Remediation Of Multi-heavy Metal Contaminated Soil By Application Of A Modified MgFe₂O₄-montmorillonite And Biochar

Montmorillonite and biochar have been shown to be effective materials for the immobilization of heavy metals in soils.On this basis,a new MgFe₂O₄-montmorillonite material with good adsorption performance was successfully prepared by hydrothermal method.The characteristics of MgFe₂O₄-montmorillonite and montmorillonite were characterized by N₂adsorption-desorption isotherms,Scanning electron microscope,Fourier transform infrared spectrometer,and X-ray diffraction.Then the modification and adsorption mechanism were analyzed.MgFe₂O₄ nanoparticles are densely and homogeneously coated on the surfaces of montmorillonite by cross-linking（This can be proved by the presence of peaks representing Si-O-metal in FTIR patterns）.After modification,the pore size of the material is larger,and the surface of the material has-COOH and-OH,meanwhile the phase purity of MgFe₂O₄ was preserved.Secondly,MgFe₂O₄-montmorillonite and biochar were mixed in proportion（0:1,1:9,3:7,4:6,1:0）to remediate the contaminated soil contaminated by multi-heavy metal（Zn,Cu,Pb,Cd）.Soil p H,soil organic matter（SOM）,water-soluble organic carbon（WSOC）,TCLP and BCR values of heavy metals,and soil bacterial community were used as evaluation indexes for remediation.The result as follows:compared with the control group,the soil p H,SOM and WSOC of the compound contaminated soil were significantly improve d by0.90%～5.07%,7.03%～43.52%and 15.77%～40.80%,respectively.The MgFe₂O₄-montmorillonite alone can increase soil alkalinity,reduce the bioavailability of heavy metals,and improve the state of complex heavy metal.The contents of Cd,Cu,Pb and Zn in the TCLP extracted states decreased by 58.41%,42.93%,50.33%and 24.71%,respectively.The combinations of MgFe₂O₄-montmorillonite and biochar of various combinations showed variable results.Compared to control,heavy metal pollution has been alleviated in different degrees.The application of remediation agents changed the structure of soil bacterial community.At the level of phylum classification,Proteobacteria,Bacteroidetes,Actinobacteria,Firmicutes and Acidobacteria were the top five dominant phyla in all experimental groups.However,there were differences in the proportion of dominant bacteria in different experimental groups.The addition of MgFe₂O₄-montmorillonite and biochar improved the diversity and richness of the contaminated soils.However,the diversity and richness of the combined application of MgFe₂O₄-montmorillonite and biochar in the experimental group were higher than that of the pure MgFe₂O₄-montmorillonite,indicating that the single application of MgFe₂O₄-montmorillonite have a greater effect on soil microorganisms than the combined application of biochar,and the MgFe₂O₄-montmorillonite may have minor ecotoxicity.The addition of biochar has effectively alleviated the negative effect.The application of MgFe₂O₄-montmorillonite alone is a feasible method when the purpose is immobilization multi-heavy metal in soil.While the combination of MgFe₂O₄-montmorillonite and biochar can play a role when it requires both the passivating of heavy metals and the attention to the soil ecological environment simultaneously.