Jiakai Zhang,† John Anawati,† Yuxiang Yao,† and Gisele Azimi*,†,‡
†Department of Chemical Engineering and Applied Chemistry, Laboratory for Strategic Materials, 200 College Street, Toronto,
Ontario M5S 3E5, Canada
‡Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario M5S 3E4, Canada
ABSTRACT:
There is a global need for efficient and environmentally sustainable processes to close the life cycle loop of waste electrical and electronic equipment (WEEE) through recycling. Conventional WEEE recycling processes are based upon pyrometallurgy or hydrometallurgy. The former is energy-intensive and generates greenhouse gas (GHG) emissions, while the latter relies on large volumes of acids and organic solvents, thus generating hazardous wastes. Here, a novel “aeriometallurgical” process was developed to recycle critical rare earth elements, namely, neodymium (Nd), praseodymium (Pr), and dysprosium (Dy), from postconsumer NdFeB magnets utilized in wind turbines. The new process utilizes supercritical CO2 as the solvent, which is safe,
inert, and abundant, along with the tributyl-phosphate−nitric acid (TBP−HNO3) chelating agent and 2 wt % methanol as a cosolvent. Nd (94%), Pr (91%), and Dy (98%) extraction was achieved with only 62% iron (Fe) coextraction and minimal waste generation. Fundamental investigations into the extraction mechanism demonstrated that metal ion charge has an important impact on the extraction efficiency. Fundamental investigations indicate that extraction proceeds by corrosion of the magnet particle’s surface layer. This work demonstrates that supercritical fluid extraction would find widespread applicability as a cleaner, a more sustainable option to recycle value metals from end-of-life products to enable the circular economy.
KEYWORDS: Supercritical fluid extraction, Waste electrical and electronic equipment recycling, Tributyl-phosphate-HNO3, NdFeB magnets