Coupling electrochemical leaching and electrodeposition in ionic solvents for critical and precious metals recovery

The development of technologies that allow us to recycle or reuse waste electrical and electronic equipment (WEEE) is paramount in order to create an environmentally sustainable economy. It is also noteworthy that the percentage of some metals in WEEE is larger than in their natural sources, thus generating economic interest in their recycling [1]. Notably, the concentration of precious metals (e.g. Au, Ag, Pd, Pt) in High Tech end-of-life products like smartphones or tablets can be ten to twenty-five times higher than in ores. Generally, precious metals sludges produced by pyrometallurgical primary treatments are treated using multi-step complex hydrometallurgical processes, that have some important limitations for workers or installation safety and remain far from sustainable development considerations. Besides, these pyrometallurgical processes dilute many “minor”, but critical metals (Sn, Sb, Ta…) in the multimetallic outgoing fraction, so that they cannot be recovered in a viable way.In this context, the promising properties of ionic solvents might be an opportunity to design new metal recovery processes being more respectful of Green Chemistry principles with less wastewater generation, less reactants used and less hazards associated. We will present the potentialities of coupling electrochemical leaching and deposition (EL-ECD) in a single cell using ionic solvents for the recovery of precious metals (Au, Pt, Pd, Ag) from rich-metallic waste issued from WEEE primary treatment. The influence of anionic part of various ionic solvents on metals electrochemical behavior was studied by electrochemical techniques. Metal speciation and kinetics parameters associated to electrochemical reactions were determined in most promising electrolytes, by spectroscopic and electrochemical transient/stationary techniques respectively. The performances of the process, namely leaching and electrodeposition efficiencies, were established in ambient atmosphere. Faradaic yields, recovery rates and selectivity for mono and bi-metallic synthetic waste were studied, thanks to the development of a large set of analytical procedures dedicated to elemental analysis in ionic solvents (ICP-OES). The feasibility of using this kind of electrolytes for Sn recovery from the solders used in PCB will also be presented. The effects of varying and mixing anions, temperature and atmosphere (Ar and air) were investigated. The results demonstrate certain conditions under which the oxidation and deposition of Sn in ILs are reversible, indicating the possibility to recover Sn in ionic solvents. The selectivity towards Pb and Cu was evaluated.[1] Marra A., Belgiorno V. 2018. Glob. Nest. J., 20, 679-69