Metastable Phase Equilibrium Of The Quinary System Li⁺,Rb⁺,Cs⁺,Mg²⁺//Cl^--H₂O At 298K And Its Partial Subsystem At Multi Temperature

Qarhan Salt Lake is the largest soluble potassium and magnesium salt mine in China.In recent years,the comprehensive utilization and development of salt brine contained with high concentration of magnesium,rubidium,cesium becomes urgent.And the study on the phase equilibrium of salt lake can provide the basic thermodynamics data effectively.An isothermal dissolution method was used to study the quinary system Li⁺,Rb⁺,Cs⁺,Mg²⁺ // Cl^--H₂ O at 298 K and three subsystem at multi temperature,that are quaternary system Li⁺,Rb⁺,Cs⁺ // Cl^--H₂ O at 298 K,323 K and 348 K;ternary system Rb⁺,Cs⁺ // Cl^--H₂ O at 298 K and 323 K;and ternary system Li⁺,Cs⁺ // Cl^--H₂ O at 298 K and 323 K.The solubility and density,refractive indices of the equilibrium liquid phase of the systems mentioned above was investigated.On the basis of the experimental data,the metastable phase diagram,the space phase diagram and water content,physicochemical properties versus composition diagrams were plotted.The results show that the ternary system Li⁺,Cs⁺ // Cl^--H₂ O at 298 K and 323 K is of a simple eutectic type.The metastable phase diagram consists of one invariant point,two univariant curves,and two crystallization fields corresponding to single salts LiCl·H₂O and CsCl.The crystalline form of salt did not change at the two temperatures.With the increase of temperature,the crystallization field of CsCl was reduced and the field of LiCl·H₂O was changed little.The ternary system Rb⁺,Cs⁺ // Cl^--H₂ O at 298 K and 323 K is a complex type,and with solid solution?Rb,Cs?Cl formed.The phase diagram consists of two invariant point,three univariant curves,and three crystallization fields corresponding to CsCl,RbCl,?Rb,Cs?Cl.With the increase of temperature,the crystalline form of salt did not change,both the crystallization fields of CsCl andRbCl were reduced,the field of solid solution?Rb,Cs?Cl was enlarged.The quaternary system Li⁺,Rb⁺,Cs⁺ // Cl^--H₂ O at 298 K,323 K,348 K is also of a complex system with solid solution?Rb,Cs?Cl formed.The system consists of two invariant point,five univariant curves,and four crystallization fields corresponding to LiCl·H₂O,CsCl,RbCl,?Rb,Cs?Cl.Salt crystallization form did not change with the temperature.With the temperature increased,crystallization area of RbCl was gradually decreased,and the remaining three crystallization areas were increased.Also the solid solution(?Rb,Cs?Cl becomes more difficult to be generated.The quinary system Li⁺,Rb⁺,Cs⁺,Mg²⁺ // Cl^--H₂ O at 298 K is a complex system.The double salt Li-carnallite,Rb-carnallite,Cs-carnallite and solid solution?Rb,Cs?Cl were formed in this system.The phase diagram consists of eight invariant point,nineteen univariant curves,and eight crystallization fields corresponding to four single salt LiCl·H₂O,RbCl,CsCl,MgCl2·6H₂O,three double salt LiCl·MgCl2·7H₂O,RbCl·MgCl2·6H₂O,CsCl·MgCl2·6H₂O and one solid solution?Rb,Cs?Cl.In the projected phase diagram saturated with LiCl or CsCl,the crystalline region of RbCl is small,nevertheless the solubility of RbCl is big.Water content,physicochemical properties of solution are depended on the water evaporation and double salt precipitation or dissolution behavior.