Simultaneous Removal of SO2 and NO Using a Novel Method of Ultraviolet Irradiating Chlorite-Ammonia Complex.

A novel advanced oxidation process (AOP) using ultraviolet/sodium chlorite (UV/NaClO2) is developed for simultaneous removal of SO2 and NO. NH4OH, as an additive, was used to inhibit the generation of ClO2 and NO2. The removal efficiencies of SO2 and NO reached 98.7 and 99.1%. NO removal was enhanced by greater UV light intensity and shorter wavelengths but was insensitive to changes in pH and temperature. SO2 at 500-1000 mg/m3 improved NO removal, especially in the absence of UV. The coexistence of SO2 and O2 facilitated the removal of NO by ClO2-. HCO3-, Cl-, and Br- enhanced NO removal, but their roles were negligible when UV was added. The generation of ClO2 and ClO•/HO• was verified by an UV-vis spectrometer, electron spin resonance (ESR), and radical-quenching tests. The mechanisms responsible for the removal of SO2 and NO were attributed to the synergism between acid-base neutralization and radical-induced oxidation. The ClO2- evolution and product composition were demonstrated by UV-vis and X-ray photoelectron spectroscopy (XPS). Kinetics analyses showed that the Hatta numbers were 329-798 and 747-1000 without and with UV. Thus, the gas-film resistance mainly controlled the mass-transfer process.