Facile path for copper recovery from waste printed circuit boards via mechanochemical approach.

Recycling copper (Cu) from waste printed circuit boards (PCBs) is a prevalent challenge. Here, we propose a new pathway and reveal mechanisms for recovering Cu from waste PCBs via a mechanochemical approach. The successful application of mechanical force avoids using inorganic acid in the Cu recovery process. Our work demonstrates that ferric chloride (FeCl) was superior to ferric sulfate and ferric nitrate as a solid-phase reagent for Cu recovery due to chloride complexation. Under the induction of mechanical force, the Cu in the waste PCBs was oxidized by Fe and complexed by Cl to form a meta-stable cuprous chloride, which was susceptible to leaching in an acidic liquid-phase system constructed by hydrolysis of ferric salt. Further mechanism analysis reveals that in the mechanochemical solid-phase reaction, Cu, metallic impurities, metal oxides, and carbon materials from waste PCBs could also reduce Fe to Fe. The optimum conditions for Cu recovery from waste PCB powder with FeCl as a solid-phase reagent were: rotational speed of 500 rpm, Cu:Fe molar ratio of 1:20, and reaction time of 120 min, achieving the highest recovery of 99.6 wt%. This study presents a facile path for Cu recovery from waste PCBs for resource circulation.