Saturday, August 11, 2012

Oxidation

Oxidation method is applied for those metals in which the impurities can be easily oxidised metals like Cu, Ag etc. can be purified by oxidation method. Oxidation can be done in following way;
            (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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