Study On Treatment Of Copper-Containing Wastewater By Ionic Liquids And Physicochemical Properties Of Ionic Liquids Solution

The pollution of heavy metal wastewater has been paid much attention by many researchers.Although there are many methods of heavy metal treatment in recent years,there are still many drawbacks in the application of these methods,which restrict their wide industrial application.Because of its persistent toxicity,heavy metal wastewater is still one of the most important sources of environmental pollution.Ionic liquids are used as organic solvents in the treatment of heavy metal wastewater.They are not only simple to operate,but also have high extraction and separation efficiency.At the same time,the ionic liquids after extraction can also be recycled.The extraction of copper ions by hydrophobic room temperature ionic liquids containing bis（trifluoromethyl）sulfonyl imide anions（[NTf₂]-）,especially ionic liquids containing nitrile functional groups,has rarely been reported at home and abroad.（1）In this paper,the hydrophobic ionic liquids 1-butyl-3-methylimidazolium bis[（trifleoromethyl）sulfonyl]imide（[BMIM][NTf₂]）,1-butyl-3-methylimidazolium bis[（trifleoromethyl）sulfonyl]imide（[BMIM][PF₆]）,1-acetonitrile-3-methylimidazolium bis[（trifluoromethyl）sulfonyl]imide（[MCNMIM][NTf₂]）,1-butyronitrile-3-methylimidazolium bis[（trifleoromethyl）sulfonyl]imide（[PCNMMIM][NTf₂]）were firstly established as extractants,and copper reagent（DDTC）was used as chelating agent.The method of liquid-liquid extraction of copper ion in water was studied.At last,an ideal extraction effect was obtained,with the extraction rate of 99.5%.A certain amount of common interfering ions would not affect the extraction of copper ions.At the same time,the method was also used to investigate the determination of copper in actual water samples,and satisfactory results were obtained.The experimental results show that the optimum p H value of each extraction system was in the range of 4-6,the amount of ionic liquid was 225μL,the extraction time was 3 minutes,the DDTC concentration of 1300μL was 0.2g/L,the centrifugal speed was 3000 rpm,the centrifugal time was 4 minutes,and all the extractions were operated at 25-30℃.The extraction mechanism of the system was preliminarily discussed.It was found that the selected ionic liquids played a synergistic role in the extraction of copper ions from water.（2）Copper ions extracted from organic phase were stripped,and various conditions of stripping were investigated.The final choice of 2 mol/L nitric acid solution as stripping agent was determined,reduction experiments at room temperature（25-30℃）,the back-extraction time is 10 min,the optimum ratio of ionic liquids to nitric acid solution is 1:2.After five cycles of recycling of recovered ionic liquids,the extraction rate of copper ions in aqueous solution is still about 98%,and the properties of ionic liquids have not changed significantly,and the extraction effect is stable.（3）Considering the relatively large viscosity of ionic liquids,some applications are still limited.In order to reduce the viscosity and expand the database,Finally,the physicochemical properties of the binary system consisting of ionic liquid 1-ethyl-3-methylimidazole bistrifluoromethylsulfonate imine（[EMIM][NTf₂]）,1-butyl-3-methylimidazole bistrifluoromethylsulfonate imine（[BMIM][NTf₂]）and diethyl carbonate（DEC）and dimethyl carbonate（DMC）were investigated.The experimental data show that the introduction of solvents greatly reduces the viscosity of ionic liquids.For the same ionic liquids or solvents with the same molar fraction,the density decreases with the increase of the cationic alkyl chain length,while the change trend of the viscosity is contrary to the density.Through calculation,the excess molar volume and excess molar viscosity are negative in the whole concentration range.The interaction between ions,especially hydrogen bonding,has an important influence on the viscosity of ionic liquids.This provides experimental data for the study of ionic liquids with high viscosity in extraction.According to the research results at this stage,this binary system has a certain practical significance in the study of copper ion extraction in water.