The solid impurities are left behind. Ni (s) + CO (g) [Ni(CO) ] (g) On heating the nickel tetracarbonyl around K, the complex decomposes to give pure metal. Ni (s) + CO (g) [Ni(CO) ] (g) XII U1 Metallurgy - XII U1 Metallurgy - - - - - Van-Arkel method for refining zirconium/titanium: This method is based on the thermal decomposition of metal compounds which lead to the formation of pure metals. Titanium and zirconium can be purified using this method.
For example, the impure titanium metal is heated in an evacuated vessel with iodine at a temperature of K to form the volatile titanium tetra-iodide.(TiI ). The impurities are left behind, as they do not react with iodine. Ti (s) + 2I (s) TiI (vapour) 550K The volatile titanium tetraiodide vapour is passed over a tungsten filament at a temperature around K. The titanium tetraiodide is decomposed and pure titanium is deposited on the filament.
The iodine is reused. Ti (s) + 2I (s) TiI (vapour) K