The compound of a metal found in nature is called a mineral. The minerals from which metal can be economically
and conveniently extracted are called ores. An ore is usually contaminated with earthy or undesired materials
known as gangue.
The scientific and technological process used for the extraction/isolation of the metal from its ore is called as
metallurgy. The isolation and extraction of metals from their ores involve the following major steps
Conversion of ore into oxide is carried out in two ways depending upon the nature of ore
The free metal is obtained by reduction of a compound, using either a chemical reducing agent or electrolysis
Reduction by other metals :
If the temperature needed for carbon to reduce an oxide is too high, for economical or practical purposes,
reduction by other metals is done.
Electrolytic reduction :
It presents the most powerful method of reduction and gives a very pure product. As it is an expensive method
compared to chemical methods
It involves the following processes
THERMODYNAMICS OF EXTRACTION :
ELLINGHAM DIAGRAM OF A METAL
The graphical representation of Gibbs energy was first used by H.J.T.Ellingham. This provides a sound basis for
considering the choice of reducing agent in the reduction of oxides
1. The graph simply indicates whether a reaction is possible or not i.e., the tendency of reduction with a reducing
agent is indicated. This is so because it is based only on the thermodynamic concepts. It does not say about the
kinetics of the reduction process (Cannot answer questions like how fast it could be ?).
Oxide ores of iron, after concentration through calcination / roasting in reverberatory furnace are mixed with lime
stone and coke and fed into a Blast furnace from its top with the help of a cup and cone arrangement. Here, the
oxide is reduced to the metal.
(a) From cuprous oxide [copper(I) oxide] : The sulphide ores are roasted/smelted to give oxides
Extraction of lead
The ore is roasted in presence of excess of air at temperature 1200 K.
Extraction of tin from cassiterite
The ore is dehydrated in a current of hydrogen chloride and the mixture of fused chlorides is
Extraction of gold and silver (MacArthur-Forrest cyanide process)
OXIDATIVE REFINING :
The method is used when the impurities present in the metal have a greater affinity for
oxygen and are more readily oxidized than the metal.
Crude gold obtained by MacArthur-Forrest cyanide and chlorination process contains Ag, Cu,
Zn, and sometimes Pb as impurity. Zn and Pb are removed by cupellation process. Cu
and Ag are removed by parting process
This process is used for the purification of copper and tin.
Some metals such as Cu, Ni, and AI are refined electrolytically. The Hooper process is a
process for the electrolytic refining of aluminum. Impure AI forms the anode and pure AI forms the
cathode of the Hooper’s cell which contains three liquid layers
VAPOR PHASE REFINING
The removal of the impurities of Ag from the commercial lead is called desilverisation of lead and is done
by Parke’s process . Thus, Parke’s process is the desilverisation of lead
This process is used for the manufacture of wrought iron from cast iron