Which ore is extracted from aluminum
Aluminum Lexicon - the material from A – Z
The classic utility metals such as iron, copper or zinc are obtained from their oxidic ores (compounds with oxygen) by "carbothermal reduction": When heated to high temperatures with carbon, the carbon reduces the ore to metal by combining with the oxygen to form carbon dioxide connects. In principle, this method is not very suitable for extracting aluminum or primary aluminum from bauxite or other aluminum ores because of the property that it easily combines with oxygen. The aluminum pioneers Davy, Oersted and Wöhler recognized this at the beginning of the 19th century. They were also hardly able to generate the necessary temperatures of over 2000 ° C, which is why other ways of extraction were sought. Since the Bayer-Hall-Héroult process was introduced around 1890, which was from then on exclusively used because it was the most economical, the aluminum industry has been striving for processes with lower energy requirements and the resulting lower costs. Among the many trails followed, four are worth mentioning.
The standard procedure
The Bayer-Hall-Héroult process comprises two stages: First, in the Bayer process, the aluminum oxide is extracted from bauxite, from which the aluminum is then separated in the fused-salt electrolysis (patented by Hall and Héroult in 1886). The average energy requirement is around 13 to 16 kilowatt hours per kilogram of aluminum (up to 95 percent less energy is required to remelt scrap into recycled aluminum).
Other interesting procedures
In 1854, Sainte-Claire Deville developed the first process that could be used for aluminum production, but was complex and only used until 1890: If aluminum chloride is heated with sodium, this combines with chlorine to form sodium chloride, leaving aluminum.
The continuing interest in carbothermal reduction is due to the principle of being able to process bauxite as well as poor aluminum ores directly. Since the first patent, issued to the British Monckton in 1862, this approach has proven impractical despite many efforts. In 1967, for example, the French company Pechiney closed a test facility in which it had extracted over 1,000 tons of aluminum since 1960, realizing that energy requirements, raw material consumption and costs were too high. At the beginning of the 1980s (as a result of the oil price increases in the 1970s), particularly in the USA, the carbothermal reduction was re-evaluated and precisely assessed. According to this, the energy requirement (with certain potential for savings) is higher than that of the Bayer-Hall-Héroult process, and there are also certain material problems to be solved. Another disadvantage is that when aluminum oxide is heated with carbon above 2100 ° C., gaseous carbon monoxide (which contains aluminum and aluminum oxide which has been vaporized as raw material loss) and liquid aluminum with 10 percent dissolved carbon are formed. The latter solution solidifies to form a mixture of aluminum and aluminum carbide, after the complex separation of which the aluminum still has to be cleaned of traces of carbon.
In the ASP process (Alcoa Smelting Process), aluminum can be deposited by the electrolysis of aluminum chloride (obtained from alumina or derived directly from bauxite). Although the energy requirement is lower than with the Bayer-Hall-Héroult process, there are technical problems in use.
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