Process simulation and life cycle assessment of hydrometallurgical recycling routes of waste printed circuit boards

Abstract

Electronic waste remains a pressing global environmental concern. Addressing the proper treatment and recycling of waste printed circuit boards (WPCBs) is imperative to mitigate environmental pollution and prevent the loss of valuable resources. In this study, a comparative analysis of acidic and alkaline leaching processes for recovering base metals (Cu, Sn, Zn, and Ni) from WPCBs was conducted by process simulation (using HSC software). Life cycle inventories were compiled accordingly. Furthermore, by incorporating an alternative method for precious metal recovery, the life cycles (using openLCA software) of both processes for recovering all metals were examined. The results revealed that while the acidic leaching process showed higher recoveries for base metals and advantages in terms of lower electricity consumption and wastewater generation, it also exhibited a more pronounced environmental impact due to the chemical input in the HNO3 leaching process. Conversely, the alkaline leaching process utilized fewer chemicals, generated less solid waste and off-gases, resulting in a lower overall environmental impact. For recycling 1 t of WPCBs, the acidic leaching process achieved recoveries of 92% for tin, 99% for copper, 79% for zinc, and 94% for nickel, whereas the alkaline leaching process yielded recoveries of 96%, 93%, 78%, and 74% for the corresponding metals. Notably, the alkaline leaching process demonstrated a lower global warming potential of 11,395 kg CO2 eq, compared to the 12,459 kg CO2 eq associated with the acidic leaching process. In the evaluation of the alkaline leaching process, most environmental impacts were found to be lower than for virgin production. As a result, while the acidic leaching process is indeed more efficient in metal recycling, the alkaline leaching process emerges as a stronger contender in terms of environmental sustainability, with great potential for further technical improvements.