Aluminium is more reactive than carbon, so carbon reduction does not work. Instead, aluminium is extracted from its ore bauxite (aluminium oxide, Al₂O₃) by electrolysis.
Aluminium oxide has a very high melting point (~2050°C), making it expensive to melt for electrolysis. Cryolite is dissolved in to lower the melting point to around 970°C, saving significant energy costs.
During electrolysis of the molten aluminium oxide:
- Cathode (negative electrode): Al³⁺ ions gain electrons and are reduced to form aluminium metal. The aluminium sinks to the bottom and is tapped off.
- Anode (positive electrode): O²⁻ ions lose electrons and are oxidised to form oxygen gas. The oxygen reacts with the carbon anode at high temperatures, burning it away — so the anodes must be regularly replaced.
This deep dive covers Aluminium From Bauxite — Electrolysis within Extracting Metals for GCSE Chemistry. Revise Extracting Metals in Chemical Changes for GCSE Chemistry with 6 exam-style questions and 6 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 5 of 14 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Extracting Metals
Which method is used to extract a metal that is MORE reactive than carbon?
Iron is extracted from haematite in a blast furnace. Describe how iron is obtained from iron oxide using carbon, and explain the term 'reduction' in this context.