Phase Equilibria And Phase Diagram Of The Quinary System (Li⁺,Na⁺,K⁺//Cl^-,CO₃^2--H₂O)

Lithium was hailed as the energy metal that will change the world in the 21st century.In response to the development and utilization of carbonate brine resources and the efficient lithium precipitation of lithium-rich brine in China,the solid-liquid equilibrium study of the quinary system(Li⁺,Na⁺,K⁺//Cl^-,CO₃^2-–H₂O),the quaternary sub-systems(Li⁺,Na⁺//Cl^-,CO₃^2-–H₂O),(Li⁺,K⁺//Cl^-,CO₃^2-–H₂O)and the ternary subsystem（Li Cl+Li₂CO₃+H₂O）were studied by isothermal dissolution equilibrium method.At the same time,the solubility of each system and the physicochemical properties including refractive index and density of the liquid phase were measured,which has practical guiding significance for the development and utilization of carbonate lake resources and the efficient separation of lithium carbonate.The ternary system（Li Cl+Li₂CO₃+H₂O）belongs to hydrate type I at 288.15 and308.15 K,and there is no solid solution and double salt formation.At 288.15 and 308.15 K,the phase diagram contains one invariant point E₁（Li Cl·2H₂O+Li₂CO₃）,E₂（Li Cl·H₂O+Li₂CO₃）,two univariate solubility curves and two single salt crystallization regions,respectively.The Li₂CO₃ crystallization areas at the two temperatures are much larger than the Li Cl·2H₂O and Li Cl·H₂O crystallization areas respectively,indicating that the solubility of Li₂CO₃ is far less than that of lithium chloride hydrate,and it is easy to crystallize and separate from the system.In addition,the lithium carbonate phase area gradually increases,and the lithium chloride hydrate crystallization area gradually decreases with the increasing of temperature.The physicochemical properties of the equilibrium liquid phase at two temperatures were measured,and they all showed regular changes with the change of Li Cl content.The quaternary system(Li⁺,Na⁺//Cl^-,CO₃^2-–H₂O)has two invariant points at288.15 K（E:Li Cl·2H₂O+Li₂CO₃+Na Cl,F:Na Cl+Li₂CO₃+Na₂CO₃·10H₂O）,five univariate solubility curves and four crystallization areas（Li Cl·2H₂O,Li₂CO₃,Na Cl and Na₂CO₃·10H₂O）.Li₂CO₃ has the largest crystallization area and is the easiest to separate out by saturated crystallization in the system.Li Cl·2H₂O has the smallest crystallization area and is not easy to separate in the system.The water value and the physicochemical properties of the equilibrium liquid phase（refractive index and density）of the quaternary system at 288.15 K show regular changes with the increase of another salt in the system.The quaternary system(Li⁺,K⁺//Cl^-,CO₃^2-–H₂O)has two invariant points at 288.15K（E:Li Cl·2H₂O+Li₂CO₃+KCl,F:KCl+Li₂CO₃+K₂CO₃·3/2H₂O）,five univariate solubility curves and four crystallization areas（Li Cl·2H₂O,Li₂CO₃,KCl and K₂CO₃·3/2H₂O）.Li₂CO₃ has the largest crystallization area and is the easiest to separate out by saturated crystallization in the system.The water value and the physicochemical properties of the equilibrium liquid phase（refractive index and density）of the quaternary system at 288.15 K show regular changes with the increase of another salt in the system.The phase diagram of the quinary system(Li⁺,Na⁺,K⁺//Cl^-,CO₃^2-–H₂O)consists of four invariant points（H₁:Na Cl+KCl+Li Cl·2H₂O,H₂:Na Cl+KCl+Na₂CO₃·10H₂O,H₃:KCl+Na₂CO₃·10H₂O+K₂CO₃·Na₂CO₃·12H₂O,H₄:K₂CO₃·Na₂CO₃·12H₂O+KCl+K₂CO₃·3/2H₂O）,nine univariant solubility curves and six crystallization regions（Na Cl,KCl,Li Cl·2H₂O,Na₂CO₃·10H₂O,K₂CO₃·Na₂CO₃·12H₂O and K₂CO₃·3/2H₂O）.The water value,lithium value and physicochemical properties in the equilibrium liquid phase show regular changes with the increase of J（2K⁺）.