Phase Equilibria And Phase Diagram Of The Quinary System Containing Lithium,Sodium,Chloride,Metaborate,and Sulfate Ions At 323.15 K

At present,the separation of salt minerals is based on phase equilibrium and phase diagram of water salt system,which can provide scientific basis for the transformation,separation and processing of salt.Based on the isothermal solution equilibrium method,the phase equilibria and diagrams of the qinary system(Li⁺,Na⁺//Cl^-,BO₂^-,SO₄^2--H₂O)and its subsystems at 323.15 K were studied for the lithium boron-rich brine resources in Qaidam Basin,China.A series of solubility data were obtained and the physical and chemical properties of each point of the system were determined,thus providing basic data and feasible scheme for the extraction of alkali metal borate from salt lake brine.The research results of each system are as follows:The ternary systems（Li BO₂+Na BO₂+H₂O）and（Li BO₂+KBO₂+H₂O）belong to hydrate type I.At 323.15 K,both systems have an invariant point（Li BO₂·2H₂O+Na BO₂·4H₂O,Li BO₂·2H₂O+KBO₂·4/3H₂O）,two dissolution curves and two solid phase crystallization regions.In the two systems,the crystallization zone of Li BO₂·2H₂O is the largest,indicating that Li BO₂·2H₂O is more easily precipitated from the saturated solution than Na BO₂·4H₂O and KBO₂·4/3H₂O.At 323.15 K,the physicochemical properties of each equilibrium liquid phase in the two systems changed regularly with the increase of Na BO₂/KBO₂ content.The physicochemical properties of the two systems were calculated by using empirical equations,and the theoretical values are in good agreement with the experimental ones.The phase diagram of the quaternary system(Na⁺//Cl^-,BO₂^-,SO₄^2--H₂O)at 323.15K has two invariant points（E and F）,five univariate solubility curves and four solid phase crystallization regions,of which Na BO₂·4H₂O has the smallest crystallization region area,Na₂SO₄ has the largest crystallization region area.In contrast,Na₂SO₄ will be preferentially precipitated from the solution.With the increase of Z（Na Cl）,the physicochemical properties of the equilibrium liquid phase of the system showed regular changes.The phase diagram of the quaternary system（Li⁺,Na⁺//Cl^-,BO₂^--H₂O）at 323.15 K has three invariant points（F₁,F₂ and F₃）,seven univariate solubility curves and five solid phase crystallization regions.The crystallization zone of Li Cl·H₂O is very small,indicating that Li Cl·H₂O is more likely to be enriched in equilibrium solution,while the crystallization zone of Li BO₂·2H₂O is the largest and will be precipitated preferentially from the solution.With the increase of J（BO₂^-）,the water content and physicochemical properties of the system change regularly.The phase diagram of the quinary system(Li⁺,Na⁺//Cl^-,SO₄^2-,BO₂^--H₂O)at 323.15K has four invariant points（H₁,H₂,H₃ and H₄）,nine univariate solubility curves and six solid phase crystallization regions.The solid phase composition of invariant points is H₁:Na Cl+Na Cl·Na BO₂·2H₂O+Na₂SO₄+Li BO₂·2H₂O,H₂:Na Cl+Na₂SO₄·Li₂SO₄+Na₂SO₄+Li BO₂·2H₂O,H₃:Na Cl+Na₂SO₄·Li₂SO₄+Li₂SO₄·H₂O+Li BO₂·2H₂O and H₄:Na Cl+Li Cl·H₂O+Li₂SO₄·H₂O+Li BO₂·2H₂O.With the increase of J（2Li⁺）,the water content,sodium content and physicochemical properties of the system show regular changes.