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

在一个人人都有智能手机、电脑或平板电脑的世界里，废弃的电子电气设备（电子废物）成为增长最快的废物流，2019年全球丢弃的废物超过5000万吨。然而，这些物品充满了有价值的材料，包括战略和关键金属，应该回收，有利于可持续发展和循环经济。电子垃圾回收存在许多挑战。随着这些电子产品的快速发展，需要新的和具体的回收协议。研究人员回顾了湿法冶金方法的金属回收过程，强调需要新的选择性浸出和提取方法来处理大多数有价金属。这些过程还需要更加环保，避免使用目前常用的强无机酸和有毒溶剂。为了面对这些挑战，提出了一个原始的研究计划，其主要目标是设计新的环保提取工艺，以选择性地从电子废物中回收目标金属。为了实现这一目标，将使用可生物降解的温和有机酸来溶解选定电子废物（lcd、电容器和荧光灯管）中的金属。然后，研究活动将朝着以下方向发展：(i)使用有前途的金属配体的选择性超临界CO2 （ScCO2）萃取工艺，以及（ii）使用新型多孔有机聚合物的固相萃取工艺。ScCO2是一种很有前途的不易燃、廉价、无毒的溶剂，可用于开发新型、绿色、高效的金属提取工艺。不同的配体（N，N-二（烷基）乙酰胺，氨基聚羧酸酯，冠醚）是ScCO2萃取的新技术，将评估直接从粉状电子废物馏分或从酸性渗滤液溶液中选择性提取铟，钽和稀土。通过这项研究，我们将在萃取性能和机理、金属配体组成、在ScCO2中的溶解度和物相分布等方面获得新的实验和理论知识。除ScCO2萃取工艺外，共价交联多孔有机聚合物以其孔隙大、比表面积大、稳定性好等优点，成为吸附酸性渗滤液中金属离子的理想材料。它们的合成和完整的表征（组成、形态、孔隙度、稳定性和吸附能力、等温线、动力学、选择性）将在这一研究领域产生突破性的进展。这一创新研究项目将为许多科学学科带来重要的实验和基础新知识，同时与工业高度相关。它将促进循环利用和可持续发展，并将使节省自然资源和能源，减少污染，并使加拿大减少对战略和关键金属国际供应商的依赖。

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.