The Extraction of Aluminium

Aluminium is a more reactive metal than is apparent in our day-to-day lives. The reason why it seems so unreactive is that as soon as any part of the metal is exposed to the air it immediately reacts with oxygen in the air to form aluminium oxide which forms a protective layer around the metal, this is called passivation. A trend among metals is that the more reactive it is, the more extreme the conditions that are necessary to obtain it.

Aluminium is made by the electrolysis of bauxite, which is a mineral made of aluminium oxide. Bauxite is named after Baux in France where it is mined. The bauxite is dissolved in molten cryolite in order to keep the running costs low because cryolite melts at a lower temperature than bauxite.

Electricity is passed through the aluminium oxide in molten solution. At the cathode (negative electrode) made of graphite, tripositive aluminium ions become reduced to metallic aluminium. The aluminium sinks into pots where they are collected and form ingots once they cool and solidify.

This process is called the Hall-Heroult process after Charles Hall and Paul Heroult who both discovered it independently of each other in 1886. Charles Hall was a 22-year-old student who heard his chemistry teacher mention that finding an economical method of extracting aluminium would make you rich.

This process replaced the old method of reacting aluminium chloride with potassium. The price of aluminium fell instantly once this newer, more economically viable method was discovered.

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