(i) State the reason for addition of caustic alkali to bauxite ore during purification of bauxite.

Question

The following questions are relevant to the extraction of Aluminium :

(i) State the reason for addition of caustic alkali to bauxite ore during purification of bauxite.

(ii) Give a balanced chemical equation for the above reaction.

(iii) 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

(i) Caustic alkali dissolves aluminium oxide forming soluble sodium aluminate while impurities remain insoluble and precipitate as red mud.

(ii)

(iii) The name of substance is Fluorspar (CaF2) and it increases conductivity of the electrolyte.