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Engineering & Science

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The Hall-Héroult Process

Alumina is dissolved in a bath of molten cryolite (a double fluoride of aluminium and sodium that occurs naturally in large quantities in Greenland) through which currents of electricity are passed. 

The electricity heats the bath to a temperature of between 960 and 1000° C keeping the cryolite and alumina in a molten state. Concurrently, it reduces the alumina, liberating oxygen to combine with the carbon of the anode to form carbon dioxide.

In the process the molten aluminium sinks to the bottom of the bath, and is tapped at regular intervals. The virgin metal is then tapped off, poured into moulds and cooled before distribution to semi-fabrication works. 

In essence, this method remains largely unchanged to this day.