(a). Cupellation: This method is used in the refining of a
crude metal which contains the impurities of another metal capable of getting
oxidised to a volatile oxide. This method is used in refining of silver
containing lead as impurities. A cupel is boat – shaped dish made up of bone
ash or cement. The crude metal is heated in a cupel placed in reverberate
furnace and a blast of air is blown over the molten surface. The impurities are
converted into volatile oxides which are swept away by the air current. In case
of silver, lead is converted into litharge (PbO) which being volatile leaves
behind pure silver.
(b). Bessemerisation: In this
method the impure or crude metal is taken in a specially designed furnace
called Bessemer Converter into which hot blasts of air and sand is
blown impurities are removed as volatile oxides which escapes leaves the metals
in the pure state. Impurities of As, Mn, P etc present in pig iron can be
removed by this method.
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