| With environmental problems have become increasingly prominent nowadays,it's an important subject for iron and steel industry that how to realize the untilizaiton of metallurgical solid waste when they faced industrial upgrading.The converter sludge,one kind of metallurgical slag preduced by steelmaking process,contains abundant iron and calcium and others valuable elements which has a great resource endowment and potential utility value.It has important meaning for saving natural resources and reducing environmetal pressure to deeply study and exploit a new method or technology for high value-added reusing this kind of secondary resource.The acid hydrolysis method was adopted in the present work to transfer some valuable elements like Fe,Ca,Mg,Al and Mn in the sladge into acidolysis solution.Then the doped CaFe2O4/?-Fe2O3 composite photocatalyst was prepared from the obtained acidolysis solution by hydrothermal reaction and calcination treatment.The estimate of this new way for materialization of the converter sludge was achieved by deeply investigating the preparation,microstructure and photocatalytic performance of the obtained products.First,the CaFe2O4/?-Fe2O3 composite materials were prepared from chemical reagents to optimize the process parameters.On this basis,the CaFe2O4/?-Fe2O3composites were produced from converter sludge and their microstructure and photocatalytic performance were characterized.The research contents and methods is detailed as follows:using the FeCl3?CaCl2 mixed solution as the reactants and preparing the precursor of CaC2O4/?-Fe2O3 by hydrothermal method.Based on investigation of microstructures and powder characteristics of the obtained precursors,the hydrothermal reaction process parameters were optimized and the temperature,pH value of the hydrothermal reaction were then determined.By adjusting the ratio of Fe to Ca in the starting solution,the precursors were produced under the condition of opitimized hydrothermal reaction,and the CaFe2O4/?-Fe2O3 composites with different component ratio were finally obtained by roasting the precursors and their photocatalytic behaviors were investigated through photodegradation of MB solution.Subsequently,acidolysis process was performed according to the characteristics of converter sludge.Based on the experimental results obtained from the chemicals system,doped CaFe2O4/?-Fe2O3 composites were successfully prepared from the acidolysis solution,and the photocatalytic preformance of the sludge-derived CaFe2O4/?-Fe2O3 composites was investigated in comparison with that of chemicals-derived ones.Based on the ability of photodegradation of MB solution,the effects of some processing factors on the photocatalytic degradation reaction were disscussed,mainly including the dosage of catalyst,initial concertration of MB solution and initial pH value of MB solution.The results of the optimization experiment for the precursor which prepared by hydrothermal method indicated that the desired precursor can be obtained from the hydrothermal process at 150°C for 6 h,and the pH value of solution is 5.XRD and SEM results showed that the obtained composite material with different component ratio is composited by?-Fe2O3?PDF#79-1741?and CaFe2O4?PDF#72-1199?.The microstructure shows a short rod-like shape when the content of Ca is higher.With decrease of Ca content,the length-diameter ratio of these short rods decreases gradually and finally becomes sphere-like particles.The single phase?-Fe2O3prepared from chemicals delivers a fine texture of sphere-like particles.The results of unbiased transient photocurrent response showed that the maximun photocurrent intensity of CaFe2O4/?-Fe2O3,700 nA/cm2,was obtained when the component ratio is1:2.The results of phtocatalytic degradation experiment on the CaFe2O4/?-Fe2O3composite showed that the CaFe2O4/?-Fe2O3 with the component ratio of 1:2 had the best photodegradation rate?95.62%in 180 min?with degradation rate constant K=1.797×10-22 min-1.CaFe2O4/?-Fe2O3 composite was successfully prepared by the converter sludge through hydrolysis with HCl solution,hydrothermal reaction and calcination process.XRF results showed that the content of Fe and Ca in the converter sludge was55.61wt%and 9.2wt%,respectively.The better acidolysis process parameters are:solid-liquid ratio is 1:10,concentration of HCl=3mol/L,acidolysis temperature is90°C,acidolysis time is 3 h.Under these conditions,the ultimate leaching rate of iron is 89.3%.The multi-doped CaFe2O4/?-Fe2O3 composite was prepared by calcinating the precursor powder synthesised by hydrothermal reaction of acid solution at 900°C for 30 min.The transient photocurrent density is about 600 nA/cm2 and the photodegradation rate on MB solution?10 mg/L?is 92.87%within 180 min.The analysis of influence factors in the photodegradation process showed that photodegradation rate was closely related to the dosage of the catalyst,initial concertration and initial pH value of MB solution.The results of the present work indicated that it was feasible and controllable to prepare the doped CaFe2O4/?-Fe2O3 compostie from the converter sludge as a sunlight active photocatalyst.This idea and technical route can simultaneously achieve the materializaiton of Fe,Ca and other useful elements in the converter sludge,being an important and positive meaning to save natural resources and protect the environment.At the same time,the results of this work can also provide a new reference to high value-added and refined utilization of other industrial solid waste. |
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