A Molten Salt Extraction Method for Palladium Recovery via the CaPd 2 Intermetallic Compound
Jiapeng Zhang, Dengjie Yan, Muwen Chen, Baoqiang Xu, Bin Yang, Bingyi Song, Lingxin KongABSTRACT
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 CaPd 2 intermetallic compound. The process is based on the formation of CaPd 2 and its subsequent oxidation by active iodine species generated in molten CaI 2 . First–principles calculations reveal a charge transfer of approximately 0.84 |e| from Ca to Pd in CaPd 2 , 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 CaPd 2 intermetallic compound was successfully synthesized and experimentally verified by X–ray diffraction and thermogravimetric analysis. In molten CaI 2 , iodine species selectively oxidize the anionic Pd species in CaPd 2 , 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.