Preparation Of Carbon-Iron Composite Based On Biomass And Its Application In Removal Of Cd²⁺/Pb²⁺

C-Fe₃O₄ composite material?C-Fe composite material?was prepared by pyrolysis of the mixture of wheat straw and siderite?hematite?at 500?.The MBC was characterized by XRF?FTIR,XRD,SEM,XPS and magnetic susceptibility device.We investigated the adsorption capacity and the mechanism of Cd²⁺(Pb²⁺)by C-Fe₃O₄?C-Fe?composites through batch static experiments,the conclusions are as follows:?1?The siderite was completely decomposed to Fe₃O₄ by wheat straw at 500?for one hour.FTIR showed that phenolic hydroxyl and carboxyl functional groups bound metal ions on the surface of MBC.The kinetic data of MBC were described well by pseudo-second-order model.The adsorption isotherm showed that Isothermal adsorption of Cd²⁺by MBC and BC500 was fitted well by Freundlich equation and the maximum adsorption capacity of MBC was 19.42mg·g^-1,which was superior to BC500.The adsorption velocity increased with an increase of pH in the region of 3-5 and then stabled at 5.The adsorption capacity of Cd²⁺decreased slightly when ionic strength increased from 1mmol?L^-1 to 100mmol?L^-1,while the desorption rate increased from 0.51%to 8.5%.The adsorption properties and characterization results illustrated the removal mechanism of Cd²⁺likely were through adsorption and ion exchange on the surface of MBC with high amount of functional groups.?2?The hematite has been completely reduced to zero valent iron by wheat straw at800?for two hours.The increase of pH from 2.5 to 5.0 leads to an increase of Pb?II?removal and stabled at 5.The pseudo second order kinetic model described the experimental data quite accurately.The Freundlich isotherm fitted well of the adsorption isothermal,and the maximum removal capacity of Pb²⁺by MBC2h was 196 mg·g^-1.The structural characterization performed with XRD,FTIR and XPS indicates the main surface of the nZVI before adsorption was Fe₃O₄,and FeOOH after exposed to Pb?II?solution which could induced hydrolysis of Pb²⁺.Chloride could promote the precipitation of Pb²⁺,Ca²⁺,Mg²⁺and other cations can promote the removal of Pb²⁺.MBC2h can better remove Pb²⁺under hypoxic conditions and the product is Pb?OH?Cl,the passivation of zero-valent iron reduces the removal of Pb²⁺,resulting in2PbCO₃·Pb?OH?₂ and Pb₃?CO₃?₂?OH?₂.Based on the analysis of the results obtained from the characterization techniques it is shown that Pb?II?is removed from the aqueous solution by various physicochemical processes such as adsorption and ion exchange on the surface of MBC2h with high amount of functional groups,redox reactions,surface-induced precipitation which dominates in the removal mechanism of Pb²⁺.In addition,magnetic adsorbents offered a significant advantage compared with other adsorbents in the aspect of separation from aqueous solution.