Removal of Cu, Ni and Zn directly from acidic electroplating wastewater by Oligo-Ethyleneamine dithiocarbamate (OEDTC)
Traditional chemical precipitation generates a large volume of sludge required by further hazardous waste disposal. For reducing this drawback, four oligo-ethyleneamine dithiocarbamates (OEDTC), including ethylenediamine-dithiocarbamate (E 1 -DTC), diethylenetriamine-dithiocarbamate (E 2 -DTC), triethylenetetramine-dithiocarbamate (E 3 -DTC) and tetraethylenepentamine-dithiocarbamate (E 4 -DTC) were synthesized to remove Cu, Ni and Zn directly from acidic wastewater. Based on S dose, which was an essential element for metal removal, the treatment effectiveness order of the four OEDTC for Cu and Ni was E 1 -DTC > E 2 -DTC > E 4 -DTC > E 3 -DTC. The theoretical molar ratios of S toward Cu, Ni and Zn for the completed metal removal from single component were 1.5:1, 2:1, 2.2:1 for E 1 -DTC; 2:1, 2.6:1, 2.9:1 for E 2 -DTC; 2:2, 3:1, 3.9:1 for E 3 -DTC; and 2:1, 2.7:1, 2.8 for E 4 -DTC, respectively. The four OEDTC had marked preference for Cu over Ni and Zn from multiple components of simulated wastewater. They showed high removal efficiency for the complex-formed Ni and Zn from actual electroplating wastewater, yielding the effluent residual 0.003–0.008 and 0.021–0.046 mg/L, respectively. When the four OEDTC were precipitated with the three metals, FT-IR suggested the coordination of metals with S and SEM indicated densely packed particle formation. The yielded OEDTC-metals sludge enriched with heavy metals exhibited potential to be recycled.
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