A green strategy for simultaneous Cu(II)-EDTA decomplexation and Cu precipitation from water by bicarbonate-activated hydrogen peroxide/chemical precipitation

Abstract

Classical chemical precipitation technology is inefficient for the removal of heavy metal-organic complexes from wastewater. In this study, a novel and green strategy of coupling bicarbonate-activated hydrogen peroxide (BHP) oxidation and alkaline precipitation was proposed for simultaneous decomplexation of Cu-ethylenediaminetetraacetic acid (Cu-EDTA) and Cu precipitation. The Cu-EDTA decomplexation efficiency reached 92.0% within 60 min of the BHP treatment, and the decomplexation process was spontaneous and endothermic. Reactive substances such as O2−, OH, and 1O2 were identified, and O2− was predominant in the Cu-EDTA decomplexation. The weak alkaline environment provided by bicarbonate favored the generation of the reactive substances and subsequent Cu-EDTA decomplexation. Relatively higher H2O2 dosage favored Cu-EDTA decomplexation, while excessive bicarbonate dosage inhibited the reaction. TOC removal efficiency and Cu removal efficiency reached 78.4% and 68.3% after 60 min treatment, respectively. The CuO and CuN bonds in Cu-EDTA were destroyed by the reactive substances, and a series of Cu-containing intermediates, small organic molecules such as ethanamine, ethylene glycol and butanediol, and NO3− were produced. The released Cu ions were precipitated as Cu2(OH)2CO3, CuCO3, Cu(OH)2, and CuO. Possible pathways of Cu-EDTA decomplexation in this system were proposed.