Improving aluminum recycling: A survey of sorting and impurity removal technologies

Aluminum recycling has a number of key environmental and economic benefits. With these energy and cost savings in mind, many producers now have targets of increasing their usage of secondary materials. However, the accumulation of impurities in these recycled material streams may provide a significant compositional barrier to these goals. A growing number of studies and literature suggest that accumulation of unwanted elements is a growing problem; for the case of aluminum, the list of problematic impurities is quite large, including but not limited to Si, Mg, Ni, Zn, Pb, Cr, Fe, Cu, V, and Mn. The removal of unwanted elements in the scrap stream is dictated by the energy considerations of the melt process. Compared to many metals, it is challenging to remove tramp elements from aluminium. Therefore, with no simple thermodynamic solution, producers must identify strategies throughout the production process to mitigate this elemental accumulation. There are a variety of solutions to deal with accumulation of undesired elements; each presents a trade-off between cost and efficacy (tramp removal). Dilution with primary is the most common solution used in industry today; this has a negative impact on recycling as the required dilution results in a compositionally determined cap to recycling rates. This article provides an overview of the expanse of upgrading technologies available at both the industrial and lab-scale to improve aluminum scrap purity and facilitate recycling. (C) 2011 Elsevier B.V. All rights reserved.