Kinetics of FeIIIEDTA complex reduction with iron powder under aerobic conditions

Abstract

Reduction of Fe^IIIEDTA is the core process in a wet flue gas simultaneous desulfurization and denitrification system by Fe^IIEDTA solution. Metal powders, such as aluminum, tin, and zinc, have been proposed to reduce Fe^IIIEDTA. In this paper, iron powder was chosen as a reductant to regenerate the absorption solution. The influences of various parameters, such as the initial concentration of Fe^IIIEDTA, the molar ratio of Fe to Fe^IIIEDTA, pH, and O₂ concentration on the reduction rate were investigated in a bubbling-type batch reactor. The mechanism and kinetics of Fe^IIIEDTA reduction by Fe were also studied. The experimental results indicate that oxygen can strongly reduce the rate of Fe^IIIEDTA reduction and cause γ-FeOOH to precipitate. During the increasing stage, the reaction rate increases with a decrease of pH. Raising the molar ratio of Fe to Fe^IIIEDTA can increase Fe^IIIEDTA conversion. Fe(II) concentration increases with an increase of the initial Fe^IIIEDTA concentration. During the decreasing stage, Fe(II) concentrations all decrease except under anoxybiotic conditions. The decreasing rate of Fe(II) becomes faster with higher O₂ concentration and lower molar ratio of Fe to Fe^IIIEDTA. The experiment of NO removal demonstrates that NO removal efficiency can be improved with the Fe^IIEDTA solution coupled with the Fe(II) regeneration by Fe powder. A kinetic equation describing the reduction of Fe^IIIEDTA by Fe powder was discussed.