Enrichment of Precious Metals from Wastewater with Core–Shell Nanoparticles of Iron

Large‐scale deployment of zero‐valent iron nanoparticles for enrichment and recovery of gold from industrial wastewater is reported. Iron nanoparticles have a core–shell structure in which a metallic iron core is enclosed with a thin layer of iron oxides/hydroxides. The two nanocomponents offer synergistic functions for rapid separation, enrichment, and stabilization of metal ions such as Au, Ag, Ni, and Cu. Thanks to the advantages of small size, large surface area, and high reactivity, only a small amount of iron nanoparticles are needed. The recovered nanoparticles thus contain precious metals well above conventional metal ores (e.g., >100 g Au ton−1). Cost‐effective recovery of precious metals from trace‐level sources such as wastewater looks promising. Nanoscale zero‐valent iron with a body‐centered‐cubic polycrystalline metallic iron core and a surface layer of short‐range periodic iron oxides/hydroxides can be synthesized in water and under room temperature. This core–shell nanomaterial has alkaline surface pH, negative surface charge, and low solution redox potential, ideal for sorption, reduction, and enrichment of precious metals such as Au, Ag, and U.