Phase Equilibria Of The Quaternary Systems Li⁺,Mg²⁺//Cl^-(SO₄^2-),borate-H₂O

The composition of brine becomes quinary system(Li+,Mg2+//Cl-,SO42-,borate-H2O)after extracting potassium and sodium.For the subsystems included in this system,phase equilibria of the quaternary system(Li+,Mg2+//SO42-,borate-H2O)at 308.15 K and the subsystem(Mg2+//SO42--borate-H2O)at 288.15 K and 308.15 K were researched.The same time,phase equilibria of the quaternary system(Li+,Mg2+//Cl-,borate-H2O)and the subsystem(Mg2+//Cl-,borate-H2O)at 308.15 K were researched.Solubilities and the physic-chemical properties including density,refractive index,viscosity and pH value were analyzed,and the solid phase were identified.On the basis of the experimental data,the phase diagrams,water content diagrams and physic-chemical property versus composition diagrams were respectively plotted.Phase equilibrium of the ternary system(Mg2+//SO42-,B4O72--H2O)belongs to hydrate type I,and neither double salt nor solid solution was generated at 288.15 K.There are one invariant point,two univariant curves,and two crystallization regions corresponding to MgSO4·7H2O and MgB4O7·9H2O.It was also found that MgB4O7·9H2O is unstable,can easily converts into Mg2B6O11·15H2O,and stably exist in Mg2B6O11·15H2O.This ternary system at 308.15 K the same as 288.15 K,and belongs to hydrate type ?,no double salt or solid solution was generated.Phase equilibrium of the ternary system(Mg2+//Cl--B4O72--H2O)was of hydrate type ?,and no double salt and solid solution generates at 308.15 K.There are one invariant point,two univariant curves,and two crystallization regions corresponding to MgCl2·6H2O and MgB4O7·9H2O.Meanwhile it has been found that the MgB4O7·9H2O is not stable,and is easily converted into the Mg2B6O11·15H2O and Mg36O10·7.5H2O.And with the increasing of MgC12,the conversion of MgB4O7·9H2O to Mg2B6O11·15H2O is inhibited,and stably exist in MgB6O10·7.5H2O.Phase equilibrium of the quaternary system(Li+,Mg2+//SO42-,borate-H2O)was of hydrate type ?,and no double salt and solid solution generates at 308.15 K.The dry-salt diagram has two invariant points(F1:Li2SO4·H2O+Li2B4O7·3H2O+Mg2B6O11·15H2O,F2:Li2SO4·H2O+MgSO4·7H2O+Mg2B6011·15H2O),five univariant solubility curves and four crystallization regions,which is Li2SO4·H2O,Li2B4O7·3H2O,MgSO4·7H2O and Mg2B6O11·15H2O,respectively.Solubilities of magnesium borate(Mg2B6O11·15H2O)is the smallest and solid phase crystallization is the biggest,easily is separated from the solution.Phase equilibrium of the quaternary system(Li+,Mg2+//Cl-,borate-H2O)was of hydrate type I at 308.15 K.The double salt(LiCl·MgC12·7H2O)was generated and no solid solution was generated.There were three invariant points(F1:Li2B4O7·3H2O+LiCl·H2O+Mg2B6O11·15H2O,F2:LiCl·MgCl2·7H2O+LiCl·H2O+Mg2B6O11·15H2O and F 3:LiCl·M9Cl2·742O+MgCl2·6H2O+Mg2B6O11·15H2O),seven univariant solubility curves and five crystallization regions,which is Li2B4O7·3H2O,LiCl·H2O,LiCl·MgCl2·7H2 O,M9Cl2·6H42O and Mg2B6O11·15H2O,respectively.LiCl and MgCl2 had a strong sa lting-out effect on Mg2B6011·15H2O,and the solubilities of magnesium borate is als o the smallest and solid phase crystallization is the biggest,easily is separated from the solution.