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

Abstract

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 (>1mgL−1) by using a factorial design. Then, the appropriately diluted leach solutions (1M 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%.