Evaluation of the recycling of coated magnesium using exergy analysis C.E.M. Meskers a, * ,1 , Y. Xiao a , R. Boom a , U. Boin b , M.A. Reuter c a Delft University of Technology, Department of Materials Science and Engineering, Mekelweg 2, 2628CD Delft, The Netherlands b Feldstrasse 8a, 61440 Oberursel, Germany c Melbourne University, Department of Civil and Environmental Engineering, Victoria 3010, Australia Received 1 December 2006; accepted 17 February 2007 Available online 6 April 2007 Abstract Coated magnesium is increasingly applied in consumer goods. After their useful life the goods are processed, creating coated scrap which is currently poorly recycled. This leaves a gap in the utilization cycle and a resource unused. Closure of the cycle in a sustainable manner requires quantification of the effect of coatings on the degree of recycling of magnesium alloys. For this purpose exergy analysis is used. This tool incorporates changes in both mass and quality of materials during recycling. Exergy analysis requires thermodynamical knowledge about the physical and chemical interaction between coating, magnesium and salt flux during melting and their effects on the products. EMF cell, solubility and lab-scale melting experiments are used to quantify this. Combination of the results with known sys- tems enables determination of the impurity’s activity in metal and salt. Subsequently the exergy is calculated. Unfavourable coating com- ponents are identified and presented in a decision table. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Recycling; Modeling; Coated magnesium; Exergy analysis 1. Introduction The magnesium consumption has been continuously increasing during the past decade. During the last ten years the production has doubled to 610 000 tons in 2005 (Kramer, 2004). About 40% (244 000 tons) of this is used for die-cast- ing. Most of the casting products are used in the automotive industry; a market that is expected to double in the next dec- ade. Magnesium castings are also used in smaller consumer applications such as cellular phones, laptop housings, bicy- cle frames, consumer electronics and power tools, because of its light weight combined with high strength. To be able to use magnesium in many of these applications it has to be coated. The coating adds extra material properties to magnesium: corrosion protection, solderability, colour and shine among others. Fig. 1 shows the magnesium utilization cycle. Coated magnesium is leaving the cycle as part of collected scrap or rejects. This scrap is currently not recycled. Therefore a source of magnesium metal is left unused. Closure of the utilization cycle in a sustainable manner is essential to preserve resources for future generations. Energy resources can be saved by means of remelting scrap instead of electrowinning of primary magnesium. Material resources can be saved as well. Magnesium-containing materials, such as coated scrap, which were previously con- sidered waste, can become valuable resources. One of the solutions is recycling of coated magnesium scrap by remelting with a salt flux. To investigate this pos- sibility, the effect of coated scrap on the remelting process and its products (metal, salt slag and off gas) will be quan- titatively predicted using thermodynamics. Remelting of coated scrap with salt flux is simulated using the thermody- namic modeling package Factsage. Based on the findings harmful coating components can be identified and their effect quantified. To be able to rank the coatings according to their effect on recycling, 0892-6875/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2007.02.006 * Corresponding author. Tel.: +31 (0) 15 2787709; fax: +31 (0) 15 2786730. E-mail addresses: c.e.m.meskers@tudelft.nl (C.E.M. Meskers), mreuter@unimelb.edu.au (M.A. Reuter). 1 Supported by SenterNovem IOP Surface Technology. This article is also available online at: www.elsevier.com/locate/mineng Minerals Engineering 20 (2007) 913–925