High-purity copper recovery from polyimide-enameled wires using pulsed discharge with a grinding pre-treatment

A promising strategy to meet growing demands for copper is to recover high-grade copper from spent enameled wires. However, spent enamel-wire recycling is challenging because the tightly bonded insulating films must be removed. Polyimide films are particularly difficult to remove because of their high heat and solvent resistance, and few studies have reported successful removal of polyimide films. The present study proposes a physical method to remove polyimide films from enameled wires by applying a grinding treatment and pulsed discharge. Pulsed discharge alone could not peel off such films; however, the grinding pre-treatment partially removed the polyimide film, which inhibited current flow to the target pieces, allowing the pulsed discharge process to effectively peeled off the film. Optimizing the grinding method increased the probability of energizing the sample, thereby enhancing the efficiency of the pulsed discharge step. The film removal rate reached 93.0 wt% using the developed combination treatment. Analytical results indicated that the film was peeled via carbonization in local high-temperature areas with radical-driven oxidation on the film surface. Meanwhile, neither carbonization nor oxidation occurred inside the polyimide film because the high dielectric strength of polyimide prevented the formation of current pathways. These results suggest that the generation of harmful substances and greenhouse gases during polyimide decomposition can be suppressed. The findings reported herein demonstrate the significant potential of pulse discharge as a physical method for rapidly removing films from spent enameled wires with low environmental impact.