Aluminium

Aluminium: the essentials

 Brief description: pure aluminium is a silvery-white metal with many desirable characteristics. It is light, nontoxic (as the metal), nonmagnetic and nonsparking. It is somewhat decorative. It is easily formed, machined, and cast. Pure aluminium is soft and lacks strength, but alloys with small amounts of copper, magnesium, silicon, manganese, and other elements have very useful properties. Aluminium is an abundant element in the earth's crust, but it is not found free in nature. The Bayer process is used to refine aluminium from bauxite, an aluminium ore.

Small and large samples of aluminium foil, sheet, wire, rod and tube like this (and aluminium alloy in rod form) can be purchased via their web catalogue from Advent Research Materials via their web catalogue.

Cartoon by Nick D Kim (nearingzero.net, used by permission).

Isolation

Isolation: aluminium would not mormally be made in the laboratory as it is so readily available commercially.

Aluminium is mined in huge scales as bauxite (typically Al₂O₃.2H₂O). Bauxite contains Fe₂O₃, SiO₂, and other impurities. In order to isolate pure aluminium, these impurities must be removed from the bauxite. This is done by the Bayer process. This involves treatment with sodium hydroxide (NaOH) solution, which results in a solution of sodium aluminate and sodium silicate. The iron remains behind as a solid. When CO₂ is blown through the resulting solution, the sodium silicate stays in solution while the aluminium is precipitated out as aluminium hydroxide. The hydroxide can be filtered off, washed, and heated to form pure alumina, Al₂O₃.

The next stage is formation of pure aluminium. This is obtained from the pure Al₂O₃ by an electrolytic method. Electrolysis is necessary as aluminium is so electropositive. It seems these days that electrolysis of the hot oxide in a carbon lined steel cell acting as the cathode with carbon anodes is most common.

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