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/NaClO 2 ) is developed for simultaneous removal of SO 2 and NO. NH 4 OH, as an additive, was used to inhibit the generation of ClO 2 and NO 2 . The removal efficiencies of SO 2 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. SO 2 at 500–1000 mg/m 3 improved NO removal, especially in the absence of UV. The coexistence of SO 2 and O 2 facilitated the removal of NO by ClO 2 – . HCO 3 –, Cl –, and Br – enhanced NO removal, but their roles were negligible when UV was added. The generation of ClO 2 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 SO 2 and NO were attributed to the synergism between acid–base neutralization and radical-induced oxidation. The ClO 2 – 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.