Describe a method for refining nickel.

Explanation

Mond process for refining nickel : (i) The impure metal is heated in a stream of carbon monoxide at around 350 K.
(ii) The nickel reacts with the CO to form a highly volatile nickel tetra carbonyl.
(iii) The solid impurities are left behind.
`Ni_((s)) + 4CO_((g)) rarr Ni(CO)_(4(g))`
(iv) On heating the nickel tetracarbonyl around 460 K, the complex decomposes to give pure metal.
`Ni(CO_(4))_((g)) rarr Ni_((s)) + 4CO_((g))`