A Molten Salt Extraction Method for Palladium Recovery via the CaPd₂ Intermetallic Compound

To address palladium scarcity and the low efficiency of conventional recovery processes, this work presents a molten-salt extraction strategy for palladium recovery via the CaPd₂ intermetallic compound. The process is based on the formation of CaPd₂ and its subsequent oxidation by active iodine species generated in molten CaI₂. First-principles calculations reveal a charge transfer of approximately 0.84 |e| from Ca to Pd in CaPd₂, resulting in an ionic bonding framework with covalent contributions arising from Ca-Pd orbital hybridization. This unique bonding characteristic confers excellent thermal stability, with a mass loss of less than 0.13% up to 1273 K. The CaPd₂ intermetallic compound was successfully synthesized and experimentally verified by X-ray diffraction and thermogravimetric analysis. In molten CaI₂, iodine species selectively oxidize the anionic Pd species in CaPd₂, enabling the direct recovery of metallic Pd. Under optimized conditions (1073 K, 1 h), palladium with a purity of 99.5 ± 0.3 wt.% was obtained. Unlike conventional pyrometallurgical and hydrometallurgical processes, the proposed approach eliminates the acid-leaching step and achieves rapid Pd recovery within 1 h. The results establish an iodine-mediated molten-salt recovery mechanism and provide a potential route for future palladium recovery from secondary resources.