122 Conversion of Large Scale Wastes into Value-added Products
be mixed with scrap from other sources in order to obtain the required alloy com-
position. Melting is carried out with a ux of sodium and potassium chloride, which
removes impurities and helps to prevent oxidation of the aluminium, although some
will occur. The salt with its impurities is separated from the molten aluminium, and
can be a signicant amount—up to 500 kg per tonne of aluminium. This salt slag
can be further treated to recover aluminium metal and aluminium oxide, and the
dissolved salts can be recrystallized and reused.
4.4.3.3 Precious Metals
Because of the value of the metals, this group of materials is the one that has
received the greatest research effort on t