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

Abstract

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.