Question

Outline the principles of refining of metals by the following method:

Vapour phase refining

Write the principles of vapour phase refining methods.

Answer 1

Vapour phase refining is the process of refining metal by converting it into its volatile compound and then decomposing it to obtain a pure metal. To carry out this process,

1. The metal should form a volatile compound with an available reagent, and
2. The volatile compound should be easily decomposable so that the metal can be easily recovered.

The following examples illustrate the procedure:

Mond process for refining of nickel: The Mond process forms nickel tetracarbonyl, a volatile compound, by treating impure nickel at 330–350 K in a carbon monoxide current.

\[\ce{\underset{(Impure)}{Ni} + 4CO ->[330-350 K] Ni(CO)4}\]

The complex thus formed on being heated to 450-470 K yields pure nickel.

\[\ce{Ni(CO)4 ->[450-470 K] \underset{(Pure)}{Ni} + 4CO}\]