Studies On Phase Equilibria In The Quinary System Na⁺,K⁺,Mg²⁺,Sr²⁺//Cl^--H₂O And Some Sub-systems Containing Strontium At 373K

The underground brine in Sichuan Basin is a treasure trove of highly mineralized resources.In order to get all kinds of needed chemical products by phase separation technology and realize the comprehensive utilization of resources,the phase equilibria of some salt-water systems containing strontium in the underground brine were studied using isothermal dissolution equilibrium method.The stable phase equilibria of the quinary system Na⁺,K⁺,Mg²⁺,Sr²⁺//Cl^––H₂O and some of its related sub-systems containing strontium at 373 K were studied.The systems studied are as follow:The ternary systems MgCl₂-SrCl₂-H₂O and CaCl₂-SrCl₂-H₂O;The quaternary systems NaCl-KCl-SrCl₂-H₂O,NaCl-MgCl₂-SrCl₂-H₂O,KCl-MgCl₂-SrCl₂-H₂O and KCl-CaCl₂-SrCl₂-H₂O;The quinary system NaCl-KCl-MgCl₂-SrCl₂-H₂O?NaCl saturated?.In this paper,the solubility data of each salt and the density values of the solution in the solid-liquid phase equilibria of the seven systems listed above were determined,respectively.The stable phase diagrams and density-composition figures of the respective systems were plotted according to the experimental results.The water content diagrams of the quaternary systems and the quinary system were also drawn.For the identification of saturated solids at each invariant point,the wet-residue method and the X-Ray powder diffraction method were used in the ternary systems,and the X-Ray powder diffraction method was used in the quaternary systems and the quinary system.At the same time,the XRD spectrums of the solid phases at corresponding invariant points were presented.The phase diagrams of the ternary systems MgCl₂-SrCl₂-H₂O and CaCl₂-SrCl₂-H₂O at 373 K belong to the simple co-saturated type,and no double salt or solid solution was formed in the equilibrium solid phases.The phase diagram of the ternary system MgCl₂-SrCl₂-H₂O contains two invariant points,three solubility curves and three crystallization zones?where the solids are MgCl₂·6H₂O,SrCl₂·2H₂O and SrCl₂·H₂O?.The phase diagram of the system at 373 K and the phase diagrams at 348 K and 323 K have been compared and discussed.The phase diagram of the ternary system CaCl₂-SrCl₂-H₂O contains one invariant point,two solubility curves and two crystallization zones,which are saturated with CaCl₂·2H₂O and SrCl₂·H₂O.The phase diagrams of the quaternary systems NaCl-KCl-SrCl₂-H₂O and NaCl-MgCl₂-SrCl₂-H₂O at 373 K are simple co-saturated type.There is neither double salt nor solid solution formation.The phase diagram of the quaternary system NaCl-KCl-SrCl2-H2O contains one invariant point,three univariant curves and three crystallization fields,which are corresponding to NaCl,KCl and SrCl2·2H2O.The phase diagram of the quaternary system NaCl-MgCl₂-SrCl₂-H₂O contains two invariant points,five univariant curves and four crystalline regions?where the solids are NaCl,MgCl₂·6H₂O,SrCl₂·2H₂O and SrCl₂·H₂O,respectively?.The quaternary systems KCl-MgCl2-SrCl2-H2O and KCl-CaCl2-SrCl2-H2O both have double salt formation at 373 K,but no solid solution was formed.The double salt KCl·MgCl₂·6H₂O?Car?was formed in the quaternary system KCl-MgCl₂-SrCl₂-H₂O.The phase diagram of this system contains three invariant points,seven univariate curves and five crystallization zones,which are corresponding to KCl,MgCl₂·6H₂O,SrCl₂·2H₂O,SrCl₂·H₂O and Car,respectively.In the quaternary system KCl-CaCl₂-SrCl₂-H₂O,a complex salt KCl·CaCl₂?Chle?was formed.The phase diagram of this system contains two invariant points,five univariate curves and four crystalline regions?where the solid phases are KCl,CaCl₂·2H₂O,SrCl₂·H₂O and Chle,respectively?.Double salt KCl·MgCl₂·6H₂O was generated in the quinary system NaCl-KCl-MgCl₂-SrCl₂-H₂O?saturated with NaCl?,and there was no solid solution formation.The phase diagram of this quinary system contains three invariant points,seven univariate curves and five crystallization zones?where the solid phases are KCl,MgCl₂·6H₂O,SrCl₂·2H₂O,SrCl₂·H₂O and Car in the condition of NaCl saturated?.