General Knowledge



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


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


Combination of gangue with flux in ores forms a fusible material which is called slag.

        SiO2     +     CaO           →       CaSiO3
    Gangue             flux                     slag


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 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 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


The reduction of oxide ore with carbon at high temperature is known as smelting.

        Fe2O3 + 3C → 2Fe + 3CO
        PbO + C → Pb + CO