Leaching Platinum Group Metals from Simulated Spent Auto-Catalyst Material Using Ozone and Hydrochloric Acid

This paper reports the development of a process for leaching Pt, Pd, and Rh from simulated spent auto-catalyst material using ozone and hydrochloric acid in order to produce a pregnant leach solution that could be fed to an industrial precious metal refinery. The effects of O3 mass flow, initial acid concentration, and temperature were investigated using a Box–Behnken experimental design with three centre-point runs and a total leach time of 6 h. Set points of 3.34, 5.01, and 6.68 g/h; 1.0 M, 3.0 M, and 5.0 M; and 30, 60, and 90 °C were used for O3 mass flow, hydrochloric acid concentration, and temperature, respectively. The optimal extractions for Pt, Pd, and Rh were 80%, 85%, and 42%, respectively, at 5.01 g/h O3, 5.0 M HCl, and 90 °C. Statistical analyses indicated high dependencies of Pd and Rh on hydrochloric acid concentration and temperature, with only Pt displaying a significant dependence on O3 mass flow.