Question

Which refining process is generally used in the purification of low melting metals ?

• A. Electrolysis
• B. Liquation
• C. Zone refining
• D. Chromatographic method

Hint:

Associate refining methods with specific properties or elements: - \textbf{Low M.P. Metal}: Liquation (e.g., Sn, Pb). - \textbf{Volatile Compound Formation}: Mond process (Ni), van Arkel method (Zr, Ti). - \textbf{High Purity Semiconductors}: Zone Refining (Si, Ge). - \textbf{Reactive Metals/High Purity Cu}: Electrolytic Refining.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks to identify the metallurgical refining process suitable for metals with low melting points.
Step 2: Key Formula or Approach:
This requires knowledge of different refining methods and the principles behind them. Each method is suited for specific types of metals and impurities. - Liquation: Separates a low-melting-point metal from high-melting-point impurities. - Electrolysis: Used for highly reactive metals (e.g., Al, Na, Mg) or for very high purity refining (e.g., Cu). - Zone refining: Used for producing ultra-pure metals, especially semiconductors (like Si, Ge), based on the principle that impurities are more soluble in the molten phase than in the solid phase. - Chromatography: Used for elements that are difficult to separate due to very similar properties (e.g., lanthanides).
Step 3: Detailed Explanation:
The process of liquation is specifically designed for metals that have a low melting point, such as tin (Sn), lead (Pb), and bismuth (Bi). The main condition is that the impurities present in the crude metal must have a higher melting point than the metal itself.
In this process, the impure metal is placed on a sloping hearth and gently heated in a furnace. The temperature is maintained just above the melting point of the metal but below the melting point of the impurities. The pure metal melts and flows down the slope, leaving the solid, high-melting impurities behind.
Step 4: Final Answer:
Liquation is the refining process used for the purification of low-melting metals.