Phase Equilibria In Quinary System Na⁺,K⁺,Mg²⁺,Sr²⁺//Cl^--H₂O And Parts Of Its Subsystem At 298 K And 323 K

In order to study the salt water system of underground brine in Sichuan Basin,this paper studied the phase equilibria of the quinary system Na⁺,K⁺,Mg²⁺,Sr²⁺//Cl-– H₂ O at 298 K and 323 K and its subsystems which included two quaternary subsystems KCl – MgCl₂ – SrCl₂ – H₂ O,NaCl – MgCl₂ – SrCl₂ – H₂ O at 298 K and 323 K,One ternary subsystem MgCl₂ – SrCl₂ – H₂ O at 298 K by isothermal equilibrium method.The density and equilibrium solubility data of the system at the corresponding temperature are measured by the liquid phase analysis.XRD is used to identifiy the compositions of the solid phases.Based on the solubility data and the equilibrium solid phase,the phase diagrams（saturated with NaCl）,the density-composition diagram,the water content and the sodium content of the quinary system are drawn,respectively.The quaternary system phase diagram,the density-composition diagram and the water content are also drawn.The ternary system phase diagram and the density-composition diagram are plotted.We can conclude that the ternary system MgCl₂ – SrCl₂ – H₂ O system at the temperature of 298 K,has no double salt or solid solution,which belongs to the simple eutectic type.Its equilibrium phase diagram contains two crystalline solid phase,including strontium chloride hexahydrate,magnesium chloride hexahydrate respectively.There are two single variable solubility curves.There is one invariant saturation point.The quaternary system NaCl – MgCl₂ – SrCl₂ – H₂ O at 298 K and 323 K are of simple quaternary systems,no solid solution or complex salt formed.Its isothermal solubility phase diagram contains three single variable solubility curves,one invariant point and three crystallization regions which corresponding to three single salt NaCl,MgCl₂·6H₂O and SrCl₂·6H₂O.The crystallization form of salt does not change at the two temperatures.The quaternary system KCl – MgCl₂ – SrCl₂ – H₂ O at 298 K and 323 K are of complex quaternary systems,has no solid solution,however,a complex salt of KCl·MgCl₂·6H₂O（Car）comes into being.The phase diagram contains five univariant curves,two invariant points and four phase regions corresponding to complex salt KCl·MgCl₂·6H₂O（Car）and three salt MgCl₂·6H₂O（Bis）,KCl and SrCl₂·6H₂O.After comparing the quaternary phase diagrams,it could be seen that the crystallization form of salt does not change with the temperature.The quinary system K⁺,Mg²⁺,Na⁺,Sr²⁺//Cl-– H₂ O at 323 K and 298 K（NaCl saturation）are of complex quinary systems,has no solid solution,however,a complex salt of KCl·MgCl₂·6H₂O（Car）comes into being.The isothermal phase diagram contains five univariant curves,two invariant points,four crystallization regions which corresponding to complex salt KCl·MgCl₂·6H₂O（Car）and four salt MgCl₂·6H₂O（Bis）,KCl,SrCl₂·6H₂O and NaCl.The crystallization form of salt does not change at the two temperatures.