Phase Equilibria Of The Quaternary Systems Containing Sodium Magnesium And Borate Ions

Phase equilibria of the quaternary systems(Na+,Mg2+//Cl-,borate-H2O),(Li+,Na+,Mg2+//borate-H2O)and subsystems(Na+,Mg2+//borate)-H2O,(Li+,Mg2+//borate-H2O)at 298.15 K were researched by isothermal dissolution equilibrium method from the salt-lake brine.Solubilities and the physico-chemical properties including density,refractive index,viscosity and pH value were analyzed,and solid phase was identified.On the basis of the experimental data,the phase diagrams,water-phase diagrams and physico-chemical property versus composition diagrams were respectively plotted.Phase equilibrium of the ternary system(Na+,Mg2+//B4O72--H2O)belongs to hydrate type I,and neither double salt nor solid solution was generated at 298.15 K.There are one invariant point,two univariant curves,two crystallization regions corresponding to Na2B4O7·10H2O and MgB4O7·9H2O.It was also found that MgB4O7·9H2O is unstable,can easily converts into Mg2B6O11·15H2O,and stably exist in Mg2B6O11·15H2O.The ternary system(Na+,Mg2+//borate-H2O)was of hydrate type I,and no double salt or solid solution was found.In the phase diagram,the system has one invariant point,two univariant curves,and two fields of crystallization Na2B4O7·1OH2O and Mg2B6O11·15H2O.Phase equilibrium of the ternary system(Li+,Mg2+//borate-H2O)was of hydrate type I,and no double salt or solid solution was found.The phase diagram consists of one invariant point,two univariant curves,two crystallization regions corresponding to Li2B4O7·3H2O and MgB4O7·9H2O.It showed Li2B4O7 had a strong salting-out effect on MgB4O7·9H2O,and the crystallization was far more than MgB4O7·9H2O so that the latter was be separated easily.Phase equilibrium of the quaternary system(Na+,Mg2+//Cl-,borate-H2O)belongs to hydrate type I,and neither double salt nor solid solution was generated at 298.15 K.Dry-salt phase diagram has two invariant points(F1:NaCl+Na2B407·1OH2O+Mg2B6O11·15H2O,F2:NaCl+MgCl2·6H2O+Mg2B6O11·15H2O),five univariant solubility isothermal curves and four crystallization regions,which is NaCl,Na2B4O7·10H2O,MgCl2·6H2O and Mg2B6O11·15H2O,respectively.The solubilities of magnesium borate(Mg2B6O11·15H2O)is the smallest and solid phase crystallization is the biggest,most easily separated from the solution.In the dry-salt phase diagram of the quaternary system(Li+,Na+,Mg2+//borate-H2O)at 298.15 K there were one invariant point(E:Li2B4O7·3H2O+Na2B4O7· 10H2O+Mg2B6O11·15H2O),three univariant solubility curves and three crystallization regions corresponding to Li2B4O7·3H2O,Na2B4O7·10H2O and Mg2B6O11·15H2O.The conversion from hungchsaoite to inderite can not be blocked and stably exist in Mg2B6O11·15H2O.Li2B4O7 had strong salting-out effect on Mg2B6011,but Na2B4O7 had salting-in effect on it.