(a) Zone refining method The principle of zone refining is that the impurities in an ingot or ore of metal are more soluble in the melt state when compared to the corresponding solid state of the impurities. (b) Vapour phase refining method This method is based on the principle that the impure metal is converted into a volatile compound and which can be collected elsewhere. It is then decomposed used to give back the pure metal. (c) Liquation method This method is based on the lower melting point of the metal than the impurities and tendency of the molten metal to flow on the sloping surface. (d) Chromatographic method This method is based on the principle, where molecules in mixture applied onto the surface or into the solid, and fluid stationary phase (stable phase) is separating from each other while moving with the air of a mobile phase. In this method, different components of a mixture are differently adsorbed on an adsorbent.