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The processing and use of minerals and metals
Bauxite to Alumina to Aluminum
Aluminum is the third most abundant element in the earth’s crust behind Oxygen and Silicon. The metal is used in airplanes, beverage cans, auto trim, cooking utensils, and building products. The ore aluminum is extracted from is called bauxite and found in tropical regions such as Australia, Brazil, Surinam, Jamaica, Indonesia, and Guinea. Bauxite is 30 to 50% Al2O3 and is separated from the gangue by solution in hot NaOH under pressure. After further treatment the resultant product is alumina, Al2O3, which is a white powder. This process is called the Bayer Process.
The bond between the aluminum and oxygen is strong. In 1884, Charles Hall, an American, and Paul Herolt, a Frenchman, almost simultaneously discovered that alumina would dissolve in molten cryolite, a sodium aluminum fluoride compound which was mined, but, now is manufactured synthetically. If electricity was passed thru the solution, the bond between the Al and O2 could be broken. The amount of electricity is significant with 8 to 12 kw-hr (kilowatt hour) required to produce one pound of aluminum.
The attraction of aluminum now becomes apparent as it can be recycled over and over again and re-melting only requires .4 to .6 kw-hr (in the form of natural gas). This is a 95% reduction in energy when compared to smelting bauxite! Scrap aluminum is valuable and the recycling mentality started in the early 1960’s when Coors made the first aluminum cans in Golden, CO.
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