Green palladium and platinum recovery by microwave-assisted aluminum chloride solution†

Abstract

Palladium and platinum are precious metals (PMs) used in industrial catalysis, and their green recycling is crucial but challenging. In this study, we aimed to create a novel leaching procedure for the environmentally friendly recovery of PMs using AlCl₃·6H₂O solution. We report here the use of a microwave-assisted AlCl₃·6H₂O solution to selectively recover Pd and Pt from spent catalysts. In a large-scale setting, our system can recover gram-scale Pd in a single batch. Electron paramagnetic resonance (EPR) and capture experiments revealed the hydroxyl radicals produced by proton dissociation and microwave coordination triggered the oxidative dissolution process. Microwave-assisted AlCl₃·6H₂O solution leaching and NaBH₄ reduction recovered high-purity Pd and Pt separately. In scale-up experiments, the dissolution performance of the microwave-assisted AlCl₃·6H₂O solution for Pd remained almost unchanged after seven cycles. Our approach uses around 1/50 and 1/20 of the energy and chemical inputs of the conventional hydrometallurgy process, respectively. Strong acids, poisonous cyanide, and volatile organic solvents were not used during the recovery process, enabling an efficient and sustainable PM recovery process and promoting an advanced oxidation process (AOPs) technology for secondary resource recycling.