Studies On Phase Equilibria Of The Quaternary System Li⁺,Na⁺?K⁺?,Sr²⁺//Br^--H₂O And Some Sub-systems Containing Lithium At 288 K

The Sichuan Basin,which is rich in underground brine resources,has unique mineral resource advantages.In order to comprehensively develop and utilize the underground brine resources,and further promote the development of chemical industry of brines,it is necessary to carry out phase equilibrium research to grasp the basic mineralization rules of underground brine salts in the Sichuan Basin.Therefore,according to the composition of the underground brine in the Sichuan Basin,the isothermal dissolution method was used to study the phase equilibria of the related sub-systems containing lithium,strontium and bromine.In this paper,the phase equilibrium experimental research was carried out on quaternary systems Li⁺,Na⁺?K⁺?,Sr²⁺//Br^--H₂O and some lithium-containing sub-systems at 288 K.The contents of research include ternary systems Li Br-NaBr-H₂O,Li Br-KBr-H₂O,and Li Br-SrBr₂-H₂O;quaternary systems Li Br-NaBr-KBr-H₂O,Li Br-NaBr-SrBr₂-H₂O,and Li Br-KBr-SrBr₂-H₂O.Among them,experimental studies of the stable phase equilibria of the ternary system Li Br-NaBr-H₂O at 273 K and 308 K were also carried out.The solubilities and density data for each salt were determined by chemical analysis method and flame atomic absorption spectrometry method.Based on the experimentally measured data,the relevant phase diagrams and density composition diagrams of the ternary and quaternary systems were drawn.The X-Ray powder crystal diffraction method was used to identify the equilibrium solid phase,and the ternary systems were also verified by the wet slag method.The experimental results of ternary system Li Br-NaBr-H₂O at 273 K,288 K and308 K show that the systems were hydrate type II,without double salt or solid solution formation.NaBr and NaBr·2H₂O appear in the equilibrium solid phases.Due to the dehydration of NaBr·2H₂O,there are two invariant points in the multi-temperature stable phase diagram.Three univariate curves also appear in the system,corresponding to three crystalline regions Li Br·2H₂O,NaBr,and NaBr·2H₂O.For experimental study on the ternary system Li Br-NaBr-H₂O at 273 K,288 K and 308 K,it was also found that the percentage of NaBr in the equilibrium liquid phase changes less.The increase and decrease in temperature have little effect on the solubility of NaBr.And the multi-temperature phase diagrams of the ternary system Li Br-NaBr-H₂O are analyzed and discussed.The experimental studies of ternary systems Li Br-KBr-H₂O and Li Br-SrBr₂-H₂O at 288 K indicate that the phase diagrams of the two systems above have no double salt or solid solution formation,and the equilibrium solid phases were Li Br·2H₂O+KBr and Li Br·2H₂O+SrBr₂·6H₂O,respectively.There is no hydrate salt or corresponding anhydrous salt,and both belong to hydrate type I saturated system.And the multi-temperature phase diagrams of ternary system Li Br-KBr-H₂O are analyzed and discussed.The stable phase diagram of quaternary system Li Br-NaBr-KBr-H₂O at 288 K has hydrate salts and corresponding anhydrous salts.There are two invariant points and five univariate curves.Li Br·2H₂O,NaBr,NaBr·2H₂O,and KBr are the four crystallization regions in this system.There is no double salt or solid solution,this system belongs to hydrate type II saturation system.It can be found that both NaBr and KBr dissolve very little in the presence of Li Br,which indicates that Li Br has salting out effect on both NaBr and KBr.The quaternary system Li Br-NaBr-SrBr₂-H₂O has hydrate salts at 288 K,which are Li Br·2H₂O,NaBr·2H₂O,and SrBr₂·6H₂O.The stable phase diagram consists of two invariant points,five univariate curves,and four crystallization regions.Among them,the four crystalline regions are Li Br·2H₂O,NaBr,NaBr·2H₂O,and SrBr₂·6H₂O,respectively.From the univariate curves of the quaternary stable phase diagram,it can be found that the salting out effect of Li Br on SrBr₂ is significantly less than that on NaBr.The experimental study of the quaternary system Li Br-KBr-SrBr₂-H₂O at 288 K indicate that SrBr₂·6H₂O was not dehydrated,without double salt or solid solution formation.It belongs to a simple co-saturated system.The three univariate curves in the phase diagram intersect at one point,which is the invariant point Li Br·2H₂O,KBr and SrBr₂·6H₂O are the three crystallization regions in this system.