A Fundamental Metric for Metal Recycling Applied to Coated Magnesium
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TRODUCTION
COATED scrap is created during the manufacturing of consumer products, in the form of rejects, and during the processing of end-of-life products indicated in Figure 1. The amount of coated magnesium scrap is considerable and will continue to increase, as the application of magnesium in consumer products is still growing. Over 150,000 tons per year in 2004[1] of diecast magnesium is used in the automotive industry and in consumer electronics such as laptop computers, mobile phones, and handheld tools. In these applications, it is often necessary to coat magnesium with conversion or anodizing coatings combined with organic coating (paint) in order to prevent corrosion and enhance appearance.[2–4] Currently, this coated scrap is not yet recycled, because the direct remelting of painted C.E.M. MESKERS, Assistant Manager, Market Research and Development, Umicore Precious Metals Refining, A. Greinerstraat 14, BE 2660 Hoboken, Belgium, is Postdoctoral Student, with the Department of Materials Science and Engineering, Delft University of Technology, 2628 CD Delft, the Netherlands. M.A. REUTER, Chief Executive Technologist, Ausmelt Ltd., 3175 Dandenong, Victoria, Australia, is Professor Fellow, with the Department of Chemical and Biomolecular Engineering, University of Melbourne, Melbourne, Victoria 3010, Australia. Contact e-mail: markus.reuter@ausmelt. com.au U. BOIN, 61440 Oberursel, Germany, is retired. A. KVITHYLD, Researcher, is with the Department of Materials Science and Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway. Manuscript submitted October 22, 2007. Article published online June 18, 2008. 500—VOLUME 39B, JUNE 2008
magnesium scrap generates large amounts of offgas, increases salt flux usage, and lowers the metal quality and yield.[5–7] Recycling retains magnesium resources within the utilization cycle and, thus, reduces primary magnesium usage. Furthermore, energy resources can be saved, as the remelting of scrap consumes only 10 pct of the energy necessary for primary production.[8] Legislation such as the End-of-Life Vehicle and Waste Electric and Electronic Equipment directives of the European Union[9,10] serve as an extra incentive for recycling. Materials cycles, such as the one for coated magnesium, have to be closed in a sustainable manner. Industrial ecology provides a suitable (conceptual) framework, because it focuses on product design and manufacturing processes.[11] Its holistic, system approach, together with its emphasis on prevention and its use of technology as a means for problem solving, are important elements. For the evaluation and optimization of recycling systems, a detailed understanding of the parts of the system itself, as well as the interconnectivity of the system and its parts with other systems, is a prerequisite.[12] Physics, thermodynamics, and material quality have to be addressed simultaneously, as they determine the overall performance of the (recycling) system.[13] Metrics that are based on first principles are necessary to evaluate
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