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

1.介绍和研究机会废旧电器和电子设备(电子废物)充满了有价值的材料，包括可以回收的有利于可持续发展和循环经济的战略和关键金属。研究人员审查了使用湿法冶金法回收金属的过程，强调需要对大多数有价值的金属采用新的选择性浸出和提取方法。这些过程还需要更环保，避免使用当今经常使用的强烈无机酸和有毒有机溶剂。为了应对这些挑战，提出了一项原创性的研究计划，包括开发一种使用有前景的金属配体的绿色和选择性超临界流体萃取过程。2.科学方法概述将使用可生物降解和温和的有机酸从选定的电子废物(液晶显示器、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、氨基多羧酸盐、冠醚)，以从反应介质中选择性地将目标金属(铟、钽或稀土)提取到作为绿色溶剂的超临界二氧化碳(ScCO2)相。二氧化碳减压将允许金属络合物的回收，该金属络合物将被处理以回收配体和感兴趣的金属。3.完成这项研究所需的设备，需要一个实验装置，该装置应包括：装有用于温度控制的电加热器和用于观察相的窗口的高压搅拌反应器、二氧化碳泵、共溶剂泵(引入配体或添加剂)、背压调节器(压力调节和连续操作模式)、产品回收容器、液体自动取样器和控制模块(计算机通信和数据采集)。4.能够开展的研究活动(I)这一装置将用于开发和优化从连续/半批/批次实验中提取二氧化碳的过程。还将研究ScCO_2对浸出效率的影响。(2)将进行SCCO2的溶解度研究(配体、金属盐和络合物以及有机酸)，这对于评估和预测物种的相分布和萃取性能是必不可少的。溶解度将通过液体取样(GC或HPLC分析)或通过浊点目视观察来测量。5.这项研究的重要性这项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，从电子废物中选择性地分离有价值的金属，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，同时具有高度的工业相关性。这项研究对环境友好，将有助于节约自然资源和能源，减少污染，并使加拿大减少对战略和关键金属的国际供应商的依赖。

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.