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Within the PEACOC project, TECNALIA (Spain) has evaluated different chemistries of deep eutectic solvents (DESs) to recover Platinum Group Metals (PGMs) selectively from end-of-life autocatalysts. TECNALIA discovered a specific DES which allows the selective recovery of PGMs from spent autocatalysts as a precipitate of PGMs mixture (95% purity) containing 67% of palladium (Pd) and 27 % of platinum (Pt), and 1% rhodium (Rh). In addition, TECNALIA also studied the reuse of DES during seven cycles, and the results do not show a significant decrease in the extraction yield of PGMs. TECNALIA submitted a patent (EP22382410.3) based on this process.

Additionally, TECNALIA has also tested the recovery of PGMs from spent autocatalysts by electrifying the DES leaching process. This technology avoids several unit operations and the use of reagents. This new approach considers a combination of organic solvents, including DES, and aqueous solutions (e.g., NaCl), to selectively dissolve metals from solid materials. Anodes will be polarized to induce the water oxidation in the electrolyte, producing one or more oxidizing agents, such as hydroxyl radicals and hydrogen peroxide (thus avoiding their external addition), releasing the metals from the solid residue. The simultaneous electrodeposition of metals may occur on the cathode, depending on the physicochemical features of the solid input residues and the operational conditions employed.

This innovation allows the leaching process to selectively recover PGMs from solid residues (82% purity) in a single reactor without adding oxidizing agents. Those results have been also submitted as a patent (PCT/EP2023/055813).