Studies On Phase Equilibria Of System Li⁺, Na⁺?K⁺?,Sr²⁺//Br-H₂O And Partial Related Subsystems At Multi-temperature

The underground brine in the Sichuan Basin has the characteristics of rich storage and excellent quality,and is widely distributed.It is a unique and excellent mineral resource in Sichuan,and its prospects for comprehensive development and utilization are very broad.The comprehensive utilization and development process of underground brine resources in the Sichuan Basin requires guidance from phase diagrams.The phase diagram is used to analyze the rule of solubility variation and precipitation areas of various salts,so as to effectively produce.In this paper,the multi-temperature phase equilibria of system Li⁺,Na⁺?K⁺?,Sr²⁺//Br^--H₂O and partial related subsystems of the underground brine in Sichuan Basin were studied experimentally.The related phase equilibria are studied by method of the isothermal dissolution equilibrium,which includes the ternary system Li Br–Sr Br₂–H₂O at 273 K,308 K and323 K,the ternary system Na Br–Li Br–H₂O at 323 K,the quaternary system Na Br–Li Br–Sr Br₂–H₂O at 308 K and the quaternary system Na Br–Li Br–Sr Br₂–H₂O and KBr–Li Br–Sr Br₂–H₂O at 323 K.In addition,the phase diagram and density diagram of the corresponding system were drawn by using the solubility data obtained in analytical experimental tests.The equilibrium solids phase of invariant points are identified by the method of X-ray powder diffraction,and the composition of solid phase in ternary system are also analyzed by the Schreinemakers wet residue method.The stable phase equilibria of the ternary system Li Br–Sr Br₂–H₂O at 273 K,308K and 323 K and Na Br–Li Br–H₂O at 323 K all belong to hydrate type I saturation,and there is no solid solution,nor double salts formation.The ternary system Li Br–Sr Br₂–H₂O at 273 K includes one invariant point,two univariate curves,two crystallization zones where the solids are Li Br·2H₂O and Sr Br₂·6H₂O,respectively.The ternary system Li Br–Sr Br₂–H₂O at 308 K and 323 K all contain two invariant points,three univariant curves and three crystallization fields,which are corresponding to Li Br·2H₂O,Sr Br₂·2H₂O and Sr Br₂·6H₂O at 308 K and Li Br·H₂O,Sr Br₂·2H₂O and Sr Br₂·6H₂O at 323 K,respectively.In this paper,the stable phase equilibrium of the ternary system Li Br–Sr Br₂–H₂O at different temperatures are compared in figure and analyzed the rule of solubility variation.It shows that Li Br has a strong salting out effect on Sr Br₂.The ternary system Na Br–Li Br–H₂O is consists of one co-saturation point,two univariate curves and two crystallization fields,which correspond to Li Br·H₂O and Na Br.The quaternary system Na Br–Li Br–Sr Br₂–H₂O at 308 K has no double salt and solid solution,which is hydrate type?saturation.The quaternary system has three invariant points,seven univariant curve and five crystallization fields corresponding to sodium bromide?Na Br?,sodium bromide dihydrate?Na Br·2H₂O?,lithium bromide dihydrate?Li Br·2H₂O?,strontium bromide dihydrate?Sr Br₂·2H₂O?and strontium bromide hexahydrate?Sr Br₂·6H₂O?.Lithium bromide dihydrate?Li Br·2H₂O?has smaller crystallization field,which means it has the highest solubility.The quaternary system Na Br–Li Br–Sr Br₂–H₂O at 323 K belongs to hydrate type I saturation,which has no double salt and solid solution.In the phase diagram,the quaternary systems Na Br–Li Br–Sr Br₂–H₂O at 323 K includes two invariant points,five univariant curve and four crystallization fields corresponding to sodium bromide?Na Br?,lithium bromide monohydrate?Li Br·H₂O?,strontium bromide dihydrate?Sr Br₂·2H₂O?and strontium bromide hexahydrate?Sr Br₂·6H₂O?.The crystallization region of Na Br is the largest,indicating its solubility is the smallest and it is the easiest to crystallize from the saturated solution.The quaternary system KBr–Li Br–Sr Br₂–H₂O at 323 K belongs to hydrate type I saturation,which has no double salt and solid solution.The quaternary systems KBr–Li Br–Sr Br₂–H₂O at 323 K includes two invariant points,five univariant curve and four crystallization fields corresponding to potassium bromide?KBr?,lithium bromide monohydrate?Li Br·H₂O?,strontium bromide dihydrate?Sr Br₂·2H₂O?and strontium bromide hexahydrate?Sr Br₂·6H₂O?.The crystallization region of KBr is the largest,indicating its solubility is the smallest and it is the easiest to crystallize from the saturated solution.