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The platinum nanoparticles used as the catalyst in proton exchange membrane fuel cells (PEMFCs) represent approximately 46 % of the total price of the cells for a large-scale production, and this is one of the barriers to their commercialization. Therefore, the recycling of the platinum catalyst could be the best alternative to limit the production costs of PEMFCs. The usual recovery routes for spent catalysts containing platinum are pyro-hydrometallurgical processes in which a calcination step is followed by aqua regia treatment, and these processes generate fumes and NO x emissions, respectively. The electrochemical recovery route proposed here is more environmentally friendly, performed under 'soft' temperature conditions, and does not result in any gas emissions. It consists of the coupling of the electrochemical leaching of platinum in chloride-based ionic liquids (ILs), followed by its electrodeposition. The leaching of platinum was studied in pure ILs and in ionic-liquid melts at different temperatures and with different chloride contents. Through the modulation of the composition of the ionic-liquid melts, it is possible to leach and electrodeposit the platinum from fuel-cell electrodes in a single-cell process under an inert or ambient atmosphere. [ABSTRACT FROM AUTHOR]

Precious metals (PM) refining from E-waste recycling are based on hazardous hydrometallurgical processes, including cyanide leaching for gold or aqua regia leaching for palladium, which generates an important wastewater production. In this paper, we present an electrochemical process, based on low viscous deep eutectic solvents ChCl:EG 1:2 and ChCl:EG 1:3. Au and Pd electrochemical leaching and deposition parameters, but also gold and palladium speciation were studied. A one-step ElectroLeaching-Electrochemical Deposition Process (EL-ECD) in a single cell is proposed with high faradic yield of metal recovery. This process avoids electrolyte degradation and is advantageous to limit solvent losses and workers exposition. Electroleaching (EL) and simultaneous ElectroChemical Deposition (ECD) cell for Au and Pd recovery – Gold deposited on glassy carbon cathode. [Display omitted] • Gold and palladium recovery was achieved by ElectroLeaching-ElectroChemical Deposition (EL-ECD) in a deep eutectic solvent. • Au and Pd ElectroLeaching (EL) leads to AuCl 2 - and PdCl 4 2- formation with a faradic yield ranged between 98 % and 100 %. • Au and Pd ElectroChemical Deposition (ECD) is controlled by metal complexes diffusion from the bulk toward the electrode. • Au and Pd Electroleaching and simultaneous ElectroChemical Deposition was achieved in ChCl:EG mixture with a faradic yield ranged between 85 % and 100 %. [ABSTRACT FROM AUTHOR]

Precious metal refining from ore or electronic devices includes hydrometallurgical processes with major concern about toxicity or wastewater production. As an alternative, one-step electroleaching-electrochemical deposition process (EL-ECD) using ionic liquid mixtures was evaluated for palladium and gold recovery. A halide based ionic liquid combined with a diluting ionic liquid was chosen among ten electrolytes after cyclic voltammetry and potentiostatic experiments. These low viscous electrolytes allow complexing Au and Pd, leading to metal leaching at low anodic potential. Moreover, the complexes formed could be simultaneously deposited at the cathode. Metal behavior is similar for all halide anions tested (chloride, bromide and iodide). Results show that chloride based mixtures are the more suitable electrolyte providing the highest leaching faradic yield. This process appears more sustainable than conventional processes (chlorination, cyanide leaching) thanks to the electrolyte stability limiting solvent losses but also workers exposition. The EL-ECD process for gold or palladium recovery in ionic liquid mixture allowing a one-step electroleaching-electrochemical deposition of metal without any solvent degradation. This process prevent wastewater production or toxic gases emission [Display omitted] [ABSTRACT FROM AUTHOR]

This paper presents recent views on a hybrid process for beneficiation of secondary raw materials by combined electroleaching of targeted metals and electrodeposition. On the basis of several case studies with aqueous solutions or in ionic liquid media, the paper describes the potential and the limits of the novel, hybrid technique, together with the methodology employed, combining determination of speciation, physical chemistry, electrochemistry, and chemical engineering. On one hand, the case of electroleaching/electrodeposition (E/E) process in aqueous media, although often investigated at the bench scale, appears nevertheless relatively mature, because of the developed methodology, and the appreciable current density allowed, and so it can be used to successfully treat electrode materials of spent Zn/MnO2 batteries or Ni/Cd accumulators and Waelz oxide. On the other hand, the use of ionic liquids as promising media for the recovery of various metals can be considered for other types of wastes, as shown here for the case of electrodes of aged fuel cells. The combined (E/E) technique could be successfully used for the above waste, in particular by the tricky selection of ionic liquid media. Nevertheless, further investigations in physical chemistry and chemical engineering appear necessary for possible developments of larger-scale processes for the recovery of these strategic resources. [ABSTRACT FROM AUTHOR]

The investigation was aimed at developing a new electrochemical process for recovery of nickel, cobalt and cadmium mainly present in the form of hydroxides in Ni–Cd batteries, in view to obtain, a solid residue composed of metal nickel and carbon, a pure cadmium-free solution of metal salts and metal cadmium. This process relies upon coupling leaching of the metal hydroxides by electrogenerated protons to electrodeposition in a single divided cell. The feasibility of the technique has been first demonstrated in a lab cell operated in batch mode: cadmium-free solution of nickel and cobalt cations could effectively be produced at the end of the 5-h run, with nearly complete leaching of the hydroxides and a current efficiency of the cathode near 73%: occurrence of side hydrogen evolution at the cathode reduced the efficiency during the last hour of the treatment because of insufficient amounts of Cd 2 + cations. In a second test, the waste (called black mass) was added at regular intervals, in view to allowing more regular transfer rates of Cd 2 + species to the cathode chamber. The more even profiles of concentrations allowed avoiding depletion of this cation, which resulted in higher current efficiency in cadmium deposition. The efficiency of fed-batch mode is finally discussed in relation to the compromise to be found between purity of the cadmium-free solution and current efficiency of cadmium. [ABSTRACT FROM AUTHOR]