Bauxite to Aluminium

Bauxite is the source material for the production of aluminium. Bauxite is refined into alumina which is then used as the input material into smelters to produce aluminium metal. Aluminium production involves two independent processes for the conversion from naturally occurring aluminium oxide ores (bauxite) to the extracted metal.

The first stage, refining bauxite ore to alumina (a compound of aluminium and oxygen), is commonly achieved by the Bayer process, patented in 1888. This process is followed by smelting the alumina through electrolytic reduction at high temperatures to extract the aluminium metal.

Typical raw material requirements to produce one tonne of alumina range between two and four tonnes of bauxite, while approximately two tonnes of alumina are consumed in the production process for one tonne of aluminium.

Given the positive long-term outlook for global aluminium demand, Cape Alumina’s bauxite project in Queensland, Australia is viewed as a potential key component of the raw material supply chain from 2013/14 for Chinese alumina refineries reliant on bauxite imports.

Traditionally, bauxite mining has been undertaken by alumina refiners and even aluminium smelters that operate fully integrated supply chains from bauxite all the way through to aluminium metal production.

In more recent times, Chinese refineries have aggressively added capacity for producing alumina to satisfy aluminium smelter feedstock needs. The ability to secure sufficient feedstock (bauxite) supply for their refineries is important to these operators as competition for the available bauxite supply increases.

Regional bauxite suppliers in Australia and India will be best able to capitalise on a raw material supply shortfall as export growth from Indonesia may slow and Chinese Central Government policies aim to phase out small-scale mining operations.

Proposed alumina refining capacity additions in bauxite producing countries will also act to consume local supplies of bauxite and reduce future exports that may otherwise have been directed to China.

Consequently, non-vertically integrated or aligned companies with mineral reserves of sufficient quality, infrastructure and relatively low operation costs will have an opportunity to supply the longer term growing demand for alumina refining.

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Bauxite Properties

The primary aluminium industry depends on supplies of bauxite that are relatively easy to mine and cheap to transport depending on distance. The world reserve base is sufficient for approximately 200 years at the present rate of mining. Some countries however, have to turn further afield for their supplies as they exhaust their own cost-competitive domestic reserves. This factor is particularly pertinent for China, as it is now the overwhelming driver of demand growth in internationally traded bauxite.

Commercially, the term bauxite is used to describe ores sufficiently rich in aluminium hydroxide minerals and low in impurities to enable them to be used for the production of pure alumina (Al2O3). Currently, the alumina content of commercial bauxite ores ranges from 30%–65%. Bauxite is classified into three basic types according to the main aluminium mineral present: gibbsite (alumina trihydrate), boehmite and diaspore (both alumina monohydrate). The difference between chemically identical boehmite and diaspore is in grindability of the ore.

To produce alumina from bauxite, digestion of the raw material in caustic soda is a key step in the Bayer process. Gibbsite is easy to extract at atmospheric pressure and with relatively little heating, but due to stronger chemical bonds, boehmite and diaspore must be treated under high pressure and temperature, thus requiring more energy. Conversely, they tend to be of higher grade overall than gibbsite.

Silica, the other main constituent in commercial bauxite, occurs in two forms:

“non-reactive” silica (usually as crystalline quartz) that can be removed during the refining process without significant losses of alumina or caustic soda

“reactive” silica, in silicate minerals that are free to react with caustic soda, and so cannot be removed without losses.

Bauxite also generally contains iron minerals including hematite and goethite. These iron minerals are the main contributors, along with clays, to the “red mud” produced in the Bayer process of alumina refining. Also common in many types of bauxite are titanium minerals, which are not recovered by the Bayer process and are carried out in the waste material.

Pisolite Hills is characterised by low levels of boehmite, being rich in gibbsite and by its low iron content.

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Bauxite Occurrence – Regional Comparisons

There are extensive reserves of gibbsite in “tropical” or “lateritic” bauxite (also described as “bayerite”) deposits throughout the world. Bayerite (which usually also contains some boehmite or diaspore) is a product of weathering, which is promoted by high atmospheric temperatures and humidity. It occurs, therefore, predominantly in tropical regions, but also (due to continental drift) in some southern hemisphere temperate zones, notably south-western Australia.

Estimated bauxite resources worldwide are between 55 and 75 billion tonnes. In a number of consuming regions, notably China and North America, reserves are inadequate to meet their long-term domestic demand.

Top Bauxite Producing Regions, 2007

Source: USGS data

Top Bauxite Producing Companies, 2007

Source: Company data

 

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