Selective recovery of platinum group metals from spent automotive catalysts by leaching and solvent extraction

Platinum group metals (PGMs) play an important role in the automotive industry as key components of exhaust catalysts. Recycling of PGMs from secondary resources, such as waste products, is encouraged to ensure their sustainability. A highly efficient and environmentally benign technique for the separation of PGMs is currently required. In the present study, the recovery of PGMs from a spent automotive catalyst was investigated using the trioctyldodecyl phosphonium chloride (P_8,8,8,12Cl) ionic liquid (IL) as the PGM extraction solvent. First, leaching from the catalyst was investigated. Pt and Pd are selectively extracted into undiluted P_8,8,8,12Cl from the 5 mol L−¹ HCl leachate containing various metals together with Pt, Pd, and Rh. Subsequently, Rh is extracted into fresh P_8,8,8,12Cl from the raffinate adjusted to an appropriate HCl concentration. Mutual separation of Pt and Pd is possible by stripping processes. Some common metals co-extracted with PGMs, such as Fe, Cu, and Zn, are removed by each stripping process. Recovery of high purity Pt, Pd, and Rh is achieved by the proposed recycling process. The results demonstrate that separation using phosphonium-based ILs is useful for recycling PGMs.