Question

In order to obtain 1 tonne of aluminium, the following inputs are required: 4 tonnes of bauxite, 150 kg of sodium hydroxide and 600 kg of graphite. The aluminium compound in bauxite is aluminium oxide and the main impurity is iron (III) oxide. Aluminium is obtained by the electrolysis of aluminium oxide dissolved in cryolite.

When bauxite is treated with sodium hydroxide solution, what happens to:

1. the aluminium oxide,
2. the iron (III) oxide?

Answer 1

1. The aluminium oxide forms sodium aluminate.
   \[\ce{Al2O3.2H2O + 2NaOH ->[150^\circ C  -  200^\circ C] 2NaAlO2 + 3H2O}\]
2. The iron (III) oxide does not dissolve in NaOH and is removed by filtration.