Résumé
Numeric transition stands on the utilization of sophisticated devices like smartphones, computers or server, which contain an important concentration of critical, rare, or precious metals. So on, metal production from primary ores or from end-of-life devices will necessary increase in the next decades. Currently, precious metals production imply many pyrometallurgical and hydrometallurgical steps and a refining process to obtain pure metals. This refining step is similar using e-waste or primary ores for production, and presents hazardous drawbacks including harmful reagent utilization (cyanide or strong acids) and important wastewater generation. The association of ionic solvents (Ionic Liquids (IL) or Deep Eutectic Solvents (DES)) to electrochemistry could represent a greener solution to this application. These solvents have a low vapor pressure and are non-flammable which considerably reduce fire hazards or worker’s inhalation. Furthermore, they have a great stability (thermal and electrochemical) and act like efficient complexing agents, two very useful properties for precious metals electroleaching without any solvent degradation. These properties have been already used to recover different metals in IL and DES at lab1 or pilot scale2.Recently, CEA Liten and Jean Lamour Institute obtained promising results using a single step electroleaching-electrodeposition (El-Ed) process using ionic liquids for Pt recovery from a membrane electrode assembly (MEA)3.In present work, we evaluate ionic solvent relevance for developing an El-Ed process for gold and palladium electrochemical recovery. We present leaching and deposition performances in IL-mixture and DES for gold and palladium, and electrochemical characteristics which are required for this process. For some ionic liquids, we obtained a gold electroleaching rate comparable to conventional cyanide solution meanwhile DES exhibit faster leaching kinetics. For these promising electrolytes, we focused on the electrodeposition steps (limiting step), and studied metals and ionic species mass transport using Walden plot, PFG-NMR and electroanalytical techniques. Finally, we discussed about relevant experimental parameters (additives, temperature, concentration) to improve mass transport in these solvents. References:1G. R. T. Jenkin, A. Z. M. Al-Bassam, R. C. Harris, A. P. Abbott, D. J. Smith, D. A. Holwell, R. J. Chapman and C. J. Stanley, Minerals Engineering, 2016, 87, 18–24.2A. P. Abbott, G. Frisch and K. S. Ryder, Annu. Rep. Prog. Chem., Sect. A: Inorg. Chem., 2008, 104, 21.3M. Balva, S. Legeai, N. Leclerc, E. Billy and E. Meux, ChemSusChem, 2017, 10, 2922–2935.