Question

A sulphide ore like ZnS is first roasted into its oxide prior to reduction by carbon because:

• A. a sulphide ore cannot be reduced to metal at all
• B. no reducing agent is found suitable for reducing a sulphide ore.
• C. the Gibbs free energy of formation of most sulphides are greater than that for $C{S}_2$.
• D. a metal oxide is generally less stable than the metal sulphide.

Answer 1

Answer: (C)

The Gibbs free energy of most sulphides are greater than that for $C{S}_2$. In fact, $C{S}_2$ is an endothermic compound. Therefore, the ${\Delta }_f{G}^o$ of MJS is not compensated. So reduction of $M_{x}S$ is difficult. Hence it is common practice to roast sulphide ores to corresponding oxides prior to reduction.