Phase Equilibria And Phase Diagram Of The Quinary System Containing Lithium Sodium,Chloride,Sulfate,and Carbonate Ions

In this paper,aiming at the development and utilization of carbonate-type brine resources in China and the efficient precipitation of lithium in lithium-rich brine,the method of isothermal dissolution equilibrium is used to develop the phase diagrams about the qinary system(Li⁺,Na⁺//Cl^-,SO₄^2-,CO₃^2-–H₂O)and its quaternary sub-system(Li⁺,Na⁺//SO₄^2-,CO₃^2-–H₂O)、(Li⁺,Na⁺//Cl^-,CO₃^2-–H₂O)、（Li Cl+Li₂SO₄+Li₂CO₃+H₂O）and ternary subsystem（Li₂SO₄+Li₂CO₃+H₂O）phase equilibrium.The phase diagrams,water diagrams and physicochemical properties-composition diagrams of the systems were drawn according to its solubilities,water percentage content and physical and chemical properties data.This way has a vital guiding worthing for the development and utilization of carbonate salt lake resources and the efficient separation of lithium carbonate from lithium-rich liquor.The ternary system（Li₂SO₄+Li₂CO₃+H₂O）has no solid solution and double salt formation at 288.15 K and 308.15 K,and belongs to simple hydrate type I.The system both have an univariate point（Li₂SO₄·H₂O+Li₂CO₃）at 288.15 K and 308.15 K,two univariate solubility curves and two crystalline regions.Comparing the two temperatures,it is found that the phase region of Li₂CO₃ is larger than that of Li₂SO₄·H₂O.Under two temperatures,the physical and chemical properties（refractive index,density）of the equilibrium system all change regularly with w（Li₂SO₄）.Meanwhile,the theoretical values of the refractive index and density of the system were calculated according to the empirical formula,indicating that the theoretical values are in good agreement with the calculated values.The phase diagram of the quaternary system（Li Cl+Li₂SO₄+Li₂CO₃+H₂O）at273.15 K has an univariate point E（Li Cl·2H₂O+Li₂SO₄·H₂O+Li₂CO₃）,three univariate solubility curves and three single-salt crystallization areas.As we can see from the phase diagrams,its water value and physicochemical properties were showed regular changes with the increase of Z（Li₂SO₄）.The phase diagram of the quaternary system(Li⁺,Na⁺//Cl^-,CO₃^2-–H₂O)at 273.15 K is a simple quaternary system.The system has two univariate points E（Li Cl·2H₂O+Li₂CO₃+Na Cl）and F（Li₂CO₃+Na Cl+Na₂CO₃·10H₂O）at 273.15 K,five univariate solubility curves and four single-salt crystallization regions.And in the presence of Li Cl,the solubility of Na Cl and Na₂CO₃ is lower than that of single salt,indicating that Li Cl has a strong salting-out effect.Meanwhile,the water content、density and refractive index of the system showed regular changes.The quaternary system(Li⁺,Na⁺//SO₄^2-,CO₃^2-–H₂O)has double salt formated at288.15 K.The system has three univariate points,namely E₁（Li₂SO₄·H₂O+Li₂SO₄·3Na₂SO₄·12H₂O+Li₂CO₃）,E₂（Na₂SO₄·10H₂O+Li₂SO₄·3Na₂SO₄·12H₂O+Li₂CO₃）and E₃（Na₂SO₄·10H₂O+Na₂CO₃·10H₂O+Li₂CO₃）,seven univariate solubility curves and five crystalline regions.The water content,density,and refractive index in the equilibrium liquid phase are all change regularly with the composition of the liquid phase.The quinary system(Li⁺,Na⁺//Cl^-,SO₄^2-,CO₃^2-–H₂O)has four univariate points at288.15 K,namely H₁（Na₂CO₃·10H₂O+Na Cl+Na₂SO₄·10H₂O+Li₂CO₃）、H₂（Li₂SO₄·3Na₂SO₄·12H₂O+Na₂SO₄·10H₂O+Na Cl+Li₂CO₃）、H₃（Li₂SO₄·H₂O+Li₂SO₄·3Na₂SO₄·12H₂O+Na Cl+Li₂CO₃）and H₄（Li₂SO₄·H₂O+Li Cl·2H₂O+Na Cl+Li₂CO₃）,nine univariate solubility curves and six crystalline regions.Similarly,the area of crystallization area of Li₂CO₃ is larger than that of Li Cl·2H₂O.The water content,lithium content,and physical and chemical properties in the equilibrium liquid phase all change regularly with the composition of the liquid phase.