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During the smelting of iron in the blast furnace, what is the main role of the limestone (CaCO3) added to the charge?
AIt supplies CaO that removes silica impurity as slag
BIt directly reduces ferric oxide to iron metal
CIt acts as the fuel that burns to give heat
DIt increases the carbon content of the iron
Answer & Solution
Correct answer: A. It supplies CaO that removes silica impurity as slag
1. Limestone decomposes in the furnace: CaCO3 gives CaO + CO2.
2. The CaO produced is a basic flux.
3. It combines with the acidic silica impurity: CaO + SiO2 gives CaSiO3 (slag).
4. So limestone provides CaO to remove silica as slag.
The actual reduction of Fe2O3 is done by carbon monoxide, not by limestone.
_Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 8 Periodic Classification of Elements "Metallurgy of Iron", p.124_
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