Study On The Selective Adsorption Of Heavy Metal Ions By Modified Chitosan Membranes

With the gradual implementation of the international"double carbon"target in the world,new energy technology,as one of the most effective carbon reduction technologies,has been developing rapidly in recent years.As a major component of new energy technology,the production capacity of power battery is also increasing year by year.A large amount of wastewater containing heavy metal ions is discharged during the manufacturing and recycling process of new energy power batteries,which brings increasingly serious pollution and hazards to the ecosystem and human health.If these heavy metal pollutants are not effectively treated in time,they will directly threaten human survival.The main focus of this investigation is the preparation of modified chitosan membrane materials for the selective removal of heavy metal ions from wastewater,with the following results.（1）Ethylenediaminetetraacetic acid（EDTA）modified chitosan membranes（ETMCSMs）were prepared by sol-gel method,for which EDTA ligands were immobilized on chitosan（CS）polymer matrix,and several characterization and adsorption performance studies were carried out on the membrane materials.The effects of p H,contact time,ambient temperature and metal concentration on the adsorption performance of membrane materials were investigated by single-factor experiments,and the experimental results were analyzed by theoretical models.The results showed that the adsorption of modified ETMCSMs on Pb²⁺and Cu²⁺was greatly improved,and the maximum adsorption amounts of ETMCSMs on Pb²⁺and Cu²⁺were9.56 mg/g and 11.43 mg/g,respectively,while the best adsorption effect was achieved at p H 5,and the adsorption equilibrium was reached at about 60 hours of submersion.The kinetics and thermodynamics of adsorption of Cu²⁺and Pb²⁺by ETMCSMs were investigated,and it was found that the kinetics of adsorption of both ions by ETMCSMs were in accordance with the Lagergren quasi primary rate adsorption model,and the linear correlation coefficients of the models were all greater than 0.9,but they were also affected by the chemisorption mechanism.the thermodynamics of adsorption of both heavy metal ions by ETMCSMs were in accordance with the Langmuir isotherm,and the linear correlation coefficients of the regression equations were all greater than 0.9for unimolecular layer adsorption.In addition,the linkage of EDTA to chitosan in this way was not secure,and the branched chains would gradually fall off at temperatures above 35℃,leading to poor adsorption.（2）Novel polyethyleneimine（PEI）-modified chitosan-based hybrid membranes（PMCHMs）were prepared by a soft chemical method,in which unmodified chitosan（CS）was first reacted with PEI to form CS-PEI precursors.Later,this CS-PEI precursor was mixed with silica gel to form a membrane solution of PMCHMs.Finally,PMCHMs were obtained by phase transformation.The multicomponent adsorption of Pb²⁺,Cu²⁺and Ni²⁺on PMCHMs in binary solutions of Pb²⁺&Cu²⁺and Pb²⁺&Ni²⁺,ternary solutions of Pb²⁺,Cu²⁺and Ni²⁺,and five-membered mixed solutions of Pb²⁺,Cu²⁺,Ni²⁺,Cd²⁺and Cr³⁺were investigated.The calculations of the effective diffusion coefficient,distribution coefficient and selectivity coefficient showed that the adsorption of Pb²⁺on PMCHMs had excellent selectivity in mixed polymetallic solutions.And the calculation of activation energy proved that the adsorption of Pb²⁺,Cu²⁺and Ni²⁺on PMCHMs was a physical adsorption process.Furthermore,the mechanistic analysis shows that the adsorption of Pb²⁺on PMCHMs can be described by the Lagergren quasi-second-order kinetic model and the Langmuir or Freundlich isothermal equation.The intraparticle diffusion process is specifically discussed.Desorption experiments demonstrate that HCl is a good desorbent for metals on PMCHMs,with membrane cycle times up to 6 times.These results indicate that PMCHMs can preferentially remove Pb²⁺from metal mixture solutions and have promising applications in the treatment of waste automotive power battery metal mixture wastewater and various other metal-containing contaminated water.