Question

In the leaching of alumina from bauxite, the ore expected to leach out in the process by reacting with NaOH is :

• A. $SiO_2$
• B. $TiO_2$
• C. $Fe_2O_3$
• D. $ZnO$

Hint:

Silica is the main impurity that must be chemically separated from the sodium aluminate solution later in the process. It's the only major impurity that leaches.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Bauxite contains impurities like \(Fe_2O_3\), \(TiO_2\), and \(SiO_2\).
During leaching with concentrated NaOH, amphoteric and acidic substances dissolve, while basic impurities remain solid.
Step 2: Detailed Explanation:
1. Alumina (\(Al_2O_3\)) is amphoteric and dissolves to form sodium aluminate.
2. \(Fe_2O_3\) and \(TiO_2\) are basic oxides and do not react with NaOH; they are filtered out as red mud.
3. \(SiO_2\) is an acidic oxide. It reacts with NaOH to form soluble sodium silicate (\(Na_2SiO_3\)).
\[ SiO_2 + 2NaOH \to Na_2SiO_3 + H_2O \]
Thus, silica leaches out along with alumina.
Step 3: Final Answer:
The correct option is (A) \(SiO_2\).