Phase Equilibria Diagrams Of The Quaternary Systems Containing Magnesium Borates

The isothermal dissolution methods was used to carry out the investigations of quaternary systems(Mg2+//Cl-,SO42-,borate-H2O),(Li+,Na+,Mg2+//borate-H2O)and(K+,Mg2+//SO42-,borate-H2O),with the analytical method of chemical to get the ion concentration of liquid phase and measuring the physicochemical properties.The phase diagram,water diagram and properties diagram of physicochemical were plotted according to the data.The solid phases were identified by the method of X-ray diffraction.The stable phase diagram of the quaternary system(Mg2+//Cl-,SO42-,borate-H2O)at 273.15 K includes a quaternary co-saturation point,three univariant curves and three solid phase crystallization regions,without solid solution formation or double salt formation.The equilibrium solid phases are MgCl2·6H2O,MgSO4·7H2O,Mg2B6O11·15H2O respectively.The crystallization area of Mg2B6O11·15H2O is the largest and the solubility is the smallest.At 308.15 K,the stable phase diagram includes 3 co-saturation points,5 univariate curves and 5 crystallization regions,and there is no solid solution or double salt formation.The equilibrium solid phases are MgSO4·7H2O,MgSO4·6H2O,,MgSO4·4H2O,MgCl2·6H2O,Mg2B6O11·15H2O respectively.As the temperature rises,the crystallization of MgSO4·7H2O and Mg2B6O11·15H2O both becomes smaller to varying degree.The quaternary system(Li+,Na+,Mg2+//borate-H2O)at 308.15 K was investigated.The stable phase diagram consist of three univariant curves,three crystallization zones and a co-saturation point,without solid solution or double salt formation.The solid phases are Li2B4O7·3H2O Na2B4O7·10H2O and Mg2B6O11·15H2O Among the three salts,Mg2B6O11·15H2O has the biggest crystallization region.The water diagram of the system changes regularly with the increase of J(Li2B4O7).In the composition diagram and refractive index composition diagram of the solution,the same change rule is shown with the increase of J(Li2B4O7).Finally,the interaction quaternary system(K+,Mg2+//SO42-,borate-H2O)was studied at 308.15 K.Results of the research show that the system includes three quaternary co-saturation points,seven univariate curves and five univariate crystallization regions.There is a double salt formation,which is picromerite(K2SO4·MgSO4·6H2O).The solid phases are picromerite(K2SO4·MgSO4·6H2O),hungchaoite(MgB4O7·9H2O),K2SO4,magnesium sulfate heptahydrate(MgSO4·7H2O)and potassium borate tetrahydrate(K2B4O7·4H2O).The crystallization area of hungchaoite(MgB4O7·9H2O)is the largest.Among those salts,K2B4O7 has strong salting-out effect on MgB4O7.Borate in aqueous solution can exist in several different species,the solution behavior is very complicated,and the equilibrium time of system containing borate is about ninety days.The experimental results of research show that the hungchaoite(MgB4O7·9H2O)exist in sulfate-type system,which inderite(Mg2B6O11·15H2O)stable in other systems.