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

ABSTRACT

The solubility and density of the thermodynamic phase equilibria ternary system (Na2SO4 + Li2SO4 + H2O) at (288 and 308) K were determined using the isothermal dissolution method. According to the experimental results of the ternary system at (288 and 308) K, the phase diagrams and the diagrams of density versus composition were plotted. In the ternary system at 308 K, four crystallization regions corresponding to thenardite (Na2SO4, Th), two congruent double salts of Li2SO4*3Na2SO4*12H2O (Db1) and Li2SO4*Na2SO4 (Db2), and lithium sulfate monohydrate (Li2SO4*H2O, Ls) were found, whereas only three crystallization regions corresponding to Ls, one incongruent double salt of Db1, and mirabilite (Na2SO4*10H2O, Mir) were found in the system at 288 K. No solid solution was found at either temperature. When the experimental phase diagram at 308 K was compared with that at 288 K, it shows that (1) a new phase region of double salt Db2 was formed and the mineral of Mir transformed into Th with the increase of temperature from (288 to 308) K and (2) the area of the crystallization region of sodium sulfate was decreased sharply and those of the crystallized regions of Li2SO4*H2O and double salt Db1 increased obviously. The solution densities of the ternary system both at (288 and 308) K change regularly with increasing lithium sulfate concentration in solution. Based on the Pitzer model and its extended Harvie-Weare (HW) model, the mixing triple interaction parameter of ?Li,Na,SO4 at (288 and 308) K and the solubility equilibrium constants Ksp of solid phases Ls, Db1, Db2, Th, and Mir at (288 and 308) K, which are not reported in the literature, were acquired by fitting the experimental solubility data of the ternary system (Li2SO4 + Na2SO4 + H2O) by the lease-square method. A comparison between the calculated and experimental results at (288 and 308) K for the ternary system shows that the predicted solubilities obtained with the extended HW model agree well with experimental data.