Aluminium Extraction:
The main ore of aluminium is bauxite (aluminium oxide). After it is mined, it is first purified by adding it in sodium hydroxide. The impurities do not dissolve and are filtered off. The dissolved aluminium oxide is then precipitated out as aluminium hydroxide by diluting with water. This is then heated to form pure white aluminium oxide, or alumina. The aluminium is then extracted by electrolysis.
The alumina is added to and electrolytic cell and melted. A compound called cryolite (another aluminium compound) is added to lower the melting point of the alumina. The electrodes are made of graphite. Oxygen gas collects at the anode. The cathode is very interesting; it is the lining of the electrolytic cell that is made the cathode. Molten aluminium collects here.
At cathode: Al3+ (l) + 3e– -> Al (l)
At anode: 2O2- (l) -> O2 (g) + 4e–
Aluminium is a more reactive metal than its apparent lack of reactivity is explained by a thin protective oxide coating. This coating (unlike iron oxide) does not flake off and makes aluminium corrosion resistant.
Aluminium metal is relatively light, corrosion resistant, and a good conductor of heat and electricity. When alloyed, it becomes quite resistant.
Aluminium can be used in making kitchen foils due to its malleability and heat conducting ability, in overhead power cables due to its light weight and electrical conducting abilities, and in aircraft construction due to its lightness and resistance to corrosion.