Question

Zone refining is based on the principle that _____

• A. impurities of low boiling metals can be separated by distillation
• B. impurities are more soluble in the melt than in solid metal
• C. different components of a mixture are differently adsorbed on an adsorbent.
• D. vapour of volatile compound can be decomposed in pure metal.

Answer 1

The correct option is B impurities are more soluble in the melt than in solid metal

Zone refining is based on the principle that the impurities are more soluble in the melt than in solid state of the metal. A circular mobile heater fixed at one end of impure metal rod. The molten zone moves along with heater in forward direction.
As the heater moves forward, the pure metal crystallises out of the melt and the impurities pass on into adjacent molten zone. The process is repeated several time and th heater is moved in the same direction.
At one end, impurities get concentrated. This end is cut off. Semiconductors like germanium, silicon and gallium etc., are refined by this method.