Electrolysis is used to remove Aluminium from it's ore:
1) Aluminium is a very abundant metal, but it is always found naturally in compounds. It's main ore is bauxite, and, after mining and purifying, a white powder is left. This is pure aluminium oxide, Al2O3. The aluminium has to be extracted using electrolysis.
Cryolite is used to lower the temperature (and costs):
1) Aluminium Oxide has a very high melting point (over 2000'C), so melting it is very expensive. Instead, the aluminuim oxide is dissolved in molten cryolite, a less common ore of aluminium. This brings the temperature down to about 900'C, which makes it much cheaper and easier.7
2) The electrodes are made of carbon (graphite), a good conductor of electricity.
3) Aluminium is formed at the negative electrode and oxygen forms at the positive electrode.
4) The oxygen then reacts with the carbon in the electrode to produce carbon dioxide. This means that the positive electrode gradually wears away and has to be replaced regularly.
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