Microwave-assisted chloride leaching for efficient recovery of platinum group metals from spent automotive catalysts: An approach for chemical reagent reduction

Abstract

The unique chemical and catalytic properties of platinum group metals play an important role in transition towards a more sustainable society. Recognizing their economic significance, the European Union (EU) has classified platinum group metals as strategic and critical raw materials. Due to the scarcity of primary sources, the EU heavily relies on imports of platinum group metals from third countries. Therefore, maximizing the recovery of platinum group metals from secondary sources, such as spent automotive catalysts, is essential. This study aims to optimize a microwave-assisted leaching process to enhance the selective extraction of palladium, platinum and rhodium efficiently while minimizing chemical reagents use. Initially, the main parameters such as concentration of reagents, reaction temperature and processing time were optimized on a small laboratory scale before scaling up. Results showed that reducing the hydrochloric acid concentration from 6 to 1.5 M and addition of sodium chloride as alternative source of chlorine anions, slightly decreased platinum group metals extraction but significantly improved selectivity towards matrix elements like aluminium, cerium, and magnesium. Applying the optimized conditions of microwave-assisted leaching in an upscaling experiment resulted in extractions of more than 90% for palladium and platinum, and almost complete extraction of rhodium. The optimized process can create opportunities for establishing small to medium-scale local hydrometallurgical plants for recovery of platinum group metals.