Bauxite. How Bauxite Forms. Mining and Processing Bauxite

Bauxite, is the ore from which almost all aluminum is produced. Bauxite contains large amounts of hydrated aluminum hydroxide, a chemical combination of aluminum oxide (Al2O3) and water. Aluminum oxide is also called alumina. Most bauxite consists of 30 to 60 percent alumina and 12 to 30 percent water. Bauxite was named for the town of Les Baux, France, where it was discovered in 1821.

The aluminum industry uses about 90 percent of the bauxite mined throughout the world. Another bauxite product, a white mineral salt called alum, purifies water and hardens plaster of Paris. Bricks that are designed to line blast furnaces are made of a mixture of bauxite and clay. Bauxite is also used in abrasives for grinding and polishing.

How bauxite forms. Bauxite deposits result from the chemical weathering of rocks that contain aluminum and silica (a compound of silicon and oxygen). Most bauxite deposits are located near the surface of the earth in regions with a hot, moist climate. In such a climate, water running slowly through the rock may remove silica but leave behind much of the aluminum.

This chemical weathering creates boehmite, diaspore, or gibbsite, minerals rich in aluminum hydroxide. Bauxite consists of one or more of these three minerals and such impurities as iron oxide, silica, and titanium oxide. The color of bauxite ranges from dark red or brown to pink or nearly white, depending chiefly on the amount of iron oxide in the ore. Most bauxite is hard and rocklike, but some is as soft as clay or dirt.

Mining and processing bauxite. Most bauxite deposits are mined by the open-pit method. First, earthmoving machines clear away the overburden — that is, the layer of rock and other material that covers the deposit If necessary, workers then blast the ore loose with dynamite. Next, power shovels load the bauxite into trucks, which haul the ore to a processing plant, where it is crushed. Some bauxite must also be washed at the processing plant to reduce the amount of silica in the ore.

Finally, the bauxite is transported to a refinery, where a chemical process removes alumina from the ore. An electrical process called smelting then removes aluminum from the alumina. See Aluminum (How aluminum is produced).

Bauxite mining companies work to renew mined-out areas. Companies perform environmental impact studies before developing a new mine. After they have finished mining, they work to restore the area's vegetation. Plants grow back because the waste products of bauxite mining are not toxic.

The bauxite industry. Australia leads the world in bauxite production. Brazil, Guinea, and Jamaica also produce large amounts of the ore. Bauxite reserves throughout the world total about 22 billion tons (20 billion metric tons). Additional potential resources are estimated to be about 20 billion tons (18 billion metric tons).

The refining and smelting of bauxite require large amounts of electric energy. As a result, bauxite is refined and smelted chiefly in the United States and other nations where such energy is plentiful and relatively cheap. The United States produces more aluminum than any other country but has no large deposits of bauxite. Almost all the bauxite used in the United States today comes from other countries. Canada, another major producer of aluminum, imports all its bauxite.

Many bauxite deposits lie in developing countries. In 1974, 11 nations with major bauxite deposits formed the International Bauxite Association (IBA) to increase their income from the ore. IBA members have raised the price of bauxite and have levied higher taxes on bauxite-producing companies. They also have promoted the construction of bauxite refineries in their countries.

 






Date added: 2022-12-31; views: 178;


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