Leaching of platinum group metals from spent automotive catalysts using organic acids

Abstract

An efficient and environmentally friendly new process is described for the recovery of platinum group metals from spent automotive catalysts. The process consists of the application of mechanical processing followed by heat treatment and leaching, with the aim of reducing the use of acids that can have adverse effects in the environment. The extraction of PGMs was carried out using HCl associated with malic, formic, and citric acids. Evaluation was made of the effects of parameters including acid concentration, volumes of inorganic and organic acids, solid to liquid (S/L) ratio, and extraction time. The automotive catalyst powders were characterized using XRD, SEM/EDS, particle size distribution, and EDXRF techniques. The spent automotive catalysts contained reasonable concentrations of Pt and Pd. Over 90% of the Pt and Pd could be recovered in a leaching process using 6 M HCl, S/L ratio of 1:30, and 20% (v/v) citric acid. The findings showed that citric acid can be used in the recovery of PGMs from spent automotive catalysts, decreasing the use of aggressive and corrosive acids often employed in the recovery of these metals. Hence, the addition of organic acids can contribute to efficient and environmentally friendly processes for the recovery of Pt and Pd.