Compaction of aluminium foil and its effect on oxidation and recycling yield

Abstract

One of the problems when recycling aluminium is its oxidation and consequent metal loss. This is especially critical for the thin sheet/foil materials used for food packaging applications. Compacting the scrap into briquettes may partly reduce such losses in addition to facilitate transport and storage. Shredded aluminium materials of different thicknesses (15-300 microns) were compacted into cylindrical briquettes of 4 cm diameter, each weighting 20 g by uniaxial pressure or moderate-pressuretorsion. A sub-set of briquettes and chips was subsequently oxidized at 650 C, while a sub-set was left untreated. Finally, all samples were re-melted under molten protective salt-flux. Compacting reduced the specific oxidation during the heat-treatment and promoted the coalescence and yield for the heat-treated materials. Both effects were most significant for the thinnest foil in the study (15 microns). The material thickness influenced the porosity and surface roughness of the resultant briquette, as well as the pressure required to reach a given bulk density.