Recovery of precious metals from WEEE in deep eutectic solvents by electro-leaching and electrodeposition: a mechanistic and kinetic study - Université de Lorraine Access content directly
Conference Papers Year : 2023

Recovery of precious metals from WEEE in deep eutectic solvents by electro-leaching and electrodeposition: a mechanistic and kinetic study

Abstract

In recent years, the excessive development of new technological tools has led to overconsumption of resources. Unfortunately, this fact not only corresponds to use of critical, rare, and precious metals, but it also causes a massive amount of waste. As a matter of fact, due to their high concentration of precious metals, waste from electrical and electronic equipment (WEEE) represent an important secondary resource in precious metals. However, the recovery of these noble metals requires several steps with the use of powerful agents e.g. cyanides or aqua regia, that are harmful for the environment. Moreover, it generates huge amounts of effluents. This work focuses on the development of a greener process for the recovery of silver, palladium, and gold from printed-circuit boards of cell phones. The process consists in coupling in a single cell, electro-leaching (EL) and electro-deposition (ED) steps using ionic solvents. Deep eutectic solvents (DES) are indeed part of this solvent group: their low volatility, their low vapor pressure and their chemical and thermal stability1, allows them to be greener, i.e. far less harmful for the environment. Among these DES, mixture of choline chloride (ChCl) (hydrogen bond acceptor) and ethylene glycol (EG) (hydrogen bond donor) called ethaline (ET), was selected following the first studies on gold and palladium recovery.2 The toxicity of the mixture is not well known. However, to make this process even more environmentally friendly, the substitution of ET with a natural deep eutectic solvent (NADES) called propeline (PROP) is considered. EG is thus replaced by propylene glycol (PG) which is far less toxic and often used in cosmetic and pharmaceutical products. Due to the strong complexing activity of these solvents, the EL step is efficient. According to EXAFS (Extended X-Ray Absorption Fine Structure) studies, silver is present as a mixture of [AgCl2]- and [AgCl3]2- in ET.3 Raman and UV-Vis spectroscopy analyses show that gold and palladium are in the leachate as [AuCl2]- and [PdCl4]2-.2,4 In these media, it was shown that both steps of the proposed process are controlled by the mass transport to the electrodes. Therefore, to improve the process, an electrochemical study on the kinetic parameters was conducted. Initially, the development of the procedure for the determination of the diffusion coefficients was carried out on the silver system which is the most stable and has a fast and simple electrochemical system with the exchange of a single electron. In order to obtain a value with an optimal and reliable precision, several methods and electrochemical laws were used. The diffusion coefficient was determined by applying the Cottrell’s, Randles-Sevcik’s and Levich’s laws on the data obtained by chronoamperometry (CA), cyclic voltammetry (CV), and CA (with rotating electrode) respectively. Moreover, combination of Randles-Sevcik and Tafel’s laws allowed to estimate for charge transfer coefficient α and rate constant k0 after fixing the formal potential E0. The slow diffusion of species in these slightly viscous media leads to a large dispersion of results due to different surface states (diffusion layer composition). To remedy this, a fine optimization of the analysis procedures allowed repeatable and reproducible measurements to be obtained by letting the surface concentration to return to that of the bulk level. Finally, these optimized methods will be applied to the more complex Pd and Au systems. Indeed, it has been shown that Au(I) dismutes slowly in the medium2. Consequently, a study on the stability of the leachate is underway to work on this complex. (1)El Achkar, T.; Greige-Gerges, H.; Fourmentin, S.. Environ. Chem. Lett. 2021, 19 (4), 3397–3408. (2)Villemejeanne, B. These de doctorat, [in French] Université de Lorraine, 2022. https://www.theses.fr/2022LORR0010 (3)Abbott, A. P.; Azam, M.; Frisch, G.; Hartley, J.; Ryder, K. S.; Saleem, S. Phys. Chem. Chem. Phys. 2013, 15 (40), 17314–17323. (4)Villemejeanne, B.; Legeai, S.; Meux, E.; Dourdain, S.; Mendil-Jakani, H.; Billy, E. J. Environ. Chem. Eng. 2022, 10 (3), 108004.
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Dates and versions

hal-04161251 , version 1 (13-07-2023)

Identifiers

  • HAL Id : hal-04161251 , version 1

Cite

Calogera Bertoloni, F. Lapicque, Eric Meux, Sophie Legeai. Recovery of precious metals from WEEE in deep eutectic solvents by electro-leaching and electrodeposition: a mechanistic and kinetic study. 74th Annual Meeting ISE, International Society of Electrochemistry, Sep 2023, Lyon, France. ⟨hal-04161251⟩
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