Question

Which among the following metal is refined by distillation?

• A. Lead
• B. Zinc
• C. Copper
• D. Tin

Answer 1

Answer:

B. Zinc

Metal Refining Techniques: An Overview

• Metal refining is the process of purifying crude or impure metals obtained from metallurgical processes. The aim is to remove impurities and obtain metals of high purity, which is crucial for various industrial applications.
• Different refining methods are employed based on the physical and chemical properties of the metal and the nature of impurities present.

1. Distillation

• Principle: This method is used for metals that have a low boiling point and are volatile, allowing them to vaporize easily while impurities (which are non-volatile or have higher boiling points) are left behind. The vaporized metal is then condensed to obtain a pure form.
• Application: This technique is primarily used for refining metals such as Zinc (Zn), Cadmium (Cd), and Mercury (Hg).
• Key Fact: Zinc has a relatively low boiling point (around 907 °C), making distillation an effective method for its purification, especially when impurities have much higher boiling points.

2. Liquation

• Principle: This method is suitable for metals that have a low melting point and are easily fusible, while their impurities have higher melting points. The impure metal is heated on a sloping hearth, causing the pure metal to melt and flow down, leaving the solid impurities behind.
• Application: Commonly used for refining metals like Tin (Sn), Lead (Pb), and Bismuth (Bi).

3. Electrolytic Refining

• Principle: This is one of the most widely used and effective methods for obtaining high-purity metals. The impure metal acts as the anode, a thin strip of pure metal acts as the cathode, and a suitable salt solution of the metal acts as the electrolyte. On passing an electric current, the impure metal at the anode dissolves, and the pure metal deposits on the cathode.
• Application: Used for refining a large number of metals including Copper (Cu), Zinc (Zn), Aluminium (Al), Nickel (Ni), Silver (Ag), and Gold (Au).
• Note: While Zinc can be refined by distillation, electrolytic refining is also a very common method, especially for large-scale production of high-purity zinc.

4. Zone Refining

• Principle: Based on the principle that impurities are more soluble in the molten state of the metal than in the solid state. A circular heater moves along a rod of impure metal, creating a molten zone. As the heater moves, pure metal crystallizes out of the molten zone, and the impurities are concentrated in the molten zone, moving along with it to one end of the rod.
• Application: This method is used for producing highly pure metals for semiconductor and electronic industries, such as Germanium (Ge), Silicon (Si), Gallium (Ga), and Indium (In).

5. Vapour Phase Refining

• Principle: Involves converting the impure metal into a volatile compound, which is then decomposed to obtain the pure metal. Two main conditions for this method are: the metal should form a volatile compound with a suitable reagent, and the volatile compound should be easily decomposable to recover the pure metal.
• Methods & Application:
  • Mond Process: Used for refining Nickel (Ni). Impure nickel is reacted with carbon monoxide to form volatile nickel tetracarbonyl, which is then decomposed at a higher temperature to yield pure nickel.
  • Van Arkel Method: Used for obtaining ultra-pure Zirconium (Zr) and Titanium (Ti). The impure metal reacts with iodine to form a volatile iodide, which is then decomposed on a heated filament to deposit pure metal.