Enhanced copper extraction from waste printed circuit boards using glycine after supercritical methanol pre-treatment: Process optimization, leaching kinetics, and thermodynamic analysis

The disposal of waste-printed circuit boards (WPCBs) poses significant environmental and health risks, as they are a major component of e-waste containing hazardous materials. However, WPCBs also contain valuable metallic elements, making them important resources for recycling. To address the dual challenge of hazardous waste management and resource recovery, sustainable approaches for metal extraction from WPCBs are imperative. The present study, thus aimed to explore the use of glycine as an environment-friendly alternative to conventional inorganic acid-leaching agents for copper extraction from WPCBs. The integration of glycine leaching with pre-treatment under supercritical conditions with methanol enhanced the copper liberation efficiency along with improved mass transfer processes. Under optimized conditions of 0.5 M glycine concentration, 5 % (v/v) H₂O₂ concentration, 1.5:100 g/mL solid-to-liquid ratio, and 40 °C temperature, a remarkably high copper extraction efficiency of 97.46 % was achieved within a 15 h leaching duration. Besides, the kinetic studies indicated a mixed-controlled reaction mechanism for the metal extraction process, with a calculated activation energy of 40.01 kJ/mol. Additionally, a thorough characterization of the recovered metal-leached salt provided insights into the compound's nature and leaching mechanism. This integrated approach developed thus offers a sustainable and environment-friendly method for reducing the hazardousness of WPCBs while simultaneously extracting valuable metals, contributing to the advancement of e-waste management practices and environmental sustainability.