Influence of fluoride on the reversible binding of NO by [FeII(EDTA)(H2O)]2-.: Inhibition of autoxidation of [FeII(EDTA)(H2O)]2-

The promising BioDeNO(x) process for NO removal from gaseous effluents suffers from an unsolved problem that results from the oxygen sensitivity of the Fe-II-aminopolycarboxylate complexes used in the absorber unit to bind NO(g). The utilized [Fe-II(EDTA)(H2O)](2-) complex is extremely oxygen sensitive and easily oxidized to give a totally inactive [Fe-III(EDTA)(H2O)](-) species toward the binding of NO(g). We found that an in situ formed, less-oxygen-sensitive mixed-ligand complex, [Fe-II(EDTA)(F)](3-), still reacts quantitatively with NO(g). The formation constant for the mixed ligand complex was determined spectrophotometrically. For [Fe-III(EDTA)(F)](2-) we found log K-MLF(F) = 1.7 +/- 0.1. The [Fe-II(EDTA)(F)](3-) complex has a smaller value of log K-MLF(F) = 1.3 +/- 0.2. The presence of fluoride does not affect the reversible binding of NO(g). Even over extended periods of time and fluoride concentrations of up to 1.0 M, the nitrosyl complex does not undergo any significant decomposition. The [Fe-III(EDTA)(NO-)](2-) complex releases bound NO on passing nitrogen through the solution to form [Fe-II(EDTA)(H2O)](2-) almost completely. A reaction cycle is feasible in which fluoride inhibits the autoxidation of [Fe-II(EDTA)(H2O)](2-) during the reversible binding of NO(g).