Flakes and Nanoparticles from Waste Ru-Plated Fashion Items through Food Waste by-Products

Ruthenium is relevant for a broad range of applications, including catalysis and electronics. Like other metals of the platinum group, ruthenium stands out as one of the rarest elements in the Earth's crust. The demand for Ru from the industry is putting pressure on its availability. Hence, its recovery from secondary sources is imperative. Fashion solid residues of the plating industry are an important waste stream for Ru. Within this context, we propose a novel approach to Ru recovery for its safe, sustainable, and economically affordable upcycling. The approach is based on peeling from waste metal wires by a green oxidizing agent, H₂O₂, in an environment acidic by lactic acid, a by-product of the food industry. Peeled flakes were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy for their structure and (surface) chemical composition and bonding. Inductively Coupled Plasma Optical Emission Spectroscopy shows the ultra-low concentration of noble metals in the leachate, thereby suggesting their quantitative recovery in their metallic state. Further, we observed the colloidal nature of the washing water of the peeled flakes. Therefore, we hypothesized the presence of nanoparticles in the washing water and went for their characterization.