Bauxite

Bauxite is an aluminum ore, consisting predominantly of the aluminum minerals gibbsite ( gibbsite ) γ -Al ( OH ) 3, boehmite γ - AlO ( OH), diaspore α - AlO ( OH), also the iron oxides hematite Fe2O3 and goethite FeO (OH ), the clay mineral kaolinite and small amounts of anatase titanium oxide TiO2 is, a very similar rock but with a higher hematite ( ie iron) content is a laterite. It owes its name to his first locality Les Baux -de- Provence in southern France, where it was discovered in 1821 by Pierre Berthier.

Formation

In the geosciences lateritic (silicate bauxites ) are distinguished from karst bauxites ( Karbonatbauxite ). The early discovered Karbonatbauxite lie primarily in Europe on carbonate rocks ( limestones and dolomites ), where they originated by lateritic weathering clay-rich inclusions or clay-rich solution residues. Its economic importance has declined sharply over the Lateritbauxiten.

The lateritic are in many countries of the whole tropical belt. They were formed by lateritic weathering of silicate rocks of very different such as granite, gneiss, basalt, syenite, clay and shale. Compared with iron-rich Lateritdecken to Bauxite form with particularly intense weathering and increased drainage, which allows a resolution of kaolinite formation of gibbsite. The thereby occurring leaching of aluminum-containing compounds not found in tropical climates rather than particularly effective because in them long rainy and dry seasons alternate. In the deposits of the aluminum- rich areas are often less than an iron -rich surface layer. In contrast to the Al as Karbonatbauxiten occurs almost exclusively on mineral gibbsite.

Occurrence and extraction

The major producing countries are Australia, China, Brazil, Guinea, Jamaica and India. Cameroon has recently discovered large deposits of 500-700 million tonnes, the opportunity to catch up. Other deposits are located, including in Russia, Venezuela and Suriname ( see table). In Europe, find the most important mining sites in Greece, Hungary and France. In 2007, world production was around 190 million tonnes. The economically mineable from today's perspective backed bauxite deposits are likely to meet the demand in the long term even with increasing production. In a depletion of inventories other aluminum bauxite raw materials are available in very large quantities. Bauxite is mostly mined in opencast. The liberated by the degradation of humic soil layers are initially stored in terms of sustainable, environmentally sound development and later used for the reclamation of the ideal case.

Source: U.S. Geological Survey, Mineral Commodity Summaries, January 2008

See also: List of the largest bauxite producer

Processing

Aluminium is produced from approximately 95% of the digested bauxite. Small amounts are in favorable composition of the production of Al- chemicals, abrasives and refractory bricks. A by-product of aluminum production is gallium.

Bauxite is heated in pressure vessels at 150 to 200 ° C in sodium hydroxide solution, with aluminum as aluminate goes into solution and the iron-rich residue ( red mud ) is filtered off ( Bayer process ). From the aluminate precipitates on cooling and addition of fine aluminum hydroxide as nucleation from pure gibbsite, which is converted by calcination into alumina Al2O3. The aluminum is melted with the addition of cryolite as flux at about 1000 ° C, and in electrolytic cells in a high energy consumption to be reduced metallic aluminum ( Hall-Héroult process, melt electrolysis ). Alone in this reduction reaction,

Which takes place at a carbon anode at a voltage of about 5 volts per kg of aluminum requires about 15 kWh of electricity and discharged around 1.22 kg CO2. The reprocessing of recycled aluminum requires only 5% of this electrical energy.

History

1821 saw the French geologist Pierre Berthier bauxite in the southern French town of Les Baux de Provence, a mineral which was named after the first locality bauxite. In Austria bauxite was over 80 years until 1964 when Unterlaussa, located in what is now Limestone Alps National Park, degraded.

Other occurrences were in Glanegg in Carinthia, as well as in Großgmain in Salzburg.