1.

Explain the metallurgy of iron.

Answer»

Solution : Iron is chiefly extracted from haematite ore `(Fe_(2)O_(3))`
(i) Concentration by Gravity Separation: The powdered ore is washed with a steam of water.As a result, the lighter sand particles and other impurities are washed away and the heavier ore particles settle down (II) Roasting and Calcination: The concentrated ore is strongly heated in a limited supply of air in a reverberatory furnace.As a result, moisture is driven out and SULPHUR, arsenic and phosphorus impurities are oxidized off
(iii) Smelting (in a Blast Furnace): The charge consisting of roasted ore, coke and limestone in the ratio 8: 4: is smelted in a blast furnace by introducing it through the cup arrangement at the top.There are three important areas in the furnace
a.The Lower Regions (combustion Zone) :
The temerature is at `15006(@)C` . In this regoins coke burns with oxygen to FORM `CO_(2)` when the charge comes in contact with a hot blast of air .
`C+ O_(2)underset(Delta)overset(1500^(@)C) to Co_(2) + ("heat")`
It is exothermic reaction since heata is liberated .

b.The Middle Regions ( Fusion Zone ) :
The temperature prevails at `100^(@)C` in this regions `Co_(2)` is reduced to Co .
`CO_(2)+ C underset(Delta) overset(1000^(@))to2CO-"Heat"`
Limestone decomposes to calcium oxide and `CO_(2)`
`CaCO_(3) underset(Delta)to CO_(2) - "Heat"`
These two reactions are endothermic due to absorption of heat . Calcium oxide combines with silica to form calcium silicate slag.
`CaO + SiO_(2)rightarrowCasiS_(3)`
c.The Upper Regions ( Reduction Zone ) : The temperature prevails at `400^(@)C`. Inthis regions carbon monoxide reduces ferric oxide to form a fairly pure spongy iron .
`Fe_(2)O_(3) + 3CO overset(400^(2)C)to 2Fe+ 3CO_(2)`
. THe molten iron is collected at the bottom of the furnance after removing the slag .
The iron this formed is called pig iron . It is remelted and cast into different moulds . This iorn is called cast iron .


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