Kinetics of FeIIIEDTA complex reduction with iron powder under aerobic conditions

Reduction of Fe(III)EDTA is the core process in a wet flue gas simultaneous desulfurization and denitrification system by FeIIEDTA solution. Metal powders, such as aluminum, tin, and zinc, have been proposed to reduce Fe(III)EDTA. 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(III)EDTA, the molar ratio of Fe to Fe(III)EDTA, pH, and O-2 concentration on the reduction rate were investigated in a bubbling-type batch reactor. The mechanism and kinetics of Fe(III)EDTA reduction by Fe were also studied. The experimental results indicate that oxygen can strongly reduce the rate of Fe(III)EDTA reduction and cause gamma-FeOOH to precipitate. During the increasing stage, the reaction rate increases with a decrease of pH. Raising the molar ratio of Fe to Fe(III)EDTA can increase Fe(III)EDTA conversion. Fe(II) concentration increases with an increase of the initial Fe(III)EDTA concentration. During the decreasing stage, Fe(II) concentrations all decrease except under anoxybiotic conditions. The decreasing rate of Fe(II) becomes faster with higher O-2 concentration and lower molar ratio of Fe to Fe(III)EDTA. The experiment of NO removal demonstrates that NO removal efficiency can be improved with the FeIIEDTA solution coupled with the Fe(II) regeneration by Fe powder. A kinetic equation describing the reduction of Fe(III)EDTA by Fe powder was discussed.