Minimization of Energy Wastage in the Electrochemical Recovery of Copper from Its EDTA Complexes in Wastewaters

For the first time, the recovery of copper from Cu(II)-EDTA complexes in waste streams, which originated from \nelectroless plating of printed circuit boards (PCB), is optimized with respect to the consumption of electrical energy required for the separation process. To narrate the sequence of arguments which result in this minimization of energy expenditure, an electrochemical reactor is set up so that the ways in which electric potential and pH influence the rate of electrodeposition of copper, and therefore power usage, can be followed closely. The initial concentrations of the components of this simulated wastewater are 0.04 mol dm-3 of Cu2+ ions and 0.13 mol dm-3 of EDTA, typical of this type of liquid waste. By applying an electric potential of -1.0V for 4 hours, recovery of copper by electrodeposition at pH = 10.7 in the electrolysis cell equipped with a cation exchange membrane is evinced, successfully removing 31% of Cu2+ ions from aqueous solution. This is carried out for demonstrative purposes, with full recovery expected to be achieved in 12 hours. Studying the rate-controlling mechanisms for the electrodeposition of copper by utilizing a rotating disc electrode reveals that the deposition process is both kinetically and mass transport controlled, down to potentials of -1.5V relative to a Standard Calomel Electrode (SCE). Favoured mass transfer mode of operation therefore exists at potentials considerably more negative than -1.5 V, in a potential region where hydrogen production is significant and therefore not viable for electrodeposition. This is the electric potential of sole interest to this work because it is to be avoided. Visual confirmation of copper deposits on the cathode confirmed feasibility of this clean technology for metal recycling. Moreover, a threshold potential of -1.0 V against which engineers can benchmark during preliminary reactor design has been identified in this pioneer work. The authors wish to emphasize that the present work focuses on the theme of "energy efficiency" for a proposed electrolytic process, and in this short space, does not seek to include elucidation of the modes of film deposition and nucleation on surfaces of electrodes by instrumental methods such as scanning electron microscopy (SEM), x-ray diffraction (XRD) or energy dispersive x-ray analysis (EDX). This will be in the domain of future work.