Phase Equilibria Of The Quaternary Systems Containing Potassium,Magnesium And Borate Ions

Phase equilibria of the quaternary systems(Li+,K+,Mg2+//borate-H2O),(K+,Mg2+//Cl-,borate-H2O)and subsystem(K+,Mg2+//borate-H2O)were measured by isothermal dissolution method.The experimental data on the solubility and the relevant physicochemical properties including density,refractive index and pH value were analyzed.According to the experimental data,the stable phase diagram of the systems and densities curves,refractive index curves,pH value curves were drawn and solid phase was identified.It has been found that the ternary system(K+,Mg2+//boorate-H2O)at 288.15 K,298.15 K and 308.15 K,there is one eutectic point,two crystallization regions corresponding to the large area of inderite(L+Mg2B6O11·15H2O)and the relative small area of potassium borate tetrahydrate(L+K2B4O7·4H2O),and two univariant isothermal dissolution curves.Neither double salt nor solid solution have been found in this system at different tempreatures.As the temperature increasing,the solubility on both salt inderite(Mg2B6O11·15H2O)and salt K2B4O7·4H2O increased gradually.The physicochemical properties changed regularly with increasing K2B4O7 concentration.The calculated values of density and refractive index using empirical equations of the ternary system are in good agreement with the experimental values.The quaternary system(Li+,K+,Mg2+//borate-H2O)is of a simple co-saturated type,and neither double salt nor solid solution was found at 288.15 K,298.15 K or 308.15 K.It has been found that there is one eutectic point,three univariant isothermal dissolution curves,and three crystallization regions corresponding to inderite(Mg2B6O11·15H2O),Li2B4O7·3H2O,and K2B4O7 4H2O.The water diagrams show that the Janecke index values of J(H2O)gradually change with increasing of J(Li2B4O7)at three temperatures.As the temperature increasing,the solubility on salt inderite(Mg2B6O11.15H2O),K2B4O7·4H2O and Li2B4O7·3H2O increased gradually.The area of crystallization region of inderite is decreased while the area of Li2B4O7·3H2O crystallization region is enlarged.As for K2B4O7·4H2O,the crystallization region is not obviously changed with the increase of temperature.The physicochemical properties change regularly with increasing Li2B4O7 concentration.The double salt camallite(KCl·MgCl2·6H2O)is found in the quaternary system(K+,Mg2+//Cl-,borate-H2O)at 308,15 K.There are three invariant points F1,F2,F3;seven univariant curves,and five crystallization regions corresponding to inderite(Mg2B6O11·15H2O),K2B4O7·4H2O KCl,camallite(KCl·MgCl2·6H2O)and MgCl2·6H2O.The Janecke index values of J(H22)change regularly with increasing of J(Mg2+).The density and refractive index curves of the equilibrium liquid phase increased gradually with the increasing of J(Mg2+),while pH value decreased with the increasing of J(Mg2+).These artificial synthesized complexes were stirred for about 90 days,according to the research,final form of magnesium borate in these systems is inderite(Mg2B6O11·15H2O),of which the crystallization region is the largest.It apparently indicates the inderite is separated easily.