Zone refining: 
This method is employed for preparing highly pure metal (such as silicon, tellurium, germanium), which are used as semiconductors. It is based on the principle that melting point of a substance is lowered by the presence of impurities. Consequently, when an impure molten metal is cooled, crystals of the pure metal are solidified, and the impurities remain behind the remaining metal.
The process consists In casting the impure metal in the form of a bar. A circular heater fitted around this bar is slowly moved longitudinally from one end to the other. At the heated zone, the bar melts, and as the heater moves on, pure metal crystallizes, while the impurities pass into the adjacent molten part In this way, the impurities are swept from one end of the bar to the other. By repeating the process, ultra pure metal can be obtained.

(i) Iron is one of the most useful metals and its alloys are used everywhere including bridges, electricity pylons, bicycle chains, cutting tools and rifle barrels.
(ii) Cast iron is used to make pipes, valves and pumps stoves etc.
(iii) Magnets can be made from iron and its alloys and compounds.
(iv) An important alloy of iron is stainless steel, and it is very resistant to corrosion. It is used in architecture, bearings, cutlery, surgical instruments and jewellery.
(v) Nickel steel is used for making cables, automobiles and aeroplane parts.
(vi) Chrome steels are used for manufacturing cutting tools and crushing machines.

(i) Van-Arkel method is based on the thermal decomposition of metal compounds which lead to the formation of pure metals.
(ii) Titanium and zirconium can be purified, using this method.
(iii) For example, the impure titanium metal is heated in an evacuated vessel with iodine at a temperature of 550 K to form the volatile titanium tetra-iodide(Til₄)
(iv) The impurities are left behind, as they do not react with iodine
\({ Ti }_{ (s) }+{ 2I }_{ 2(s) }\longrightarrow { Til }_{ 4 }(vapour)\)
(v) The volatile titanium tetraiodide vapour is passed over a tungsten filament at a temperature around 1800 K.
(vi) The titanium tetraiodide is decomposed and pure titanium is deposited on the filament
(vii) The iodine is reused.
\({ Til }_{ 4 }(vapour)\longrightarrow { { Ti }_{ (s) } }+{ 2I }_{ 2(s) }\)

(i) Froth flotation method is commonly used to concentrate sulphide ores such as galena (PbS), zinc blende (ZnS) etc.
(ii) In this method, the metallic ore particles which are preferentially wetted by oil can be separated from gangue.
(iii) In this method, the crushed ore is suspended in water and mixed with frothing agent such as pine oil, eucalyptus oil etc.
(iv) A small quantity of sodium ethyl xanthate which acts as a collector is also added.
(v) A froth is generated by blowing air through this mixture.
(vi) The collector molecules attach to the ore particle and make them water repellent.
(vii) As a result, ore particles, wetted by the oil, rise to the surface along with the froth.
(viii) The froth is skimmed off and dried to recover the concentrated ore.
(ix) The gangue particles that are preferentially wetted by water settle at the bottom.