Explain the stages involved in the extraction of cast iron.

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. 

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