Studies On Phase Equilibria Of Related Subsystems In Quinary System Na⁺,K⁺,Mg²⁺,Sr²⁺//Br^--H₂O At 298K

With the continous exploration of the resources in Sichuan Basin,it was found that the underground brine resources in Sichuan Basin were rich.The contents of these useful mineral components in the brines reached or exceeded their corresponding industrial grades.But these useful components were often mixed together with others,so it was difficult for people to exploit the useful components easily.It was necessary for us to analyze the equilibrium relationship of dissolving-precipitating and the characteristic of each component.The useful components could be separated from the kinds of components.The solubility of every component was an important feature in separation of different components.The phase diagram of the components were drawn through the experiment method?Phase equilibria and phase diagrams were the theoretical basis of the exploitation and utilization of the underground brine resource.In this paper,the phase equilibria of the quinary system Na+,K+,Mg2+,Sr2+// Br--H2O and its related subsystems at 298 K were the main research work.A ternary system MgBr2-SrBr2-H2O,two quaternary systems Na+,Mg2+,Sr2+// Br--H2O and K+,Mg2+,Sr2+// Br--H2O,quinary systems Na+,K+,Mg2+,Sr2+// Br--H2O(SrBr2 6H2 O saturated)and Na+,K+,Mg2+,Sr2+// Br--H2O(KBr saturated)at 298 K were included.Besides,the research on the ternary system MgBr2-SrBr2-H2O at 323 K also was made.Because the depth of underground brine was different,the environment temperature was different.In addition,the phase equilibria of the two ternary systems NaBr-Na2SO4-H2O and KBr-K2SO4-H2O at 398 K were studied.Based on the experimental results,phase diagrams and density content diagrams of the listed above four ternary systems,two quaternary systems and the quinary systems under the two projective planes were plotted.The water content diagrams of the two quaternary systems,the water content diagrams of the quinary systems under the two projective planes,the Sr+ content diagram and the K+ content diagram of the quinary systems were drawn.The wet crystals were analyzed by X-ray diffraction to ascertain their crystalloid form.The ternary systems Mg Br2-SrBr2-H2O at 298 K and 323 K are both a type of simple common saturation and without complex salt and solid solution.In the phase diagrams,both the two ternary systems have one eutectic point,two univariant curves and two regions of crystallization corresponding to magnesium bromide hexahydrate(MgBr2·6H2O)and strontium bromide hexahydrate(SrBr2·6H2O).The crystallization region of MgBr2·6H2O is smaller,which shows the solubility of MgBr2·6H2O is bigger.The results show that the ternary system NaBr-Na2SO4-H2O at 398 K is a simple type with no complex salts or solid solutions formed.The phase diagram has one eutectic point,two univariant curves and two regions of crystallization.The crystallization regions in NaBr-Na2SO4-H2O are composited of sodium bromide(NaBr)and sodium sulfate(Na2SO4).The ternary system KBr-K2SO4-H2O at 398 K has no double salt or solid solution formed.The phase diagram has one eutectic point,two univariant curves and two regions of crystallization corresponding to potassium bromide(KBr)and potassium sulfate(K2SO4).There is no double salt or solid solution formed in the quaternary system NaBr-MgBr2-SrBr2-H2O at 298 K.In the phase diagram,the quaternary system at 298 K has two eutectic points,five univariant curves and four crystallization fields corresponding to sodium bromide(NaBr),sodium bromide dihydrate(NaBr·2H2O),magnesium bromide hexahydrate(MgBr2·6H2O)and strontium bromide hexahydrate(SrBr2·6H2O).The salt NaBr·2H2O has the larggest crystallization field,which means the salt NaBr·2H2O has the smaller solubility.The salt Na Br·2H2O can be easily separated from solution.The quaternary system KBr-MgBr2-SrBr2-H2O at 298 K has a double salt(KBr·MgBr2·6H2O)and no solid solution was found.In the phase diagram,the quaternary system at 298 K has two eutectic points,five univariant curves and four crystallization fields corresponding to potassium chloride(KBr),magnesium bromide hexahydrate(MgBr2·6H2O),strontium bromide hexahydrate(SrBr2·6H2O)and double salt(KBr·MgBr2·6H2O).The salt KBr has the larggest crystallization field,which means the salt KBr has the smaller solubility.The salt KBr can be easily separated from solution.The quinary system NaBr-KBr-MgBr2-SrBr2-H2O(saturated with Sr Br2·6H2O)at 298 K has a double salt(KBr·MgBr2·6H2O)and no solid solution.In the phase diagram,the quinary system at 298 K has three eutectic points,seven univariant curves and five crystallization fields corresponding to potassium bromide(KBr),magnesium chloride hexahydrate(Mg Br2·6H2O),sodium bromide dihydrate(NaBr·2H2O),sodium bromide(NaBr)and double salt(KBr·MgBr2·6H2O).There is a double salt(KBr·Mg Br2·6H2O)but no solid solution formed in the quinary system NaBr-KBr-MgBr2-SrBr2-H2O(saturated with KBr)at 298 K.The phase diagram of this system consist of one eutectic point,three univariant curves and three crystallization fields.The three crystallization fields represent strontium chloride dihydrate(Sr Br2·6H2O),strontium chloride dihydrate(NaBr·2H2O)and double salt(KBr·MgBr2·6H2O),respectively.