Radical-induced oxidation removal of multi-air-pollutant: A critical review

Sulfur dioxide (SO2), nitric oxide (NO) and elemental mercury (Hg-0) are three common air pollutants in flue gas. SO2 and NO are the main precursors for chemical smog and Hg-0 is a bio-toxicant for human. Cooperative removal of multi-air-pollutant in flue gas using radical-induced oxidation reaction is considered as one of the most promising methods due to the high removal efficiency, low cost and less secondary environmental impact. The common radicals used in air pollution control can be classified into four types: (1) hydroxyl radical ((OH)-O-center dot), (2) sulfate radical (SO4 center dot-), (3) chlorine-containing radicals (Cl-center dot, ClO2, ClO center dot, HOCl center dot- etc.) and (4) ozone. This review summarizes the generation methods and mechanism of the four kinds of radicals, as well as their applications in the removal of multi-air-pollutant in flue gas. The reactivity, selectivity and reaction mechanism of the four kinds of radicals in multi-air-pollutant removal were comprehensively described. Finally, some future research suggestions on the development of new technique for cooperative removal of multi-air-pollutant in flue gas were provided.