: 240
The blast furnace extracts iron from haematite (Fe2O3) using coke and limestone flux. It operates with four temperature zones from bottom to top.
Combustion zone (~2000 K, bottom): C + O2 -> CO2 (highly exothermic, provides all heat). Reduction zone (~1200 K): CO2 + C -> 2CO (Boudouard reaction); then CO reduces iron oxide: Fe2O3 + 3CO -> 2Fe + 3CO2. CO is the actual reducing agent, not carbon directly. Slag formation zone (~1500 K): CaCO3 -> CaO + CO2 (calcination); CaO + SiO2 -> CaSiO3 (liquid slag floats on molten iron). Charge zone (500-800 K, top): Stepwise reduction Fe2O3 -> Fe3O4 -> FeO -> Fe by CO.
Products differ by carbon content: pig iron (~4% C, Si, Mn — brittle, direct blast furnace product), cast iron (~3% C — shaped by moulding), steel (0.2-2% C — optimal strength), wrought iron (<0.2% C — malleable, puddled from pig iron).
The slag has commercial uses: cement additive, road construction material, insulation. Understanding the zone-specific reactions and their temperatures is essential for JEE, as questions frequently test which reaction occurs at which temperature.