Enhanced extraction of copper from electronic waste via induced morphological changes using supercritical CO2

Electronic waste (e-waste) is one of the fastest growing waste segments in the world. This study investigates the use of supercritical CO2 (scCO2) and aqueous acid as co-solvent for the treatment of e-waste, specifically for the extraction of copper. Printed circuit board (PCB) was selected as the e-waste of study. In order to perform controlled experiments, melt-pressed Cu foil and polycarbonate sheets were prepared as surrogates for PCBs. It was found that a scCO2 and acid pre-treatment induced drastic morphological changes in the polymer, creating pores, cracks, and delamination. This finding was translated to the actual waste PCB system. This unique process involved the pre-treatment of the PCB with scCO2 and aqueous sulfuric acid at 120 °C and 148 atm for 30 min followed by leaching of the treated PCB in a solvent containing 2 M sulfuric acid and 0.2 M hydrogen peroxide at ambient conditions. Experimental results showed that 82% of the copper contained in the PCB was extracted in under 4 h. The characterization of the PCB demonstrated that the pre-treatment with scCO2 and acid induced the crystallization of the plastics (polymer component), creating pores and weakening the structure of the PCB, thereby enhancing the transport of the solvent to the buried metal interfaces. This novel process using scCO2 could reduce physical processing (e.g. grinding of the PCB) and acid usage during the extraction of Cu from e-waste, providing a greener alternative for current methods of recycling of metals, which are energy intensive with large environmental footprints.