Decomplexation of Ni-EDTA enhanced by Fe(III) reduction in the Fenton reaction: Insight into the role of carbonyl groups

Abstract

The slow Fe(II)/Fe(III) cycle during the Fenton reaction process strongly impedes oxidation efficiency in practical applications. In this study, an activated carbon (AC) assisted Fenton reaction system was used to treat electroplating wastewater containing Ni-ethylenediaminetetraacetic acid (Ni-EDTA). AC was found to enhance the removal of Ni-EDTA in Fenton/Fenton-like reactions. The reported results revealed that AC could effectively promote the regeneration of Fe(II) from Fe(III) species via electron transfer to improve the reaction rather than directly enhancing the H2O2 decomposition to accelerate the production of hydroxyl radicals (•OH). Quenching experiments and EPR also demonstrated that •OH and •O2− took part in the radical oxidation process, in which the contribution of •OH was dominant. XPS and FT-IR analysis further confirmed that the carbonyl group (CO) on the surface of AC could indeed act as the dominant active site and an electron donor to directly reduce Fe(III). In addition, electrochemical tests indicated that AC could increase the oxidation potential of Fe(III) to boost the reaction between Fe(III) and H2O2, thus enabling the transfer of electrons from H2O2 to Fe(III) to facilitate the Fe(II)/Fe(III) cycle. This study might contribute to a new insight into the mechanisms of AC-catalyzed Fenton oxidation processes for the decomplexation heavy metal-EDTA.