Aluminium

Publisher Summary

This chapter presents that the element aluminum is the third most common element in the earth's crust, comprising some 8%. Currently, bauxite is by far the major source of aluminum, although some Russian metal is derived from nepheline. The term, "bauxite" is used to describe the ores that are sufficiently rich in aluminum hydroxide minerals and low in impurities to allow them to be converted to alumina. This chapter describes that aluminum is an extremely versatile metal, employed in a wide range of industries in a large number of applications. It discusses the major end-use markets and consumption trends of aluminum. Although it was by no means all one-way traffic, the aluminum market enjoyed considerable success in 2004, recovering from 18 months of weak prices. While it can be argued that much of the strength was driven by speculative interest, there is no doubt that strong demand growth and a substantial drawdown in London Metal Exchange (LME) stocks were underpinning factors.

Outline

2.1. Resources and extraction

2.1.1. Bauxite

2.1.2. Alumina

2.1.3. Aluminium

2.1.3.1. Africa

2.1.3.2. Western Europe

2.1.3.3. Asia

2.1.3.4. Latin America

2.1.3.5. North America

2.1.3.6. Oceania

2.1.3.7. The Former Soviet Union

2.1.3.8. China

2.2. Consumption

2.2.1. Major end-use markets

2.2.1.1. Transport

2.2.1.2. Packaging

2.2.1.3. Construction

2.2.1.4. Other end-uses

2.2.2. Consumption trends

2.3. The market

2.4. Appendix

2.A.1. Western world alumina production (kt)

2.A.2. Western world aluminium production (kt)

2.A.3. Global consumption of primary aluminium (kt)

2.1 Resources and extraction

The element aluminium (atomic number 13, atomic weight 26.97) is the third most common element in the earth's crust, comprising some 8%. At present bauxite is by far the major source of aluminium, although some Russian metal is derived from nepheline. The term bauxite is used to describe ores that are sufficiently rich in aluminium hydroxide minerals and low in impurities to allow them to be converted to alumina. The alumina content of commercially exploited bauxite ores ranges from around 30 to 65% Al2O3. The name bauxite is derived from the town of Les Baux in France, where in 1821 the chemist P. Bertier discovered a material containing aluminium hydroxide minerals and impurities of iron oxide, silica and titanium.

Well over 90% of bauxite is mined using open-pit methods, underground mining being restricted to karstic deposits in France and the former Yugoslavia. Lateritic bauxites, consisting mainly of alumina and trihydrate, are sedimentary rocks and low-silica igneous and metamorphic rocks. With the apparent exception of mainland North America demonstrated bauxite deposits occur in every continent, although the major deposits are found within a broad band, which spans the equator.

On some surface deposits there is no overburden, while others may be covered to some depth by rock or clay. In deposits that are hardened blasting may be required to release the ore. Loosened ore is transported by road or rail to crushing or washing plants. Unlike the ores of other base metals, bauxite does not require complex processing because most is of an acceptable grade or can be improved by the relatively simple and inexpensive process of removing clay.

Bauxite is washed, ground and dissolved in caustic soda (sodium hydroxide) at high pressure and temperature. The resulting liquor contains a solution of sodium aluminate and undissolved bauxite residues containing iron, silicon and titanium. These residues sink gradually to the bottom of the tank and are removed. They are known colloquially as red mud. The clear sodium aluminate solution is pumped into a huge tank called a precipitator. Fine particles of alumina are added to seed the precipitation of pure alumina particles as the liquor cools. The particles sink to the bottom of the tank, are removed, and are then passed through a rotary or fluidised calciner at 1100°C to drive off the chemically combined water. The result is a white powder, pure alumina.

Only bauxite ores with low-reactive silica (preferably less than 5%) are suited to the conventional Bayer process. Roughly speaking, it takes two tonnes of bauxite to make one tonne of alumina and two tonnes of alumina to make one tonne of aluminium. This latter process takes place in a smelter.

The Hall-Heroult process used for smelting aluminium dates back to the latter part of the nineteenth century, when Hall in the USA and Heroult in France simultaneously, but independently, developed an electrolytic method for the production of aluminium, whereby aluminium and oxygen (the components of alumina) become separated.

The process takes place in cells, more commonly known as pots, which are joined to form a potline. These pots contain a lining of either thick carbon blocks or a mixture of carbon and pitch, and an anode, which is either a pre-baked carbon block or a combination of unbaked petroleum coke and coal tar pitch, which is then baked using the heat of the pot. Alumina is placed in the pot containing a bath of molten cryolite (sodium aluminium fluoride) at a temperature of 1000°C and a direct current of high amperage is passed along the potline from cathode to anode.

During the course of the electrolytic process, oxygen is separated from the aluminium to become carbon monoxide or dioxide by combining with a carbon anode, while the aluminium becomes pure molten metal at the cathode, from which it is removed by vacuum siphoning.

The electric current used can be from 50000 amps up to 300000 amps in the most modern smelters, but a voltage of just 4-5 volts is all that is needed. Pots are connected in a series, with the anodes of one attached to the cathodes of the next.

Two technologies have been developed to accommodate this process. In the older Soderberg system, a single anode is continuously generated in each cell by feeding in a paste comprising petroleum coke and pitch, with the heat of the cell continuously baking the paste into carbon anode. An improved Soderberg system employs dry anode technology, which reduces anode consumption and improves environmental performance. In the more modern prebake smelters, multiple anodes are suspended in each cell. These anodes are produced at separate facilities, with new ones replacing spent ones and the latter being recycled.

The amount of electrical power needed to produce one tonne of aluminium has fallen significantly through time. Latest figures from the International Aluminium Institute indicate that the average in 2003 was 15202 kiloWatt hours, about half that required in the 1930s. The most modern smelters use around 13000 kWh per tonne, and as more are built the average will continue to fall.

2.1.1 Bauxite

The production of bauxite takes place in a comparatively small number of countries and output is concentrated in but a few of these. Since 1960 Western world bauxite production has more than quintupled. In 1960 four countries - Jamaica, Surinam, Guyana and France - between them accounted for around 62% of Western production. Jamaica alone accounted for over-one quarter of the total, producing 5.8 Mt.

Although a decade later Jamaica retained its position as the West's major producer, with output in 1970 of 10.5 Mt, Australia had by then established itself in second place with an output of 9.3 Mt. During the 1960s both Surinam and Guyana had also greatly increased their output, and in 1970 between them these four countries produced almost 32 Mt, again around 62% of the Western total. By this time, however, France had been displaced from fourth place. Nevertheless, Western European production did grow markedly over the period, reflecting the expansion of mining in Greece and Yugoslavia, and by 1970 had reached 7.1 Mt compared with 4.03 Mt a decade earlier.

During the 1970s the transformation of the industry continued apace, to the extent that by 1980 not only had Australia established itself as the leading producer, but its output exceeded that of all the South American countries put together, despite a marked improvement in Brazilian output. In that year the 27.2 Mt Australia produced accounted for over a third of the Western total, whereas South American production of 25.1 Mt represented 31%.

It was also during the 1970s that Africa rose to prominence, almost entirely reflecting the...