Explain: (i) Zone refining (ii) Column chromatography.

ZONE-REFININGMeals of very high purity can be obtained by this method by removing an impurity, which shows difference in solubility of the liquid and solid states of the metal. A circular heater is fitted around a rod of impure metal and is slowly moved down the rod. At the heated zone, the rod metls and as the heater passes on, pure metal crystallizes while impurities pass into the adjacent molten part. In this way, the impurities are swept over one end of the rod, which is finally discarded. The heater may have to be moved from one end to the other more than once. Ge, Si and ga used as semiconductors are refined in this manner; gallium-arsenide and indium-antimonide are also zone refined.

hromatography is based on the differential adsorption of the various components in a mixture on a suitable adsorbent. In its various forms like column chromatography, TLC (Thin Layer Chromatography), GLC (Gas Liquid Chromatography), Ion-exchange chromatography and Paper chromatography, it is widely used for the separation of mixtures and concentration, identification and refining of materials.