The Study On Stabilization And Mechanism Of Biochar-supported MnFe₂O₄ On Zn²⁺ And Cu²⁺ Co-contaminated Soil

Soil contaminated by heavy metals is becoming more and more serious.In this study,a novel magnetic biochar-MnFe₂O₄ nanocomposite（BC/FM）was prepared using low-cost corn straw and MnFe₂O₄ by sol-gel/pyrolyzing route with egg white which have abundant functional groups（-NH₂ and-COOH）.Following that,its composition,morphology and structure was characterized by various techniques including SEM-EDX,XRD,VSM,FTIR,XPS.Batch experiment of adsorption for Zn²⁺and Cu²⁺including influence of pH,kinetic,isotherm and thermodynamics was also studied.The effects of BC/FM on the physical and chemical properties of soil and the stabilization effect on the heavy metal zinc and copper in soil were also discussed through the simulated soil culture experiment.The main contents and results were as follows:（1）The results demonstrated that biochar could effectively support MnFe₂O₄ which displayed high dispersion on the surface of biochar and possessed abundant functional groups.Therein,MnFe₂O₄ with high magnetism is convenient for separation of magnetic BC/FM from aqueous medium.Adsorption experiment results indicated that Zn²⁺and Cu²⁺removal by BC/FM were closely related to pH with the best value of pH 5.0 and 6.0,respectively.And the adsorption process reached equilibrium at 90min.The adsorption process was described well by the pseudo-second-order kinetic model.The fitting results of adsorption isotherm equations consistent with the Langmuir and Freundlich adsorption isotherm model for Zn and Cu,respectively.Thermodynamic studies suggested that the adsorption process was spontaneous and exothermic.In bi-solute system,the preferential adsorption order of BC/FM for two metals was Cu²⁺prior to Zn²⁺.Finally,FTIR and XPS analysis verified that the main mechanism of Zn²⁺and Cu²⁺removal by BC/FM was formation complexation of carboxyl and hydroxyl and ion exchange.Therefore,the prepared magnetic BC/FM composite,as a excellent adsorbent,exhibited potential application for wastewater containing Zn²⁺and Cu²⁺.（2）In order to study the effects of BC and BC/FM on the remediation of weak alkaline Zn-Cu co-contaminated chestnut soil,the effects of BC and BC/FM on soil pH,cation exchange capacity（CEC）,organic matter（SOM）and soil electric conductivity（EC）,and the fraction distribution change of Zn and Cu and TCLP leaching toxicity were studied by soil culture experiment.The results showed that the application of BC and BC/FM significantly increased soil pH,CEC and SOM,and effectively promoted the transformation of Zn and Cu from bioavailable to stable state.The dosage of BC had a highly significant positive correlation with pH,CEC,EC and SOM（P<0.01）,the dosage of BC/FM had a highly significant positive correlation with pH and SOM（P<0.01）,and a highly significant negative correlation with EC（P<0.01）,but no significant correlation with CEC.Two materials can reduce the TCLP-extracted content of Zn and Cu in soil effectively.The immobilization ability showed BC/FM>BC.The two materials are expected to be applied to stabilization remediation of Zn-Cu contaminated soils.