(350c) Environmentally Sustainable Pathways for Extracting Valuable Elements from Electronic Wastes

Electronic wastes including printed circuit boards (PCBs) are some of the fast-growing wastes threatening our environment. Meanwhile, industrial mining continues to provide materials for fast-growing electronic industry. Thus, there is a strong need for sustainable resources for electronic materials. Interestingly, the high metal content of PCBs makes it an excellent source for urban mining and the recovery of metals from PCBs will provide a sustainable pathway to reduce the conventional mining and the landfilling of electronic wastes. Within the PCB board, the metal connectors contain considerable amount of coated gold, thus making them the most valuable resource to recover. In terms of total quantity, copper is a valuable resource that can be recovered from PCBs.

Unfortunately, the current resource recovery methods for PCBs, including intensive physical separation, pyrometallurgy, and hydrometallurgy with strong acids, are energy intensive, and environmentally hazardous. Most importantly, the complex compositions of PCBs connectors include multiple layers of metals, fiber glass board, solder masks, surface finishing, etc., which increases the difficulty to recover valuable resource without generating environmental and human health concerns.

In this study, a greener method to extract the metals (e.g. Au, Pd, Cu) from waste PCBs connectors is investigated, which aims to lower the environmental and human health hazards generated during the extraction process. This study employs supercritical CO2 to facilitate physical separation and/or hydrometallurgy extraction. Our study shows that the utilization of CO2 can reduce the use of strong acids during metal leaching, and inherently recover precious and base metals at different stages and in different forms, thus enhancing the overall sustainability of the PCB treatment processes. The feasibility and mechanisms of using CO2 (either in its liquid or supercritical forms) to enhance the metal recovery is analyzed and the role of CO2 in the physical and chemical alterations of polymer-metal matrix in PCBs is investigated.