Repurposing of aluminum scrap into magnetic Al0/ZVI bimetallic materials: Two-stage mechanical-chemical synthesis and characterization of products

Abstract Bimetallic materials—well-known for their strong reducing properties—are promising tools to recover battery/critical elements from waste streams for resources conservation and decontamination. To date, however, their synthesis has been limited to the use of pure monometallic elements. In this study, we synthesized magnetic bimetallic materials from aluminum wastes (Al-scrap) using a two-stage mechanical-chemical method composed of (1) polishing to remove protective coatings, and (2) etching-cementation for zero-valent iron (ZVI) deposition. Argon-etching using X-ray photoelectron spectroscopy (XPS) showed the effective removal of anodized/polymeric coatings on Al-scrap but the exposed Al0 was rapidly passivated by an Al-oxyhydroxide/oxide film composed of corundum, bayerite, and boehmite. In the etching-cementation stage, the Al-oxyhydroxide/oxide film was removed using NaCl–HCl and Fe3+ was deposited in corrosion pits on Al-scrap. Strong “magnetic susceptibility” was observed in 1.0 M Fe3+/3.5 M Cl− synthesized products but not in 0.5 M Fe3+/2 M Cl−. This difference could be attributed to the prevalence of ZVI formation in the former but akaganeite precipitation in the latter. The results also showed “targeted” recovery of copper dissolved from Al-scrap on ZVI regions of synthesized product. Finally, two pathways are proposed for Fe3+ reduction: (i) direct cementation (Fe3+→ZVI), and (ii) sequential reduction (Fe3+→Fe2+→ZVI).