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The extraction of aluminium Aluminium is a reactive metal and cannot be extracted from its ore, Bauxite (Al2O3, through reduction with carbon. Instead it is extracted through the process of electrolysis? - the metal is oxidised in a solution and then reduced again as a pure metal. The ore needs to be in a liquid state for this to be achieved. However Bauxite has a melting point of 2000'C - which would be a too high temperature to heat it up economically. Instead the Bauxite is dissolved in molten cryolite, which lowers the melting point significantly to about 900'C. This still requires lots of energy and usually aluminium plants have their own power stations nearby. The electrodes in the electrolysis of Bauxite are both carbon. Once the ore is in molten state, its ions are free to move around. The reaction at the negative cathode is: Al3+ + 3e- -> Al Here the aluminium is being reduced - the addition of electrons. The aluminium then sinks to the bottom and is tapped off. The positive cathode oxidises the oxygen from Bauxite, and then it reacts with the carbon electrode to carbon dioxide: 2O2- -> O2 + 2e- O2 + C -> CO2 This cathode needs to be replaced often due to it turning in to carbon dioxide. Despite the cost of electrolysis aluminium is a cheap and widely used metal. |
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