Study On The Effect And Mechanism Of Manganese Modified Biochar And Iron Manganese Oxide On Heavy Metal Contaminated Sediment Remediation

Metal oxides are widely present in soil and sediments.They have the characteristics of high capacity,fast speed and strong targeting in the adsorption of heavy metals.They are environmentally friendly and excellent adsorption materials and have broad application prospects in soil or sediment remediation.Biochar can be produced by pyrolysis of waste biomass under high temperature and oxygen-limited conditions.It has large oxygen-containing functional groups,porosity and specific surface area,which provides a new idea for resource utilization and environmental pollution remediation.The remediation methods of heavy metal contaminated sediments mainly include dredging and in-situ remediation technology.For the sediments contaminated by high concentration of lead and cadmium,the contaminated sludge after dredging needs further harmless treatment,while the in-situ capping technology has low treatment efficiency.Therefore,it is of great practical significance to develop an efficient,sustainable and environmentally friendly in-situ remediation material for heavy metal contaminated sediments.In this study,metal oxides were combined with biochar to prepare sludge-based biochar（BC）,manganese-modified biochar（MBC）,and iron-manganese composite oxide（FMBO）.The structure and composition of the three materials were characterized.The results showed that manganese was successfully doped into biochar,and it was mainly MnO₂.The content ratio of Fe and Mn in FMBO was roughly in line with the preparation ratio of 3:1.The ratio of Fe²⁺and Fe³⁺indicated the presence of Fe₃O₄,and Mn was mainly Mn₃O₄,and FeMnO_Xstructure was formed.Pb²⁺and Cd²⁺were selected as typical pollutants to investigate the adsorption performance of the three adsorption materials.After manganese modification,the adsorption capacity of biochar to Pb²⁺and Cd²⁺increased from 12.338 mg/g and 8.929 mg/g to 176.887 mg/g and 43.967 mg/g,which was greatly improved.The adsorption capacity of FMBO to Pb²⁺and Cd²⁺was 210.534 mg/g and 16.083 mg/g,which had excellent adsorption performance.After that,the effects of different pH and dosage conditions on the adsorption effect were studied,and before and after adsorption the BC,MBC and FMBO were characterized to explore the adsorption mechanism.The simulated sediment remediation experiment with excellent adsorption performance was selected,and different proportions of MBC and FMBO were added to the high-concentration lead-cadmium-contaminated sediments for 15 days.After 15days,the proportion of acid extractable state（F1）of Cd and Pb in the sediments decreased by 8.73%～11.81%,the content of oxidizable state（F3）and residual state（F4）increased,the content of DGT effective state generally increased.It shows that MBC and FMBO can effectively immobilize Pb and Cd.The microbial community composition of the cultured sediments was determined by 16Sr RNA.Compared with the control group,the MBC and FMBO showed short-term toxic effects and long-term promotion effects on microorganisms in sediment remediation microcosms.In summary,MBC and FMBO have good adsorption properties for Pb and Cd and play a certain fixation role in the remediation of high concentration Pb and Cd contaminated sediments,but they show certain biological toxicity to sediments,and also affect the microbial community composition.This study aims to explore the combination of metal oxides and biochar and provide some data support for the application of heavy metal remediation in sediments.