Unlike gold and some other metals, aluminium is not found in nature, other elements are always combined with it. Often the other element is
oxygen, forming a compound called aluminium oxide, or alumina.
ELECTROLYSIS IS a way of breaking down alumina into its two parts: aluminium and oxygen. Alumina is placed in large containers which have a positive and a negative pole. It is first dissolved by chemicals so that electricity can flow through easily. When the current passes through the mixture, it breaks down the alumina into aluminium and oxygen. Molten aluminium sinks at the bottom of the pots.
When enough molten metal has accumulated, it is siphoned out of the pot and poured into moulds where it solidifies into aluminium ingots.
The ingots are next made into useful products. This is done in two major steps. First, it can be flattened into long sheets by rolling, or squeezed into shaped strips by extrusion, or melted again to be recast into numerous forms.
Next, the semi-finished products are then reworked to become the things we know - foil, window
frames, house siding, kitchen utensils, motors, airplanes, electric wires, lamp posts, boats ... the list of things made out of aluminium is endless.
1 - Bauxite is ground into a powder.
2 - The powder is stirred into liquid caustic soda and the mixture heated under pressure. Slowly but surely the alumina dissolves in the caustic soda, a little like sugar dissolving in a hot beverage.
3 - Next, the mixture is filtered. Because the alumina is already dissolved in the liquid, it passes through the filter, but the impurities, being solid, do not get through.
4 - The next step is to get alumina out of the liquid. This is done by getting it to precipitate in the form of crystals, in the same way that snow is made from water vapour in clouds.
5 - The alumina crystals are gathered and baked at a very high temperature to remove the water that is still left. The result is a white powder resembling table salt, called calcined alumina.
6 - Now we move to the next stage of making aluminium, called electrolysis. As the name suggests, electrolysis uses a great deal of electric power. Aluminium is processed in countries where rivers are a major source of electricity.
