Study on enameled wire pyrolysis of CO2 for high-quality recovery of copper and suppression of product toxicity

Abstract

Waste motor windings in end-of-life electric spindles are recognized as a valuable resource for high-purity copper recovery, but conventional pyrolysis methods suffer from the toxicity of pyrolysis products and embrittlement of recycled copper. In this study, a CO₂-assisted pyrolysis method was proposed for efficient copper recovery and toxic compound suppression. High-purity copper (99.99 wt%) was recovered from waste motor windings by combined CO₂ pyrolysis and mechanical sieving, achieving a copper recovery efficiency of 99.51 %. The product distribution was restructured under CO₂ atmosphere, a 13.80 % reduction in benzene derivatives and a 12.03 % decrease in polycyclic aromatic hydrocarbons in the pyrolysis oil were observed. The favorable results were mainly attributed to the gas-phase reactions between CO₂ and volatile compounds, which suppressed polyaromatic condensation pathways and promoted oxidative cracking of volatile organics. In addition, the homogeneous reaction between CO₂ and pyrolysis products reduced the accumulation of hydrogen in copper, and the elongation of copper wire obtained at a CO₂ gas flow rate of 100 mL/min was enhanced by 134 % compared to that under N₂. This study suggested that CO₂ could be a sustainable alternative to N₂ in pyrolysis for the effective recovery of higher quality copper from enamelled wires.