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