1 . Conversion to oxide . 2 . Reduction of the oxides to metal .
Conversion to Oxides
( i ) Calcination It is the process of converting an ore into its oxides by heating it strongly , below its melting point in a limited supply of air or in absence of air .
During calcination , volatile impurities as well as organic matter and moisture are removed .
Calcination is used for metal carbonates and hydroxides and is carried out in reverberatory furnace .
( ii ) Roasting It is the process of converting an ore into its metallic oxide by heating it strongly . below its melting point m excess of air . This process is commonly used for sulphide ores and is carried out in blast furnace or reverberatory furnace . Roasting helps to remove the non-metallic impurities and moisture .
The furnaces used in calcination and roasting employ refractory materials which resist high temperature and do not become soft .
Acidic refractories : SiO2 and SiO2 + Al2O3
Basic refractories : CaO and MgO Neutral refractories : Graphite , chromites . etc .