Recovery of palladium, platinum, rhodium and ruthenium from catalyst materials using microwave-assisted leaching and cloud point extraction

• Environmentally friendly recovery of PGEs (Pd, Pt, Rh, Ru) was studied.
• Microwave-assisted leaching was combined with cloud point extraction (CPE).
• Effect of temperature, leaching agent and L/S ratio on leaching of PGEs was studied.
• CPE method was optimized and applied for diluted leach solutions (1 M HCl).
• In the future, PGEs from dilute waste solutions could be recovered by using CPE.

The recovery of Pd, Pt, Rh and Ru from an automotive catalyst and from an alumina-supported Ru catalyst was studied. Microwave-assisted leaching of Pd, Pt, Rh and Ru was combined with cloud point extraction to obtain an environmentally friendly recycling method. A series of leaching experiments with HCl, HNO3 and aqua regia at five different temperatures (90–210 °C) was performed in a microwave oven. Aqua regia and HCl were able to leach > 90% of Pd, Pt, Rh and Ru at temperatures above 150 °C. At 120 °C slightly lower recoveries were observed, but also the leaching of the matrix elements was decreased. A cloud point extraction (CPE) method was applied to the samples obtained after HCl leaching at 120 °C. The method was first optimized to a suitable concentration level of Pd, Pt, Rh and Ru (> 1 mg L− 1) by using a factorial design. Then, the appropriately diluted leach solutions (1 M HCl) were extracted and the recoveries of 91 ± 6% for Pd, 91 ± 5% for Pt, 85 ± 6% for Rh and 66 ± 11% for Ru were achieved. Simultaneously, the concentrations of the matrix elements (Al, Ce, Zr) were reduced by over 95%.