Aluminium Smelting
Aluminium is the most common metal, accounting for about 8% of the earths crust, unfortunately it is found in highly stable compounds and is difficult to separate out as a pure metal. In the time of Napoleon III aluminium plates were reserved for the emperors table, the lesser nobles had to make do with gold and silver. The first British Aluminium Foundry was set up by Sir William Mills at Sunderland in 1885 at which time Aluminium was a precious metal, with a value slightly higher than gold, the principal method of obtaining the metal was a complex chemical process.
The first patents for extracting the metal on a commercial scale using electricity date from 1886, at this time it was still very much a semi-precious metal, valued at over three pounds and ounce. The extraction process has two stages, firstly the Bayer Process is used to extract aluminium oxide (alumina) from bauxite ore. Next the Hall-Heroult process is used to extract the oxygen, leaving behind the pure metal. This process was independently discovered by Hall (1863-1914) in America and by Heroult in France but it was the American who set up the first commercial production company in 1888. The British Aluminium Company set up their Scottish works using the new processes in 1894.
Bauxite is named after the French town of Les Baux, where it was first discovered. Bauxite, which can contain between thirty and seventy percent alumina, comes in various colours depending on the impurities, it can be white, cream, yellow, brown grey or red. It is composed of aluminium oxide, iron oxide and water with traces of silica and titanium oxide.
To make one ton of aluminium you need 4 tons of bauxite, which is dissolved in a hot solution containing about 3 cwt of caustic soda (sodium hydroxide or 'lye'). The result of this process is a liquid which is filtered to remove unwanted oxides (mainly iron) and placed into tall cylinders, here it is 'seeded' with crystals of aluminium hydroxide and stirred. The aluminium forms more hydroxide on the crystals which grow and sink to the bottom of the tower. The crystals are then washed filtered and 'calcined' (cooked to reduce it to a powder) to produce the alumina (aluminium oxide). You get about 2 tons of alumina from the four tons of bauxite you started with, the caustic soda is recycled.
The Hall-Heroult process takes the two tons of oxide, adds a small amount of Cryolite to act as a catalyst and three quarters of a ton of carbon to serve as an anode. Cryolite is a compound of aluminium and sodium with a little fluorine, naturally occurring only in Greenland it is usually made synthetically.
You put this lot into a container lined with heat resistant brick and pass electricity through it, the electricity required takes about four to six tons of coal to produce. The molten aluminium collects at the cathode (mounted at the bottom of the chamber) and is siphoned off once every day or two.
The electrolytic process required considerable quantities of electricity and the British Aluminium Company (BAC, established in 1894) decided that hydroelectric power was the answer and so located their factory at Foyers beside Loch Ness in about 1900. A few years later they built another bigger plant (power station and smelter) at Kinlochleven and in the 1920s, a third and still larger operation was set up at Fort William. This latter factory is still operating in the early 21st century (now owned by Alcan) but the Kinlochleven smelter closed in the 1990s (the power station is still in use feeding the National Grid).
A new method, called the Toth process, has been developed which can recover aluminium from high-alumina clays such as kaolin (otherwise known as 'china clay'). This process uses much lower temperatures than the Hall process (only 260 degrees centigrade) and so requires much less electricity.
In the early 21st century there are four aluminium smelters in the UK, Northumberland and Anglsey both have large plants and there are two smaller plants in Scotland. The resulting aluminium is passed to works (principally in the Midland) where much of it is extruded.
British Alcan has a factory at Burntisland near Edinburgh to produce alumina from bauxite, but it also imports alumina powder via its private terminal at Blyth. Alumina is shipped in quantity in hopper wagons, the LNER and to a lesser extent LMS both built wagons for this traffic. British Alcan operated their own fleet of unfitted wagons in this traffic until the late 1980's and redundant grain wagons of the Peco fifteen foot wheelbase Grano type were also used in the 1980's. Alumina is used in making paper, abrasives, ceramics, light bulbs and motor engine spark-plugs as well as for producing aluminium.
Aluminium is used for structural engineering where its low weight is an advantage, it is also used in powder form in making protective paints for wood and metal. When the National Grid electricity distribution system was established light weight aluminium wire, wound on a steel core, was used for the power cables.
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