Decomplexation of EDTA-chelated copper and removal of copper ions by non-thermal plasma oxidation/alkaline precipitation

EDTA-chelated metals, which widely occur during heavy metal contaminated-soil remediation by EDTA washing, are difficult to remove by traditional chemical precipitation because of the strong complexation between EDTA and heavy metal ions. A strategy, i.e., non-thermal plasma (NTP) oxidation/alkaline precipitation, was developed to remove the EDTA-chelated metals; EDTA-chelated copper (EDTA-Cu) was used as the model pollutant and the influences of some concomitant ions on EDTA-Cu decomplexation and Cu release were evaluated. The concomitant anions Cl− and NO3− favored EDTA-Cu decomplexation, whereas CO32− disfavored this process; the concomitant positive ions Ni2+ and Fe3+ both promoted EDTA-Cu decomplexation via replacement or Fenton-like effects. These effects were also characterized by total organic carbon and Cu2+ release analysis. The contributions of O3, O, 1O2, OH, and O2− to EDTA-Cu decomplexation were quantitatively analyzed. Ethanamine, acetamide, glycolic acid, acetic acid, formamide, ethylene glycol, and butanedioic acid were monitored using gas chromatography-mass spectrometry, and a possible decomposition pathway of EDTA-Cu was proposed. Furthermore, the chemical compositions of the precipitates were diagnosed by energy dispersive X-ray spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermal gravimetric analysis.