Study On Removal Of Sb（Ⅲ） Wastewater By Magnetite Loaded Nanoscale Zero-valent Iron And Thiol-functionalized MnFe₂O₄-MCM-41

Due to the exploitation and use of antimony ores resources,lots of antimony was discharged into the environment,resulting in significant water and soil contamination.Antimony exists mainly as Sb（III）and Sb（V）in water bodies,and Sb（III）is ten times more toxic than Sb（V）.Antimony and its compounds have potential toxicity and carcinogenicity towards humans.Thus,the World Health Organization（WHO）,the United States Environmental Protection Agency（USEPA）,and European Union（EU）have listed antimony and its compounds as priority pollutants.To minimize the health risks of antimony and preserve the ecological environment,the removal of antimony was investigated in this research.In recent years,nanoscale zero-valent iron and partial iron base materials have become a research hotspot in the field of pollution treatment due to their large specific surface area,easy separation and recovery.However,the problems of poor stability and easy agglomeration of particles limit its practical application.Therefore,in order to improve its performance,we take measures of loading and modification for iron base materials.In this study,magnetite loaded nanoscale zero-valent iron（nZVI/Fe₃O₄）and MnFe₂O₄-MCM-41-SH were synthesized in the laboratory to remove Sb（III）from wastewater.The removal efficiencies of Sb（III）by nZVI/Fe₃O₄ and MnFe₂O₄-MCM-41-SH and the impacts of relevant factors were explored by batch experiments.And X-ray diffraction（XRD）,transmission electron microscopy（TEM）,specific surface area analyzer（BET）,Fourier transform infrared spectroscopy（FTIR）,vibrating sample magnetometer（VSM）,and X-ray photoelectron spectroscopy（XPS）were used to characterize the physicochemical properties of the samples before and after reaction.Combining the characterization of the samples before and after the reaction and the removal effect of antimony,the removal mechanisms of Sb（III）by nZVI/Fe₃O₄ and MnFe₂O₄-MCM-41-SH were proposed,respectively.The main conclusions of this study are as follows:（1）The removal efficiencies of Sb（III）by nZVI/Fe₃O₄ were 97.0%-100.0%at the pH range of 3.0-11.0.The magnetic separation experiment indicated that nZVI/Fe₃O₄ is easy to be separated from solution.In the fifth cycle,the Sb（III）removal efficiency was around89.1%by nZVI/Fe₃O₄ with desorption treatment and reuse.The adsorption behavior of Sb（III）onto nZVI/Fe₃O₄ conformed to the Langmuir model and pseudo-second-order kinetic model.And the adsorption process was exothermal.（2）The removal mechanism of Sb（III）by nZVI/Fe₃O₄ was as follows:At the beginning,Sb（III）in solution was adsorbed onto the surface of nZVI/Fe₃O₄.Then,partial adsorbed Sb（III）was oxidized to less toxic Sb（V）by electrons transfer between Sb（III）adsorbed on the surface of nZVI/Fe₃O₄ and the generated Fe（III）oxyhydroxide in solution.And the generated Sb（V）was further adsorbed on the surface of nZVI/Fe₃O₄.（3）MnFe₂O₄-MCM-41-SH is a mesoporous material with a specific surface area up to676.47 m²/g.Its excellent magnetic properties make it easy to be separated from the solution.The removal efficiency of Sb（III）by MnFe₂O₄-MCM-41-SH can reach 98.6%-99.5%at the pH range of 3.0-11.0.Nitrate,sulfate,and phosphate have slight effect on removal efficiency of Sb（III）in the process of Sb（III）removal by MnFe₂O₄-MCM-41-SH.In the fifth cycle,the Sb（III）removal efficiency was around 89.1%by MnFe₂O₄-MCM-41-SH with desorption treatment and reuse.The adsorption behavior of Sb（III）onto MnFe₂O₄-MCM-41-SH conformed to the Langmuir model and pseudo-second-order kinetic model.The maximum adsorption capacity of Sb（III）by MnFe₂O₄-MCM-41-SH is 164.8 mg/g.And the adsorption process of Sb（III）by MnFe₂O₄-MCM-41-SH was exothermal.（4）The reaction mechanism between Sb（III）and MnFe₂O₄-MCM-41-SH was complex,involving surface adsorption,oxidation,and reduction.At the beginning,Sb（III）in solution was adsorbed onto the surface of MnFe₂O₄-MCM-41-SH.Then,partial adsorbed Sb（III）was oxidized to less toxic Sb（V）by electrons transfer between adsorbed Sb（III）and superficial Fe（III）on MnFe₂O₄-MCM-41-SH.In addition,partial Sb（III）was reduced to Sb（0）by electrons transfer between Sb（III）and superficial Mn（II）on MnFe₂O₄-MCM-41-SH.Ultimately,the generated Sb（V）and Sb（0）were further adsorbed on MnFe₂O₄-MCM-41-SH.