Negative-Carbon Recycling of Copper from Waste as Secondary Resources using Deep Eutectic Solvents

Copper plays a crucial role in the low-carbon transformation of global communities with prevalent use of electric vehicles. This study proposed an environmentally friendly approach that utilizes a deep eutectic solvent (DES), choline chloride-ethylene glycol (ChCl-EG), as green solvent for the selective extraction of copper from scrap materials. With hydrogen peroxide as an oxidizing agent, the copper species from the printed circuit boards (PCBs) scraps were efficiently leached by the DES through oxidation-complexation reactions (conditions: 25 min, 20 °C, and 5 wt.% H2O2). Molecular dynamics and density functional theory were performed to simulate the intricate cascade of interactions between copper species and hydrogen bond donors/acceptors of DES, providing insights into the mechanistic processes involved. Copper was selectively recovered from the DES leachate containing impurities (e.g., Pb2+, Sn2+, and Al3+) through electrodeposition via a diffusion-controlled reaction under a constant potential mode. A comprehensive life cycle assessment of the process demonstrated that the utilisation of DES in the extraction of copper from waste PCBs could result in significant reduction in carbon dioxide emissions (-93.6 kg CO2 eq of 1000 kg waste PCBs), thus mitigating the carbon footprint of global copper use through the proposed solvometallurgical recycling process of secondary resources. The recycling of waste copper resources is a critical approach in achieving the worldwide low-carbon transition, as printed circuit boards (PCBs) comprise a substantial quantity of valuable copper resources. However, secondary pollution to the environment may result from the organic bromine and heavy metals present in discarded PCBs. A methodology for extracting copper resources from discarded PCBs through the utilization of deep eutectic solvents has been delineated. This approach can prevent the use of corrosive reagents in hydrometallurgical processing, including acid and alkali. It also possesses low-carbon properties because of inhibiting the combustion of brominated epoxy resin during pyrometallurgical processing