Information

Bauxite


Characteristics:

Surname: Bauxite
other names: /
mineral class:
chemical formula: approximately Al2O3 · H2O
Chemical elements: Aluminum, oxygen, hydrogen
Similar minerals: Laterite
colour: brown-red
shine: /
crystal structure: ?
mass density: ?
magnetism: not magnetic
Mohs hardness: approx. 2.8
stroke color: ?
transparency: opaque
use: for the production of aluminum, building material

General information about bauxite:

bauxite describes an aluminum ore consisting of various aluminum minerals, iron oxides, clay minerals and titanium oxide. Bauxit owes its name to the town of Baux-de-Provence in southern France, where the rock was discovered and described for the first time in 1821 by Pierre Berthier. It is formed in the course of the so-called Allitic weathering, when high temperature with simultaneous heavy rains such as during the monsoon decomposes different rocks and thereby minerals are dissolved. This is particularly the case in the humid tropics, subtropics and in the climatic zones of the Equator, where a high humidity promotes a low pH, which is responsible for the intensity of the hydrolysis. As a result, residual deposits of laterites, aluminum-rich limestone, silicates and calcrets form. The weathering caused by the ion leaching within the rock layers has the result that during the rainy periods at the Earth's surface stable minerals are formed. In times of extreme dryness, such as those in the tropics following the monsoon season, the ions evaporate, leaving behind a layer of salt, which is washed away in the following rainy season. The underlying material consists almost exclusively of aluminum and iron oxides in a strong concentration caused by the leaching and of silica.
As a highly aluminous laterite, bauxite in the warm tropics, where rainy and dry seasons alternate, can be found on almost any rock containing aluminum, and has different compositions depending on the intensity of leaching and drainage. Depending on the nature of the repository and the underlying rock layer, a distinction is made between two types of bauxite. Aluminum-rich rocks produce laterite or silicate building oxides in the tropical climates, which are economically very important due to their high content of iron and aluminum. Lime bauxites, which are also mined in Europe, now make up a small proportion of the mined rocks and are also found in Europe.

Occurrence and localities:

Countries that have important sources of economic development for lateritex include Jamaica, Brazil, Guinea, Australia India, Venezuela, Sierra Leone, and some southern areas of the United States. In Europe, among others, Croatia, France, Spain, Greece and Turkey are significant, but the total production of this region does not reach those of Jamaica. Bauxite is also being mined in some parts of China and Russia. More than 130 million tonnes of bauxite are extracted worldwide each year.

Use:

Almost 95 percent of the world's bauxite is used to produce aluminum-metal in the course of the so-called Bayer process, a wet leaching process that filters the iron-rich residue known as red mud. What remains is an aluminate liquor, which is fed to aluminum hydroxide after cooling. Subsequently, this is reduced by fused-salt electrolysis to aluminum-metal. The by-product is gallium, which is used as a non-toxic substitute for mercury in thermometer fillings, but is hardly economically significant due to its high price. The remaining five percent of the world's bauxite is processed into abrasives, fire-resistant bricks, and aluminum-rich chemicals.