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Of Bauxite and Alumina: The History of Aluminium
Mystery of science
The history of aluminium, or aluminum as it was called by its discoverer and is known to Americans, is one of the great mysteries of science. How is it that one of the most abundant elements on earth, comprising something like 8 per cent of the earth's crust--a proportion only exceeded by oxygen and silicon--was not identified until 1808? How could a substance known to have been used by the ancient Egyptians, Greeks and Romans not be recognized as a metal? How could a material first employed in the fifth century B.C. be described as 'the most modern of common metals'? How could an element that is present in nearly all vegetation, animals and rocks (although only in microscopic quantities in sandstone and limestone) avoid detection for so darn long?
Part of the answer to all these questions lies in the fact that, because of its peculiar affinity to oxygen, aluminium never occurs in a metallic or natural form in nature. It exists only as a chemical compound.
The most valuable commercial source of aluminium is bauxite, which usually contains about 50 to 60 per cent of alumina. In real terms, this means that most bauxite will produce aluminium on a ratio of about 4:1. Physically, bauxite ranges from clay through to soft rock and can be white, pink, yellow, red or brown, or various combinations of these colors. Chemically, it consists mainly of aluminium oxide together with oxides of iron, silicon, titanium and other elements, and varying small percentages of clay and other silicates.
What's in a name?
The name aluminium is derived from alumen, the Latin name for alum, which was in fact a simple aluminium compound. It first appeared in human history around the fifth century B.C. when both the Egyptians and the Greeks were using it as an astringent for dressing wounds and to fix dyes in textiles; its use as such continued until the Middle Ages. By the thirteenth century, some purification was occurring and by the seventeenth century, it was being separated from the clays in which it was found.
By the beginning of the eighteenth century, there was a suspicion that alumina had a metallic base which could probably be isolated. This suspicion was confirmed by the French scientist Antoine-Laurent de Lavoisier in 1787. In 1808, the eminent British scientist and chemist, Sir Humphrey Davy, attempted to isolate the metal using electrolysis, but managed only to produce aluminium alloyed with iron. Davy suggested that the metal be called 'aluminum' but agreed to change the spelling to 'aluminium' a short time later in order to conform with the "ium" ending given to the names of most newly-discovered elements at that time. This spelling became the accepted standard worldwide until, in 1925, the American Chemical Society made the decision to revert to the original spelling.
Long road to production
Not until sixteen years later, in 1825, was the metal first produced. In a laboratory experiment, the Danish physicist and chemist, Hans Christian Oersted, created a reaction between diluted potassium amalgam and anhydrous aluminium chloride. After distilling the mercury away, Oersted was left with a few grains of impure aluminium.
It is to Oersted that the credit for first isolating the element must go, but two years after Oersted's discovery, the German chemist, Friedrich Wöhler managed to produce a larger, though still quite small, quantity of aluminium by substituting potassium metal for Oersted's potassium amalgam.
The next significant step occurred in 1854 (and was continued for the next five years) when the French chemist Henri Sainte-Claire Deville dramatically improved Wöhler's process by using the cheaper sodium rather than potassium. This process produced a double salt flux (NaCl AlCl3), which allowed aluminium globules to form. The importance of this discovery was twofold. Firstly, it brought down the price of aluminium, which had previously been more expensive than gold, and secondly, it opened the way for commercial exploitation of the mineral.
In the same year that Deville was cheapening the purification process, the German scientist, Robert Wilhelm von Bunsen, was demonstrating that aluminium could be purified using electrolysis. He had succeeded where Sir Humphrey Davy had failed, but the process was very expensive and commercially impractical.
However, Bunsen and Deville had created the framework for efficient aluminium extraction and in 1886, simultaneously yet independently of each other, the American and French inventors Charles Martin Hall and Paul L. T. Héroult synthesized the discoveries of 1854 and established the scientific basis upon which the modern aluminium industry is based.
Little known fact
Prior to Hall and Héroult's discovery of the electrolysis process in 1886, aluminium cost £1 per pound (0.45 kilograms) in England. Ten years later, and as a direct result of the discovery, the price had dropped to £180 a ton or 1s 7½d a pound.
The Hall and Héroult processes are identical. Basically, aluminium oxide (Al2O3) is dissolved in molten cryolite and electrolysed. Under electrolysis, the aluminium is separated from the oxygen. The aluminium drops below the molten cryolite and is tapped off as more alumina is added.
Aluminium electrolysis is a large consumer of electricity, using anywhere from 15,000 to 16,000 kilowatt hours of electricity to produce one tonne of aluminium. This has meant that modern aluminium smelters must be located near sources of cheap energy.
In terms of both tonnage and wealth of applications, aluminium is second only to iron as the world's most important metal. Over 11 million tons of this strong, lightweight and corrosion-resistant metal are used annually in industry for making anything from beer cans and saucepans to luxury boats and aircraft bodies.