| A large amount of research shows that tungsten has adverse effects on the environment and human health.As China has the largest reserves and mining output of tungsten in the world,it is inevitable to encounter tungsten pollution in water bodies.Therefore,it is urgent to adopt effective methods to treat W(Ⅵ)in water.Adsorption is currently the most economical and efficient method for heavy metal pollution treatment in water bodies,but traditional adsorbents have certain limitations in subsequent treatment.At the same time,tungsten is a high-value metal,and previous research has been limited to its removal without considering its enrichment and recovery.Magnetic adsorbents are expected to make up for this deficiency,among which magnetic nanoparticles of iron oxide(Fe3O4 NPs)are highly favored due to their large specific surface area,small particle size,high adsorption reaction activity,and convenient synthesis and low cost.This paper first synthesized Fe3O4 NPs,and then modified them through polyethyleneimine(PEI)or PO43-grafting to study the adsorption and enrichment behavior of these materials on W(Ⅵ)in water one by one,with a focus on the effects of different pH values,coexisting anions,contact time,W(Ⅵ)initial concentration,adsorption kinetics,adsorption mechanism,and material reusability.The main research results are as follows:1.Fe3O4 NPs were prepared by hydrothermal method.Characterization results confirmed the successful preparation of Fe3O4 NPs,which were spherical and poorly dispersed,with a saturation magnetization intensity of 79.9 emu/g.The adsorption experiment results showed that the lower the pH value of the solution,the more favorable the adsorption was.The adsorption process of Fe3O4 NPs on W(Ⅵ)was more in line with the pseudo-second-order kinetic model and Langmuir model,and the maximum adsorption capacity was 23.76 mg/g.A 2 mol/L NaOH solution could desorb Fe3O4 NPs and enrich and recover 63.7%of the adsorbed W(Ⅵ).The material reusability of Fe3O4 NPs was average.2.Fe3O4 NPs were modified with PEI to prepare Fe3O4@PEI NPs composite material with PEI coating on the surface.The characterization results showed that PEI was successfully coated on the surface of Fe3O4 NPs,and Fe3O4@PEI NPs had good dispersion with a saturation magnetization of 63.9 emu/g.Adsorption experiments showed that a lower pH value was more favorable for adsorption,and the adsorption process of Fe3O4@PEI NPs for W(Ⅵ)was more consistent with the pseudo-second-order kinetic model and Langmuir model,with a maximum adsorption capacity of 43.24 mg/g,which was 1.9 times higher than that of Fe3O4 NPs.2 mol/L NaOH solution could desorb Fe3O4@PEI NPs and recover 85.2%of the adsorbed W(Ⅵ),indicating the excellent reusability of Fe3O4@PEI NPs.The adsorption mechanism includes two parts:firstly,W(Ⅵ)forms polytungstate anions([H2W12O40]6-)in acidic environments and is attracted to the surface of Fe3O4@PEI NPs by electrostatic forces;then,[H2W12O40]6-undergoes complexation with the hydroxyl and amine groups on the surface of Fe3O4@PEI NPs.3.Fe3O4 NPs were modified by irradiation to prepare NaH2PO4/Fe3O4 composite material with sodium dihydrogen phosphate(NaH2PO4)loading.The characterization results confirmed the successful synthesis of NaH2PO4/Fe3O4 material with a saturation magnetization of 21.7 emu/g.Adsorption experiments showed that a lower pH value was more favorable for adsorption,and the adsorption process of NaH2PO4/Fe3O4 for W(Ⅵ)was more consistent with the pseudo-second-order kinetic model and Langmuir model,with a maximum adsorption capacity of 64.09 mg/g,which was 2.7 times higher than that of Fe3O4 NPs.2 mol/L NaOH solution could desorb NaH2PO4/Fe3O4 and recover 80.3%of the adsorbed W(Ⅵ),indicating the excellent reusability of NaH2PO4/Fe3O4 material.The adsorption mechanism includes two parts:firstly,W(Ⅵ)forms polytungstate anions([H2W12O40]6-)in acidic environments and is attracted to the surface of NaH2PO4/Fe3O4 material by electrostatic forces;then,[H2W12O40]6-undergoes complexation with the phosphate on the surface of NaH2PO4/Fe3O4 material. |
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