Self-initiated radical leaching for the green recovery of precious metals

Abstract

Palladium (Pd) and platinum (Pt) are widely used precious metals (PMs) in modern industrial catalysis, yet their recovery from spent catalysts remains a challenge. In this work, we demonstrate a self-initiated radical leaching strategy for Pd and Pt recovery using a low-concentration inorganic AlCl3 solution as a green leaching agent. Mechanistic investigations combining electron paramagnetic resonance, radical capture experiments and DFT calculations revealed that the spent PMs catalysts activate O2 to generate hydroxyl radicals, which promote the oxidative dissolution of the embedded PMs. High-purity Pd and Pt were successfully recovered via a mild lixiviant leaching and N2H4·H2O reduction process, minimizing costs while eliminating the need for harsh acids, toxic cyanides, or volatile organic solvents. This approach offers an environmentally sustainable route for PMs recovery, highlighting the underexplored self-initiated radical leaching mechanism of spent catalysts during oxidative dissolution.