First it was observed that in the presence of salt the recovered
scraps mostly arose by the formation of droplets. This may be
attributed to the fact that the salt can facilitate the coalescence
of molten aluminum droplets (Roy and Utigard, 1998). The metal
recovery is shown in Fig. 10a as a function of the mass ratio of
added salt to input aluminum. The salt generally reduces the metal
recovery (up to 5 wt.% for containers) as the molten salt corrodes
the formed aluminum oxide links, thereby promoting the stripping
of the aluminum oxide layer (Roy and Utigard, 1998). In contrary,
for larger amounts of salt the recovery appears to slightly increase.
This effect was the strongest for the thin foils for which the recovery
was even larger than for the case without salt. A likely explanation
is that the small scraps were trapped into molten salt that
effectively shielded them from oxidization. Overall, the sodium salt
causes higher metallic aluminum losses in low concentrations but
may in fact increase the recovery rate in very high concentrations.
The latter effect is utilized in the recycling of aluminum scrap
where molten aluminum is retained in a salt flux (Majidi et al.,
2007). Fig. 10b shows the results for acidic and basic contaminations.
The influence on the losses was mostly negligible; the acid
had no notable influence at all and the basic contamination caused
at most 3.6 wt.% additional losses for the thin foils.