Applied Kinetics Aspects of Ferric EDTA Complex Reduction with Metal Powder

Abstract

Nitrogen and sulfur oxides (NO x and SO x ) emitted from fossil-fuel-fired facilities can be simultaneously absorbed into aqueous mixed solutions of sulfite and Fe II L, a ferrous ion coordinated to a ligand L (a chelate compound). Usually, the ligand L represents an anion of ethylenediaminetetraacetic acid (EDTA or edta). Nitrogen oxide (NO) sparingly soluble in water is promptly bound to the [Fe II (edta)(H 2 O)] 2− complex to form the [Fe II (edta)(NO] 2− compound. However, [Fe II (edta)(H 2 O] 2− chelate is oxidized to form [Fe III (edta)(H 2 O)] − by NO, NO 2 , and O 2 , normally coexisting in flue gases.Because the ferric complex does not react with NO, the suppression of these undesired oxidation processes is a very important technological problem to be overcome. Thus, in this work, the reduction kinetics of ferric ion by metal was discussed on the basis of the kinetic data regarding the ferric ion reduction in aqueous solutions of [Fe III (edta)(H 2 O)] − containing such pulverized metals as aluminum, tin, and zinc. The rate expression for the reduction of [Fe III (edta)(H 2 O] − by a metal powder was derived in terms of the rate-determining step approximation method. Laboratory-scale experiments were conducted in a recirculation-type glass reactor filled with 250 cm 3 of solution. The influence of the following parameters on the reduction rate was investigated: (1) [Fe III (edta)(H 2 O)] 0 − = 0.100−0.010 M, (2) [metal] 0 /[Fe III (edta)(H 2 O)] 0 − = 10−100, (3) pH 0 = 3−9, and (4) temperature = 20−80°C. Zinc and aluminum powders were found to be effective reducing agents for ferric ions coordinated to EDTA. Similar experiments were carried out using a working solution in a simultaneous NO and SO 2 removal process as a solvent of [Fe III (edta)(H 2 O)] − solution.

The regeneration of Fe-EDTA denitration solutions by nanoscale zero-valent iron

“…The 0.02 M Fe(II)EDTA solution was freshly prepared with equal mol FeSO 4 and Na 4 EDTA at desired acidity, adjusted by diluted NaOH and HCl and recorded by pH meter. The 0.02 M Fe(III)EDTA solution was prepared with Fe(NO 3 ) 3 and Na 4 EDTA of the same molar ratio at the desired pH. The expired Fe-EDTA solution was prepared by exposing the freshly made Fe(II)-EDTA solution (0.02 M) to air in a transparent jar for three days.…”

“…Only strong reductants like dithionite ion and hydrazine, or active metals such as aluminum and zinc powder, could be considered as suitable candidates to reduce Fe(III)EDTA effectively. 3,14,15 According to references, 3,16 the redox equation of Fe(III)EDTA with iron powder or NZVI can be written stoichiometrically as:…”

“…1 Therefore, developing a method to recycle or regenerate the nitrosyl complex solution is of great interest for many research groups in this eld. [1][2][3][4][5][6] Biological reduction of NO chelated by Fe(II)-EDTA, a novel chemical absorption-biological reduction integrated process, is regarded as a promising alternative to the conventional selective catalytic reduction process. The ferrous chelate absorbent can be regenerated by microorganisms to sustain a persistent NO removal capacity.…”

“…Chemicals with reducibility, such as polyphenols, dithionite, hydrazine, metal powder, etc., are screened and adopted directly in the absorption/regeneration process. 3,4,[12][13][14][15][16][17] Feiqiang et al investigated the mechanism and kinetics of Fe(II)EDTA-NO and Fe(III) EDTA reduction by iron powder. 15,16 Adam et al found that zinc powder can effectively reduce Fe(III)EDTA aqueous solution at 20 C, with a noticeably higher reduction rate compared to aluminum and tin powder.…”

“…In addition, the reduction capability of nanoscale zinc powder was about 11 times higher than that of normal-sized zinc. 3,18 Recently, nanoscale zero-valent iron technology has been extensively adopted in wastewater treatment. [19][20][21][22][23][24] This perspective of applying nanoscale chemicals to water treatment encouraged us to develop NZVI technology to regenerate the absorption liquid.…”