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The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminium oxide) and was developed by Carl Josef Bayer.Bauxite, the most important ore of aluminium, contains only 30–60% aluminium oxide (Al 2 O 3), the rest being a mixture of silica, various iron oxides, and titanium dioxide. [1]
Bauxite is the main source of the rare metal gallium. [17] During the processing of bauxite to alumina in the Bayer process, gallium accumulates in the sodium hydroxide liquor. From this it can be extracted by a variety of methods. The most recent is the use of ion-exchange resin. [18]
Calcination is thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O 2 fraction of air), generally for the purpose of removing impurities or volatile substances and/or to incur thermal decomposition.
The aluminium hydroxide is calcined to produce alumina. The process was used in France at Salindres until 1923 and in Germany and Great Britain until the outbreak of the Second World War. [5] While it has largely been replaced by the Bayer process, an updated version is still in use for processing high-silica bauxite. [6]: 90, 92–93
Annual production of bauxite in the United States, 1900-2013. Bauxite mining in the United States produced an estimated 128,000 metric tonnes of bauxite in 2013. [1] Although the United States was an important source of bauxite in the early 20th century, it now supplies less than one percent of world bauxite production.
In pyroprocessing industries such as lime,calcined bauxite, refractories or cement manufacture, the loss on ignition of the raw material is roughly equivalent to the mass loss it will experience in a kiln. Likewise, in minerals, the loss on ignition indicates the material actually lost during smelting or refining in a furnace or smelter.
The preheater recuperates most of the heat in the combustion gases, dehydrates and de-hydroxylates the bauxite and de-carbonates the limestone. The calcined material drops into the "cool end" of the melt bath. The melt overflows the hot end of the furnace into molds in which it cools and solidifies. The system is fired with pulverized coal or
Bauxite mining was the main industry in Linden, and so the reduction of bauxite mining led to many workers having to find employment outside of the city. [22] In 2009, 57 employees of the Bauxite Company of Guyana Inc. were fired for participating in a strike to campaign for higher wages and better workers' rights. [25]