Synergetic utilization of microwave-modified fly ash and carbide slag for simultaneous desulfurization and denitrification

A higher efficiency and lower cost catalytic absorption technology for the synergetic utilization of microwave-modified fly ash and carbide slag (FA-CS) with Fe2O3 as the catalyst and absorbent was proposed for systematic desulfurization (De-SOx) and denitrification (De-NOx) in this paper. The influence of different factors on the simultaneous desulfurization and denitrification (De-SO2 and De-NOx) performance of the catalyst was investigated. The optimal preparation and adsorption parameters of the 6% Fe2O3/FA-CS catalyst were an immersion time of 2 h, a roasting temperature of 550 °C, a microwave power of 800 W, and a reaction temperature of 120 °C. Under these conditions, the maximum adsorption capacities of SO2 and NO are 0.61 mg/g and 0.05 mg/g, respectively. Based on the characteristic and analytical results of Fe2O3/FA-CS, the synergetic utilization mechanism of microwave-modified FA-CS was proposed for the De-NOx and De-SO2 process. The coexisting Fe2+/Fe3+ in the 6% Fe2O3/FA-CS catalyst was reversibly oxidized and reduced, which was beneficial for catalytic activation to promote the oxidization reaction from N2+ to N4+ and S4+ to S6+. NO and SO2 were oxidized to NOx and SOx by the active oxygen (O*) provided by the redox pair Fe2+/Fe3+ in the Fe2O3/FA-CS and Fe3O4/FA-CS catalysts, in which the newly formed NOx and SOx easily combined to form unstable sulfur-nitrogen complexes in the De-SO2 and De-NOx process. However, the activation sites of CaO as an adsorbent and coexisting Fe2+/Fe3+ ions on the surface of the Fe2O3/FA-CS and Fe3O4/FA-CS catalysts could be poisoned by NOx(abs) and SOx(abs) to form stable (Ca, Fe)SOx or (Ca, Fe)NOx, leading to a decline in adsorbent activity.