Environment | Economic | Recycling | Noise and air pollution (greenhouse effect, acid rain) involved in these operations. | The high cost of the process because of the huge amounts of electricity it uses. This is so high because to produce 1 mole of aluminium which only weighs 27 g you need 3 moles of electrons. You are having to add a lot of electrons (because of the high charge on the ion) to produce a small mass of aluminium (because of its low relative atomic mass). | Saving of raw materials and particularly electrical energy by not having to extract the aluminium from the bauxite. Recycling aluminium uses only about 5% of the energy used to extract it from bauxite. | Loss of landscape due to mining, processing and transporting the bauxite. | Energy and material costs in producing the cryolite, some of which gets lost during the electrolysis. | (Offsetting these to a minor extent) Energy and pollution costs in collecting and transporting the recycled aluminium. | Energy and material costs in constantly replacing the anodes. | Avoiding the environmental problems in the extraction of aluminium from the bauxite. Not having to find space to dump the unwanted aluminium if it wasn't recycled. | aluminium is used for | because | aircraft | light, strong, resists corrosion | other transport such as ships' superstructures, container vehicle bodies, tube trains (metro trains) | light, strong, resists corrosion | overhead power cables (with a steel core to strengthen them) | light, resists corrosion, good conductor of electricity | saucepans | light, resists corrosion, good appearance, good conductor of heat |

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Note:
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*Aluminium is released at the cathode
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* Oxygen is produced initially at the anode.
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* Although the carbon lining of the cell is labelled as the cathode, the effective cathode is mainly the molten aluminium that forms on the bottom of the cell. Molten aluminium is syphoned out of the cell from time to time, and new aluminium oxide added at the top. The cell operates at a low voltage of about 5 - 6 volts, but at huge currents of 100,000 amps or more. The heating effect of these large currents keeps the cell at a temperature of about 1000°C.
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*Aluminium is too high in the electrochemical series (reactivity series) to extract it from its ore using carbon reduction. The temperatures needed are too high to be economic.
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*Instead, it is extracted by electrolysis. The ore is first converted into pure aluminium oxide by the Bayer Process, and this is then electrolysed in solution in molten cryolite - another aluminium compound. The aluminium oxide has too high a melting point to electrolyse on its own.
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*The usual aluminium ore is bauxite. Bauxite is essentially an impure aluminium oxide. The major impurities include iron oxides, silicon dioxide and titanium dioxide.
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