Study On The Effect Of AlMnMg Doping On Structure And Photocatalystic Activity Of ?-Fe₂O₃ Based On Materialization Of Metallurgical Dusts Into Zn Fe₂O₄/?-Fe₂O₃ Composite

In today's world,the increasingly serious resource and environmental situation makes the resource utilization of solid wastes become a research hotspot.The zinc-bearing furnace dust?Zn-dust?and the steel rolling sludges?SR-sludge?are the by-products of the steelmaking process.The Zn-dust contains plenty of valuable elements such as iron and zinc,and the SR-sludge contains a great deal of iron.In addition,they all contain a variety of valuable metal elements,showing a great resource endowment and potential utility value.It is very significant for conservation of natural resources and environmental protection to deeply research the related theories and new technologies for reusing this kind of secondary resource in high added value.In the present work,an acid hydrolysis method was used to transfer the valuable elements?Zn,Fe,Al,Mn,Mg?from the mixture of Zn-dust and SR-sludge into acidolysis solution,and the doped ZnFe₂O₄/?-Fe₂O₃ composite was sythesized through coprecipitation and calcination routes.In order to optimize the technological parameters of synthesis of ZnFe₂O₄/?-Fe₂O₃ from the Zn-dust and SR-sludge,the effects of Al,Mn and Mg co-doping on the microstructures and photocatalytic properties of ?-Fe₂O₃ were discussed in the present work,and the doped ?-Fe₂O₃ samples incorporated with the different concentration and combination of Al,Mn and Mg were all prepared by sol-gel method.First,the uncalcined Zn-dust is used in this work to mix with the SR-sludge.After acid hydrolysis step,the titrimetry results showed that the concentration of Fe3+in the acid solution was 0.4423 mol/L,and the concentration of Zn2+ was 0.1027mol/L,Zn/Fe?molar ratio?= 1/4.31?1/4.The concentration of Al,Mn,and Mg ions in the acidolysis solution of the prepared compounded dusts was measured by ICP,and the molar ratio of Al to Mn and Mg is 1 : 0.157 : 0.637.The precursor prepared from the acidolysis solution of compounded dust was calcined at different temperatures,and the properties of the obtained samples were characterized by XRD,SEM,and the degradation of MB.The XRD results show that the crystallinity and the crystal shape of the samples are gradually improved with the increase of calcination temperature.ZnFe₂O₄/?-Fe₂O₃ composites with good crystal structure are successfully synthesized,and there are no detectable impurity phases.SEM results show that the particle size of the samples increase gradually with the increase of calcination temperature.The particle size is about 24 and 38 nm for 600 and 700 °C samples.When the calcination temperature rised to 800 °C,the particle size increased to about 55 nm and show uniformly distributed spher-like particles.The ICP and EDS results of ZnFe₂O₄/?-Fe₂O₃ which calcined at 800°C for 4 h indicate that the synthesized ZnFe₂O₄/?-Fe₂O₃ composites are successfully doped with Al,Mn and Mg.The results of photocatalytic degradation of MB show that ZnFe₂O₄/?-Fe₂O₃ calcined at 800°C for 4 h exhibit the highest photocatalytic activity,which achieve the highest MB degradation rate of 98.08% within 180 min and the best rate constant?k=1.835×10-2 min-1?.The Al,Mn,and Mg series doped ?-Fe₂O₃ with doping amount?The molar ratio of doping element to ?-Fe₂O₃?of 1%,2%,3% 4% and 5% were prepared by sol-gel method from chemical reagent.The XRD results show that all the doped ?-Fe₂O₃ calcined at 600°C for 4 h in an oxygen atmosphere exhibit single phase powders,which can be indexed as hexagonal crystal ?-Fe₂O₃?PDF# 99-0060?.The enlarged view of?104?peak in the XRD patterns of all samples show a certain shift in the peak position,indicating that the elements are successfully doped into ?-Fe₂O₃ crystal lattice.The SEM results show that the microstructures of the samples are rough and the platelets gathered together.The shape,size and distribution of grains are not uniform.The doping concentration of the sample has little effect on its surface morphology,but there is a tendency to increase the grain size.On the whole,the doped ?-Fe₂O₃ samples show the similar morphology to the undoped ?-Fe₂O₃ prepared under the same conditions.The results of photocatalytic degradation of MB,transient photocurrent response and UV-vis DRS tests show that different amounts of one element,binary and ternary doping of Al,Mn,Mg have effects on the photocatalytic activity of ?-Fe₂O₃.According to the value of band gap obtained by Tauc-Plot method,doping changes the bandgap width of ?-Fe₂O₃.Within the range of 1% to 5% doping,the doping amount of Al needs to be further optimized,the doping amount of Mn should be less than 1%,and Mg should be controlled at about 4% to 5%.The Al,Mn binary-doping amount should be controlled below 1%,Mn,Mg binary-doping needs further optimization,Al,Mg binary-doping should be controlled at about 3% to 4%.Al,Mn,Mg ternary-doping should be controlled below 1%.The results show that the multi-doped ZnFe₂O₄/?-Fe₂O₃ photocatalytic composites can be successfully prepared by compounding Zn Ds and the SR-sludge together as raw materials.Doping of Al,Mn and Mg can bring certain effects on the photocatalytic properties of ?-Fe₂O₃.Mg doping has the greatest contribution to the photocatalytic activity of ?-Fe₂O₃,and the contribution of Al doping is not significant,while Mn doping inhibits the photocatalytic activity of ?-Fe₂O₃.Therefore,it should be paid attention to the synergistic effect of Al,Mn,and Mg elements on the photocatalytic activity of?Al Mn Mg?-codoped ZnFe₂O₄/?-Fe₂O₃ composites derived from metallurgical dusts.In the process of dust materialization,the incorporation of Al should be controlled and that of Mn should be reduced as far as possible,and the dosage of Mg should be appropriately increased,achieving the purpose of improving the photocatalytic activity of the dusts-derived ZnFe₂O₄/?-Fe₂O₃ composites.