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:

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

Answer 1

(a) Caustic soda (Sodium Hydroxide) is added because Aluminium oxide is amphoteric, meaning it reacts with the strong base to form soluble Sodium Meta-aluminate. This allows the aluminium to dissolve while leaving insoluble impurities (such as iron oxide and silica) behind, which are filtered out as “red mud”.

(b) \[\ce{Al2O3.2H2O + 2NaOH -> 2NaAlO2 + 3H2O}\]