Reaction Behavior and Influencing Mechanisms of Different Fly Ashes on the NO Removal by Using the Ultraviolet...

Our previous work had demonstrated that UV/NaClO₂ was the best advanced oxidation method in terms of nitric oxide (NO) removal, but we have not studied the impact of the fly ash on NO removal under such conditions. For this, this paper selected six kinds of fly ashes and studied their effects on NO removal. The micromorphology, elemental composition, and the elemental oxidation states of these six fly ashes were characterized by scanning electron microscopy-energy-dispersive X-ray spectra, X-ray photoelectron spectroscopy, and inductively coupled plasma methods. The main inorganic components in the six fly ashes are metal oxides (Fe₂O₃/Fe₃O₄, SiO₂, Al₂O₃, ZnO, MgO, and TiO₂), carbonates (Na₂CO₃ and CaCO₃), and chlorides (NaCl, KCl, and MgCl₂). The experimental results suggested that high solubility was the premise condition for the fly ashes exhibiting an inhibitory effect on NO removal. Among all of the metal compounds, Fe₂O₃/Fe₃O₄ exhibited the highest inhibitory contribution rate to the NO removal (22.9-45.7%). The anions of Cl^- and CO₃ ^2- acted as scavengers for the free radicals which greatly impaired the oxidation of NO. Based on the simulation experimental results and the UV-vis analysis, the order of inhibitory contribution rates of various metal compounds to the NO removal was determined as Fe₂O₃/Fe₃O₄ > TiO₂ ≈ Na₂CO₃ > Al₂O₃ ≈ ZnO ≈ MnO₂ > CaCO₃ > NaCl > KCl ≈ SiO₂ ≈ MgCl₂.