Oxidation kinetics of Iron(II) complexes of trans-1,2-diaminocyclohexanetetraacetate (cdta) with dissolved oxygen: Reaction mechanism, parameters of activation and kinetic salt effects

The present investigation takes concern about a spiny environmental problem afflicting the pulp mill industry exploiting the Kraft sulfate-pulp process where dilute total reduced sulfur contaminants are co-mixed with oxygen in large-volume gas effluents. A potential Redox process for removing the total reduced sulfurs consists in oxidizing them by means of iron(III) organometallic complexes while the co-mixed oxygen mediates the oxidative regeneration of iron(II) into iron(III) complexes. In this work, the oxidation kinetics of iron(II) trans-1,2,-diaminocyclohexanetetraacetate (cdta) complexes with molecular oxygen (O2) as the source oxidant was investigated for a wide pH range (1.7510pH>10, was found to be less reactive than Fe3+cdta4-Fe3+cdta4- with the superoxide intermediate (O2·-), thus reducing the effect of the reverse step at higher pH. A study on the effect of electrolytes on the reaction rate led to the conclusion that salts increase the rate constant k1,appk1,app. Finally, kinetic results in acidic conditions leading to the formation of other iron(II)–cdta complexes (i.e., Fe2+cdta4-H+Fe2+cdta4-H+) and another superoxide intermediates (HO2·) are reported and discussed.