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

According to the composition of the Pingluo underground old brines,the metastable phase equilibria were studied by using an isothermal evaporation method for the following systems: ternary systems K⁺,Cs⁺ // Cl^--H₂ O 298 K and 323 K,quaternary systems Li⁺,Cs⁺,Mg²⁺ // Cl^--H₂ O 298 K,323 K,348 K and quinary system Li⁺,K⁺,Cs⁺,Mg²⁺ // Cl^--H₂ O 298 K.The solubility,density and refractive index of the equilibrated solution were measured experimentally.Based on the experimental data,the metstable phase diagrams,the density vs J?CsCl?diagram and refractive index vs J?CsCl?diagram of two ternary systems;the metstable phase diagrams,the density vs J?MgCl₂?diagram,water content vs J?MgCl₂?and refractive index vs J?MgCl₂?diagram of three quaternary;the space phase diagrams,the planar projection diagrams?satruated with KCl and LiCl?,the density vs composition diagram,water content vs composition and refractive index vs composition diagram of three quaternary systems were constructed.The ternary system K⁺,Cs⁺ // Cl^--H₂ O is of a complex type.at 298 K and 323 K,with solid solution?K,Cs?Cl formed.Its metastable phase diagram consists of three univariant curves,two invariant points and three crystallization fields.The comparisons between the metastable phase diagrams at 298 K and 323 K show that the solubility of simple salt KCl,CsCl and solid solution?K,Cs?Cl in water are influenced by temperature.With the increase of temperature,the solubility of solid solution?K,Cs?Cl increases and its crystallization area decreases obviously,while crystallization fields of KCl and CsCl increase.The quaternary system Li⁺,Cs⁺,Mg²⁺ // Cl^--H₂ O at 298 K,323 K and 348 K is of a complex type.The metastable phase diagrams contain seven univariant curves,three invariant points and five crystallization fields.The size of crystallization areas of salt is in the order CsCl·MgCl₂·6H₂O>CsCl>LiCl·H₂O>MgCl₂·6H₂O> LiCl·MgCl₂·7H₂O.The comparisons between the metastable phase diagrams at 298 K,323 K and 348 K show that there is no change in the crystallization forms,but the size of crystallization fields of salts have changed.Along with the increase of temperature,the size of the crystallization fields of CsCl·MgCl₂·6H₂O,LiCl·MgCl₂·7H₂O become larger,and that of the salt CsCl,LiCl·H₂O and MgCl₂·6H₂O become smaller.The results show that in production,it is feasible to seperate lithium chloride and cesium chloride by increasing temperature,.through with the lithium or cesium in brines turning to lithium carnallite or cesium carnallite,respectively.The quinary system Li⁺,K⁺,Cs⁺,Mg²⁺ // Cl^--H₂ O 298 K is of a complex type,which contain six invariant points,eighteen univariant curves and eight crystallization fields.Ths eight crystallization fields are corresponding to simple salt LiCl·H₂O,CsCl,KCl,MgCl₂·6H₂O,double salt LiCl·MgCl₂·7H₂O,KCl·MgCl₂·6H₂O,CsCl·MgCl₂·6H₂O and solid solution?K,Cs?Cl.The size of crystallization fields of?K,Cs?Cl is the biggest,while the size of crystallization fields of KCl is the smallest.In this system,alkali metals Li,K,and Cs are easy to form different carnallite with MgCl₂.Meanwhile,because of the similar atomic radius for K⁺ and Cs⁺,and the same cubic crystal of KCl and CsCl,the solid solution?K,Cs?Cl is easy to formed.