Mineral Resource of the Month: Aluminum

by U.S. Geological Survey
Wednesday, June 13, 2018

E. Lee Bray, a mineral commodity specialist for the U.S. Geological Survey, compiled the following information about aluminum, an element that is the second-most used metal.

Aluminum is the third-most abundant element in Earth’s crust, after oxygen and silicon. In nature, aluminum is bonded to iron, oxygen, potassium, silicon and other elements in common rock-forming minerals. In tropical conditions, potassium, silicon and other elements can be naturally leached from rocks to leave behind bauxite — a rock composed mainly of aluminum hydroxide with iron oxides and clay — which is the most commonly used aluminum ore. Aluminum has also been recovered from alunite, anorthosite and clay, but the cost of producing aluminum from these sources tends to be higher than from bauxite.

Despite its abundance in Earth’s crust, metallic aluminum was not produced until 1825 when Hans Christian Oersted, a Danish chemist, was the first to isolate it in the laboratory. In 1886, Charles Martin Hall, an American chemist, and Paul Louis Toussaint Heroult, a French scientist, independently and simultaneously discovered a method of separating aluminum metal from aluminum oxide, or alumina, by passing an electric current through a carbon anode into a molten mixture of alumina and cryolite, a sodium aluminum fluoride salt. This electrolytic smelting method, known as the Hall-Heroult process, is still used today.

Approximately 15 kilowatt-hours of electricity are used to smelt 1 kilogram of aluminum from alumina, necessitating that primary aluminum smelters be close to abundant power sources. Historically, smelters have been located near major hydroelectric power plants such as those in the Columbia River Basin in Oregon and Washington or other major river systems. In recent years, limited demand for power from power plants in Iceland, Russia and the Persian Gulf region has led to construction of smelters in these areas.

Aluminum’s melting point is 660 degrees Celsius, relatively low compared with that of other metals, which makes aluminum ideal for recycling. Melting aluminum scrap only requires about 5 percent of the energy needed to produce aluminum from alumina. Scrap supplies about one-third of the U.S. aluminum supply.

Compared with other metals, aluminum is lightweight, corrosion-resistant and an excellent conductor of electricity and heat. About 37 percent of aluminum consumed in the United States is used for transportation products such as aircraft, automobile engines, boats, rail cars and truck trailers. Containers and packaging are the second-leading category of aluminum consumption, primarily for beverage cans and foil wrapping. Other major use categories include construction materials, electrical transmission wires, machinery and consumer durables.

For more information on aluminum and other mineral resources, visit: http://minerals.usgs.gov/minerals.

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Aluminum production and consumption:

• World bauxite production in 2011 was estimated to be 220 million metric tons. Australia represented about 30 percent of the total, with China, Brazil and India the other leading producers.

• World alumina production in 2011 was estimated to be 93 million metric tons. China represented about 37 percent of the total, with Australia, Brazil, India and the United States the other leading producers.

• U.S. apparent consumption of aluminum in 2011 was estimated to be 3.9 million metric tons, including about 1.4 million metric tons of scrap aluminum and 320,000 metric tons of net imports of metal and scrap.

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Fun facts:

• The top of the Washington Monument is an aluminum pyramid that functions as a lightning rod.

• Aluminum powder has been used as a component of solid rocket fuel in the U.S. space program.

• The compound aluminum zirconium octachlorohydrex glycine is the active ingredient in common antiperspirant deodorants.