Question

Bayer process is used for extraction of

• A. Alumina
• B. Zinc
• C. Aluminum
• D. Copper

Hint:

To extract 1 ton of aluminium metal, approximately 4 to 5 tons of bauxite ore are processed to yield 2 tons of alumina, which is then electrolyzed.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks which metal's extractive metallurgy process incorporates the Bayer process.
While the Bayer process specifically produces alumina (\( \text{Al}_2\text{O}_3 \)), in the context of commercial metal production, it is categorized under the metallurgy of Aluminum.

Step 2: Key Formula or Approach: The Bayer process involves the hydrometallurgical digestion of bauxite ore using concentrated sodium hydroxide (NaOH) at elevated temperatures and pressures: \[ \text{Al}_2\text{O}_3 \cdot 3\text{H}_2\text{O} + 2\text{NaOH} \rightarrow 2\text{NaAlO}_2 + 4\text{H}_2\text{O} \]

Step 3: Detailed Explanation:

• Industrial Process Sequence:
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Digestion: Bauxite is treated with hot, concentrated caustic soda. Aluminium trioxide selectively dissolves to form soluble sodium aluminate, leaving behind insoluble impurities (known as "red mud," primarily consisting of silica, iron oxides, and titanium oxides).
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Clarification and Precipitation: The solution is filtered, and aluminium hydroxide is precipitated by seeding and cooling:
\[ \text{NaAlO}_2 + 2\text{H}_2\text{O} \rightarrow \text{Al(OH)}_3 \downarrow + \text{NaOH} \]
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Calcination: The precipitate is calcined at temperatures above \( 1000^\circ\text{C} \) to produce pure, anhydrous alumina:
\[ 2\text{Al(OH)}_3 \rightarrow \text{Al}_2\text{O}_3 + 3\text{H}_2\text{O} \]
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Hall-Héroult Process: This pure alumina serves as the direct feedstock for the Hall-Héroult electrolytic reduction process, which yields liquid aluminium metal.

• Thermodynamic Reason: Direct reduction of alumina is extremely difficult due to the highly negative free energy of formation of \( \text{Al}_2\text{O}_3 \).
Thus, a multi-stage process involving the Bayer process followed by electrolysis is required to extract aluminium metal.


Step 4: Final Answer:
According to the official exam answer key, the Bayer process is associated with the extraction of aluminum, matching Option (C).