermal dissolution equilibrium method. The solubility and physicochemical properties (density and refractive index) of the equilibrium solution were measured. Moreover, the composition of the solid phase were identified using X-ray diffraction method. There are seven solids formed in this system at research temperature, including four single salts and three double salts, those are lithium sulfate monohydrate (Li2SO4*H2O), sodium sulfate (Na2SO4), sodium sulfate decahydrate (Na2SO4*10H2O), cesium sulfate (Cs2SO4), double salts Li2SO4*Cs2SO4, 3Li2SO4*Cs2SO4*2H2O and 3Na2SO4*Li2SO4*12H2O, respectively. Thus, the stable phase diagram of the quaternary water-salt system contains five invariant points, eleven univariant curves, and seven crystallization regions. The size order of the salts crystalline phase region is Li2SO4*Cs2SO4 greater than 3Na2SO4*Li2SO4*12H2O greater than 3Li2SO4*Cs2SO4*2H2O greater than Na2SO4*10H2O greater than Li2SO4*H2O greater than Na2SO4 greater than Cs2SO4. Obviously, the double salts have larger crystallization fields, means that in the sulfate system coexisted with lithium, sodium and cesium, double salts are relatively easier to form than a single salt of various components. As a result, lithium and cesium are scarcely possible separated as Li2SO4 and Cs2SO4 from this system at 298.2 K.