Preparation Of Ionic Liquid Extraction Gel Membrane And Its Application In The Removal Of Pb²⁺ From Water

The demand of lead in the industry is increasing continuously,which is followed by serious lead pollution.The research on efficient recovery of lead from lead-containing wastewater has both environmental and economic benefits.In this project,ionic liquid(IL)was introduced to the gel layer formed on the outer surface of a hydrophilic membrane support to prepare the ionic liquid extraction gel membrane(IL-EGM).It was used in extraction and recovery of Pb²⁺from water.The extraction efficiency of Pb²⁺by IL-EGM prepared at different reacting conditions was studied and the preparing condition was optimized.Firstly,the extraction efficiencies of Pb²⁺,Cd²⁺and Cu²⁺by 1-octyl-3-methylimidazol-hexafluorophosphate([Bmim][PF₆]),1-octyl-3-methylimidazol-hexafluorophosphate([Omim][PF₆])and 1-octyl-3-methylimidazol-tetrafluoroborate([Omim][BF₄])in the presence of the complexing agent dithizone were studied respectively.According to their extraction efficiencies,[Bmim][PF₆]was finally selected as the extraction solvent,and Pb²⁺as the target metal ion.Both the extraction and stripping conditions and efficiencies of lead separation by dithizone-[Bmim][PF₆]from water were investigated.The influences of temperature,complexing agent content,p H value of the liquid phase,the volume ratio of the extraction system to the water phase as well as interference ions on the extraction efficiency were studied.Furthermore,the screening of the stripping agent was carried out.The influences of the stripping concentration and operating temperature on the stripping efficiency were investigated,and finally,the best stripping conditions were obtained.The research results showed that at the extraction conditions of 35?,p H 6,complexing agent dithizone content 0.72%,extraction system and water phase volume ratio of 1/4,the extraction rate of lead ions from water is as high as 98.0%.In this system,the existence of interference ions has less effect on the extraction rate of Pb²⁺,and it can be used for selective separation of lead from various metal ions in wastewater.At 35?,using1mol·L^-1 HNO₃as the stripping solution,the above-mentioned loaded extraction liquid was effectively extracted at a rate of 97.0%.Finally,the mass transfer efficiencies of the multiple extraction/stripping were investigated.The results showed that the extraction rate of the system still reached 80.0%after three times of extractions,and the stripping rate was 65.0%Secondly,the IL-EGM was prepared by coating a layer of IL containing gel on the outer surface of PVDF hydrophilic hollow fibers.The prepared IL-EGM was characterized by a variety of analytical methods and compared with PVDF support membranes to obtain the basic physical and chemical properties of IL-EGM.The results showed that the addition of dithizone-[Bmim][PF₆]did not affect the formation of the gel.The gel was uniform and integral.The PVDF support and IL-EGM surface section were characterized by various analytical testing methods such as pure water flux,contact angle,AFM and SEM.,which proved that the coated gel layer on the support is continuous,dense and complete.The IL-EGM surface has good hydrophobicity and can be used to effectively separate the water phases on both sides of the IL-EGM.Finally,the effects of the preparation conditions of IL-EGM on the extraction and back extraction efficiency and mass transfer stability of the gel were analyzed through the simultaneous extraction and back extraction experiments of the two-way countercurrent circulation system.The optimal extraction efficiency and stability of IL-EGM were achieved when the IL volume percentage is 10%,the dithizone content is5.8%,the IL-EGM the ratio of 10:2.0:0.20 for PDMS/TEOS/DBTL,coating time is30 min,the total extraction rate is 46.5%,the stripping rate is 37.6%,and the flux decay rate is 31.4%in 6 h.