Efficient And Selective Extraction And Separation Of High-Concentration Cd(Ⅱ) In Wastewater By Hydrophobic Ionic Liquids And Their Derivatives

With the rapid development of industry,cadmium has been widely used in metal smelting,mining,electroplating,battery manufacturing and other industries,and metal ions are the main pollutants in the production wastewater of these industries.Such metal ions are not biodegradable,and some are toxic and carcinogenic.If they are directly discharged without treatment,they will cause irreversible damage to the environment and organisms.Solvent extraction is the core technology of metallurgical industry and has good effect in the recovery of heavy metal ions.In this paper,cadmium in wastewater is taken as the research object,and hydrophobic ionic liquid and its derivatives are used as extractants to achieve efficient and selective extraction and separation of cadmium from high-concentration metal mixed solution.Firstly,the C₆MIm T/[C₆MIm]P_F6was used as the extraction system to achieve sustainable and highly selective extraction of Cd（Ⅱ）from high concentration solutions.By comparing[C₆MIm]BF₄and[C₆MIm]PF₆,it is found that the hydrophobicity inhibits the ion exchange between cations and Cd（Ⅱ）,which significantly reduces the loss of extractant.The C₆Mim T/[C₆Mim]PF₆system extracts Cd mainly through the coordination of C=S and Cd（Ⅱ）,which is a neutral complex.Due to the high compatibility between C₆Mim T and[C₆Mim]PF₆,C₆Mim T-Cd can be efficiently separated from the aqueous phase.When the concentration of Cd（Ⅱ）was2000 mg/L,the extraction rate could reach 89.75%.The extraction process conformed to a pseudo-second-order kinetic model.Compared with Pb,Zn,Mg,Cr,Fe,it has obvious coordination competitive advantages.The extracted Cd（Ⅱ）was isolated in the form of precipitate after back-extraction.The extraction rate of the C₆Mim T/[C₆Mim]PF₆extraction system remained unchanged after multiple extraction-stripping cycles.Secondly,using[C₆MIm][DDTC]/[C₆MIm]PF₆as extractant,the selective extraction of Zn and Cd from high concentration metal mixed solution was realized.By comparing[C₆MIm]Cl and[C₆MIm]PF₆,it is found that their extraction effect on Cd（Ⅱ）is negligible.[C₆MIm][DDTC]/[C₆MIm]PF₆system extracts Cd（Ⅱ）mainly through the coordination of[DDTC]^-and Cd（Ⅱ）to form Cd[DDTC]₂precipitation.When the concentration of Cd（Ⅱ）is lower than 1000 mg/L,the extraction rate of Cd（Ⅱ）solution by this system can reach 100%.Likewise,there is a high degree of compatibility between[C6MIm][DDTC]and[C₆MIm]PF₆,and[C₆Mim]^-and[C₆Mim]PF₆can be recovered by stripping.Compared with Pb,Mg,Cr,Fe,Zn,Cd and[C₆MIm][DDTC]have obvious competitive advantages.Furthermore,using a single hydrophobic ionic liquid[A-336][TS]as an extractant,the extraction of Pb,Zn,and Cd from a high-concentration metal mixed solution was achieved.The extraction of Cd by[A-336][TS]is mainly through the coordination of the N atom on[A-336]⁺with Cd（II）under acidic conditions to form Cd(NO₃,Cd（NO₃）to form R₄NCd（NO₃）₃,（R₄N）₂Cd（NO₃）₄,the combination of[A-336][TS]and Cd（Ⅱ）is an acidic complex.When the concentration of Cd（Ⅱ）in the solution is lower than10000 mg/L,the extraction rate can reach More than 89.75%.[A-336][TS]is extracted again after extraction-stripping,and the extraction rate still reaches 62.8%after 5 cycles.[A-336][TS]has high selectivity to Zn,Pb,Cd For Cr,Fe and Mg,Zn,Pb and Cd can be selectively extracted from mixed metal solutions.Finally,using[A-336][TS],C₆MIm T/[C₆MIm]PF₆,[C₆MIm][DDTC]/[C₆MIm]PF₆system to extract high-concentration Cd（Ⅱ）solution in turn can achieve the purpose of complete extraction and enrichment;Alternatively,three systems are used to extract the high-concentration metal mixed solution in turn,so that the three metal elements of Zn,Pb and Cd can be extracted and separated from the high-concentration metal mixed solution respectively.