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The Hall–Héroult process consumes substantial electrical energy, and its electrolysis stage can produce significant amounts of carbon dioxide if the electricity is generated from high-emission sources. Furthermore, the process generates fluorocarbon compounds as byproducts, contributing to both air pollution and climate change. [2] [3]
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.
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.
Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal behind. The reducing agent is commonly a fossil-fuel source of carbon , such as carbon monoxide from incomplete combustion of coke —or, in earlier times, of charcoal . [ 1 ]
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] This decrease is attributed to the increase in the ...
The Cowles process was the immediate predecessor to the Hall-Héroult process—today in nearly universal use more than a century after it was discovered by Charles Martin Hall and Paul Héroult and adapted by others including Carl Josef Bayer. Because of the patent landscape, the Cowles companies found themselves in court.
The primary aluminium and the semiconductor manufacturing industries are the major emitters of hexafluoroethane using the Hall-Héroult process. Together with trifluoromethane it is used in refrigerants R508A (61%) and R508B (54%). It is used as a tamponade to assist in retinal reattachment following vitreoretinal surgery. [3]