Phase Equilibria Of The Quaternary Systems Li⁺,Na⁺//SO₄^2-(Cl^-),BO₂^--H₂O

It is well known that salt-water phase equilibria and phase diagram play an important role in for separating and purifying minerals from the salt lake brines.In this paper,phase equilibria of the quaternary systems(Li+,Na+//Cl-,BO2--H2O),(Li+,Na+//SO42-,BO2--H2O)and subsystem(Li+,Na-//BO2--H2O)were measured by isothermal dissolution method.Chemical analysis of equilibrium liquid phase percentage content,determination of physical and chemical properties data of equilibrium liquid phase,phase diagram,water diagram and physicochemical property vs composition diagrams and identification of solid phase.The phase diagrams of the ternary system(Li+,Na-//BO2--H2O)at 288.15 K and 298.15 K are all hydrate type I,neither double salt or solid solution is formed.The phase diagram has a co-saturation point(NaBO2·4H2O+LiBO2·8H2O),two crystallization regions,corresponding to lithium metaborate octahydrate(LiBO2·8H2O+L)in the larger crystalline region and sodium metaborate tetrahydrate(NaBO2·4H2O+L)in the smaller crystalline region.and two univariate solubility curves.As the temperature increasing,the solubility on both salt LiBO2·8H2O and NaBO2·4H2O increased gradually.The comparison shows that the physical-chemical properties(refractive index,density and pH)at both temperatures show regular changes as the NaBO2 content increases,reaching a turning point at the co-saturation point.The calculated values of density and refractive index using empirical equations of the ternary system are in good agreement with the experimental values.For the quaternary system(Li+,Na+//Cl-,BO2--H2O)at 288.15 K and 298.15 K,phase diagram includes four invariant points F1(NaCl·NaBO2·2H2O+LiBO2·8H2O+NaBO2·4H2O),F2(NaCl·NaBO2·2H2O+LiBO2·8H2O+NaCl),F3(LiBO2·8H2O+NaCl+LiBO2·2H2O),F4 is(LiBO2·8H2O+LiCl·2H2O+LiBO2·2H2O)at 288.15K and(LiBO2·8H2O+LiCl·H2O+LiBO2·2H2O)at 298.15K;nine univariate dissolution curves,five single salt crystallization regions and one double salt crystallization region,the largest crystallization region at 288.15K is LiBO2·8H2O,the smallest crystallization region is LiCl 2H2O;at 298.15 K,the largest crystalline region is LiBO2·8H2O,and the single salt crystalline region is LiCl·H2O.As the temperature increasing,the solubility of all four salts increased gradually.At both temperatures,the physicochemical properties(refractive index,density and pH)changed regularly with the increase of J(NaBO2).For the quaternary system(Li+,Na+//SO42-,BO2--H2O)at 288.15 K and 298.15 K,phase diagram includes three constant points F1(Li2SOH2O+Li2SO4·3Na2SO4·12H2O+LiBO2-8H2O),F2(Li2SO4·3Na2SO4·12H2O+LiBO2-8H2O+Na2SO4·10H2O),F3(LiBO2·8H2O+Na2SO4·10H2O+NaBO2·4H2O);seven univariate dissolution curves,four single salt crystallization regions and one double salt crystallization region,the largest crystallization region is LiBO2·8H2O,the smallest region is Li2SO4·H2O.As the temperature increasing,the solubility of all four salts increased gradually.At both temperatures,the physicochemical properties(refractive index and density)changed regularly with the increase of J(NaBO2).According to the research,it took approximately 20 days to reach the equilibrium state for the ternary system(Li+,Na+//BO2--H2O)and about 45 day for the quaternary systems(Li+,Na+//BO2--H2O)and(Li+,Na+//SO42-,BO2--H2O).