Non-thermal plasma oxidation of Cu(II)-EDTA and simultaneous Cu(II) elimination by chemical precipitation

Cu2+ readily complexes with ethylenediaminetetraacetic acid (EDTA) to form a heavy metal complex (Cu-EDTA) that is typical in the effluents from mining and electroplating industries. It was difficult for the classical alkaline precipitation method to eliminate the heavy metal complex due to the strong bonding ability between Cu(II) and EDTA. Cu(II) release and removal performance after Cu-EDTA decomplexation in a non-thermal plasma oxidation system was carried out in this study. The removal process was characterized by chemical oxygen demand, total organic carbon, atomic force microscopy, and electroconductivity analysis. The toxicity effect of the treated Cu-EDTA solution was also tested by photobacterium bioassay. The experimental results showed that 80.2% of Cu was released and removed within 60 min of the non-thermal plasma treatment/alkaline precipitation. Relatively higher energy input, lower Cu-EDTA concentration, and acidic conditions were necessary to obtain greater Cu release and removal performance, and there existed an appropriate air flow rate for high-efficient Cu release and removal. O2−, OH, 1O2, and O3 were the main active substances leading to Cu2+ release. Its residual toxicity to P.phosphoreum sp.-T3 was significantly reduced after treatment. [Display omitted] •EDTA-chelated copper removal is studied by discharge plasma/alkaline precipitation.•Effects of operating parameters on Cu release and removal are evaluated.•Contributions of reactive substances to Cu release and removal are analyzed.•Residual toxicity after Cu release is explored via photobacterium bioassay.