(i) This method is based on the principle that the impurities are more soluble in the molten state of metal (the melt) than in the solid state. In the process of zone refining, a circular mobile heater is fixed at one end of a rod of impure metal. As the heater moves the molten zone of the rod also moves with it. As a result pure metal crystallizes out of the melt and the impurities pass onto the adjacent molten zone. This process is repeated several times, which leads to segregation of impurities at one end of the rod. Then the end with impurities is cut off. Silicon, boron, gallium, indium etc can be purified by this process.
(ii) Column chromatography is a technique used to separated components of mixture where components are in minute quantities. In chromatography there are two phases : mobile phase and stationary phase. The stationary phase is immobile and immiscible. Al2O3 column is usually used as the stationary phase in column chromatography. The mobile phase may be a gas, liquid or super critical fluid in which the sample extracts dissolves. Then the mobile phase is forced to wave through stationary phase. The component that is more strongly absorbed on the column takes a longer time to travel than the component weakly , absorbed.
