Recovery of Platinum Group Metals from Spent Automobile Exhaust Catalysts

Spent automobile exhaust catalysts are a typical platinum group metal secondary resource. In the traditional hydrometallurgical process, the extraction of platinum group metals by oxidative acid leaching will lead to the problem of a low palladium leaching ratio. In this paper, the E-pH diagram of platinum group metals and chloride ions is drawn. The existing forms of platinum group metals under different pH and potential conditions are analyzed, and the reason for this phenomenon is explained. It is proposed to use ferric chloride as oxidant to efficiently leach palladium in a hydrochloric acid system. The leaching ratio of palladium reached 97.67%, which is 6.77% higher than that of hydrogen peroxide as oxidant. The leaching residue is then oxidized by hydrogen peroxide. The comprehensive leaching ratios of platinum, palladium, and rhodium can reach 97.72%, 98.92%, and 99.53%, respectively.