Development of green supercritical fluid extraction processes for the selective recovery of strategic and critical metals from e-waste products

1. 废弃的电子电气设备（e-waste）充满了有价值的材料，包括可以回收的战略和关键金属，有利于可持续发展和循环经济。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，避免使用目前经常使用的强无机酸和有毒有机溶剂。为了应对这些挑战，提出了一个原创的研究计划，包括开发一种绿色的、选择性的超临界流体萃取工艺，使用有前途的金属配体。2. 生物可降解和温和的有机酸将用于从选定的电子废物（lcd，电容器和荧光灯管）中溶解金属。然后将评估不同的配体（N，N-二（烷基）乙酰胺，氨基聚羧酸盐，冠醚），以选择性地从反应介质中提取目标金属（铟，钽或稀土）到超临界二氧化碳（ScCO2）相，后者将作为绿色溶剂。二氧化碳减压将允许金属配合物的恢复，金属配合物将被处理以恢复配体和感兴趣的金属。3. 为了完成这项研究，需要一个实验装置，应该包括：高压搅拌反应器，配有温度控制的电加热器和相观察的窗口，二氧化碳泵，共溶剂泵（配体或添加剂的引入），背压调节器（压力调节和连续操作模式），产品回收容器，液体自动进样器和控制模块（计算机通信和数据采集）。4. 启用的研究活动(i)该设置将用于开发和优化连续/半批/批实验的ScCO2提取工艺。还将研究ScCO2对浸出效率的影响。（ii）将进行ScCO2中的溶解度研究（配体、金属盐和螯合物以及有机酸），这对评价和预测物相分布和萃取性能至关重要。溶解度将通过液体取样（气相色谱或高效液相色谱分析）或云点目视观察来测量。5. 本研究的重要性本研究计划的许多方面都是原创的，值得研究。将ScCO2萃取与新型配体相结合，选择性地从电子废物中分离有价金属，将为许多科学学科（过程工程、采矿、冶金）带来重要的实验和基础知识，同时在工业上具有高度相关性。这项研究是环境友好型的，将有助于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。

1. Introduction and research opportunity Waste electrical and electronic equipment (e-waste) are full of valuable materials, including strategic and critical metals which can be recovered favoring sustainable development and circular economy. 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 organic solvents frequently used today. To face these challenges, an original research program is proposed including the development of a green and selective supercritical fluid extraction process using promising metal ligands. 2. Summary of the scientific approach Biodegradable and mild organic acids will be used to solubilize metals from selected e-waste (LCDs, capacitors, and fluorescent tubes). Different ligands (N,N-di(alkyl)acetamide, aminopolycarboxylates, crown ethers) will then be evaluated to selectively extract targeted metals (indium, tantalum or rare-earths) from the reaction medium to a supercritical carbon dioxide (ScCO2) phase which will act as green solvent. The CO2 decompression will allow the recovery of the metal complex which will be treated to recover the ligand and the metal of interest. 3. Requested equipment To accomplish this research, an experimental setup is needed and should include a: high-pressure stirred reactor equipped with an electric heater for temperature control and windows for phases observations, CO2 pump, co-solvent pump (ligands or additives introduction), back-pressure regulator (pressure regulation and continuous mode of operation), product recovery vessel, liquid autosampler, and control module (computer communication and data acquisition). 4. Enabled research activities (i) This setup will be used for the development and optimization of the ScCO2 extraction processes from continuous/semi-batch/batch experiments. The impact of ScCO2 on the leaching efficiency will also be studied. (ii) Solubility studies (ligands, metal salts and chelates, and organic acids) in ScCO2 will be performed and are essential to evaluate and predict the species phase distribution and extraction performances. Solubility will be measured either by liquid sampling (GC or HPLC analysis) or by cloud point visual observation. 5. Importance of this research Many aspects of this research program are original and deserve to be investigated. The combination of ScCO2 extraction with novel ligands to selectively separate valuable metals from e-waste will bring vital experimental and fundamental knowledge to many scientific disciplines (process engineering, mining, metallurgy) while being industrially highly relevant. This research is environmentally friendly and will enable saving natural resources and energy, reducing pollution, and make Canada less dependent to international suppliers of strategic and critical metals.