Closed-Loop Electrochemical Recycling of Spent Copper(II) from Etchant Wastewater Using a Carbon Nanotube Modified Graphite Felt Anode.

Developing effective technologies for treatment of spent etchant in printed circuit boards industries is of paramount for sustainable copper reuse and reducing copper discharge. We developed a novel closed-loop electrochemical cell for on-site regeneration of spent acidic cupric chloride etchant. It does not have any emissions and recycles all the copper using a three-dimensional graphite felt anode decorated with carbon nanotube (CNT/GF). The CNT/GF anode oxidizes Cu(I) to Cu(II) so that the spent cuprous chloride can be converted to cupric chloride and reused. The decorated CNT layer with abundant oxygen-containing functional groups significantly enhanced the electrocatalytic activity for Cu(II)/Cu(I) redox. The CuCl32- is oxidized to CuCl+ at the anode and the CuCl+ is reduced to Cu(0) at the cathode. The closed-loop cycle system converts the catholyte into the anolyte. On average, the energy consumption of Cu(I) oxidation by CNT/GF is decreased by 12%, comparing to that by untreated graphite felt. The oxidation rate of Cu(I) is determined by the current density, and there is no delay for the mass transport of Cu(I). This study highlights the outstanding electrocatalytic performance, the rapid mass-transfer kinetics, and the excellent stability of the CNT/GF electrode, and provides an energy-efficient and zero-emission strategy for the regeneration of etchant waste.