(i) Zone refining:

It is a method is based on the fact that impurities are more soluble in the molten state of metal (the melt) than in the solid state. 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 along with it. Due to this, pure metal crystallizes out and the impurities pass to the adjacent molten zone. This process is repeated several times, which leads to the segregation of impurities at one end of the rod. Then, the end with the impurities is cut off. Silicon, boron, gallium, indium etc. can be purified by this process.

(ii) Electrolytic refining:

It is the process of refining impure metals by using electricity. Impure metal is used as the anode and a strip of pure metal is used as the cathode. A solution of a soluble salt of the same metal is taken as the electrolyte. When an electric current is passed, metal ions from the electrolyte gets deposited at the cathode as pure metal and the impure metal from the anode dissolves into the electrolyte in the form of ions. The impurities present in the impure metal gets collected below the anode and is known as anode mud.

(iii) Vapour phase refining:

It is the process of refining metal by converting it into its volatile compound and then, decomposing it to obtain a pure metal. To carry out this process,

(i) the metal should form a volatile compound with an available reagent, and 

(ii) the volatile compound should be easily decomposable so that the metal can be easily recovered. Nickel, titanium, etc. are refined using this method.