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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.
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 ...
[h] Hall co-founded the Pittsburgh Reduction Company in 1888 and initiated production of aluminium. [88] Hall's patent was granted in 1889. [74] [i] In 1889, Hall's production began to use the principle of internal heating. [j] By September 1889, Hall's production grew to 385 pounds (175 kilograms) at a cost of $0.65 per pound. [91]
In 1891 after Cowles began to advertise "pure aluminum" they were sued by the Pittsburgh Reduction Company. The judge announced his decision in January 1893, finding them to be infringing the patent of Hall and having gained knowledge of his process by hiring away a chemist named Hobbs who was the foreman in Pittsburgh.
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 [ 18 ] thus making the extraction of aluminium more economical.
Subsequently, a process of spraying molten aluminium to create a powder of droplets was developed by E. J. Hall in the 1920s. The resulting powder might then be processed further in a ball mill to flatten it into flakes for use as a coating or pigment. [1] Aluminium powder features low density with high conductivity. [2]
Charles Martin Hall (December 6, 1863 – December 27, 1914) was an American inventor, businessman, and chemist.He is best known for his invention in 1886 of an inexpensive method for producing aluminum, which became the first metal to attain widespread use since the prehistoric discovery of iron.