Question

The following questions are relevant to the extraction of Aluminium:

1. State the reason for the addition of caustic alkali to bauxite ore during the purification of bauxite.
2. Give a balanced chemical equation for the above reaction.
3. Along with cryolite and alumina, another substance is added to the electrolyte mixture. Name the substance and give one reason for the addition.

Answer 1

1. During bauxite extraction, caustic alkali is used to remove the insoluble fraction of the ore and precipitate the alumina.
2. The reaction is as follows:
   \[\ce{Al2O3.2H2O + 2NaOH -> 2NaAlO2 + H2O}\]
3. Fluorspar, cryolite, and alumina are added to make the combination fuse at 950°C rather than 2050°C, resulting in liquid aluminium.