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 R. 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 R, 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.