Describe a method for refining nickel.

Explanation

When impure nickel is healted in a current of CO at 330 - 350 K, it forms volatile nickel tetracarbonyl complex leaving behind the impurities. The nickel tetracarbonyle thus obtained is then heated to a higher temperature (450 - 470 K ), when it undergoes thermal decomposition to give pure nickel.
` underset ("Impure nickel")(Ni) + 4 CO overset (330 - 350 K ) to underset ("Nickel tetracarbonyl")(Ni (CO)_4) overset (450 - 470 K )to underset ("Pure nickel ") (Ni ) + 4 CO `.
The method is commonly called as Mond process for refining of nickel.