Kinetics of FeIIIEDTA complex reduction with iron powder under aerobic conditions
Abstract
Reduction of FeIIIEDTA 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 FeIIIEDTA. 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 FeIIIEDTA, the molar ratio of Fe to FeIIIEDTA, pH, and O2 concentration on the reduction rate were investigated in a bubbling-type batch reactor. The mechanism and kinetics of FeIIIEDTA reduction by Fe were also studied. The experimental results indicate that oxygen can strongly reduce the rate of FeIIIEDTA 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 FeIIIEDTA can increase FeIIIEDTA conversion. Fe(II) concentration increases with an increase of the initial FeIIIEDTA 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 FeIIIEDTA. 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 FeIIIEDTA by Fe powder was discussed.