Studies On The Phase Equilibria In Quinary Li⁺,Na⁺,Mg²⁺//Cl^-,B₄O₇^2--H₂O And Its Partial Related Sub-systems At 273 K

There are many Saline Lakes in Qinghai Tibet Plateau,which contain rich mineral resources.The effective exploitation and utilization of these resources can not only solve the problem of shortage of resources in our country,but also play a significant role in promoting the development of society and economy.The studies on the phase equilibria of water-salt systems have practical guiding significance for the development and utilization of Saline Lake resources.Therefore,this paper has carried out the corresponding phase equilibria researches in view of the features of the Saline Lake resources in the Qinghai Tibet Plateau.In this paper,the phase equilibrium relationships of the quinary system Li⁺,Na⁺,Mg²⁺//Cl^–,B₄O₇^2––H₂O and some of its related sub-systems at 273 K were investigated.In the experiment,the metastable phase equilibria of the ternary systems Na₂B₄O₇–MgB₄O₇–H₂O and K₂B₄O₇–MgB₄O₇–H₂O were studied by isothermal evaporation method.The isothermal dissolution method was used to study the stable phase equilibrium relationships of the ternary system Na₂B₄O₇–MgB₄O₇–H₂O,the quaternary systems LiCl–NaCl–MgCl₂–H₂O,LiCl–KCl–MgCl₂–H₂O,Li₂B₄O₇–Na₂B₄O₇–MgB₄O₇–H₂O,NaCl–Na₂B₄O₇–MgCl₂–MgB₄O₇–H₂O and the quinary system Li⁺,Na⁺,Mg²⁺//Cl^-,B₄O₇^2--H₂O.Through the study of the stable and metastable phase equilibria of the ternary system Na₂B₄O₇–MgB₄O₇–H₂O,the phase diagrams and the density diagrams were drawn.There are two univariant curves,two crystallization zones and one invariant point in this phase diagram.The crystalline regions in the stable and metastable state are both Na₂B₄O₇·10H₂O and MgB₄O₇·9H₂O,and the metastable phenomenon of this system is more obvious,Na₂B₄O₇ has a significant salting out effect on MgB₄O₇.The metastable phase equilibrium of the ternary system K₂B₄O₇–MgB₄O₇–H₂O was studied and the solubilities and densities of this system were measured.The phase diagram and density diagram were plotted based on the experimental data.There are one invariant point,two univariant curves and two crystalline zones in this phase diagram,which are corresponding to K₂B₄O₇·4H₂O and MgB₄O₇·9H₂O.The study of the phase equilibrium of the quaternary system Li₂B₄O₇–Na₂B₄O₇–MgB₄O₇–H₂O shows that the system belongs to the simple co-saturated type.There are one invariant point,three univariant curves and three crystallization zones in this isothermal phase diagram.The equilibrium solid phases at the invariant point are Li₂B₄O₇·3H₂O+Na₂B₄O₇·10H₂O+MgB₄O₇·9H₂O,and the crystalline regions are Li₂B₄O₇·3H₂O,Na₂B₄O₇·10H₂O and MgB₄O₇·9H₂O,respectively.Among them,the crystallized area of MgB₄O₇·9H₂O is the largest.Finally,the equilibrium solid phase were determined by using the X-ray diffraction method.Double salt LiCl·MgCl₂·7H₂O was formed in the quaternary system LiCl–NaCl–MgCl₂–H₂O.The isothermal phase diagram,water diagram and density composition diagram of this system were plotted based on the experimental data and the corresponding equilibrium solid phases.The phase diagram consists of two invariant points,five univariate curves,and four crystallization zones.The corresponding equilibrium phases at the two invariant points are NaCl+LiCl·2H₂O+LiCl·MgCl₂·7H₂O and NaCl+LiCl·MgCl₂·7H₂O+MgCl₂·6H₂O.The crystalline regions are NaCl,LiCl·2H₂O,MgCl₂·6H₂O and LiCl·MgCl₂·7H₂O respectively.The crystallized area of double salt LiCl·MgCl₂·7H₂O is the smallest and the crystallized area of NaCl is the largest.The study of the quaternary system LiCl–KCl–MgCl₂–H₂O shows that there are two complex salts KCl·MgCl₂·6H₂O and LiCl·MgCl₂·7H₂O in this system.The isothermal phase diagram consists of three invariant points,seven univariate curves,and five crystalline regions.The equilibrium solid phases of the three invariant points are KCl+LiCl·2H₂O+KCl·MgCl₂·6H₂O,MgCl₂·6H₂O+KCl·MgCl₂·6H₂O+LiCl·MgCl₂·7H₂O and KCl·MgCl₂·6H₂O+LiCl·MgCl₂·7H₂O+LiCl·2H₂O.The crystalline regions are LiCl·2H₂O,MgCl₂·6H₂O,KCl,KCl·MgCl₂·6H₂O and LiCl·MgCl₂·7H₂O,respectively.Among them,the crystallized zone of KCl is the largest,and it is the most easily to crystallize.The quaternary system NaCl–Na₂B₄O₇–MgCl₂–MgB₄O₇–H₂O is the simple co-saturated type.The phase diagram of this system consists of two invariant points,five univariate curves,and four crystallization zones.The equilibrium solid phases at its invariant points are NaCl+MgCl₂·6H₂O+MgB₄O₇·9H₂O and MgCl₂·6H₂O+NaCl+Na₂B₄O₇·10H₂O.The crystalline regions are NaCl,MgCl₂·6H₂O,MgB₄O₇·9H₂O and Na₂B₄O₇·10H₂O,respectively.The crystallized area of MgB4O7·9H2O is the largest,while that of MgCl2·6H2O is the smallest.Therefore,MgB₄O₇·9H₂O is most easily to be separated from the solution.The phase equilibrium of the quinary system Li⁺,Na⁺,Mg²⁺//Cl^-,B₄O₇^2--H₂O was investigated.The dry salt diagram,sodium diagram,water diagram and density diagram of this system were plotted with NaCl saturated.There is double salt LiCl·MgCl₂·7H₂O formed in the system.The dry salt diagram of this system consists of four invariant points,nine univariate curves and six crystallization zones.The crystalline areas are single salts Li₂B₄O₇·3H₂O,Na₂B₄O₇·10H₂O,MgB₄O₇·9H₂O,LiCl·2H₂O,MgCl₂·6H₂O and double salt LiCl·MgCl₂·7H₂O,respectively.The phase region of Na₂B₄O₇·10H₂O in the crystalline region is the largest.