Metallurgy
Metallurgy
The process of extracting metal in pure form from its ore is known as metallurgy.
» Minerals :
The compound of a metal found in nature is called a mineral. A mineral may be a single compound or a complex mixture.
» Ores :
Those minerals from which metal can be economically and easily extracted are called ores.
All ores are mineral but all minerals are not ores.
» Gangue (or matrix) :
The ore is generally associated with earthy impurities like sand, rocks and limestone known as gangue or matrix
Flux
A substance added to ore to remove impurities is called flux. There are two types of flux —
(i) acidic flux
(ii) basic flux
Acidic flux is added to remove basic impurity
SiO2 + FeO → FeSiO3
acidic flux basic impurity Ferrous silicate
Basic flux is added to remove acidic impurity.
CaCO3 + SiO2 → CaSiO3 + CO2
basic flux acidic impurity Calcium silicate
Slag
Combination of gangue with flux in ores forms a fusible material which is called slag.
SiO2 + CaO → CaSiO3
Gangue flux slag
Concentration
The process of removal of gangue from the ore is known as concentration of ore. Concentration of ore can be carried out in the following ways depending upon the nature of the ore :
(i) Gravity separation
(ii) Magnetic concentration
(ii) Froth flotation process
(iv) Chemical methods
Calcination
Calcination is a process in which ore is heated, generally in the absence of air, to expel water from hydrated oxide or carbon dioxide from a carbonate at temperature below their melting point example :
Al2O3 . 2H2O → A12O3 + 2H2O
CaCO3 → CaO + CO2
Roasting
Roasting is a process in which ore is heated usually in the presence of air, at temperatures below its melting points.
ZnS + 2O2 → ZnSO4
CuS + 2O2 → CuSO4
Smelting
The reduction of oxide ore with carbon at high temperature is known as smelting.
Fe2O3 + 3C → 2Fe + 3CO
PbO + C → Pb + CO