Extraction of Iron from Hematite
Section: 9. Metals | Syllabus: Cambridge IGCSE Chemistry (0620)
The Blast Furnace
Iron is extracted from its ore, hematite (mainly iron(III) oxide, Fe₂O₃), by reduction with carbon monoxide in a blast furnace. Iron is below carbon in the reactivity series, so this cheaper method works (unlike aluminium, which needs electrolysis).
Three raw materials are added at the top of the furnace, and hot air is blasted in near the bottom:
| Raw material | Formula | Role |
|---|---|---|
| Iron ore (hematite) | Fe₂O₃ | source of iron |
| Coke (carbon) | C | fuel and reducing agent |
| Limestone | CaCO₃ | removes impurities as slag |
| Hot air | O₂ (+N₂) | burns the coke, provides heat |
Molten iron (denser) collects below the floating layer of molten slag
The Five Key Reactions
| Step | Equation | Purpose |
|---|---|---|
| 1. Coke burns | C + O₂ → CO₂ | provides heat for the furnace |
| 2. CO₂ is reduced to CO | C + CO₂ → 2CO | produces the actual reducing agent, CO |
| 3. Iron(III) oxide is reduced | Fe₂O₃ + 3CO → 2Fe + 3CO₂ | produces the iron |
| 4. Limestone decomposes | CaCO₃ → CaO + CO₂ | thermal decomposition, produces CaO |
| 5. Slag forms | CaO + SiO₂ → CaSiO₃ | removes acidic impurities (mainly sand, SiO₂) |
These five symbol equations are Supplement content. At Core level, you only need to describe each step in words - naming the equations is not required.
Worked Example: Classifying the Reactions
- Question: Fe₂O₃ + 3CO → 2Fe + 3CO₂ and CaCO₃ → CaO + CO₂ both occur in a blast furnace. What type of reaction is each? [1]
- Answer: reaction 1 is a redox reaction - iron is reduced (Fe³⁺ → Fe⁰) while carbon monoxide is oxidised (C²⁺ → C⁴⁺ in CO₂); reaction 2 is thermal decomposition - one compound (CaCO₃) breaks down into two simpler substances on heating, with no change in oxidation state.
Products of the Blast Furnace
- Molten iron - the densest liquid, sinks to the bottom and is tapped off
- Molten slag (CaSiO₃) - less dense than iron, floats on top and is tapped off separately; used in road-building and cement
- Waste gases - mainly CO₂ and N₂, escape from the top
Common Mistakes
- ❌ Thinking carbon (coke) itself reduces the iron ore directly
- ✓ the actual reducing agent is carbon monoxide (formed in step 2); coke's first role is simply to burn and provide heat (step 1)
- ❌ Forgetting why limestone is added
- ✓ limestone removes acidic impurities like sand (SiO₂) from the iron ore, by decomposing to CaO which then reacts with SiO₂ to form slag
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