Proton-Driven Multistage System Enables Selective Recovery of Gold and Palladium from Electronic Waste Leachate

Selective extraction of precious metals from urban mines plays a crucial role in mitigating the risk of depletion of precious metal resources and reducing waste pollution. However, a major obstacle in precious metal extraction lies in the difficulty of distinguishing the subtle differences in the physicochemical characteristics between them, especially gold and palladium. Herein, a proton-driven separation system was presented for cascade recovery of gold and palladium from waste-printed circuit boards (W-PCBs) leachate using poly(amidoxime) (PAO) hydrogel. This exhibits an ultra-high capacity, extra-fast rate, and excellent selectivity for the extraction of Au(Ⅲ) and Pd(Ⅱ). Notably, the separation of Au(Ⅲ) and Pd(Ⅱ) can be achieved with high selectivity at pH = 0, resulting in a remarkable separation factor of k_{Au(Ⅲ)/Pd(Ⅱ)} = 36.5. This was demonstrated to originate from the differential mechanism of PAO hydrogel for the capture of Au(Ⅲ) and Pd(Ⅱ) under proton-mediated conditions. Drawing inspiration from the mechanism, the proton-driven cascade recovery system demonstrates remarkable efficiency in sequentially recovering 99.92% of gold and 99.05% of palladium from W-PCBs acid leachate. This research opens up a strategy to precisely separate and recover precious metals from e-waste of urban mines.