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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]
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.
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.
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 ...
An electrolytic process is the use of electrolysis industrially to refine metals or compounds at a high purity and low cost. Some examples are the Hall-Héroult process [ 1 ] used for aluminium , or the production of hydrogen from water .
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.
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 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 ...