Master Extraction of Fe, Cu, Al, Zn: Metallurgy Guide

Iron, copper, aluminium and zinc are four of the most-used metals in the world, and each is extracted from its ore by a different industrial process. Iron comes from haematite in a blast furnace, copper from sulphide ores by matte smelting, aluminium from bauxite by electrolysis, and zinc from zinc blende by roasting and carbon reduction. The method for each follows from its ore chemistry and compound stability.

These four processes are the backbone of the metallurgy chapter and appear in every major examination. They also show how the same thermodynamic principles produce very different plants — a blast furnace, a converter, an electrolytic cell and a retort.

Key Concepts

• Ores: haematite (Fe₂O₃), copper pyrites (CuFeS₂), bauxite (Al₂O₃·2H₂O), zinc blende (ZnS) — concentration precedes extraction.
• Iron — blast furnace: CO from burning coke reduces haematite: Fe₂O₃ + 3CO → 2Fe + 3CO₂. Limestone gives CaO, which captures silica as floating slag.
• Copper — matte smelting: roasted ore forms matte (Cu₂S + FeS); in the converter, FeS is slagged off and Cu₂S self-reduces: 2Cu₂O + Cu₂S → 6Cu + SO₂ (blister copper).
• Aluminium — Hall–Héroult: alumina dissolved in molten cryolite (Na₃AlF₆) is electrolysed with carbon anodes: 2Al₂O₃ + 3C → 4Al + 3CO₂.
• Zinc — pyrometallurgy: roasted ZnS gives ZnO (2ZnS + 3O₂ → 2ZnO + 2SO₂), reduced by coke: ZnO + C → Zn + CO. Zinc (b.p. 907 °C) distils off as vapour.
• Refining: blister copper and crude zinc are electrolytically refined; blast-furnace iron becomes steel after excess carbon is removed.

Formulas

• Iron reduction: Fe₂O₃ + 3CO → 2Fe + 3CO₂. 160 g of Fe₂O₃ yields 112 g of Fe — pure haematite is 70 percent iron by mass.
• Copper self-reduction: 2Cu₂O + Cu₂S → 6Cu + SO₂.
• Hall–Héroult: 2Al₂O₃ + 3C → 4Al + 3CO₂. Assumes carbon anodes; inert anodes would give oxygen instead but are not yet commercial.
• Zinc reduction: ZnO + C → Zn + CO, carried out above zinc's boiling point so the metal distils away from impurities.

Worked Example

A plant processes 1 tonne (1000 kg) of pure haematite (Fe₂O₃) in a blast furnace operating at 90 percent metal-recovery efficiency. Calculate the mass of iron obtained.

1. Molar mass of Fe₂O₃ = 2(55.85) + 3(16) ≈ 160 g/mol.
2. Mass of iron in one mole = 2 × 55.85 = 111.7 g, approximately 112 g.
3. Iron fraction = 112 ÷ 160 = 0.70, i.e. 70 percent by mass.
4. Theoretical iron from 1000 kg = 0.70 × 1000 kg = 700 kg.
5. At 90 percent efficiency, actual iron = 0.90 × 700 kg = 630 kg.

Common Misconceptions

• "All metals are extracted by heating their ore with coke." Corrected: coke works for iron and zinc but not alumina (needs electrolysis), and copper uses self-reduction of its sulphide.
• "Bauxite is directly electrolysed." Corrected: bauxite is first purified to alumina by the Bayer process; only pure alumina is electrolysed in cryolite.
• "Slag is just waste with no purpose." Corrected: slag formation is deliberate — it captures impurities that would contaminate the metal, and blast-furnace slag is recycled into cement.

Real-World Applications

• Steel industry: virtually all primary steel starts as blast-furnace iron.
• Electrical industry: electrolytic refining produces the 99.99 percent pure copper needed for wires and electronics.
• Transport: Hall–Héroult aluminium gives the lightweight metal for aircraft and vehicles.

To summarise: iron is won by CO reduction in the blast furnace, copper by matte smelting and self-reduction, aluminium by electrolysis in cryolite, and zinc by roasting plus carbon reduction with distillation. Learn one equation and one key condition for each metal, and the chapter falls into place.