Alloy selective optical sorting of mixed post-consumer aluminum scrap streams

Shredded post-consumer aluminum scrap streams contain a mixture of cast and wrought aluminum pieces with very different compositions, resulting in downcycling of the mixed scrap into non-structural cast aluminum alloys and parts. In this paper, we introduce a chemical treatment method to color-code scrap aluminum pieces by alloy family and demonstrate low-cost optical sorting of cast from wrought pieces to upgrade the scrap stream. The color difference enabled > 95 % purity in the optically sorted cast and wrought fractions. We also colored wrought aluminum pieces and scrap by alloy families, such as 5xxx and 6xxx, which has the potential to create a circular supply chain in which wrought aluminum alloys are sorted from the mixed scrap stream and recycled back to high-value wrought products. Our TEA and LCA show feasibility of our coloring method and optical sorting, and we discuss the implications for the U.S. aluminum and transportation industries.