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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.
The process produces a quantity of fluoride waste: perfluorocarbons and hydrogen fluoride as gases, and sodium and aluminium fluorides and unused cryolite as particulates. This can be as small as 0.5 kg per tonne of aluminium in the best plants in 2007, up to 4 kg per tonne of aluminium in older designs in 1974.
Molten cryolite is used as a solvent for aluminium oxide (Al 2 O 3) in the Hall–Héroult process, used in the refining of aluminium. It decreases the melting point of aluminium oxide from 2000–2500 °C to 900–1000 °C, and increases its conductivity [16] thus making the extraction of aluminium more economical. [17]
The conversion of alumina to aluminium is achieved by the Hall–Héroult process. In this energy-intensive process, a solution of alumina in a molten (950 and 980 °C (1,740 and 1,800 °F)) mixture of cryolite (Na 3 AlF 6) with calcium fluoride is electrolyzed to produce metallic aluminium.
Aluminium recycling is the process in which secondary commercial aluminium is created from scrap or other forms of end-of-life or otherwise unusable aluminium. [1] It involves re-melting the metal, which is cheaper and more energy-efficient than the production of virgin aluminium by electrolysis of alumina (Al 2 O 3 ) refined from raw bauxite ...
The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminium oxide) and was developed by Carl Josef Bayer.Bauxite, the most important ore of aluminium, contains only 30–60% aluminium oxide (Al 2 O 3), the rest being a mixture of silica, various iron oxides, and titanium dioxide. [1]
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Hall and Heroult share credit for inventing aluminium electrolysis. [9] The Hall–Heroult method is the primary method of producing modern aluminium and requires high purity alumina to produce aluminium. The Bayer process produces high purity alumina which is then used in the Hall–Heroult process as the main raw material. [9]