| Heavy metal pollutants are characterized by non-degradability in the environment,great mobility,high concealment and strong toxicity.They can enter the human body via direct contact and food chains,seriously threatening the ecosystem and public health.For the removal of heavy metals in the environment,the magnetic biochar adsorption technique has attracted much attention because it is cost-effective,more efficient and environmental friendly.Nano zero-valent iron(nZVI)has become one of the hot materials for environmental and chemical remediation due to the high reducibility and magnetism.However,easy oxidation and agglomeration of nZVI on biochar restrained its effectiveness.In order to improve the performance of nZVI@BC,in this study,humic acid(HA)extracted from lignite was used to modify the biochar derived with kitchen waste cabbage leaves as biomass raw materials.Moreover,the synthesized novel magnetic biochar composite(HFBC)was applied as adsorbent to the removal of heavy metal Cr(Ⅵ)ions in water.The main research contents and results of this article are as follows.(1)HA-nZVI@BC composite(HFBC)was successfully prepared respectively by three synthesis methods: complexing method,coating method and one pot method.HFBC-1 obtained from complexing method displayed better properties.Humic acid contributed to the uniform distribution of nZVI particles on the surface of biochar,which effectively improved the pore structure of HFBC.The specific surface area was increased from 49.49 m2/g to 127.68 m2/g.The analysis of FTIR and XPS showed that the introduction of humic acid increased the number of functional groups-OH and-COOH on the surface of biochar,providing more adsorption sites.(2)As Cr(Ⅵ)was the target heavy metal ion,the influence of preparation,coating of HA,the initial concentration of Cr(Ⅵ),p H value,temperature,mass ratio of HA to nZVI to BC in the composite on the Cr(Ⅵ)adsorption process of HFBC-1was investigated.When the initial concentration of Cr(Ⅵ)was 150 mg/L,p H=2,humic acid: biochar: zero-valent iron(mass ratio)was 0.05:1:2,HFBC-1 dosage was1 g/L,the maximum adsorption capacity of HFBC-1 for Cr(Ⅵ)at 25°C reached140.35 mg/g and the removal rate reached 100%.The saturation magnetization of HFBC-1 was 62.38 emu/g,which was conducive to the separation and recovery after the adsorption.After four cycles,the removal rate of Cr(Ⅵ)was maintained at more than 85%.(3)The adsorption kinetics and adsorption equilibrium process of Cr(Ⅵ)on HFBC-1 were studied,and thermodynamic analysis was carried out.Langmuir and Freundlich isothermal models,pseudo-first-order,pseudo-second-order,intraparticle diffusion models,and Elovich kinetic equations were employed for the experimental data fitting.The results showed that the pseudo-second-order kinetic model can describe the adsorption kinetics of Cr(Ⅵ),indicating that the removal process of Cr(Ⅵ)was mainly controlled by the chemical adsorption rate.The correspondence of Langmuir isothermal adsorption model confirmed the single-layer adsorption on the surface of HFBC-1.SEM,XRD,FTIR and XPS detection technologies were used to characterize the surface morphology,crystal structure,surface functional groups and element morphological changes of materials to study the interfacial chemical behavior of the material surface.The analysis results revealed that the adsorption mechanism of HFBC composites for Cr(Ⅵ)included electrostatic adsorption,chemical redox and complexation reaction. |
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