Extraction of Metals

This lesson covers the extraction of metals from their ores as required by the Edexcel GCSE Combined Science specification (1SC0). You need to understand the link between the reactivity series and extraction methods, reduction with carbon, electrolysis for reactive metals, and the importance of recycling metals.

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Metals and Their Ores

Most metals are found in the Earth's crust as ores — rocks that contain enough metal or metal compound to make extraction worthwhile. Very unreactive metals like gold and platinum are found native (uncombined) because they do not react with other elements.

Metal	Ore Name	Main Compound in Ore
Iron	Haematite	Iron(III) oxide, Fe₂O₃
Aluminium	Bauxite	Aluminium oxide, Al₂O₃
Copper	Malachite, chalcopyrite	Copper carbonate CuCO₃, copper iron sulfide CuFeS₂
Zinc	Sphalerite	Zinc sulfide, ZnS
Tin	Cassiterite	Tin oxide, SnO₂

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The Link Between Reactivity and Extraction

The position of a metal in the reactivity series determines how it is extracted from its ore:

graph TD
    A["Where is the metal<br/>in the reactivity series?"]
    A -->|"Above carbon<br/>(K, Na, Li, Ca, Mg, Al)"| B["Extracted by<br/>ELECTROLYSIS<br/>(very expensive)"]
    A -->|"Below carbon<br/>(Zn, Fe, Sn, Pb, Cu)"| C["Extracted by<br/>REDUCTION WITH CARBON<br/>(cheaper)"]
    A -->|"Very unreactive<br/>(Au, Pt)"| D["Found NATIVE<br/>(uncombined)<br/>in the ground"]

    style A fill:#2c3e50,color:#fff
    style B fill:#e74c3c,color:#fff
    style C fill:#27ae60,color:#fff
    style D fill:#f39c12,color:#000

Why Does the Method Depend on Reactivity?

• Metals above carbon in the reactivity series are too reactive to be reduced by carbon. They hold on to oxygen (or other non-metals) very tightly. Electrolysis is needed to break apart the strong ionic bonds using electricity.
• Metals below carbon can be reduced by heating with carbon (a cheaper, simpler process). Carbon is more reactive than these metals, so it can displace them from their oxides.

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Reduction with Carbon

For metals below carbon in the reactivity series, the metal oxide is heated with carbon (in the form of coke or charcoal) in a blast furnace or similar setup.

General Equation

metal oxide + carbon → metal + carbon dioxide

Example 1: Extraction of Iron

iron(III) oxide + carbon → iron + carbon dioxide

2Fe₂O₃ + 3C → 4Fe + 3CO₂

This takes place in a blast furnace at very high temperatures (~1500 °C).

Example 2: Extraction of Zinc

zinc oxide + carbon → zinc + carbon dioxide

2ZnO + C → 2Zn + CO₂

Example 3: Extraction of Tin

tin oxide + carbon → tin + carbon dioxide

SnO₂ + C → Sn + CO₂

Example 4: Extraction of Copper (from its oxide)

copper oxide + carbon → copper + carbon dioxide

2CuO + C → 2Cu + CO₂

What Is Happening in These Reactions?

In each case:

• The metal oxide is reduced — oxygen is removed from the metal.
• The carbon is oxidised — carbon gains oxygen to form carbon dioxide.
• This is a redox reaction — reduction and oxidation occur simultaneously.

Exam Tip: Remember that "reduction" means the removal of oxygen (or gain of electrons). Carbon acts as the reducing agent because it removes the oxygen from the metal oxide.

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Electrolysis for Reactive Metals

Metals above carbon in the reactivity series (potassium, sodium, lithium, calcium, magnesium, aluminium) cannot be extracted by reduction with carbon. Instead, they are extracted by electrolysis of their molten compounds.

Example: Extraction of Aluminium

Aluminium is extracted from purified aluminium oxide (Al₂O₃) dissolved in molten cryolite (Na₃AlF₆). Cryolite lowers the melting point of aluminium oxide, reducing energy costs.

Feature	Detail
Electrolyte	Aluminium oxide dissolved in molten cryolite
Cathode (−)	Carbon (graphite) — aluminium ions are reduced here
Anode (+)	Carbon (graphite) — oxide ions are oxidised here
At the cathode	Al³⁺ + 3e⁻ → Al (aluminium metal is deposited)
At the anode	2O²⁻ → O₂ + 4e⁻ (oxygen gas is produced)
Problem	Oxygen reacts with the carbon anodes, forming CO₂ — anodes must be regularly replaced
Cost	Very expensive due to huge amounts of electricity needed

Exam Tip: If asked why electrolysis of aluminium is expensive, there are two key reasons: (1) the very high temperatures needed to melt the electrolyte (even with cryolite) and (2) the large amount of electricity consumed continuously.

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Recycling Metals

Recycling metals is important for several reasons:

Reason	Explanation
Conserves ore	Finite metal ore supplies are preserved for longer
Saves energy	Recycling uses far less energy than extracting from ore (especially for aluminium)
Reduces landfill	Less metal waste going to landfill sites
Reduces mining	Less environmental damage from quarrying and mining
Reduces CO₂ emissions	Less burning of fossil fuels for energy, less CO₂ from reduction with carbon

Recycling Aluminium

Recycling aluminium saves approximately 95% of the energy that would be needed to extract it from bauxite by electrolysis. This is why recycling aluminium is particularly worthwhile.

Challenges of Recycling

• Metals need to be sorted and separated, which takes time and effort.
• Scrap metal may be contaminated with other materials.
• Transport costs for collecting scrap metal.
• Some metals are difficult to recycle if they are in alloys or complex products.

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Biological Methods of Extraction (Brief Overview)

Scientists are developing biological methods to extract metals, particularly copper from low-grade ores:

• Bioleaching — bacteria are used to produce solutions containing dissolved metal compounds, from which the metal can be obtained.
• Phytoextraction — plants absorb metal ions through their roots; the plants are harvested and burned, and the metal is extracted from the ash.

These methods are slower but more environmentally friendly and can extract metals from ores that are too low-grade for traditional methods.

Exam Tip: You do not need to know details of bioleaching and phytoextraction for the core specification, but you should be aware that they exist as alternative, more sustainable extraction methods.

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Summary