Extraction of Aluminium from Bauxite (Cambridge O Level Chemistry)

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Alexandra Brennan

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Extraction of Aluminium from Bauxite

  • Aluminium is a reactive metal, above carbon in the reactivity series 
  • Its main ore, is bauxite, which contains aluminium oxide
  • Aluminium is higher in the reactivity series than carbon, so it cannot be extracted by reduction using carbon
  • Instead, aluminium is extracted by electrolysis  

Aluminium extraction, IGCSE & GCSE Chemistry revision notesDiagram showing the extraction of aluminium by electrolysis

  • Bauxite is first purified to produce aluminium oxide, Al2O3
  • Aluminium oxide is then dissolved in molten cryolite 
    • This is because aluminium oxide has a melting point of over 2000°C which would use a lot of energy and be very expensive
    • The resulting mixture has a lower melting point without interfering with the reaction
  • The mixture is placed in an electrolysis cell, made from steel, lined with graphite
  • The graphite lining acts as the negative electrode, with several large graphite blocks as the positive electrodes
  • At the cathode (negative electrode)
    • Aluminium ions gain electrons (reduction) 
    • Molten aluminium forms at the bottom of the cell
    • The molten aluminium is siphoned off from time to time and fresh aluminium oxide is added to the cell

Al3+ +  3e-   →  Al 

  • At the anode (positive electrode):
    • Oxide ions lose electrons (oxidation)
    • Oxygen is produced at the anode:

2O2- →   O2 + 4e-

  • The overall equation for the reaction is:

2Al2O3 → 4Al  +  3O2

  • The carbon in the graphite anodes reacts with the oxygen produced to produce CO2

C (s) + O2 (g)   →   CO2 (g)

  • As a result the anode wears away and has to be replaced regularly
  • A lot of electricity is required for this process of extraction, this is a major expense

Examiner Tip

Use OIL RIG to remember whether oxidation or reduction has occurred at the electrodes:

OILRIG, downloadable AS & A Level Biology revision notes

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Alexandra Brennan

Author: Alexandra Brennan

Expertise: Chemistry

Alex studied Biochemistry at Newcastle University before embarking upon a career in teaching. With nearly 10 years of teaching experience, Alex has had several roles including Chemistry/Science Teacher, Head of Science and Examiner for AQA and Edexcel. Alex’s passion for creating engaging content that enables students to succeed in exams drove her to pursue a career outside of the classroom at SME.