Performance and mechanism of oxidation, and removal of trace SeO2 in flue gas utilizing a H2O2, NaClO2, and Ca2+ slurry

Selenium (Se) is one of the toxic trace elements in flue gas emitted from coal-fired power plants. A method for oxidation and absorption of selenium dioxide (SeO2) by hydrogen peroxide (H2O2) and sodium chlorite (NaClO2) in a calcium-based slurry is proposed, in which hydrated lime (Ca(OH)2) and calcium carbonate (CaCO3) were selected to be absorbents, and H2O2 and NaClO2 were used to oxidize SeO2 and selenite ion to selenate ion to reduce their toxicities. The effects of reaction temperature, H2O2 and NaClO2 concentrations, solution pH, and SeO2 concentration were investigated, from which the optimal reaction conditions were established. The results indicated that the oxidation efficiency was affected significantly by the solution pH, and H2O2 and NaClO2 concentrations. The oxidation efficiency of SeO2 and selenite ion to selenate ion was below 40% using H2O2 and that increased to 92% with NaClO2 at the optimal conditions. For removal, Ca(OH)2 and CaCO3 slurries were used as absorbents and the efficiencies were affected by the slurry temperature. Oxidation behavior and mechanism were analyzed based on the characterization of removal products using hydride generation-atomic fluorescence spectrometry and X-ray photoelectron spectroscopy. SeO2 and selenite ion can be oxidized to selenate ion, which is less toxic, by active species such as hydroxyl radicals (HO·) and chlorine dioxide (ClO2), which are released during the decomposed processes of H2O2 and NaClO2 in acid conditions.