Phase Equilibria Of The Quinary System And Its Subsystems Containing Lithium,Sodium,Cesium,Chloride And Sulfate Ions At 298.15K

The exploitation and utilization of salt lake resources can effectively solve the shortage of solid resources in China and is of great significance to guide industrial production.The study of the salt system of multiple alkali metals in Qaidam basin can provide an effective theoretical basis for the separation and extraction of salt lake resources in this area.The isothermal solution method is used to study the solid-liquid equilibria as well as their physicochemical properties on the quinary system(Li-Na~+,Cs~+//Cl-,SO42--H2O)and its one ternary system at(288.15&308.15)K and two quaternary systems at 298.15 K.Through the determination of the solubilities and physical properties of the equilibrium solutions in those systems,the following results have been achieved:The phase diagram of ternary system(Cs~+//Cl-,SO42--H2O)at(288.15&308.15)K all contain one invariant point(CsCl+Cs2SO4),two univariant isothermal dissolution curves,and two crystallization regions corresponding to CsCl and Cs2SO4.There are no double salts or solid solution in this system and it belongs to the simple type of salt-water ternary system.The area of Cs2SO4 crystallization region is larger than that of CsCl,so Cs2SO4 is easy to crystallize out from the solution.The physicochemical properties(p,nD,pH)change regularly with the liquid compositions.The physicochemical properties including density and refractive index calculated by using the empirical equations agree well with the experimental results.The phase diagram of siample quaternary system(Li-,Na~+,Cs~+//Cl--H2O)at 298.15 K includes three invariant points(E1,2CsCl·LiCl·4H2O+LiCl·H2O+NaCl;E2,2CsCl·LiCl·4H2O+[Cs1-x(Na·H2O)x]Cl+NaCl;E3,2CsCl·LiCl·4H2O+[Cs1-x(Na·H2O)x]Cl+NaCl),seven univariant isothermal dissolution curves,and five crystallization zones corresponding to LiCl-H2O,CsCl·2NaCl·2H2O,2CsCl·LiCl·4H2O,[Cs1-x(Na·H2O)x]Cl and NaCl.The area of crystallization region of NaCl is the largest than that of salts coexisted,which indicates that NaCl is more easily separated by crystallizing out.The physicochemical properties(p,nD)change regularly with the liquid compositions.In the phase diagram of reciprocal quaternary system(Na~+,Cs~+//Cl-,SO42--H2O)at 298.15 K shows three invariant points(E1,Cs2SO4+Na2SO4+[Cs1-x(Na·H2O)x]Cl;E2,[Cs1-x(Na·H2O)x]Cl+Na2SO4+CsCl·2NaCl·2H2O;E3,Na2SO4+CsCl·2NaCl·2H2O+NaCl),seven univariant isothermal dissolution curves,and five crystallization zones corresponding to Cs2SO4,Na2SO4,NaCl,[Cs1-x(Na·H2O)x]Cl,CsCl·2NaCl·2H2O and Na2SO4·10H2O.The crystallization area of Na2SO4 in the phase diagram is the greatest than those salts existed in the system,so Na2SO4 is easy to crystallize out from the solution.The physicochemical properties(?,nD)change regularly with the liquid compositions.In the reciprocal qinary system(Li~+,Na~+,Cs~+//Cl-,SO42--H2O)at 298.15 K,which is all co-siturated by NaCl,it is currently known to be composed of 8 single-salt crystal regions,9 solubility curves,and 5 invariant points.In the phase diagram,a new complex salt is formed,which is 9Li2SO4·2Cs2SO4·3Na2SO4.In the physicochemical property-composition diagram,the density and refractive index change regularly with J(SO42-).