摘要：The gradient solar pond technique is an economic separating process employed in the inorganic chemical industrial production of salt lake chemical engineering processes. In this paper, a novel isothermal evaporation experimental method was employed to simulate the evaporation phase equilibrium for the reciprocal quaternary system (LiCl+NaCl+Li2SO4+Na2SO 4+H2O) at 348.15 K to serve as a useful guide for lithium salt production via the depth solar ponds.The isothermal evaporation equilibrium solubilities and physicochemical properties,including the densities and pH values, were experimentally investigated. The dry-salt phase diagram,water-phase diagram, and the diagram of the physicochemical properties versus composition were plotted with respect to the experimental data. The dry-salt phase diagram consists of three invariant points,seven univariant solubility curves, and five crystallization regions, specifically halite(NaCl,Ha),thenardite (Na2SO4,Th),double salt (Li2SO4 · Na2SO4 , Db2), lithium sulfate monohydrate (Li2SO4 ·H2O, Ls), and lithium chloride monohydrate(LiCl·H2O, Lc). Based on Pitzer and its extended HMW model, the Pitzer single salt parameters, mixing ion interaction parameters, and thermodynamic stable equilibrium constants for the quaternary system at 348.15 K were obtained. The calculated phase diagram and experimental isothermal phase diagram at 348.15 K exhibited a great difference. Based on these results, the isothermal evaporation phase diagram can truly reflect the salt sedimentary in salt lakes and can be applied as a useful guide for the solar pond process.

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