Research On The Adsorption Performance And Mechanism Of Arsenic And Cadmium In Water By Novel Iron And Manganese Oxides

How to deal with the pollution of arsenic and cadmium in water with high efficiency and environmental protection has been a hot research topic at home and abroad all the time.In view of the current severe and urgent situation of arsenic and cadmium pollution in water environment,a new type of Fe-Mn material with strong affinity to arsenic was prepared by combining with the widely concerned adsorption technology,and further research was carried out.The main work includes optimizing the synthesis process of Fe-Mn Binary Oxides?FMBO?,preparing three kinds of stabilization adsorption materials,starch FMBO,gelatin-FMBO and CMC FMBO by using starch,gelatin,and sodium carboxymethyl cellulose?CMC?.And starch-FMBO material was selected to further study the adsorption mechanism and environmental factors.Finally,in order to make starch-FMBO have better adsorption performance in more complex solution environment,this paper considered the composite polluted environment with the coexistence of arsenic and cadmium,by modifyng the surface of starch-FMBO?SFMBO?to obtain Ca-SFMBO.A novel starch-FMBO was synthesized by optimizing synthesis process?Fe/Mn ratio=1.00-2.00,pH=2.0?.Starch,as a synthetic stabilizer,plays an important role in controlling the particle size.Due to its large specific surface area and loose structure,the arsenic removal efficiency of starch-FMBO increased by 150%compared with that of FMBO,and the adsorption capacity of As?III?reached 161.3 mg/g.Based on the preparation method of starch-FMBO,CaCO₃ was used for chemical binding modification on the surface of SFMBO.The modified material could increase the adsorption capacity of Cd?II?in single-metal Cd solution by 35.9%.In the material adsorption performance experiment,the optimal co-adsorption pH of As?III?-Cd?II?was 6.0,and Ca-SFMBO could stabilize the pH of As?III?solution,Cd?II?solution or As?III?-Cd?II?solution within a wide pH range.In the dual-adsorption system,the adsorption of As?III?to low Cd?II?concentration was enhanced by 33.3%,while the adsorption of As?III?was inhibited with the increase of Cd?II?concentration.The increase of As?III?concentration would promote the increase of Cd?II?adsorption,up to nearly doubling.This is because H₂AsO₄^-and HAsO₄^2-was partly adsorbed on the surface of Ca-SFMBO and generated new anion adsorption sites.The cation on the surface of Cd?II?produces an electrostatic attraction,and finally,a new stable bond,ternary complex,was formed at the adsorption site.Scanning electron microscopy?SEM?,energy dispersive spectroscopy?EDS?,X-ray diffraction analysis?XRD?and other microscopic characterization techniques were used to analyze the adsorption materials such as FMBO,starch-FMBO and Ca-SFMBO prepared in the laboratory.The prepared adsorption materials were all amorphous oxide particles.According to X-ray photoelectron spectroscopy?XPS?analysis,hydroxyl functional groups played an important role in the adsorption of As?III?by iron and manganese materials.The hydroxyl groups of Mn?IV?and Fe?III?were closely related to oxidation of As?III?and adsorption of As?III?/As?V?,respectively.For Ca-SFMBO,the addition of calcium carbonate during the surface modification process destroyed the acid-base balance in the synthesis process of starch-FMBO,resulting in the generation of heterogeneous Ca-SFMBO particles and the reduction of Mn?IV?oxidation rate.In the As?III?-Cd?II?co-adsorption experiment,the analysis of Fourier transform infrared spectroscopy?FTIR?and EDS predicted the formation of Fe-As-Cd ternariate complex on the surface of Ca-SFMBO.In conclusion,,the new iron and manganese materials prepared in this paper have good application prospects,worthy of further research and exploration,in the treatment of arsenic pollution or arsenic and cadmium co-polluted wastewater.