|Name: aluminium||Group number: 13|
|Symbol: Al||Group name: (none)|
|Atomic number: 13||Period number: 3|
|Atomic weight: 26.981538 (2)||Block: p-block|
|CAS Registry ID: 7429-90-5||Voice: |
|Standard state: solid at 298 K||Colour: silvery|
|Classification: Metallic||Availability: |
Nearing Zero cartoon included by kind permission of Nick Kim.
IsolationHere is a brief summary of the isolation of aluminium.
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.