Recycling of e-waste power cables using microwave-induced pyrolysis – process characteristics and facile recovery of copper metal

Abstract

This article reports on recycling e-wastes using a VVF power cable as a model through a rapid pyrolytic process following exposure to microwave radiation. This occurred via three possible pathways: (i) discharges at the copper wire on exposure to microwaves, with heat produced causing the thermal decomposition of the covering material – a relationship exists between the length of the copper wire and the wavelength of the microwaves; (ii) microwave heating softened the wire's covering material and ultimately led to its decomposition – in addition, the coating material carbonized by the discharge is rapidly heated by microwaves; (iii) the carbonaceous component present in the covering material absorbed the microwaves, causing the thermal decomposition. On the other hand, for VVF cables longer than 12 cm canceled the wavelength-dependent process, and the longer the VVF cable was, the more efficient was the microwave-induced pyrolysis, therefore eliminating the need to pre-cut the waste VVF cable into smaller pieces. The microwave-induced pyrolysis showed that chlorine could be recycled as HCl and the carbon and activated carbon produced could be recovered as carbon black. While conventional pyrolysis might produce tar substances and polycyclic aromatic compounds, microwave pyrolysis has been shown to enable extremely rapid resource recovery, with only C₆ to C₁₂ linear alcohols produced as intermediates; no formation of tar-like substances, polycyclic aromatic compounds, or dioxins were detected. Clearly, microwave-induced pyrolysis has proven suitable for recycling/recovery of e-waste containing metals and requires no pre-treatment to separate the plastics from the metals.