Natural minerals are chemical compounds. Aluminum is found in many minerals – more than 270 species – in combination with oxygen, silicon, alkali and alkaline earth metals and fluorine, as well as in the form of hydroxides, sulfates and phosphates. For example, feldspars – the most abundant minerals in the Earth’s crust (about 50%) – are aluminosilicates.
Metal aluminum in nature
Natural metal aluminum is sometimes found in the absence of oxygen as a minor step, for example, inside certain volcanoes. It is also found in minerals such as braille, cryolite, garnet, spinel and turquoise.
Gemstones
Impurities in Al 2 O 3 oxide crystals, such as chromium or cobalt, form precious stones such as rubies and sapphires, respectively. Pure Al 2 O 3 oxide is known as corundum – one of the hardest materials.
Bauxite
Although aluminum is a very common natural element, most aluminum ores cannot be an economical source of the metal. Almost all primary aluminum metal is produced from bauxite ores called (or bauxite), with the general chemical formula (ALO X (OH) 3-2x) [1].
Bauxite occurs in nature as a substrate weathering product with small amounts of iron and silicon in tropical climates. Natural bauxites contain different forms of hydrated aluminum oxide that have different crystal systems and also differ in the amount of hydration (number of water molecules per molecule of Al 2 O 3).
Alumina production
About 90% of aluminum ore – bauxite – goes to primary aluminum production, the remaining 10% – to other industrial applications.
Industrial production of primary aluminum has two main stages:
- Production of pure alumina – alumina from the original bauxite ore;
- Electrochemical reduction of this oxide to aluminum metal in molten chlorite bath.
Bauxite
Bauxite is not a mineral or chemical compound. This name – bauxite (or more often, bauxite) – is used to identify the types of aluminum ores that contain aluminum compounds, mainly the types of hydroxides.
Industrial bauxite consists of three main types of hydroxide minerals:
- gibbsite: Al 2 O 3 · 3H 2 O
- Bohemite – Al 2 O 3 · H 2 O
- diaspore – Al 2 O 3 · H 2 O.
These types of hydroxides in terms of physical properties such as:
- Water content
- Crystal system
- Hardship
- density,
- Dehydration temperature
- Solubility in technological solutions.
Natural bauxite ores are usually composed of one of these types of hydroxides, although in some cases the same aluminum ore may contain mixed hydroxides.
Bauxite varies in color from cream to dark brown with high levels of iron.
