Remediation Of Pb And Cd In Red Soil By Modified Bagasse Biochar Passivation

In this paper,ordinary bagasse biochar（BC）was prepared from agricultural and forestry waste bagasse biomass at 600℃and N₂ atmosphere.At the same time,manganese modified bagasse biochar（MBC）and iron and manganese modified bagasse biochar（FMBC）were prepared by modification of bagasse biomass.The physicochemical properties of biochar before and after modification were analyzed by a series of characterization methods,and the modified biochar was successfully prepared.Passivation tests were carried out to study the passivation effects of two modified biochar materials on heavy metals Pb and Cd in red soil,and to clarify the mechanism of action of two modified biochar materials on heavy metals.Pot experiment were condected to explore the effects of two modified biochar on the accumulation and transfer of heavy metals Pb and Cd in plants.The results provide theoretical basis and data reference for remediation of Pb and Cd contaminated red soil with BC,MBC and FMBC materials.The research results of this paper are as follows:（1）Compared with the unmodified BC material,the two modified bagasse biochar materials have the advantages of strong aromatic structure,rich functional groups and large specific surface area,which can improve the stabilization efficiency of heavy metals lead and cadmium.（2）When BC and MBC materials were added to Pb and Cd contaminated red soil,In the three addition levels,with the increase of the addition level,the soil pH value and organic matter content showed an increasing trend,and the improvement effect was the most obvious under 5%treatment,and MBC was higher than BC treatment.Manganese modified biochar improved soil environmental quality to a certain extent,promoted microbial metabolic activities,and increased soil catalase and urease activities,which increased with the increase of MBC application amount.When the addition level was 5%,the stabilization efficiency of BC to EDTA-Pb and EDTA-Cd was 22.11%and 12.79%,respectively.The passivation efficiency of MBC material is 33.98%and 20.09%.The application of MBC could change the proportion of Pb and Cd in soil to a certain extent,and 5%MBC treatment changed the most.After 60 days of culture,the content of extractable Pb of weak acid in red soil under 5%MBC treatment decreased by 9.07%,reducible Pb decreased by 13.7%,oxidizable Pb and residue Pb increased by 7.43%and 15.34%,respectively,compared with the control group.Compared with the control group,reducible Cd decreased by 11.97%and residual Cd increased by31.65%.The results showed that MBC material could reduce the bioavailability of Pb and Cd in red soil and reduce the ecotoxicity.（3）After FMBC was applied to red soil,soil pH content and organic matter content increased gradually with the increase of FMBC,and reached the maximum value at 5%treatment.The activities of catalase and urease in soil were related to the content of available Pb and Cd in soil,while the application of FMBC reduced the content of available heavy metals and increased the enzyme activities.The soil urease activity under 5%FMBC treatment was the highest,reaching 0.44 mg/g.At the end of culture,the stabilization efficiency of EDTA-Pb and EDTA-Cd in red soil by 5%FMBC reached 42.65%and 31.4%,respectively.FMBC treatment can change the existing forms of heavy metals in soil,and promote Pb and Cd from unstable weak acid extractable state to a stable residue state that is not easily absorbed and utilized by plants.The repair effect was best when the FMBC supplemental level was 5%.Compared with the control group,the content of Pb and Cd in residue increased by 16.32%and 32.11%,respectively.The mechanism of FMBC passivation of Pb and Cd in soil mainly includes deposition of heavy metal ions with CO₃^2-and OH^-,formation of complexes with-O groups,and formation of stable single-tooth or multi-tooth inner spherical complexes with Fe Ox-Mn Ox and other substances（such as Fe-Mn-O-Pb and Fe-Mn-O-Cd）.（4）The pot experiment of Pakchoi showed that the application of BC,MBC and FMBC materials could reduce the accumulation of Pb and Cd in pakchoi to a certain extent and increase the biomass of pakchoi.Among them,MBC and FMBC materials have better treatment effect.The biomass of Pakchoi increased by 82.76%～115.52%after 1%-5%MBC was applied.The biomass of 1%～5%FMBC increased by 73.56%～122.98%.The accumulation capacity of Cd in aboveground and underground parts of Pakchoi was stronger than that of Pb,and the accumulation of heavy metals was mainly concentrated in the root system of underground part.Compared with unmodified bagasse biochar,the two modified bagasse biochar could reduce the bioavailability of Pb and Cd,hinder the accumulation of Pb and Cd in the root of pakchoi,and thus reduce the toxic effect of Pb and Cd on pakchoi.