Coated magnesium: Designed for sustainability?

Design for consumer products such as cars and electronics requires the selection and combination of various materials. At the end of the product life, the product has to be recycled back to materials suitable for manufacture of new products. To evaluate the sustainability of a material cycle metrics are necessary that quantify the impact of proudct design on product recyclability. In this thesis such a recycling metric was developed for coated magnesium. Its parameters are based on exergy and kinetic analysis. The metric and its parameters can be implemented in Design for Recycling optimization models to optimize recycling and the material cycle.Mechanical Maritime and Materials Engineerin

A Fundamental Metric for Metal Recycling Applied to Coated Magnesium

A fundamental metric for the assessment of the recyclability and, hence, the sustainability of coated magnesium scrap is presented; this metric combines kinetics and thermodynamics. The recycling process, consisting of thermal decoating and remelting, was studied by thermogravimetry and differential thermal analysis (TG/DTA) experiments and thermodynamic simulations. Decoating phenomena are interpreted using kinetic analysis, applying existing reaction models. The derived kinetic model parameters ln A and E a /(RT p ) are used to characterize the decoating process. The impact of inorganic coating components on remelting is quantified using exergy. Oxidation and entrapment losses, quality losses, and material resource depletion caused by the inorganic components are expressed in exergy units and combined into the single parameter . Based on the results, the coating characteristics favorable for recycling are derived. The obtained metric is a three-dimensional (3–D) combination of ln A, E a /(RT p ), and , which represent the decoating velocity, the ease of decoating, and the impact of coating materials on the remelting process, respectively. The metric, therefore, directly links coating characteristics, coating design, and product design with process technology and recyclability, enabling the ranking of coating alternatives in terms of their respective recyclability. Therefore, the key idea of this article is to use fundamental metallurgical theory to express the recyclability of postconsumer scrap in a unique combination of parameters. This should pave the way for ranking the sustainability of different materials.Mechanical, Maritime and Materials Engineerin

Recycling light metals: Optimal thermal de-coating

Thermal de-coating of painted and lacquered scrap is one of the new innovations developed for aluminum recycling. If implemented in all recycling and optimized as suggested in this article, recovery would be improved with considerable economic impact. Generally, contaminated scrap is difficult to recycle. Direct re-melting of coated scrap results in the generation of gaseous emissions, with increased metal oxidation, contamination, and salt flux usage. By thermal de-coating of the scrap these problems are avoided. Thermal de-coating followed by remelting of aluminum scrap is now common practice, while painted magnesium scrap is not currently de-coated and recycled. This article presents observations during heating of the contaminated light metals together with the mass loss, evolved gases, and residue after de-coating in order to give a general description of the de-coating process. It is argued that the main behavior during de-coating may be described as two distinct regimes—scission and combustion—regardless of metal substrate and coating. Monitoring the combustion regime should assure optimum de-coating.Mechanical, Maritime and Materials Engineerin

Exergy-based efficiency analysis of pyrometallurgical processes

Exergy-based efficiency analysis provides a powerful tool for optimizing industrial processes. In this article, the use of this technique for pyrometallurgical applications is explored in four steps. First, the exergy concept is introduced, the outline of exergy calculations is presented, and the role of a reference state is discussed. Second, it is shown that an unambiguous exergy calculation for pyrometallurgical streams with a complex, unknown phase composition is not straightforward. Hence, a practical methodology is proposed in which a suitable phase-based stream description is estimated prior to the actual exergy calculation. For this, the equilibrium phase composition is calculated, whereas all known stream properties are incorporated as boundary conditions. Third, the proposed methodology is validated by recalculating literature results. This reveals significant deviations for exergy values of the same pyrometallurgical streams. Our results are probably more accurate because of the incorporation of additional phase-related information. And fourth, a full analysis of a zinc-recycling process is presented. In a base case scenario, the total exergetic efficiency turns out to be only 1.2 pct. Based on this result, different process modifications are suggested and evaluated quantitatively. We find that significant efficiency gains are possible