Leaching of Platinum Group Metals from Spent Automotive Catalytic Converters Using Deep Eutectic Solvents: A Review

Platinum group metals (PGMs), platinum (Pt), palladium (Pd) and rhodium (Rh), are critical for automotive emission control, chemical manufacturing and emerging energy technologies, yet their supply is limited and geographically concentrated. Their designation as critical raw materials (CRMs) in the EU has intensified recycling efforts, especially from spent automotive catalysts. Conventional pyrometallurgical and acid-based hydrometallurgical routes achieve high recovery efficiencies but rely on aggressive reagents and energy-intensive processing. Deep eutectic solvents (DESs) have emerged as greener leaching media capable of dissolving PGMs under milder and tunable conditions. This review outlines the conventional hydrometallurgical framework, summarizes DES fundamentals relevant to metals dissolution, and critically assesses recent advances in DES-based leaching of PGMs from spent catalysts. The influence of solvent composition, oxidants and complexing ligands on PGMs speciation and recovery is discussed, together with emerging reporting guidelines and research priorities. Overall, DES-based leaching offers a promising and potentially safer route for autocatalyst recycling but the technology remains at an early stage of development, requiring further mechanistic insight and sustainability evaluation.