Experiments And Theoretical Calculations Of Solid-liquid Equilibria In Li⁺,Na⁺(K⁺,Mg²⁺),Sr²⁺//Cl^--H₂O Systems And Its Related Subsystems At 308K

The underground brine in Sichuan Basin is very rich and is an important liquid mineral resource.In order to achieve the effective exploitation and utilization of the resource,the stable phase equilibrium in Li⁺,Na⁺(K⁺,Mg²⁺),Sr²⁺//Cl^--H₂O systems and its related subsystems were studied at 308 K by using isothermal dissolution equilibrium method in this paper.It mainly consists of four ternary subsystems:LiCl-SrCl₂-H₂O,NaCl-SrCl₂-H₂O,KCl-SrCl₂-H₂O and MgCl₂-SrCl₂-H₂O,and three quaternary systems:LiCl-NaCl-SrCl₂-H₂O,LiCl-KCl-SrCl₂-H₂O and LiCl-MgCl₂-SrCl₂-H₂O.On this basis,Pitzer model was used to predict the solubility of some containing lithium or containing strontium systems,there are mainly partial lithium-containing systems at 298 K,and strontium-containing systems NaCl-SrCl₂-H₂O at 308 K and KCl-SrCl₂-H₂O under multi-temperature conditions.In the experimental study of LiCl-SrCl₂-H₂O and MgCl₂-SrCl₂-H₂O systems,both LiCl and MgCl₂ have very strong salting-out effect on SrCl₂.There are two invariant points,three univariate curves and three solid phase crystallization zones.The three solid phase crystallization zones in LiCl-SrCl₂-H₂O system are LiCl·H₂O,SrCl₂·6H₂O and SrCl₂·2H₂O,and the three solid phase crystallization zones in MgCl₂-SrCl₂-H₂O system are MgCl₂·6H₂O,SrCl₂·6H₂O and SrCl₂·2H₂O.In NaCl-SrCl₂-H₂O and KCl-SrCl₂-H₂O systems,it was found that SrCl₂ has strong salting out effect on NaCl and KCl.There is only one invariant point,two univariate curves and two solid-phase crystallization zones.The two solid-phase crystallization zones in NaCl-SrCl₂-H₂O system are NaCl and SrCl₂·6H₂O,and the two solid-phase crystallization zones in KCl-SrCl₂-H₂O system are KCl and SrCl₂·6H₂O.In addition,the multi-temperature comparison of each system was also discussed in this paper.The results show that there are two invariant points at 273 K,298 K,308 K and 313 K in LiCl-SrCl₂-H₂O system,and there is co-crystallization of SrCl₂·6H₂O and SrCl₂·2H₂O.In the NaCl-SrCl₂-H₂O system,the mass fraction of sodium chloride in the equilibrium liquid phase first decrease and then slightly increase,while the mass fraction of strontium chloride always increases with the increase of temperature.In the KCl-SrCl₂-H₂O system,before the dehydration of SrCl₂·6H₂O,the mass fraction of potassium chloride in the equilibrium liquid did not change significantly with the increase of temperature.In the MgCl₂-SrCl₂-H₂O system,the mass fraction of strontium chloride and magnesium chloride in the equilibrium liquid phase increased with increasing temperature.In the experimental study,no double salt or solid solution is formed in the equilibrium solid phase of the quaternary systems LiCl-NaCl-SrCl₂-H₂O and LiCl-KCl-SrCl₂-H₂O,and there are two invariant points,four solid phase crystallization zones and five univariate curves.The four solid phase crystallization zones in LiCl-NaCl-SrCl₂-H₂O system are LiCl·H₂O,NaCl,SrCl₂·6H₂O and SrCl₂·2H₂O,and the four solid phase crystallization zones in LiCl-KCl-SrCl₂-H₂O system are LiCl·H₂O,KCl,SrCl₂·6H₂O and SrCl₂·2H₂O.The double salt lithium carnallite（LiCl·MgCl₂·H₂O）is formed in the quaternary system LiCl-MgCl₂-SrCl₂-H₂O,there are two invariant points,five solid phase crystallization zones（LiCl·MgCl₂·H₂O,LiCl·H₂O,MgCl·6H₂O,SrCl₂·6H₂O and SrCl₂·2H₂O）and six univariate curves.There is a dissolution equilibrium univariate curve of strontium chloride hexahydrate and strontium chloride dihydrate.In the theoretical calculation of some lithium-containing and strontium-containing systems,the Pitzer model was used to predict the solubilities of lithium-containing systems at 298 K in the paper.The detailed solubility data were given and compared with the experimental data.It was found that the calculated data were in good agreement with the experimental values.For the theoretical calculation of NaCl-SrCl₂-H₂O at 308 K and KCl-SrCl₂-H₂O under a multi-temperature condition,the single salt parameters and mixed ions interaction parameters that have not been reported in the literature were fitted in this paper:θ_Na,Sra,Sr andΨ_Na,Sr,Cla,Sr,Cl at 308K,β^（0）,β^（1）,C^?,θ_K,Sr,Sr andΨ_K,Sr,Cl under the conditions of 273 K,288 K,318 K and323 K.On this basis,the solubilities of systems NaCl-SrCl₂-H₂O at 308 K and KCl-SrCl₂-H₂O at 273 K,288 K,298 K,308 K,318 K and 323 K were predicted.The calculated values of invariant points were compared with experimental values and found to be in good agreement with the experimental data.