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The Hall–Héroult process is the major industrial process for smelting aluminium. It involves dissolving aluminium oxide (alumina) (obtained most often from bauxite , aluminium 's chief ore, through the Bayer process ) in molten cryolite and electrolyzing the molten salt bath, typically in a purpose-built cell.
This is an electrolytic process, so an aluminium smelter uses huge amounts of electric power; smelters tend to be located close to large power stations, often hydro-electric ones, in order to hold down costs and reduce the overall carbon footprint. Smelters are often located near ports, since many smelters use imported alumina.
The difficulty of separating aluminium from oxygen in the oxide ores was overcome by the use of cryolite as a flux to dissolve the oxide mineral(s). Pure cryolite itself melts at 1012 °C (1285 K), and it can dissolve the aluminium oxides sufficiently well to allow easy extraction of the aluminium by electrolysis. Substantial energy is still ...
The Hall-Héroult process for aluminium production from alumina was invented in 1886 by Charles Hall and Paul Héroult. [17] Carl Josef Bayer created a multi-step process to convert raw bauxite into alumina in 1888. [18] As aluminium production rose with the use of these two processes, aluminium recycling grew too.
Oxygen equivalents react at the red-hot carbon anode, forming a mixture of carbon monoxide (that subsequently becomes carbon dioxide) and carbon dioxide. For one tonne of aluminium, 1.55 tonnes of CO result, becoming 2.4 tonnes of CO 2. However, if all the oxygen were instead directly converted to CO 2, then only 1.56 tonnes of CO 2 would ...
The Bayer process produces high purity alumina which is then used in the Hall–Heroult process as the main raw material. [9] In 1900, aluminium was valued at the equivalent of 100 current US dollars, but over the next 50 years decreased in price to approximately 20 current US dollars. [ 10 ]
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Large tonnages of aluminium hydroxide, from which alumina is derived, are used in the manufacture of zeolites, coating titania pigments, and as a fire retardant/smoke suppressant. Over 90% of aluminium oxide, termed smelter grade alumina (SGA), is consumed for the production of aluminium, usually by the Hall–Héroult process .