Selective recovery of palladium from actual acidic wastewater using a covalent triazine framework: The critical enabling role of chloride ions

Driven by escalating demand and constrained primary supply, the efficient recovery of palladium (Pd) from secondary resources has become paramount. However, selective separation remains challenging in chloride-rich acidic wastewaters and leachates from electroplating and spent-catalyst recycling, where Pd is stabilized as chloro complexes. Here, chloride ions are shown to play an active and insufficiently explored role in regulating Pd speciation, interfacial coordination, and selective adsorption in acidic aqueous systems. Using a nitrogen-rich covalent triazine framework (CTF-FUM) as a model adsorbent, highly efficient and selective Pd capture is achieved in acidic chloride media, achieving a maximum adsorption capacity of 460.28 mg·g^‒1 and a Pd/Pt separation factor of 93.40. Significantly, chloride concentration defines a narrow but effective selectivity window that enables preferential Pd binding, while excessive chloride suppresses selective adsorption by over-stabilizing Pd chloro complexes. Importantly, this chloride-regulated behavior aligns well with the intrinsic chemistry of real industrial effluents, allowing >98.23% Pd recovery from actual electroplating wastewater and spent catalyst leachates under mild conditions. This work highlights the critical role of anion-mediated speciation control in metal separation and provides new insights for designing selective adsorbents for precious metal recovery from complex environmental matrices.