Refining of Metals:
Metals extracted from their ores by any of the above methods are often associated with impurities such as the very small amounts of the other metals and non-metals, uncovered oxides or sulfides, dissolved gases and even small amount of slag. Refining of crude metal is carried out to remove these impurities when the desired metal is obtained in a very high state of purity.
The crude metals obtained are generally thermally refined by –
i. Oxidation of easily oxidizable impurities by passing air through the molten metal such as Cu, Sn, etc.
ii. Distillation of easily volatile metals such as Hg, Zn, etc.
iii. By liquation of easily fusible metals such as Sn, etc.