Question

Bauxite is the principal ore used in the commercial extraction of aluminium. The Bayer’s process is used to refine bauxite into pure alumina, with caustic soda playing a crucial role in the initial stage of the process. Based on this, answer the following questions: 

(a) Explain the reason behind the addition of caustic soda during the Bayer’s process. 
(b) Write a balanced chemical equation representing the reaction between bauxite and caustic soda during the Bayer’s process. 
 

Hint:

The Bayer’s process is specifically a chemical method of refining, whereas the subsequent Hall-Héroult process is an electrolytic method of extraction.

Answer 1

(a) Reason for Caustic Soda: Caustic soda (Sodium Hydroxide) is added because aluminium oxide is amphoteric. It reacts with the hot concentrated alkali to form soluble Sodium Meta-aluminate, while the main impurities in bauxite (like Ferric Oxide) are basic and do not dissolve, allowing them to be filtered out as "red mud."

(b) Balanced Equation: [ Al_2O_3 cdot 2H_2O + 2NaOH 2NaAlO_2 + 3H_2O ] (Bauxite reacts with sodium hydroxide to produce sodium meta-aluminate and water).