Effect Of Nano-iron-chitosan Modified Biochar Input On Soil Physicochemical Properties And Cd,Cr And Pb Morphology

In order to clarify the transformation pattern of soil heavy metal fugitive forms under the input of zero-valent iron nanocomposite chitosan modified biochar,this study was conducted on a sandy loam soil without the addition of modified biochar treatment as a control to investigate the effects of 1%～3%zerovalent iron nanocomposite chitosan modified biochar input under the contamination conditions of different concentrations of CdCl2,CrCl2 and PbCl2 solutions on soil pH,organic carbon(SOC),microbial carbon(MBC),soluble carbon(DOC),cation exchange capacity(CEC),water-stable agglomerates and distribution of heavy metal forms.To provide some theoretical basis and technical support for the remediation of contaminated soils.Future research can explore the remediation effect and mechanism research of different types and sources of heavy metal contaminated soils.The results showed that.1.for unpolluted sandy loam soils,in terms of soil physicochemical properties,the application of 1%zero-valent iron nanocomposite chitosan modified biochar significantly improved soil physicochemical properties,including 67.00%increase in large particle agglomerates,4.94%increase in soil pH,40.37%increase in CEC,11.19%increase in SOC,52.85%increase in MBC,42.11%increase in DOC 42.11%,more modified biochar input had a smaller enhancement effect.2.For sandy loam soils contaminated with high concentrations of heavy metals(Cd,Cr,Pb),the application of 3%zero-valent iron nanocomposite chitosan modified biochar was most effective in improving soil structure.Compared with the control treatment,pH increased by 10.99%～13.90%on average,CEC increased by 24.83%～37.10%on average,large particle agglomerate content increased by 7.71%～156.89%on average,and soil SOC increased by 75.63%～157.76%on average.3.The effect of zero-valent iron nanocomposite chitosan modified biochar on the remediation of heavy metals Cd>Pb>Cr.After applying 3%zero-valent iron nanocomposite chitosan modified biochar,for Cd contaminated soil,the percentage of weak acid extracted state with the largest content of Cd fugitive form was significantly reduced by 12.61%,and the percentage of residue state with the lowest content was significantly increased by 19.34%;under the condition of Pb contaminated soil,the percentage of Under the conditions of Pb-contaminated soil,the percentage of the more hazardous Pbreducible state and the weak acid-extracted state were reduced by 5.22%and 4.24%respectively,and the percentage of the stable residue state was increased by 8.12%.The application of modified biochar can reduce the activity of the effective state Cd and Pb,and can enhance the conversion of the effective state to the ineffective state,thus reducing the hazard for the purpose of treating Cd and Pb contaminated soil.4.From the results of pathway analysis,the change of soil pH and CEC after the application of zerovalent iron nanocomposite chitosan modified biochar was the key pathway factor for the change of soil Cd and Pb effectiveness,and the change of modified biochar application and the change of weak acid extraction state and reducible state of Cd and Pb were mutually key pathway factors.Soil macroparticle agglomerates are also directly affected by changes in SOC and have a direct effect on the weakly acidextracted and reducible states of Cd and Pb.The application of modified biochar can have an indirect effect on soil macroparticle aggregates through a direct effect on soil CEC.In summary,under the present experimental conditions,the best effect on soil structure improvement was achieved under 1%input of zero-valent iron nanocomposite chitosan modified biochar without heavy metal contamination;for Cr-contaminated soil,zero-valent iron nanocomposite chitosan modified biochar was not effective in its remediation;for soil contaminated with high concentrations of Cd and Pb,3%input of zero-valent iron nanocomposite chitosan modified biochar could significantly reduce the weak acid extracted and reducible states.extractable and reducible states,reducing the biological effectiveness of Cd and Pb,and at the same time improving the soil structure.