Question

Give the basic requirement for vapour phase refining.

Hint:

The beauty of this method is that the impurities do not form volatile compounds and are left behind in the first stage, ensuring the final metal is extremely pure.

Answer 1

Concept: Vapour phase refining is a technique used to obtain metals in a very high state of purity. It relies on converting the impure metal into a volatile compound and then decomposing that compound to recover the pure metal.
For a metal to be refined using this method, two essential conditions must be met: • Formation of a Volatile Compound: The metal should be able to form a volatile compound with an available reagent at a relatively low temperature. • Easy Decomposition: The volatile compound formed must be easily decomposable at a higher temperature so that the pure metal can be recovered effortlessly.
These requirements are the basis for two famous industrial processes: • Mond Process (for Nickel): Nickel reacts with Carbon Monoxide to form volatile Nickel Tetracarbonyl, which decomposes at a higher temperature. Ni + 4CO 330-350K Ni(CO)₄ 450-470K Ni + 4CO • van Arkel Method (for Zirconium/Titanium): The metal reacts with Iodine to form a volatile iodide, which is then decomposed on a tungsten filament. Zr + 2I₂ 870K ZrI₄ 2075K Zr + 2I₂