Performance, mechanism, and kinetics of NO removal using ligand-enhanced UV-Fenton driven by O2 from flue gas

Wet free radical advanced oxidation technology such as Fenton reaction is thought to be a very efficient method to remove NO from flue gas, but it requires the consumption of additional oxidants to achieve high removal efficiency. For this purpose, a ligand-enhanced UV-Fenton system without additional oxidants was proposed for NO removal. Three common chelating ligands, EDTA, NTA, and Citrate, were selected to promote UV-Fenton reaction for NO removal. The NO removal performance, mechanism, and kinetics of three different ligand-enhanced photochemical Fenton systems including EDTA/UV/Fe(II), NTA/UV/Fe(II), and Citrate/UV/Fe(II), were studied. Results showed that ligand addition can greatly promote a NO removal in the UV-Fenton system, in the following order of efficiency: EDTA > NTA > Citrate. The mechanism research indicated that these ligands not only enhanced NO oxidation removal by promoting the generation of •OH, but also provided NO complexation removal, which synergized oxidative denitrification and complexation denitrification in the same reaction system, greatly promoting wet NO removal. NO from simulated flue gas was mainly converted into NO3-, NO2-, NH4+, N2, and N2O through synergistic complexation-oxidation. The optimum ratio of ligand to Fe(II) was 1:1 for EDTA and NTA and 3:1 for citrate. NO removal efficiency was increased and then decreased with the increase in pH value or O2 concentration. The low temperature was found to be favorable for NO removal. Furthermore, the kinetics demonstrated that the L/UV/Fe(II) system reaction was a pseudo-first-order process involving nitric oxide. Finally, compared with other Fenton and Fenton-like denitrification systems, EDTA(NTA)-enhanced UV-Fenton system had shown great priority in terms of removal performance, absorbent cost, and waste disposal.