3) Using electrolysis to extract metals

• Metals that are more reactive than carbon can be extracted from their ares using electrolysis.
• Electrolysis requires lots of heat and electrical energy, making it an expensive process.
• Aluminium is obtained by the electrolysis of aluminium oxide that has been mixed with cryolite (a compound of aluminium).
• Cryolite lowers the melting point of the aluminium oxide, meaning less energy is needed (cheaper energy costs).
• Aluminium forms at the negative electrode.
• Oxygen gas forms at the positive carbon electrode and reacts with the carbon, forming carbon dioxide.

  This wears away the positive electrode, which is replaced regularly.