Development of environmentally friendly extraction processes for the selective recovery of strategic and critical metals from e-waste products

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In a world where everyone now has a smartphone, a computer or a tablet, waste electrical and electronic equipment (e-waste) became the fastest growing waste stream with over 50 million tons discarded worldwide in 2019. However, these items are full of valuable materials, including strategic and critical metals, which should be recovered to favor sustainable development and circular economy. Many challenges exist with e-waste recycling. With the fast development of these electronic products comes a need for new and specific recycling protocols. Reviewing metal recovery processes using hydrometallurgical methods, researchers emphasized the need for new selective leaching and extraction approaches for most of the valuable metals. These processes also need to be greener, avoiding the use of strong inorganic acids and toxic solvents commonly used today. To face these challenges, an original research program is proposed having as main objective to design new environmentally friendly extraction processes to selectively recover targeted metals from e-waste. To achieve this goal, biodegradable and mild organic acids will be used to solubilize metals from selected e-waste (LCDs, capacitors, and fluorescent tubes). Research activities will then be directed toward the development of: (i) selective supercritical CO2 (ScCO2) extraction processes using promising metal ligands, and (ii) solid-phase extraction processes using new porous organic polymers. ScCO2 is a promising non-flammable, inexpensive, and nontoxic solvent that can be integrated to develop novel, green and highly efficient metal extraction processes. Different ligands (N,N-di(alkyl)acetamide, aminopolycarboxylates, crown ethers), new to ScCO2 extraction, will be evaluated to selectively extract indium, tantalum and rare-earths, either directly from powdered e-waste fractions or from acid leachate solutions. From this research, new experimental and theoretical knowledges will emerge concerning: extraction performances and mechanisms, metal-ligand composition, solubility in ScCO2, and species phase distribution. Besides ScCO2 extraction processes, covalently cross-linked porous organic polymers have emerged as a new class of functional materials which, with their substantial pores, large specific surface area and excellent stability, are ideal candidate to adsorb metal ions from acid leachate solutions. Their synthesis and complete characterization (composition, morphology, porosity, stability, and adsorption capacity, isotherms, kinetics, selectivity) will produce groundbreaking advances in this research field. This innovative research program will bring crucial experimental and fundamental new knowledge to many scientific disciplines while being industrially highly relevant. It will promote recycling and sustainable development, and will enable saving natural resources and energy, reducing pollution, and make Canada less dependent to international suppliers of strategic and critical metals.