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Παρασκευή, 28 Φεβρουαρίου 2014

Bauxite, Alumina and Aluminium


Bauxite is the primary source of aluminium metal, and about 85% of bauxite mined is processed via the Bayer Process to make alumina trihydrate (ATH), then smelter grade alumina (SGA) from which aluminium metal is derived.

The respective processes take place in an alumina refinery and aluminium smelter, which may or may not be integrated.

The remaining 15% of crude bauxite mined is used to produce a range of non-metallurgical bauxite grades and non-metallurgical alumina grades.

Bauxite
There are three main bauxites types – boehmite, diaspore, and gibbsite – which each differ in chemical and physical characteristics, and each have predominance in certain regions of the world.

Owing to their different characteristics, bauxites are carefully selected for non-metallurgical uses as demanded by the required end use specifications of the derived bauxite and alumina grades.

According to the USGS, 201m. tonnes of bauxite was mined in 2009.

Although metallurgical grade bauxite may be suitable for certain non-metallurgical applications, such as in cements and slag conditioning, most non-metallurgical bauxites are confined to specific regions in Australia, Brazil, China, France, Guinea, Greece, Guyana, Turkey and the USA.

The primary sources of non-metallurgical bauxite are China, Greece, Guyana and Turkey.

About 5% of bauxite is mined and processed for direct use as non-metallurgical bauxite grades. Raw, uncalcined bauxite is used for cement, slag conditioning, and chemicals.

Calcined bauxite is produced to make abrasive, refractory, welding, and proppant grades.

Abrasive grade bauxite is fused to manufacture brown fused alumina used in abrasives and refractories.

Alumina

The remaining mined bauxite, about 10%, is processed using the Bayer Process to manufacture ATH, the precursor to a range of non-metallurgical grade alumina (NMGA) grades which serve a wide variety of end uses.

Although there are specific NMGA plants, some SGA refineries also host a certain amount of capacity for NMGA production. This may change as market demand for SGA and NMGA dictates.

This NMGA market is estimated to total 5.5-5.8m. tpa. The bulk of the NMGA market is termed “commodity hydrate”, eg. used to make aluminium sulphate for water treatment (see pie charts), although fine grades are used as high value flame retardants.

The remainder, some 2.8m. tpa is defined as “speciality” or “premium” grades, which are based on calcined aluminas. These are used in higher value end uses, such as in refractories, ceramics, and polishing.

Calcined aluminas are also the feedstock to produce high value, high purity grades of tabular alumina and white fused alumina.

Bauxite producers
Bosai Minerals Group – China
Demireller Mining – Turkey
Hellenic Mining Enterprises – Greece
S&B Industrial Minerals – Greece

Alumina producers
Alcoa – USA
Almatis – Germany
Aluchem – USA
MAL Magyar Aluminium – Hungary
Martinswerk – Germany
Nabaltec – Germany
Rio Tinto Alcan – France

Fused alumina producers
C-E Minerals (part of Imerys) – USA
Elfusa – Brazil
Henan Mianchi Great Wall Corundum – China
Treibacher Schleifmittel – Austria
Washington Mills Electro Minerals – USA