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Bauxite

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Bauxite

Summary: Bauxite is the main ore of aluminium, containing aluminium oxide (Al₂O₃). Aluminium is extracted from purified bauxite by electrolysis in the Hall-Héroult process, using molten cryolite to lower the melting point. Tags: igcse chemistry definition metals extraction Created: 2026-07-14 Last Updated: 2026-07-23

Bauxite is a reddish-brown rock and the primary ore of aluminium. It contains aluminium oxide (Al₂O₃) mixed with impurities such as iron(III) oxide and silicon dioxide. Bauxite is mined from the earth’s crust in countries including Australia, China, and Guinea.

From Bauxite to Aluminium

  1. Bauxite is mined and purified to obtain pure aluminium oxide (Al₂O₃) — details of purification are NOT required for IGCSE
  2. Aluminium oxide has a very high melting point (~2000°C)
  3. To reduce energy costs, Al₂O₃ is dissolved in molten cryolite (Na₃AlF₆)
  4. The mixture melts at about 950°C — much lower than pure Al₂O₃
  5. Electrolysis is carried out in carbon-lined steel cells

Why Electrolysis?

Aluminium is above carbon in the reactivity series. This means:

  • Carbon is NOT a strong enough reducing agent to reduce Al₂O₃
  • Electrolysis is the ONLY method that can extract aluminium from its oxide
  • Electrical energy provides the driving force for the reduction

Role of Cryolite

  • Cryolite (Na₃AlF₆) is a mineral added to the aluminium oxide
  • It acts as a solvent for Al₂O₃
  • Dissolves Al₂O₃ and lowers the melting point from ~2000°C to ~950°C
  • This significantly reduces energy costs and makes the process economically viable

Key Facts

  • Bauxite = main ore of aluminium, contains Al₂O₃
  • Aluminium extracted by electrolysis (Hall-Héroult process)
  • Al₂O₃ dissolved in molten cryolite to lower melting point to ~950°C
  • Electrolysis needed because aluminium is above carbon in the reactivity series
  • Carbon anodes need regular replacement (they react with O₂ produced → CO₂)
  • The process is expensive due to high electricity consumption

See Also

This is a key term definition page — part of the IGCSE Chemistry (0620/0971) keyword glossary.

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