Question

Explain the smelting process.

Answer 1

Smelting (in a Blast Furnace): The charge consisting of roasted ore, coke, and limestone in the ratio 8 : 4: 1 is smelted in a blast furnace by introducing it through the cup and cone arrangement at the top. There are three important regions in the furnace.

Blast Furnace

(a) The Lower Region (Combustion Zone): The temperature is at 1500°C. In this region, coke bums with oxygen to form CO₂ when the charge comes in contact with a hot blast of air.

\[\ce{C + O2->[1500°C][\Delta]CO2 + Heat}\]

It is an exothermic reaction since heat is liberated.

(b) The Middle Region (Fusion Zone): The temperature prevails at 1000°C. In this region, CO₂ is reduced to CO.

\[\ce{CO2 + C ->[1000°C][\Delta]2CO - Heat}\]

Limestone decomposes to calcium oxide and CO₂

\[\ce{CaCO3->[][\Delta]CaO + CO2 - Heat}\]

These two reactions are endothermic due to the absorption of heat. Calcium oxide combines with silica to form calcium silicate slag.

CaO + SiO₂ → CaSiO₃

(c) The Upper Region (Reduction Zone): The temperature prevails at 400°C. In this region, carbon monoxide reduces ferric oxide to form a fairly pure spongy iron.

\[\ce{Fe2O3 + 3CO->[400°C]2Fe + 3CO2}\]

The molten iron is collected at the bottom of the furnace after removing the slag.

The iron thus formed is called pig iron. It is remelted and cast into different molds. This iron is called cast iron.