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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.
Alumina is extracted from the ore bauxite by means of the Bayer process at an alumina refinery. 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 ...
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 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 ]
The Hall–Heroult process produces aluminium with a purity of above 99%. Further purification can be done by the Hoopes process. This process involves the electrolysis of molten aluminium with a sodium, barium, and aluminium fluoride electrolyte. The resulting aluminium has a purity of 99.99%. [46] [143]
The process consumes the anode at a rate of roughly 450 kg of anode per tonne of aluminium produced. [ 1 ] "Spent" anodes have little industrial use and are generally discarded; however, anodes that have been used to process aluminium fluoride may contain some amount of hydrogen fluoride and require hazardous waste disposal procedures. [ 2 ]
It uses 13 percent of New Zealand's electricity, [5] [6] and is reported to account for 10 percent of the Southland region's economy. [ 7 ] Rio Tinto has threatened to close the smelter several times, for example in 2013 and 2020, but to date closure has been deferred after renegotiation of the price it pays for electricity.
[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]