Enhanced decomplexation of Cu-EDTA and simultaneous removal of Cu(II) by electron beam irradiation accompanied with autocatalytic fenton-like reaction: Synergistic performance and mechanism

Abstract

Widely existing heavy metal complexes with high stability and poor biodegradability are intractable to be eliminated by conventional methods. In this study, electron beam (EB) irradiation characterized by rapidly producing strong oxidizing radicals was employed to effectively decompose Cu-ethylenediaminetetraacetic acid (Cu-EDTA) with almost complete elimination at 5 kGy. In terms of heavy metal removal, EB irradiation at relatively low doses was insufficient to remove copper ions, which was only 17.2% under 15 kGy. However, with the extra addition of 8 mM H2O2, such an irradiation dose could result in 99.0% copper ions removal. Mechanism analysis indicated that EB irradiation combined with spontaneously induced Fenton-like reactions were responsible for its excellent performance. The prime function of EB irradiation was to destroy the structure of Cu-EDTA with in-situ produced ·OH, and the subsequent released Cu-based intermediates could activate H2O2 to initiate autocatalytic chain reactions, correspondingly accelerating the degradation of complexes and the liberation of metal ions. Highly oxidative ·OH and O2·− were demonstrated as main active species acted on different positions of Cu-EDTA to realize gradual decarboxylation, synchronously generating low molecular weight compounds. XRD and XPS analysis showed that the released copper ions were mainly precipitated in the form of CuO, Cu(OH)2 and Cu2(OH)2CO3. In general, EB/H2O2 was an adoptable strategy for the disposal of such refractory heavy metal complexes.