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

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.