Bauxite & Aluminium
Extraction & Transport
Depending on the distance and localization between the mine and the refinery, several means of transportation can be used: conveyor belts, trucks, trains, barges and ships. In recent years, the transport of bauxite slurry is used to feed the alumina refinery. The process of bauxite extraction is a classic strip mining activity with prospection, surface stripping (sometimes using explosives) and possible treatment of the ore; mainly crushing and washing.
The Refining of Bauxite into Alumina
The first step in the commercial production of aluminum is the separation of aluminum oxide from the iron oxide in bauxite. This is accomplished in a refinery or alumina plant using a technique developed by Karl Joseph Bayer, an Austrian chemist, in 1888. In the Bayer Process, bauxite is mixed with caustic soda, or sodium hydroxide, and heated under pressure. The sodium hydroxide dissolves the aluminum oxide, forming sodium aluminate. The iron oxide remains solid and is separated by filtration. Finally, aluminium hydroxide introduced to the liquid sodium aluminate causes aluminium oxide to precipitate, or come out of solution as a solid. These crystals are washed and heated to get rid of the water. The result is pure aluminum oxide, a fine white powder also known as alumina.
The Bayer Process
Usually, bauxite ore is heated in a pressure vessel along with a sodium hydroxide solution at a temperature of 150 to 200 °C. At these temperatures, the aluminium is dissolved as an aluminate using the Bayer process.
Alumina
Alumina is a handy material in its own right. Its hardness makes it useful as an abrasive and as a component in cutting tools. It can also be used to purify water and to make ceramics and other building materials. But its primary use is to act as a starting point to extract pure aluminium.
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