Ans. The stages in the extraction of cast
iron from its ore are as under.
1.
Washing: - In this method the crushed and finely powdered iron one is
washed with stream of water to remove lighter gangue particles. When the
lighter gangue particles are washed away and the heavier mineral ore settle
down to the bottom.
2.
Magnetic separation: - This process of concentration of an ore is used, if the given
ore is magnetic. The crushed ore is allowed to fall on the moving belt of a
magnetic separator, the magnetic components of the ore is attracted by the
magnetic roller and forms a heap and the nonmagnetic impurities (gangue) fall
away and form a separate heap. Thus, iron ore i.e. magnetite is enriched by
this process.
3.
Smelting in the blast
furnace: - The iron ore is mixed with coke and
lime stone. This mixture is called charge. The charge is introduced in a blast
furnace from the top by means of a cup and cone arrangement. A blast of hot air
is introduced through the blow – pipes near the base of the furnace. In the
blast furnace, coke from descending charge is oxidised to carbon dioxide. This
reaction is highly exothermic.
C(s) + O2 → CO2(g)
+ Heat
The liberated
heat brings about various endothermic reactions in the furnace. The lime stone
decomposes to calcium oxide (lime).
At
the high temperature (about 12000C – 20000C) both
metallic iron and slag are in the molten state. As the slag (CaSiO3)
is lighter then the molten iron, it floats on the molten iron. The slag
prevents the oxidation of iron in the blast of hot air. The molten iron is
removed from the lower outlet, while the molten slag is removed from the upper
outlet of the blast furnace.
