Write the principle behind the following methods of refining :
(i)Hydrauic washing
(ii) Vapour phase refining.

Explanation

The principle behind the given methods of refining are :
(i) Hydraulic Washing : This method is based on difference of gravity between ares and
gangue. An up ward stream of water is used to wash the powdered ore. The lighter
gangue particles are washed away, leaving behind that heavier ones.
(ii) Vapour-phase refining : Vapour-phase refining is the proces of refining metal by
converting it into its volatile compound and then, decomposing it to obtain a pure metal to carry out this proces,
(i) The metal should form a volvatile compound with an available reagent.
(ii) The volatile compound should be easily decomposable, so that the metal can be easily recovered. This method is used for refining nickel, zirconium and titanium.