When Bauxite is boiled with aqueous NaOH solution, sodium metal aluminate solution is formed. This part in metallurgy of aluminium is called as:

A. Liquation

B. Amalgamation

C. Leaching

D. Calcination

In the context of metallurgy, when bauxite is treated with aqueous sodium hydroxide (NaOH), the process you’re referring to is known as leaching. This is a crucial step in the extraction of aluminum from its ore. Let’s break down why leaching is the correct answer and how it fits into the overall process of aluminum production.

Understanding the Process

Bauxite, primarily composed of aluminum oxide (Al2O3), is the main ore from which aluminum is extracted. When bauxite is mixed with sodium hydroxide and heated, the aluminum oxide reacts with the NaOH to form sodium aluminate, which is soluble in water. This reaction can be summarized as follows:

• Reaction: Al2O3 + 2NaOH + 3H2O → 2NaAl(OH)4

This soluble sodium aluminate solution is then separated from the impurities present in bauxite through a process called clarification. The remaining impurities settle at the bottom, allowing for the extraction of the sodium aluminate solution.

Why Leaching?

Leaching is a method used to extract valuable metals from ores by dissolving them in a solvent. In this case, the solvent is sodium hydroxide. The term "leaching" specifically refers to the process of extracting a substance from a solid by dissolving it in a liquid. This is distinct from other processes like liquation, amalgamation, or calcination:

• Liquation: This involves separating metals based on their melting points, typically used for lead and tin.
• Amalgamation: This is a process where metals are extracted using mercury, commonly associated with gold extraction.
• Calcination: This refers to heating a substance to high temperatures in the absence of air, often to remove volatile substances or to induce thermal decomposition.

Steps Following Leaching

After leaching, the sodium aluminate solution undergoes further processing. The next steps typically include:

• Precipitation: Aluminum hydroxide is precipitated from the sodium aluminate solution by adding water and adjusting the pH.
• Calcination: The aluminum hydroxide is then heated to produce aluminum oxide (Al2O3).
• Electrolysis: Finally, aluminum oxide is subjected to electrolysis in a molten cryolite bath to produce aluminum metal.

Conclusion

In summary, the boiling of bauxite with aqueous sodium hydroxide to form sodium metal aluminate solution is classified as leaching. This process is integral to the extraction of aluminum, allowing for the efficient separation of aluminum from its ore. Understanding these steps is essential for grasping the broader concepts of metallurgy and the extraction of metals.