• Bertoloni, Calogera
• Lapicque, François
• Mendiljakani, Hakima
• Menut, Denis
• Ekomo, Vitalys Mba
• Meux, Eric
• Dumas, Thomas
• Billy, Emmanuel
• Michel, Stéphanie
• Legeai, Sophie

Abstract

Nowadays, the recovery of precious metals (Ag, Au, Pd...) is mainly carried out using pyro- or hydrometallurgical processes consisting of numerous steps which generate a lot of waste products. In particular, due to the use of toxic compounds e.g. cyanides with strong complexing properties, these wastes require additional specific treatments before their disposal. For the sake of greener processes, ionometallurgy appears an attractive alternative. Indeed, this route uses ionic solvents with high complexing and conductive properties in addition to being thermally (low volatility) and electrochemically stable (working in a wide range of potential). This last criterion is very important here with the use of a single electrochemical cell allowing electro-leaching at the anode and electro-deposition at the cathode, to recover precious metals e.g. Au, Pd and Ag from electronic waste. Previous work on this subject revealed the effectiveness of a 1:2 mixture of choline chloride (ChCl) (hydrogen bond acceptor) with ethylene glycol (EG) (hydrogen bond donor), called ethaline (ET). Thus, from these first encouraging results and to make the process greener, this work focuses on the substitution of EG by propylene glycol (PG), another hydrogen bond donor of similar structure but far less toxic, actually used in cosmetics and pharmaceuticals. The mixture of PG and ChCl is called propeline (PROP). Bulk properties of PROP required in the electrochemical process, density, viscosity, conductivity, electrochemical stability have been determined. Then, PROP and ET were compared when used in the electrochemical cell, indicating comparable performance in the leaching of Au, Ag and Pd. An analytical method for elemental analysis by ICP-OES in leachates was developed for this purpose. Furthermore, metal speciation in the PROP- or ET leachates by spectroscopic methods such as UV-Vis, and EXAFS/XANES at SOLEIL facility was shown very similar. Finally, the electrochemical deposition step was evaluated by the electrochemical determination of kinetic parameters and the diffusion coefficients of the electroactive metal species of the above determined chemical nature.This work was funded by ANR within EE4Precious project ANR-20 –CE08-0035-01

Topics

• Deposition
• density
• impedance spectroscopy
• compound
• laser emission spectroscopy
• viscosity
• Hydrogen
• leaching
• atomic emission spectroscopy
• elemental analysis
• extended X-ray absorption fine structure spectroscopy