Describe the principle controlling each of the following processes:

1. Zone refining of metals

2. Electrolytic refining of metals

1. Metals like Germanium are purified using Zone refining. It is based on the principle that the impurities are more soluble in the molten state than in the solid state of metal.

In the zone refining process, a circular movable heater is fixed at one end of a metal rod which is made of the impure metal. Now, this heater is moved slowly across the metal rod,due to which, the metallic impurities melt temporarilyon this heater. The melt containing the impurities moves forward along with the heater as the metal rod progresses further. As the heater moves along the rod, the pure metal is left to solidify. As discussed, the impurities are more soluble in their melt state, so the concentration of the impurities in the melt increases as the heater moves forward. Finally, the impurities are accumulated at one end of the metal rod. This process is done several times. The accumulated impurities are removed, leaving behind the pure metal.

2. In electrolytic refining of metals, first the impure metal is made the anode and the cathode is made of the thin sheet of pure metal. Salt of the metal is used as an electrolyte.

On passing current, metal from the anode goes into the solution. Simultaneously, the ions in the solution reduce on cathode leading to deposition of pure metal. In this way we get the pure metal through electrolytic refining.