Aluminum compounds are found in all types of clay, but bauxite is the
most useful ore for producing pure aluminium. Bauxite is composed of
45-60% aluminium oxide and other impurities such as sand, iron, and
other metals. Although some bauxite deposits are hard rock, the majority
are relatively soft dirt that can be easily extracted from open-pit
mines. Australia produces more than one-third of the world's bauxite
supply. 1 lb (0.5 kg) of aluminium metal requires approximately 4 lb (2
kg) of bauxite.
To separate the aluminium compounds found in
bauxite from the impurities, caustic soda (sodium hydroxide) is used to
dissolve them. Small amounts of other chemicals may be used in the
extraction depending on the composition of the bauxite ore.
Aluminum
is produced in two stages: the Bayer process, which involves refining
bauxite ore to produce aluminium oxide, and the Hall-Heroult process,
which involves smelting the aluminium oxide to produce pure aluminium.
made of aluminium Some examples include starch, lime, and sodium sulphide.
The
electrolyte (current-conducting medium) in the smelting process is
cryolite, a chemical compound composed of sodium, aluminium, and
fluorine. Cryolite was once mined naturally in Greenland, but the
compound is now synthesised for use in the production of aluminium. To
lower the melting point of the electrolyte solution, aluminium fluoride
is added.
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Carbon is another important component in the smelting
process. Carbon electrodes conduct electricity through the electrolyte.
Some of the carbon is consumed during the smelting process as it
combines with oxygen to form carbon dioxide. In fact, for every pound
(2.2 kg) of aluminium produced, approximately half a pound (0.2 kg) of
carbon is used. Some of the carbon used in aluminium smelting comes from
oil refining, while the rest comes from coal.
Aluminum smelting
necessitates a large amount of electrical energy because it involves
passing an electric current through a molten electrolyte. On average, it
takes 15 kilowatt-hours (kWh) to produce 2 lb (1 kg) of aluminium.
Electricity costs roughly one-third of the cost of smelting aluminium.
More information: http://www.madehow.com/Volume-5/Aluminum.html#ixzz7aybRvthI
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