The various metallurgical operations in the extraction of pure metals from their respective ores are given below:
(i) Concentration of the ore: Removal of gangue or matrix from the powdered ore is known as concentration or dressing of the ore. It can be carried out in the following ways:
(a) Levigation: Also called gravity separation or hydraulic washing where the lighter gangue particles are removed from heavier ore particles by washing in a current of water. It is generally used for oxide ores and carbonate ores. It is based on difference in densities of the ore particles and impurities.
(b) Froth – floatation: It is used for concentration of sulphide ores. Foaming agent like pine oil is added which raises the lighter ore particles to the top in the form of froth while the heavier gangue particles settle down.
Adsorption phenomenon is involved in this method.
(iii) Calcination: Ore is heated strongly in absence or limited supply of air (air is used here as carrier of heat and moisture). Carbonates and hydrated oxide ores are converted to their respective oxides.
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