Explain smelting process .

Explanation

Smelting ( in a Blast Furnance ) :
(i) The charge consisting of roasted ore, cok and limestone in the ratio 8:1 .
(ii) Smelted in a blast furnance by introducing it through the cup and cone arrangement at the top.
There are three important regions in the furnance.

(a) The Lower Region (Combustion Zone ) :
(i) The temperature is at `1500^(@)C`.
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 an exothermic reaction since heat is liberated .
(b) The Middle Region ( Fusion Zone ) :
(iii) The temperature prevails at ` 1000^(@)C`.
(iv) `CO_2` is reduced to ` CO`
`CO_2+C underset(Delta)overset(1000^(@)C)to2CO+"Heat"`
Limestone decomposes to calcium oxide and `CO_2`.
`CaCO_3 underset(Delta)toCO_2+"Heat"`
(v) These two reactions are endothermic due to absorption of heat .
(vi) Calcium oxide combines with silica to form calcium silicate slag.
`CaO+SiO_2 to CaSiO_2`
(c) The Upper Region ( Reduction Zone ) :
(i) The temperature prevails at ` 400^(@)` C .
(ii) Carbon monoxide reduces ferric oxide to form a fairly pure spongy iron.
`Fe_2O_3+3CO overset(400^(@)C) to 2Fe+3CO_2`
The molten iron is collected at the bottom of the furnance after removing the slag .
(iii) The iron thus formed is called pig iron.
(iv) It's remelted and cast into different moulds. This iron is called cast iron.