Studies On The Metastable Phase Equilibria Of The Quinary System Na⁺,K⁺,Cs⁺,Mg²⁺//Cl^--H₂O And Its Partial Subsystems At Multi-temperature

Pingluo underground brine,located in Sichuan Basin of China,has abundant reserves and high salinity.Besides the high content of potassium,it also has many characteristics and trace components?rubidium and cesium?,which both reach and exceed the general industrial standard,and have high exploitation value.The studies on the phase equilibrium aimed at the characteristic component of Pingluo underground brine can provide basic thermodynamic data for the development of the brine.In this paper,according to the composition characteristics of underground brine and old brine in Sichuan Pingluoba,the isothermal evaporation method was used to study the metastable phase equilibrium of the following systems:the quaternary system Na⁺,K⁺,Cs⁺//Cl^--H₂O at 298.2 K,323.2 K;the quaternary system Na⁺,Rb⁺,Cs⁺//Cl^--H₂O at 298.2 K,323.2 K;the quinary system Na⁺,K⁺,Cs⁺,Mg²⁺//Cl^--H₂O at 298.2 K and 323.2 K.The solubility and physicochemical properties?density and refractive index?data of the equilibrium liquid and the identification of the equilibrium solid phase were obtained.According to the experimental data,the isothermal evaporation phase diagram of the quaternary system,the water content vs composition diagram,the density vs composition diagram,the refractive index vs composition diagram and the contrast diagram of the metastable phase diagram at different temperatures were drawn;The Stereo diagram of dry salt,projection diagram saturated with NaCl or MgCl₂,water content vs composition diagram,the density vs composition diagram,and the refractive index vs composition diagram were drawn.The quaternary system Na⁺,K⁺,Cs⁺//Cl^--H₂O at 298.2 K,323.2 K is of a complex system and the system has solid solution?K,Cs?Cl formed at 298.2 K and323.2 K.The metastable phase diagram is composed of five univariate curves,two invariant points and four crystalline regions.The four crystallization fields correspond to the salts NaCl,KCl,CsCl and solid solution?K,Cs?Cl.The crystalline forms of salts are the same at 298.2 K and 323.2 K.With the increase of temperature,the crystallization area of KCl and CsCl decreases while the crystalline area of NaCl and solid solution?K,Cs?Cl increases.The quaternary system Na⁺,Rb⁺,Cs⁺//Cl^--H₂O is of a complex system at 298 K and 323.2 K,with solid solution?K,Cs?Cl formed.The metastable phase diagram is composed of five univariate curves,two invariant points and four crystalline regions.The four crystallization fields correspond to the NaCl,RbCl,CsCl and?Rb,Cs?Cl.The crystalline forms of salts has no change with the temperature at 298.2 K and323.2 K.With the increase of temperature,the crystallization area of RbCl decreases while the crystalline area of NaCl,CsCl and solid solution?Rb,Cs?Cl increases.The quinary system Na⁺,K⁺,Cs⁺,Mg²⁺//Cl^--H₂O at 298.2 K is a complex system consisting of double salt KCl·MgCl₂·6H₂O,CsCl·MgCl₂·6H₂O and solid solution?K,Cs?Cl.The system is composed of eight invariant points,seven crystalline areas,and twenty-one univariate curves.The seven crystallization zones correspond to the single salts NaCl,KCl,CsCl,MgCl2·6H2O,double salts KCl·MgCl₂·6H₂O,CsCl·MgCl₂·6H₂O and solid solution?K,Cs?Cl.respectively.Among them,the crystallization zone of NaCl is the largest and the crystallization zone of MgCl₂·6H₂O is the smallest.The quinary system Na⁺,K⁺,Cs⁺,Mg²⁺//Cl^--H₂O at 323.2 K is also of a complex system consisting of double salt KCl·MgCl₂·6H₂O,CsCl·MgCl₂·6H₂O and solid solution?K,Cs?Cl.The system is composed of eight invariant points,seven crystalline areas,and twenty one univariate curves.The seven crystallization zones correspond to the single salts NaCl,KCl,CsCl,MgCl2·6H2O,double salts KCl·MgCl₂·6H₂O,CsCl·MgCl₂·6H₂O and solid solution?K,Cs?Cl.respectively.Among them,the crystallization zone of NaCl is the largest and the crystallization zone of MgCl₂·6H₂O is the smallest.With the increase of temperature,the crystal form and crystal species of the system has no change.