High-efficient decomplexation of Cu-HA by discharge plasma: Process and mechanisms

Abstract It is difficult to remove heavy metals-humid acid (HA) complexes with stable properties by traditional precipitation method, and they can bring potential threats to human health. The decomplexation of heavy metal-HA complex (Cu-HA as a model) was explored using non-thermal plasma (NTP) in this study, and influences of coexisting ions on Cu-HA decomplexation were assessed. High-efficient Cu-HA decomplexation performance was obtained by the NTP oxidation, and it reached 89.3% in a treatment period of 15 min; and the pseudo-first order kinetics was suitable to describe this process. The presence of Fe2+ favored Cu-HA decomplexation process via displacement and Fenton-like effects. Whereas some amounts of Cl-, NO3- and SO42- with low dosages promoted this process. Active species including O3, O2·- and ·OH played primary roles in Cu-HA decomplexation, but the role of high-energy electrons could be neglected. NTP oxidation broke the chromophoric group, Cu-O, Cu-N, and unsaturated bonds of the Cu-HA complex. Some decomplexation intermediates including benzoic acids, amines, esters, and phenols were generated. Meanwhile, the precipitation processes were analyzed via energy dispersive X-ray, X-ray photoelectron spectrum, thermal stability, fourier transform infrared spectroscopy, and X-ray diffraction.