Studies On Phase Equilibria For The Quinary System Containing Alkaline Metal Pentaborates At 298.15 K

The development and utilization of salt lake resources is great significance to solve the shortage of solid resources in China.Qaidam Basin is rich in alkali borates,and the study of phase equilibrium can provide theoretical basis for the separation and extraction of salt lake resources.The isothermal solution method is used to study the solid-liquid equilibria as well as their physicochemical properties including density(?)and refractive index(nD)on the quinary system(Li+,Na+,K+//Cl-1,B5O8--H2O)and its two ternary systems and three 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(K+//Cl-,B5O8--H2O)at 298.15 K contains one invariant point(KCl+KB5O8·4H2O),two univariant isothermal dissolution curves,and two crystallization regions corresponding to KCl and KB5O8·4H2O.The area of KB5O8·4H2O crystallization region is larger than that of KCI,so KB508 is easy to crystallize out from the solution.The physicochemical properties(?,nD)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 ternary system(K+//SO42-,B5O2--H2O)at 298.15 K has one invariant point(K2SO4+KB5O8·4H2O),two univariant isothermal dissolution curves,and two crystallization regions corresponding to K2SO4 and KB5O8·4H2O.The area of KB508.4H2O crystallization region is larger than that of K2SO4,so KB508 is easy to crystallize out from the solution.The physicochemical properties(p,nD)change regularly with the liquid compositions.The physicochemical properties calculated by using the empirical equations agree well with the experimental results.The phase diagram of siample quaternary system(Li+,Na+,K+//B5O8--H2O)at 298.15 K includes one invariant point(LiB5O8·5H2O+NaB5O8·5H2O+KB5O8-4H2O),three univariant isothermal dissolution curves,and three crystallization zones corresponding to LiB5O8·5H2O,NaB5O8·5H2O and KB5O8-4H2O.The area of crystallization region of KB5O8.4H2O is the largest than that of salts coexisted,which indicates that KB5O8 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(Li+,K+//Cl-,B5O8--H2O)at 298.15 K has two invariant points(LiCl·H2O+LiB5O8·5H2O+KB5O8·4H2O and LiCl·H2O+KC1+KB5O8·4H2O),five univariant isothermal dissolution curves,and four crystallization zones corresponding to LiCl·H2O,LiB5O8·5H2O,KB5O8·4H2O and KCl.The crystallization area of KB5O8·4H2O in the phase diagram is the biggest that that of other salts,so KB5O8 is easy to crystallize out from the solution.The physicochemical properties(?,nD)change regularly with the liquid compositions.In the phase diagram of reciprocal quaternary system(Na+,K+//Cl-,B5O8--H2O)at 298.15 K shows two invariant points(NaCl+NaB5O8·5H2O+KB5O8-4H2O and NaCl+KCl+KB5O8-4H2O),five univariant isothermal dissolution curves,and four crystallization zones corresponding to NaCl,NaB5O8·5H2O,KB5O8·4H2O and KCl.The crystallization area of KB5O8·4H2O in the phase diagram is the greatest than those salts existed in the system,so KB5O8 is easy to crystallize out from the solution.The physicochemical properties(p,nD)change regularly with the liquid compositions.In the reciprocal qinary system(Li+,Na+,K+//Cl-,B5O8--H2O)at 298.15 K,which is all co-siturated by NaCl,there are three invariant points(LiCl·H2O+NaCl+KCl+LiB5O8·5H2O,NaCl+KCl+LiB508·5H2O+KB5O8-4H2O and NaCl+LiB5O8-5H2O+NaB5O8·5H2O+KB5O8.4H2O),seven univariant isothermal dissolution curves into five crystallization regions.The physicochemical properties(?,nD)change regularly with the liquid compositions.