Kinetics of FeEDTA complex reduction with iron powder under aerobic conditions

Reduction of FeEDTA is the core process in a wet flue gas simultaneous desulfurization and denitrification system by FeEDTA solution. Metal powders, such as aluminum, tin, and zinc, have been proposed to reduce FeEDTA. 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 FeEDTA, the molar ratio of Fe to FeEDTA, pH, and O concentration on the reduction rate were investigated in a bubbling-type batch reactor. The mechanism and kinetics of FeEDTA reduction by Fe were also studied. The experimental results indicate that oxygen can strongly reduce the rate of FeEDTA 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 FeEDTA can increase FeEDTA conversion. Fe(ii) concentration increases with an increase of the initial FeEDTA 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 concentration and lower molar ratio of Fe to FeEDTA. The experiment of NO removal demonstrates that NO removal efficiency can be improved with the FeEDTA solution coupled with the Fe(ii) regeneration by Fe powder. A kinetic equation describing the reduction of FeEDTA by Fe powder was discussed.