The main chemical in bauxite is aluminium oxide (alumina for short).
Aluminium is a very reactive metal. It is too reactive to obtain by displacement. Electrolytic reduction has to be used.
The alumina has to be in the liquid state so that the ions from which it is made are free to move around and they can be attracted to the electrodes.
The alumina has a very high melting point (over 20000C) , so it is dissolved in molten cryolite (at about 970 0 C)
Cryolite is a compound of aluminium that melts at a much lower temperature.
The electrodes are made from carbon.
Molten aluminium is formed at the cathode. This can easily be run off from the bottom of the cell and cast into blocks.
Oxide ions (which were originally oxygen atoms) are negative and are attracted to the anode. Each oxide ion has negative charge because it has two electrons more than an atom of oxygen. At the anode, each oxide ion loses these two electrons and become atom of oxygen again and it reacts with the carbon of the anode, forming carbon dioxide.
When an ion loses one or more electrons, it is said to have been oxidized.
Aluminium ions have three electrons less than an atom of aluminium.
This means that they have positive charge and will be attracted to the cathode. At the cathode, they gain three
electrons and become atoms of aluminium again.
When an atom gains one or more electrons, it is said to have been reduced. This means that the aluminium has been reduced and the oxygen has been oxidised.
Where reduction and oxidation happen together, it is called 'redox'.
The ore of aluminium is bauxite.