Question

Which refining method is most suitable for zinc?

• A. Vacuum distillation
• B. Electro refining
• C. Fire refining
• D. Zone refining

Hint:

The large difference in boiling points between Zinc (\( 907^\circ\text{C} \)), Cadmium (\( 767^\circ\text{C} \)), and Lead (\( 1749^\circ\text{C} \)) makes fractional distillation a highly logical and thermodynamic choice for refining crude zinc.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the most suitable refining process used to produce high-purity zinc metal from crude zinc.

Step 2: Key Formula or Approach: The refining technique depends on the differences in physical properties—specifically the boiling point and vapor pressure—between zinc and its common impurity elements (like Lead, Cadmium, and Iron).

Step 3: Detailed Explanation:

• High Volatility of Zinc: Zinc has a exceptionally low boiling point of \( 907^\circ\text{C} \) compared to other common metals.
This high volatility makes distillation processes highly efficient for its purification.

• Vacuum Distillation Process: In vacuum distillation (or fractional distillation using the New Jersey column system), crude zinc is heated under reduced pressure.
Because vapor pressure is higher under vacuum, boiling and vaporization occur at lower temperatures, which saves energy and prevents oxidation.
Zinc is selectively vaporized and condensed as high-purity metal, while less volatile impurities like iron and lead remain in the liquid residue. Volatile impurities like cadmium can be separated in a subsequent distillation column.

• Comparison with Other Options:
-

Electro refining (Option B) is highly suitable for copper but is less economical for zinc than distillation.
-

Fire refining (Option C) is used for copper and lead but cannot yield the ultra-high purity levels of zinc achieved by distillation.
-

Zone refining (Option D) is reserved for semiconductors and silicon where extreme purity is needed at a very small scale, making it economically unfeasible for commodity metals like zinc.


Step 4: Final Answer:
Hence, vacuum distillation is the most suitable refining method for zinc, corresponding to Option (A).