Extraction of Nickel (Mond's process) : Nickel is extracted from sulfide ore by roasting followed by reduction with carbon, but the
process is complicated by the fact that nickel is found in association with other metals. The refining is rather unusual, for nickel forms a complex with carbon monoxide
tetracarbonylnickel(O) [Ni(CO)4]. This substance is molecular in molecular in structure and readily volatilized (boiling point 43ºC). It is made by heating nickel powder to 50ºC, in a stream of CO and then decomposed at 200ºC. Any impurity in the nickel sample remains in the solid state and the gas is heated to 230ºC, when it decomposes, giving pure metal and CO, which is recycled. Ni(CO)4 is gaseous and may be produced by warming nickel with
CO at 50ºC.
The sequence of reaction is
H2O(g) + C +-> CO(g) + H2
Ni(s) + 4 CO(s)-->(50ºC) [Ni(CO4)](g)
[Ni (CO)4](g) (200ºC )--> Ni + 4CO(g)
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