Extracting metals using electrolysis
Shiny element that is a good conductor of electricity and heat, and which forms basic oxides. are found in A rock containing enough quantities of a mineral for extraction to be possible. combined with other A substance made of one type of atom only.. The decomposition (breakdown) of a compound using an electric current. can be used to The process of obtaining a metal from a mineral, usually by reduction or electrolysis. a more reactive metal from the ore.
Using bacteria to extract metals from their ores. is used to extract small quantities of metals from mining waste heaps. Electrolysis can be used to extract the metal from the leachate solution produced during the process.
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Extraction of aluminium
Aluminium is the most abundant (found in large quantities) metal in the Earth's The outer layer of the Earth on top of the mantle.. It is expensive, largely because of the amount of electricity required in the extraction process.
Aluminium ore is called A rock that can be used to make aluminium.. The bauxite is purified to produce aluminium oxide, a white powder from which aluminium can be extracted.
The extraction is done by electrolysis. The ions in the aluminium oxide must be free to move so that electricity can pass through it. Aluminium oxide has a very high The temperature at which a solid changes into a liquid as it is heated. (over 2000掳C) so it would be expensive to melt it. Aluminium oxide does not When a substance breaks up and mixes completely with a solvent to produce a solution. in water, but it does dissolve in molten cryolite. This is an aluminium A substance formed by the chemical union of two or more elements. with a lower melting point than aluminium oxide. The use of cryolite reduces some of the energy costs involved in extracting aluminium.
The diagram shows an aluminium oxide electrolysis cell. The negative electrodes (The negative electrode during electrolysis.) and the positive electrodes (The positive electrode during electrolysis.) are made of graphite, a form of carbon.
During electrolysis:
- positively charged aluminium ions gain electrons from the cathode, and form molten aluminium
- oxide ions lose electrons at the anode, and form oxygen molecules
The oxygen reacts with the carbon in the electrodes, forming carbon dioxide which bubbles off. Carbon is therefore lost from the positive electrodes, so they must be replaced frequently. This adds to the cost of the process.