Leaching of Pt, Pd and Rh from Automotive Catalyst Residue in Various Chloride Based Solutions

Abstract

Platinum-group metals (PGM) are important precious metals in many industrial fields. However, their natural resource deposits are strictly limited. Accordingly, their recycling process from wastes and/or secondary resources must be considered. In this study, the leaching of PGM from automotive catalyst residue was performed based on the formation of their chloro-complexes in various concentration of acidic solution. The recovery of platinum, palladium and rhodium from the samples after hydrogen reduction pretreatments was examined in the leaching process by using a mild solution mixture of NaClO–HCl and H₂O₂ at 65°C for 3 h. Effect of other solution mixtures on the extraction of the precious metals was also compared with NaClO–HCl–H₂O₂, such as HCl–H₂O₂ and NaClO–HCl. The optimum condition to dissolve platinum, palladium and rhodium was achieved by the mixture of 3 vol% NaClO, 5 kmol·m⁻³ HCl and addition of 1 vol% H₂O₂. The recovery of platinum, palladium and rhodium after 3 h leaching reaches 88%, 99%, 77%, respectively.