Supercritical water-assisted acid leaching for efficient copper recovery from waste circuit boards: Mechanisms, optimization, and sustainable metal extraction

Waste printed circuit boards (WPCBs) represent a valuable resource for recovery owing to their substantial metallic content. Nonetheless, efficient metal extraction is hindered by the robust epoxy resin matrix. This study introduced a novel supercritical water (SCW)-assisted acid leaching process to achieve rapid epoxy resin decomposition and high-efficiency Cu recovery. A systematic analysis was conducted on the decomposition behavior of epoxy resin and its monomer, bisphenol A diglycidyl ether (BADGE) in supercritical water. Through product characterization, the mechanism of co-action involving hydrolysis, free radical reactions, and solvolysis during the decomposition of epoxy resin has been elucidated. Response surface methodology (RSM) was employed to optimize hydrothermal parameters for BADGE decomposition and predict optimal reaction conditions. Subsequent acid leaching of SCW-decomposed products achieved a high leaching efficiency (98.9 %) and selectivity (99.9 %) of Cu. This integrated SCW-acid leaching process offers a promising and effective solution for WPCB recycling, aligning with the dual goals of environmental sustainability and efficiency in resource recovery.