To remove NO and SO2 from flue gas simultaneously, a heterogeneous catalytic oxidation system was developed with the nanoscale zero-valent iron (nZVI), vaporized H2O2, and sodium humate (HA-Na) acting as the catalyst, oxidant, and absorbent, respectively. The experimental results indicated that the desulfurization was mainly influenced by the absorption, and the denitrification was significantly affected by the catalytic oxidation parameters. Under the optimal conditions, the simultaneous removal efficiencies of SO2 and NO were 100 and 88.4%, respectively. The presence of ·OH during the removal process was proved by the scavenger tests, and the production of ·OH with and without nZVI was indirectly evaluated by the electron paramagnetic resonance (EPR) and methylene blue experiments. Moreover, the fresh and aged nZVI were characterized by a series of techniques and the results suggested that the redox pair Fe2+/Fe3+ released by nZVI could react with H2O2 to provide the sustainable ·OH, which was important for the oxidation from NO and SO2 to NO3- and SO42-. The removal mechanism was proposed preliminarily based on the correlative experiments, characterizations, and references.
Keywords: Heterogeneous Fenton; Hydroxyl radicals; Nanoscale zero-valent iron; Simultaneous removal of NO and SO2.