Metals are very important for us. Many useful things like utensils, different types of tools, vehicles, tanks etc are made up of metals. But, metals are not easily available. Only a few metals are found in free state. Maximum metals are found in the combined form i.e. mineral in earth’s crust.
Ore : A mineral from which the extraction of a metal is feasible and economical is called an ore.
Abundance of metals : Aluminium is the most abundant element among metals. It is 8.3% by weight in earth’s crust. The main ores of some important metals are as follows:
|AlOx(OH)3-2x Where 0<x<1 </x<1
CuCO3 . Cu(OH)2
|Zinc Blende or Sphalerite
Metallurgy : The whole technological and scientific process of the isolation of a metal from its ore is called metallurgy.
Gangue : An ore contains several unwanted impurities with a metal which are called gangue.
Concentration of ores : The process of removing guange from an ore is called the concentration of ore.
There are different methods of the concentration of the ores of different metals. Some of them are as follows :
1. Hydraulic washing : This method is based on the difference in specific gravities of the ore and the gangue particles.
Procedure : In this method, water with high speed is drawn on ore particles due to which lighter gangue particles flow with water and ore particles are left behind.
2. Magnetic separation method : This method is based on the differences in magnetic properties of the ore components.
Procedure : In this method, the powdered ore is placed over a conveyer belt which passes over a magnetic roller. The ore particles fall near the roller due to the attraction and gangue particles fall far from the roller.
◆ Refining : Metals obtained from the extraction process are not pure. They still have some impurities. The process of removing these impurities is called refining. For different metals, different refining processes are used.
I. Distillation(Zn/Hg) : The metals with low boiling points are refined by distillation. In this method, the metal with impurities is heated, due to the low boiling point metal vaporizes and it is collected in a flask and impurities are left behind.
II. Liquation(Sn) : This method is suitable for metals having low melting points. In this method, the metal with impurities is heated, due to the low melting point metal vaporizes and it is collected in a flask and impurities are left behind due to their high melting point.