Kinetics of the Reaction of Fe^II(EDTA) with Oxygen in Aqueous Solutions

Abstract

The kinetics of the reaction of oxygen with aqueous Fe II (EDTA) solutions has been determined in a range of process conditions (C Fe II (EDTA) ) 15-60 mol/m 3 , P O2 ) 5-20 kPa, pH ) 5-8, T ) 298-328 K, C NaCl ) 0-15 kg/m 3 ) using a gas-liquid stirred cell reactor. The oxygen absorption rates were modeled using an expression derived by De Coursey using the penetration theory of mass transfer. Within the range of process conditions applied, the reaction was shown to be first order in oxygen and second order in iron chelate. The temperature dependence of the kinetic constant may be expressed as (pH ) 7, no salt addition): k 12 ) 5.3 × 10 3 e -4098/T m 6 /(mol 2 ‚s). The kinetic constant is essentially independent of the pH in the range 5 < pH < 8. When applying a NaCl concentration of 15 kg/m 3 , the kinetic constant increases ∼35% (T ) 328 K). The oxidation of Fe II (EDTA) to Fe III (EDTA) is not the sole oxygen-consuming reaction. The extent of side reactions, possibly related to EDTA ligand degradation, is a function of the pH and the oxygen concentration. A remarkable, unprecedented step change in the selectivity of the reaction was observed when the reaction was performed at a higher oxygen concentration.

High-efficiency removal of NO x by a novel integrated chemical absorption and two-stage bioreduction process using magnetically stabilized fluidized bed reactors

“…Nevertheless, the removal efficiency declined at a higher liquid-circulation rate. As reported by Gambardella et al [42], the oxidation of Fe(II)EDTA was a first-order reaction with respect to Fe(II)EDTA concentration. Thus, increasing the liquid-circulation rate will increase the oxidation rate of Fe(II)EDTA.…”

Experimental and modelling studies on the simultaneous absorption of NO and O2 in aqueous iron chelate solutions

“…The kinetic constants of the reaction between Fe II (EDTA) 2− and oxygen as a function of the temperature were measured earlier in our group and may be expressed as (Gambardella et al, 2005b):…”

“…At low concentrations (< 10 mol/m 3 ), the reactions is first order in iron whereas it becomes second order at higher concentrations. At typical BiodeNOx absorption conditions (T = 50.55 • C, C FeII(EDTA) = 10.50 mol/m 3 , C NO = 0.250 vppm, C O 2 = 10.20%, pH = 7), the reaction was proven to be first order in oxygen and second order in iron chelate (Gambardella et al, 2005b). Under these conditions and using a typical laboratory gas-liquid stirred cell contactor, the oxidation reaction takes place in the intermediate regime between fast and instantaneous (Gambardella et al, 2005b;Wubs and Beenackers, 1993).…”

Corrosion of Metal Inclusions In Bulk Vitrification Waste Packages

“…This decrease in the Fe-EDTA complexes imparts additional negative charge, weakening the remaining Fe-EDTA chelate bonds and increasing the dissociation kinetics as a function of pH (Sunda and Huntsmann 2003;Gambardella et al 2005). At pH(23°C) ≥ 10.24, adsorption of EDTA onto Amasteel is inhibited resulting in surface complexation by hydroxyl ions or the release of iron hydroxide complexes into solution, which may undergo secondary precipitation as iron oxyhydroxides (Rubio and Matijevic 1979).…”