Study On Hydrothermal Synthesis Of Magnetic MnFe₂O₄-sludge Biochar Composites And Its Mechanism For Pb²⁺ Adsorption In Wastewater

Lead(Pb)is considered as an extremely dangerous environmental contaminant due to its persistence,difficulty in biodegradability,high biological toxicity,and potential bioaccumulation.It is a task of great significance to control the environmental pollution caused by Pb²⁺.As a simple and efficient environmental remediation method,adsorption has been developed widely in treatment of heavy metal wastewater.The adsorption performance of pure hydrothermal sludge biochar and MnFe₂O₄ on heavy metals is not ideal.To explore a more efficient,low-cost,and environment-friendly adsorbent,this study mainly took the dewatered sludge from sewage treatment plant to prepare magnetic MnFe₂O₄-sludge biochar composites by hydrothermal method for Pb²⁺removal from water.In this experiment,the prepared materials were characterized to analyze the physical properties and composition of the material.Combined with the analysis of adsorption experimental data of MnFe₂O₄-sludge biochar composites for Pb²⁺in water and the characterization of the composites,the adsorption performance and main mechanism for Pb²⁺were investigated.The main research work and results are as follows:(1)Magnetic MnFe₂O₄-sludge biochar composites were prepared by one-step hydrothermal method,and the hydrothermal carbonization of sludge and the preparation of MnFe₂O₄ were realized simultaneously.Among the raw sludge biochar SBC,MnFe₂O₄ and MnFe₂O₄-sludge biochar composites with different sludge contents,the adsorption capacity of SBC and MnFe₂O₄ on Pb²⁺was significantly lower than that of MnFe₂O₄-sludge biochar composites,and MnFe₂O₄-sludge biochar composites with sludge content of 1.5 g(MFSB-1.5)showed the highest adsorption efficiency for Pb²⁺.(2)The characterization results of prepared adsorbents demonstrated that MFSB-1.5 composites were successfully synthesized,which prevented the agglomeration of MnFe₂O₄ and enhanced the mechanical structure of hydrothermal sludge biochar,and endowed MFSB-1.5 composites with magnetism(29.94 emu/g)and higher specific surface area(129.293 m²/g).The experimental results indicated that the process of Pb²⁺removal by MFSB-1.5 composites could be better depicted by the Pseudo-second-order model and the Langmuir isotherm,with a maximum adsorption amount of 174.216 mg/g.Thermodynamic analysis showed spontaneous and endothermic process of Pb²⁺adsorption by MFSB-1.5 composites.(3)The Pb²⁺removal by composites was affected by the dosage of MFSB-1.5composites and p H value of Pb²⁺solution.MFSB-1.5 composites could effectively remove Pb²⁺from aqueous solution in binary system with Pb²⁺ions and metal ions(Na⁺,K⁺,Ca²⁺,Mg²⁺).However,the co-existence of Cu²⁺and Cd²⁺significantly inhibited the Pb²⁺adsorption by MFSB-1.5 composites,with stronger inhibition from Cu²⁺than Cd²⁺,which was mainly related to the interaction of adsorption mechanism and the properties of metal ions.(4)The main mechanisms of Pb²⁺removal by MFSB-1.5 composites from aqueous solution were physical adsorption,electrostatic attraction,co-precipitation and complexation reaction,and the complexation reaction contributed the most to the removal of Pb²⁺.O was the key element of MFSB-1.5 composites for the good adsorption capacity of Pb²⁺.In this study,the prepared magnetic MnFe₂O₄-sludge biochar composites have great potential and significance in the removal of Pb²⁺from wastwater with the merits of effortless preparation,good Pb²⁺adsorption performance,esay magnetic separation and sludge resource utilization.