Bauxite

Bauxite is a type of rock from which the metal aluminum is extracted. Aluminum is the most abundant metal in the earth's crust, and the crust's third most common element after oxygen and silicon. It is lightweight and is the second easiest metal to shape after pure gold; therefore, it is a good choice for making many products, ranging from kitchen tools to airplane parts. Aluminum resists corrosion and is more durable than many other metals. It also is a good conductor of electricity, adding to its usefulness. Bauxite is the source of most of the aluminum produced throughout the world.

Background

Bauxite ore is found in laterite soil, a reddish clay type of material found most often in subtropical or tropical regions. There are several types of bauxite ore; these are based on the type of aluminum hydroxide materials each contains. These include gibbsite, boehmite, and diaspore.

Although 90 percent of the world's bauxite supply is located in West Africa, South America, India, and Australia, it was originally discovered in France. Pierre Berthier, a French geologist and mining engineer, identified the ore in Les Baux-de-Provence in the southern portion of his home country. In 1847, another French geologist, Armand Dufrenoy, named Berthier's find "beauxite." It was renamed bauxite in 1861 by French chemist Henri Sainte-Claire Deville. Six years earlier, Sainte-Claire Deville had developed an efficient way to separate larger amounts of aluminum from the ore. By 1887, Austrian chemist Karl Josef Bayer developed and patented a process for removing alumina, also known as aluminum oxide, from bauxite. The Bayer process is still used in the twenty-first century to extract aluminum oxide from bauxite. Nearly 70 percent of all mined bauxite is treated with the Bayer process.

Bauxite is nearly always found near the earth's surface in layers that can range from 3 feet to 131 feet, with the most common deposits measuring about 13 to 19 feet thick. The ore can be found just below the surface dirt or as deep as 65 feet under a layer of dirt and rock. Heavy machinery and sometimes explosives are used in mining the ore from the material that covers it. Large ore chunks are then moved by means of trucks or trains to areas where it is broken into smaller pieces and washed in preparation for refining.

The Bayer process used to refine the ore includes several steps. After the bauxite is crushed into smaller pieces and washed, excess silica is removed to prevent impurities in the final product. Then sodium hydroxide, a hot and very caustic soda solution, is used to dissolve the portions of the ore that contain aluminum. The resulting solution is cooled and allowed to sit in large tanks so the aluminum-containing particles can settle to the bottom. This sediment is then filtered and washed to remove impurities and the caustic soda residue. The resulting solution is again cooled, allowing aluminum trihydroxide crystals to form and grow. These crystals are categorized by size. Smaller crystals are used to help the process of growing new crystals in future batches of processed ore. The larger crystals are once again heated to very high temperatures to dry them—a process known as calcination—resulting in alumina solids. It is these solids that are shipped to manufacturers to make aluminum products.

While most of the world's larger bauxite reserves have been found in Africa and South America, other smaller deposits have been found in southern Europe, the Caribbean, Malaysia, China, Hungary, Russia, and the United States. The leading producers of bauxite are Australia, China, Brazil, India, Guinea, and Jamaica. About 359.2 million metric tons of bauxite were mined in 2020, most often through surface strip mining techniques. Although it takes two to three tons of bauxite to create one ton of useable alumina raw material, experts estimate it will be several centuries before the world's known reserves are depleted.

Bauxite mining requires that the land be cleared of vegetation, and this has caused some environmental concerns. Many bauxite mining operations replace soil removed in the mining process and reseed and replant the land, but not all do this. The mining process also creates pollutants and other problems. This has been a special concern in the areas producing the most bauxite, particularly Malaysia.

Other Uses

In addition to being processed to release the aluminum solids within, bauxite has a number of other industrial uses. Calcined bauxite, which has been roasted or treated with extreme heat, is very hard and can serve as an abrasive agent. It is used in the production of some sandpapers as well as polishing agents such as powders and suspensions.

Bauxite can also be treated by pulverizing it to a powder and applying heat to form the powder into small round beads. These beads can then be used in sandblasting. Bauxite abrasives are very hard and durable, which makes them efficient, but their rounded shape helps to protect the equipment that applies them.

When bauxite powder is sintered, or pressed into a mass, it can be used as what is known as a proppant in the process of drilling for oil and natural gas. Hydraulic fracturing—sometimes known as fracking—uses liquids under extreme pressure to break the rock holding back oil and natural gas supplies. Once the first cracks are made, proppants, or small but strong suspended particles of material, are forced into the cracks. These proppants literally "prop" the crack open to allow the oil or natural gas to flow out of the rocks in which they are contained and into a well. Bauxite is well suited for compacting into small but very strong beads through the sintering process. These beads are made in several sizes and resist crushing, making them nearly ideal proppants.

Bibliography

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