CC3.3 — Metal extraction (Edexcel 1SC0)

Choice of extraction method

Depends on the metal's position in the reactivity series:

• Above carbon (e.g. Al, Mg, Na): extracted by electrolysis (too reactive to reduce with carbon).
• Below carbon (e.g. Fe, Cu): extracted by reduction with carbon (or CO).
• Below hydrogen (e.g. Cu, Ag, Au): found native or reduced by carbon.

Reduction with carbon — iron extraction (blast furnace)

1. Iron ore (haematite, Fe₂O₃) + coke C + limestone heated.
2. Coke burns: C + O₂ → CO₂, then CO₂ + C → 2CO.
3. Carbon monoxide reduces iron ore: Fe₂O₃ + 3CO → 2Fe + 3CO₂.
4. Limestone removes impurities: CaCO₃ → CaO + CO₂; CaO + SiO₂ → CaSiO₃ (slag).
5. Molten iron sinks; slag floats → removed separately.

Electrolysis of aluminium oxide

1. Al₂O₃ dissolved in molten cryolite (lower melting point).
2. Electrodes: carbon anodes and cathode.
3. At cathode: Al³⁺ + 3e⁻ → Al (reduction).
4. At anode: 2O²⁻ → O₂ + 4e⁻ (oxidation); carbon anode oxidised by O₂ → must be replaced.

Phytomining and bioleaching (alternative copper extraction)

• Phytomining: plants absorb copper compounds from soil; burned; copper extracted from ash.
• Bioleaching: bacteria oxidise copper sulfide ore → copper sulfate in leachate → copper extracted.

Both are lower energy and use lower-grade ores than traditional smelting.