Extraction of iron: the blast furnace template

Blast furnace for GCSE, IGCSE and NCERT Class 12: the charge (haematite, coke, limestone), hot-air blast, molten slag above molten iron, and the reactions of each temperature zone (combustion of coke, C + CO₂ → 2CO, stepwise reduction of Fe₂O₃ by CO, CaCO₃ → CaO and slag formation).

What the template shows

• Coke burns to CO₂, CO₂ + C gives CO, CO reduces the iron oxides; limestone removes sand as slag
• The furnace
• molten slag (CaSiO₃)
• molten iron
• Charge: iron ore (haematite, Fe₂O₃), coke (C), limestone (CaCO₃)
• waste gases
• slag tapped
• iron tapped
• Reactions in each zone
• Upper zone: reduction by CO
• Middle zone: CO formed, slag formed
• endothermic, ΔH = +172 kJ mol⁻¹: makes the reducing agent
• CaCO₃(s) → CaO(s) + CO₂(g)
• limestone decomposes, ΔH = +178 kJ mol⁻¹
• CaO(s) + SiO₂(s) → CaSiO₃(l)
• basic oxide + acidic sand impurity → slag
• Bottom: coke burns in the hot air
• exothermic, ΔH = −394 kJ mol⁻¹: heats the furnace
• overall reduction of haematite (GCSE)
• Carbon monoxide is the main reducing agent: it takes oxygen from Fe₂O₃ (oxidation state +3) to give iron (0); Fe₂O₃ is reduced, CO oxidised to CO₂.
• Burning coke heats the furnace; above it CO₂ reacts with more hot coke to give CO. Iron can be reduced by carbon because carbon is more reactive than iron.
• Limestone decomposes to CaO, a basic oxide that reacts with acidic SiO₂ (sand) to form molten calcium silicate slag, which floats on the iron, protects it from reoxidation and is used for roads and cement.
• Pig iron from the furnace contains about 4% carbon and is brittle; blowing oxygen through it (basic oxygen process) removes carbon to make steel.
• Every part of this figure is editable · sources on the template card

Drawn with 729 shapes – every one editable in MolDraw.

Sources

• Housecroft & Sharpe, Inorganic Chemistry, 5th ed., Pearson 2018, ch. 8 Textbook
• NCERT, Chemistry Part I, Class XII (pre-2023 edition), ch. 6 General Principles and Processes of Isolation of Elements Textbook