Synthesis And Lithium Extraction Of Acid Base Controlled Phase Transfer Ionic Liquids

In recent years,the lithium battery market has expanded greatly,and the extraction of lithium is very important to meet the market demand.At present,the typical extraction separation system of lithium is tributyl phosphate（TBP）-Fe Cl₃-sulfonated kerosene extraction system,but there are the following problems in the process of extraction separation of lithium:（1）easy to form the third phase;（2）environmental pollution;（3）need to add synergistic agent.In order to solve these problems,four kinds of dibutyl phosphate ionic liquids with different carbon chain lengths were synthesized,namely 1-butyl-3-methylimidazolium dibutyl phosphate[Bmim][DBP],1-butyl-3-ethylimidazolium dibutyl phosphate[Beim][DBP],1-butyl-3-propylimidazolium dibutyl phosphate[Bpim][DBP]and 1-butyl-3-butylimidazolium dibutyl phosphate[Bbim][DBP],and their physicochemical properties were studied.It was used in the study of lithium extraction;the best conditions of lithium extraction by[Bmim][DBP]were explored,and the extraction effects of four kinds of ionic liquids were compared;and the mechanism of lithium extraction by[Bmim][DBP]was preliminarily studied.This paper mainly includes the following four parts:（1）TBP reacted with 1-methyl imidazole,1-ethyl imidazole,1-propyl imidazole and n-butyl imidazole to form four kinds of tributyl phosphate ionic liquids with different carbon chain lengths,namely[Bmim][DBP],[Beim][DBP],[Bpim][DBP]and[Bbim][DBP].The four ionic liquids were characterized.（2）The physicochemical properties of four kinds of ionic liquids were determined:the viscosity was below 2.50 Pa·S.The ionic liquids were titrated by G20s compact titrator and the dissociation constants were obtained.The extraction system has the property of acid-base regulating the phase transfer of ionic liquid.In the extraction section,the ionic liquid is fully complexed with lithium ion.In the phase separation section,the ionic liquid is separated from the aqueous phase and enters the organic phase by acid regulation.It not only ensures the efficient extraction of lithium,but also greatly reduces the dissolution loss of ionic liquid.（3）The organic phase of ionic liquid-dichloromethane and the aqueous phase of lithium chloride solution were used to extract lithium.Under the optimal conditions of 25℃,30 min extraction time,0.50 g/L Li⁺concentration,2/1 volume ratio of organic phase and water phase（O/A）,0.80 mol/L H⁺concentration and the volume ratio of ionic liquid[Bmim][DBP]to dichloromethane（DCM）was 4:6,the maximum extraction rate of lithium by[Bmim][DBP]can reach 70.12%.The extraction efficiency of four kinds of ionic liquids for lithium was compared:[Bmim][DBP]>[Beim][DBP]>[Bpim][DBP]>[Bbim][DBP],that is,the longer the carbon chain,the lower the extraction efficiency of lithium.（4）The mechanism of lithium extraction by[Bmim][DBP]was studied.The extraction process does not conform to the cation exchange mechanism,and the mass spectrum analysis shows that the anion[DBP]^-of[Bmim][DBP]is combined with Li⁺in a stoichiometric ratio of 2/1,which is supposed to be a neutral complex mechanism.