(i) Froth Floatation Process-The method has been in use for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water. To it, collectors and froth stabilisers are added. Collectors (e.g., pine oils, fatty acids, xanthates, etc.) enhance non-wettability of the mineral particles and froth stabilisers stabilise the froth.
(ii) Zone refining : This method is based on the principle that the impurities are more soluble in the melt than in the solid state of the metal. A circular mobile heater is fixed at one end of the rod of the impure metal. The molten zone moves along with the heater which is moved forward. As the heater moves forward, the pure metal crystalises out of melt and the impurities pass on into the adjacent molten zone. This process is repeated several times and the heater is moved in the same direction. At one end, impurities get concentrated.
This method is very useful for producing semiconductor and other metals of very high purity like germanium, silicon, boron etc.
(iii) Refining by liquation : In this method, a low melting metal like tin can be made to flow on a slopping surface. In this way it is separated from higher melting impurities.
