Why is it advantageous to roast a sulphide ore to oxide before reduction?

Question

(i) Why is it advantageous to roast a sulphide ore to oxide before reduction?

(ii) Name a metal which is purified by vapour phase refining. Describe the process in brief.

Answer 1

(i) Oxides can be more easily reduced to the respective metals using carbon or hydrogen as reducing agent. On the other hand sulphides cannot be reduced by carbon or hydrogen because Δ_rG for such reactions are positive and hence these reactions are not feasible.

(ii) Zirconium is purified by vapour phase refining the process is known as van Arkel Process. In this process/ impure zirconium is heated with iodine vapour at about 870 K. Zirconium volatilizes as

ZrI₄. When ZrI₄ is passed over fungsten filament at 1800k, it decomposes to give pure zirconium.