A novel recycling route for aluminum alloys: Synthesis of Fe/Al bimetallic materials and magnetic separation

Abstract

Aluminum (Al) is one of the most important non-ferrous metals used in modern society, but its production from primary ores (e.g., bauxite) requires high energy input, emits large CO2, and generates huge amounts of solid wastes. In contrast, the production of Al from recycled scrap—also known as secondary Al production—only requires 5–8% of the energy for producing Al from bauxite and generates less amount of solid waste than that of the primary Al production, thus having both economic and environmental benefits. In general, scrap Al alloys are treated by physical-based separation techniques to remove impurities, and then mixed aluminum alloys are charged into the furnace for further refining. The ideal way of recycling Al scrap is to process each Al alloy by remelting/refining processes. To this end, this study investigated the surface modification of aluminum alloys by iron (Fe) deposition, followed by their separation by magnetic separation.When Al powder was treated with an acidified ferrous chloride solution (FeCl2-HCl-NaCl solution), dissolved Fe concentration decreased with time while releasing Al3+ into the solution, indicating that Fe cementation on Al occurred. X-ray photoelectron spectroscopy (XPS) analysis of treated Al powder showed that its surface was covered with zero-valent iron (ZVI) as well as its oxidation products (e.g., Fe(II)/Fe(III)-oxyhydroxide). The synthesis of Fe/Al bimetallic materials from Al alloys—1050, 2024, 3003, 5083, 6061, and 7075—was strongly dependent on HCl concentration as well as reaction temperature. Moreover, the kinetics of Fe cementation on Al alloys and the amounts of Fe cemented were determined not only by the rest potentials of the Al alloys but also their corrosion resistance. After treating Al alloys with FeCl2-HCl-NaCl solution, each Al alloy could be sequentially recovered by magnetic separation.