[Publication] Halide based ionic liquid mixture for a sustainable electrochemical recovery of precious metals

Tuesday, February 22, 2022 - 18:33
Sous titre
The IJL researchers develop soft chemical technologies applied to metal recycling. Among them are ionometallurgic processes, using ionic liquids (IL) or deep eutectic solvents (DES) which are characterized by a low vapor pressure, a low flammability and a high chemical inertness. In the framework of his PhD thesis, Benoît Villemejeanne studied the applicability of an electrochemical process using ionic liquid mixtures, which relies on simultaneous electroleaching (EL) and electrochemical deposition (ECD) of metals in a single cell, with a focus on palladium and gold.

The use of IL mixtures is an interesting way to combine their useful and various properties. In the field of metal recycling, the association of a diluting IL having a low viscosity and high thermal/chemical stabilities and of a metal complexing IL is quite promising.

In this paper, several IL mixtures were tested, based on 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as diluting IL (C4C1Im NTf2) and C4C1 as complexing IL (X=Cl, Br, I, NO3, MeSO3, OTf, NTf2, DMP, DCA, OAc). Among the ten electrolytes studied, gold and palladium electrochemical leaching could be achieved quantitatively only in chloride based IL mixture.

The electroleaching/electrochemical deposition coupling (EL-ECD) was implemented in this electrolyte and quantitative recovery of palladium and gold was achieved in ambient atmosphere, without any degradation of the solvent. This approach could represent a sustainable alternative to harmful and complex hydrometallurgical existing routes for the recovery of precious metals, based on the use of concentrated acid solutions and toxic reagents such as cyanides, and could thus avoid the generation of large quantities of toxic wastewater.  This process is of high interest in the recycling field of precious metal rich resources such as waste electrical and electronic equipment (WEEE), but one can also think about applications in electroplating industry.

References:

Titlee: Halide based ionic liquid mixture for a sustainable electrochemical recovery of precious metals

Authors: B. Villemejeanne, S. Legeai, E. Meux, S. Dourdain, H. Mendil-Jakani et E. Billy

Journal: Journal of Environmental Chemical Engineering

Date of publication (online) : December 2021

Link: https://doi.org/10.1016/j.jece.2021.107063

Image caption: EL-ECD process implemented in C4C1ImNTf2 + C4C1ImCl 0.1 M IL mixture

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EL-ECD process implemented in C4C1ImNTf2 + C4C1ImCl 0.1 M IL mixture