Dr. César A C Sequeira

Abstract:

Recently, the European Commission carried out an assessment of 83 raw materials and identified several elements including heavy rare earths, light rare earths, platinum group metals, non-metallic elements in supply risk, and other metals in supply risk within criticality zone of high economic importance (³ 2.8) and supply risk ((³ 1) [1], which place serious pressure related to sustainable supply chains and environmental issues. This ongoing technological evolution has resulted in a rapidly growing generation of electronic waste and toxic substances, leading to significant harmful effects on the environment and human health [2]. Therefore improving the efficiency of recovery of metal from either primary mining processing or from secondary waste, as well as sustainable urban mining /recycling, is of utmost importance to both the economy and environment. Contrary to traditional recovery techniques, which are chemically intensive and often require large pH or thermal swing [3], electrochemically mediated technologies offer modular approaches as alternatives of traditional chemical / thermal swing-based separations [4,5]. In this context we present here recent considerations on hydrometallurgical and electrochemical approaches that can benefit critical materials recycling, especially for rare earth elements and other valuable transition metals. More specifically, we provide insights into the mechanisms and applications for different electrochemical techniques [6,7], namely electrodeposition, electrosorption, electrodialysis and electrocoagulation, as well as recovery techniques at an interface electrode level, using porous capacitive electrodes, intercalation electrodes and redox active electrodes. In parallel,  judicious electrochemical engineering (e.g., the design of counter electrodes, types of electrical stimuli, optimizing electrochemical parameters) can significantly improve the separation and energy efficiency. In sum, the increasing demand and decreasing supply of global critical raw materials call for the development of the sustainable recovery and recycling of the valuable elements. Hydrometallurgical processes have been studied for various recycling applications, with increasing industrial-scale implementations in the last decades. There have been significant improvements but, at the same time, several issues with regard to chemical footprint, generation of wastes, slow leaching, and molecular selectivity still remain. In mitigating these challenges, electrochemical separations can be naturally coupled with existing hydrometallurgical processes, and we believe that this combination of electrochemical and hydrometallurgical separation steps, can pave a path toward sustainable materials recycling and critical element recovery.