Nickel is refined by Mond's process. In this process, nickel is heated in the presence of carbon monoxide to form nickel tetracarbonyl, which is a volatile complex.

Ni + 4CO \(\overset{330-350K}\longrightarrow\) Ni(CO)₄

Then, the obtained nickel tetracarbonyl is decomposed by subjecting it to a higher temperature (450 - 470 K) to obtain pure nickel metal.

Ni(CO)₄ \(\overset{450-470K}\longrightarrow\) Ni + 4CO