How Is Aluminum Produced From Its Ore?
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Abundant Metal Element
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Aluminum is the most abundant metallic element in the earth's crust, making up about 8.3 percent of it by weight. Aluminum bonds easily with oxygen, so it is almost never found naturally in its pure state. Instead, aluminum is usually found in some form of aluminosilicate ore, such as feldspar, or in minerals such as beryl, garnet, turquoise, ruby and sapphire. The only real economical source of aluminum for refinement, however, is bauxite, an ore produced by the weathering of bedrock, often in tropical climates. Bauxite appears in abundance in Australia, Brazil, Ghana, Indonesia, Jamaica and Russia.
3 Steps in Processing
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There are three steps in converting bauxite ore into metallic aluminum. The first, called the Bayer Process, has the ore physically crushed to increase its surface area and then mixed with sodium hydroxide. In a container called a digester, high temperature and pressure catalyze chemical reactions that dissolve aluminum oxide and keep it in solution. Heavier elements like silicon, lead, and titanium fall to the bottom of the digester and can be easily removed. Then, by evaporating the remaining liquid, the aluminum oxide is isolated.
The aluminum oxide precipitates out of the solution in crystalline form. These are carefully washed and dried before the second step begins. The goal of the Hall-Heroult Process is to split the aluminum oxide and capture pure aluminum. To do this, a form of electrolysis is used. Once the aluminum oxide is placed in an electrolytic cell, an electrically charged carbon rob is introduced to pull the oxygen atoms away from the aluminum. The result is carbon monoxide, carbon dioxide and pure aluminum, which sinks to the bottom in a powder form.
The final step is simply to gather the powdered aluminum at the bottom of the Hall-Heroult cell and take it to a furnace, where it's melted into the more familiar forms of bars or ingots. During the melting step, the aluminum may be superheated to remove remaining oxides and other metals, or may have chlorine bubbled through while in a molten state to remove impurities.
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Applications and Recycling
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The bars produced by the ore refinement process are sent to fabricating shops where they are re-melted and poured into molds and/or combined with other ingredients to form alloys. The leading consumers of aluminum are the container and packaging industry, the transportation industry, and the building and construction industry. As might be expected, most aluminum goes to make engine and body parts for cars and aircraft, window and door frames, beverage cans, doors, siding and, of course, aluminum foil.
Recycling and reusing aluminum is much less expensive and requires much less energy than refining aluminum from ore. Thus, about 40 percent of aluminum in the United States is recovered for reuse and this secondary refining makes up most of aluminum processing activity.
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Resources
- Photo Credit USGS/Mineral Information Institute
