Reduction of FeII(EDTA)-NO by Mn powder in wet flue gas denitrification technology: stoichiometry, kinetics, and thermodynamics

Conversion of Fe II (EDTA)-NO or Fe III (EDTA) into Fe II (EDTA) is a key process in a wet flue gas denitrification technology with Fe II (EDTA) solution. In this work, the stoichiometry, kinetics, and thermodynamics of Fe II (EDTA)-NO reduction by Mn powder were investigated. We first studied the Fe II (EDTA)-NO reduction and product distribution to speculate a possible stoichiometry of Fe II (EDTA)-NO reduction by Mn powder. Then, the effects of major influencing factors, such as pH value, temperature, and Mn concentration, were studied. The pseudo-second-order model was established to describe the Fe II (EDTA)-NO reduction. Simultaneously, according to Arrhenius and Eyring-Polanyi equations, the reaction activation energy ( E a ), enthalpy of activation (∆ H ‡ ), and entropy of activation (∆ S ‡ ) were calculated as 23.68 kJ/mol, 21.148 kJ/mol, and − 149.728 J/(k mol), respectively. Additionally, simultaneous reduction of Fe III (EDTA) and Fe II (EDTA)-NO was investigated to better study the mechanism of Fe II (EDTA) regeneration, suggesting that there was a competition between the two reduction processes. Finally, a simple schematic mechanism of NO absorption by Fe II (EDTA) combined with regeneration of manganese ion and ammonium was proposed. These fundamental researches could offer a valuable guidance for wet flue gas denitrification technology with Fe II (EDTA) solution.