Self-initiated radical leaching for green recovery of precious metals

Abstract

Palladium (Pd) and platinum (Pt) are precious metals (PMs) that are widely used 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 spectroscopy, radical capture experiments and DFT calculations revealed that the spent PM 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 PM recovery, highlighting the underexplored self-initiated radical leaching mechanism of spent catalysts during oxidative dissolution.