| Mercury is the only heavy metal element that mainly exists in the atmosphere in the form of gaseous phase,and coal combustion has become the main source of man-made mercury emissions.Every year,a large amount of mercury enters the atmosphere,and emissions increase year by year.There are three main forms of mercury in the flue gas:Hg2+ is soluble in water and easily adheres to particulate matter,so it is easily to be removed;Hgp has a very short residence time in the atmosphere and can be collected by dust removal equipment;Hg0 is volatile and hardly soluble in water,and it is difficult to be trapped.It is easy to form a large-scale mercury contamination,which is extremely harmful to human health and the surrounding environment.In this study,the use of Fenton-like catalysts in the homemade diffusion reactor is used to electrochemically oxidize Hg0 to Hg2+,to achieve efficient conversion of Hg0 to Hg2+ and solve the technical difficulties of Hg0 removal.The main research results of this paper are as follows:(1)The electrochemical method was used to achieve the removal of Hg0 in a self-made reactor.On the basis of the former study of the research group,an iron-based Fenton catalyst was attempted,and the removal efficiency of Hg0 was improved by changing the catalytic oxidation conditions.(2)Iron-based Fenton catalysts were prepared by a hydrothermal method.According to the elemental composition,they were named Fe3-xCuxO4,Fe3-xMnxO4 and Fe3-xCoxO4,respectively.Scanning electron microscope(EDS,SEM),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)were used to characterize the three catalysts in terms of surface morphology,elemental composition and content,internal structure,and elemental chemical state.The results show that the prepared catalyst has a smooth surface,many pores,good gas permeability,and a high degree of match with the ideal material.(3)The.catalyst was loaded on hydrophobic carbon paper by coating method,and the Hg0 catalyzed oxidation of simulated flue gas was studied in a reaction device,the effects of voltage,inlet flow rate,electrolyte concentration,initial Hg0 concentration,and pH on the mercury removal efficiency were investigated.The result shows that the higher the voltage,the higher the removal efficiency.When the electrolytic voltage is increased from 3 V to 6 V,the removal efficiency can be increased from 20%to 90%,which is more than four times higher.The removal efficiency of Hg0 is the best at the inlet flow rate of 100 mL/min,and the removal efficiency is low at the low flow rate(25 mL/min),respectively.The highest Hg0 removal efficiency is achieved at a concentration of 0.8 mol/L of electrolyte,up to a maximum of 80%.The initial concentration of Hg0 fluctuates greatly on its mercury removal efficiency,achieving the best removal efficiency at 600 μg/m3.The pH has a great influence on the removal efficiency of Hg0.Under the condition of peracid or overbase,the catalytic activity is reduced,and the removal efficiency of Hg0 is not high.In contrast,the best Hg0 removal efficiency can be achieved in a pH=7 neutral environment.(4)The H2O2 content in the solution before and after the reaction was measured by spectrophotometry,and it was confirmed that the H2O2 in the solution was consumed during the removal of Hg0.The degradation of nitrobenzene was measured by gas chromatography,and it confirmed that hydroxyl radical(·OH)played an oxidation role.In the process of electrochemical oxidation of Hg0,O2 is mainly used to generate H2O2 through oxidation and reduction of the electrode,and part of H2O2 can directly react with Hg0 to oxidize it to Hg22+ or Hg2+.The vast majority of H2O2 reacts with Fe,Cu/Mn/Co redox pairs on the surface of the catalysts and decomposes into hydroxyl radical(.·OH)that react with Hg0 to remove Hg0.(5)The effects of three catalyst loadings on Hg0 removal efficiency were comprehensively compared.Under the same conditions,according to the removal efficiency of Hg0,the catalytic performance was:Fe3-XCuxO4,Fe3-xCoxO4,Fe3-xMnxO4. |
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