Production Method 1 - Making the Electrolyte

Pure aluminium oxide is not used for electrolysis. Its melting point is too high, and it is not a good conductor. Instead it is dissolved at about 5% concentration in molten sodium aluminium fluoride ("cryolite").

Aluminium Oxide

The chemistry used to obtain pure aluminium oxide ("alumina") from bauxite was first developed by the German chemist Karl Bayer in 1888, and the process is still referred to as the "Bayer Process".

diagram: bayer process
diagram: bayer process diagram: bayer process diagram: bayer process
diagram: bayer process
diagram: bayer process
diagram: bayer process
diagram: bayer process
diagram: bayer process
diagram: bayer process
diagram: bayer process

Bayer Process Chemistry

Aluminium forms an amphoteric oxide that will react with sodium hydroxide, whereas the other metal oxides in bauxite do not.
There are four main stages in producing pure aluminium oxide for electrolysis. Click on the four stages in the diagram to find out more each one.

Making Cryolite

During electrolysis the aluminium oxide is dissolved in "cryolite", which is sodium aluminium fluoride (Na3AlF6). Cryolite is made using sodium aluminate and hydrogen fluoride, which is manufactured from the mineral fluorspar using sulphuric acid.


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