Efficient extraction of critical elements from end-of-life automotive catalytic converters via alkaline pretreatment followed by leaching with a complexing agent

Abstract

Spent automotive catalytic converters are one of the fastest-growing waste streams that could be considered as a potential industrially demanded source of platinum group metals (PGMs), rare earth metals (REEs), and other critical elements. In this research, an integrated recycling approach was proposed based on the characteristics of the waste and its refractory nature. The proposed process focused on enriching REEs and mobilizing other critical metals from waste through alkali roasting pretreatment followed by oxalic acid leaching. In this regard, suitable parameters include the roasting temperature of 700 °C, waste powder to NaOH ratio of 1:3 (w/w), roasting time of 1.5 h, the oxalic acid concentration of 0.15 M, and pulp density of 5 g/L were obtained. High extraction of Pd (99.90%) and Pt (98.69%) along with other elements (Zn (98.44%), Mn (96.93%), Fe (99.87%), Al (99.15%), Si (99.23%), Ti (99.78%), and Sr (50.43%)) was obtained simultaneously while REEs such as Ce, Nd, Pr, and La were enriched during the process. The structural, morphological, and physicochemical analyses showed that the proposed approach could successfully overcome waste complexities and extract most metals.