Competitive Adsorption Of Chitosan Sorptive Membrane For The Removal Of Heavy Metal Ions From Wastewater

As the only basic polysaccharide in nature,there are primary hydroxyl,secondary hydroxyl and amino/acetyl functional groups in the structure of chitosan,which make it have the highest metal coordination ability when adsorbed in natural polymer-s.Meanwhile,the CS polymer chain can be decomposed into CO,H,O,CH,humus and other natural substances by microbial enzymes in the bioactive environment,avoid-ing secondary pollution and having good biocompatibility,repeatability and degradabil-ity.If the membrane separation technology is combined with chitosan and its derivative-s,it can give full play to the technological advantages of membrane water treatment and make the heavy metal wastewater treatment process more efficient and environ-mentally friendly.Based on this,this study intends to prepare chitosan membrane by sol-gel method,and recycle four heavy metal ions of Cu²⁺,Cd²⁺,Ni²⁺and Pb²⁺in electr-onic waste solution.In this experiment,chitosan casting film solution was prepared by sol-gel method,then chitosan adsorption film was prepared by flow casting film method,and then immersed in 1 mol/L Na OH solution for solidification operation,water washing,air drying,and ready for use.The prepared CS film material was characterized by infrared spectroscopy,thermogravimetric analysis,XRD and SEM,and the functional group structure,thermal stability and surface morphology of the adsorbed heavy metals on CS film material were studied.SEM and EDS were used to test the membrane surface structure before and after adsorption.The effects of adsorption temperature,p H value,adsorption time and initial concentration of metal ions on the adsorption of Pb²⁺,Cu²⁺,Ni²⁺and Cd²⁺single ions by chitosan membrane were investigated by single factor experiment.The optimal adsorption conditions for each ion were determined,so as to further study the adsorption mechanism of heavy metal ions.To be specific,the quasi-first-order kinetic model and quasi-second-order kinetic model of each ion on the membrane were fitted by using the data of adsorption time to explore whether the membrane adsorption process is physical adsorption or chemical adsorption.The Freu-ndlich and Langmuir adsorption isotherm models were fitted with the initial concen-tration data to explore the adsorption mechanism.Temperature adsorption data were used to determine whether the adsorption process was endothermic.Five desorption operations were carried out with the help of hydrochloric acid(HCl)to study the desorp-tion effect and repeat utilization rate of the membrane after adsorption of four ions in the optimal conditions obtained in the experiment.According to the adsorption results of single ion solution system,a membrane was selected for competitive adsorption study of mixed ion solution system.That is,binary(Cu²⁺/Pb²⁺,Cu²⁺/Ni²⁺,Pb²⁺/Ni²⁺,Cu²⁺/Cd²⁺),ternary(Cu²⁺/Pb²⁺/Ni²⁺,Cu²⁺/Cd²⁺/Ni²⁺),quaternary(Cu²⁺/Pb²⁺/Ni²⁺/Cd²⁺)and simulated electroplating industrial wastewater(Na⁺/Ca²⁺/Mg²⁺/Cu²⁺/Pb²⁺/Ni²⁺/Cd²⁺/Cr³⁺)were studied,and the influence of solution acidity,adsorption time,initial ion concentration,adsorption temperature and adsorp-tion state was studied.By comparing the adsorption capacity of each ion and the adsorption capacity of single ion in the mixed system,the internal influence of each ion adsorption process was judged.The experimental results show that the adsorption capacity of each ion system follows the following rules:Pb²⁺>Cu²⁺?Ni²⁺>Cu²⁺?Pb²⁺>Ni²⁺?Cu²⁺>Cd²⁺?Cu²⁺>Pb²⁺>Ni²⁺?Cu²⁺>Cd²⁺>Ni²⁺?Cu²⁺>Ni²⁺>Pb²⁺>Cd²⁺?Cu²⁺>Cr³⁺>Pb²⁺>Ca²⁺>Ni²⁺>Mg²⁺>Cd²⁺.