Question

Why are Sulphide ores converted to oxide before reduction?

Answer 1

1. In the process of extraction of metal Sulphide ores to metals, it is a much harder process compared with metal oxides to metals.
2. The process of converting the Sulphide ores to oxides in the presence of high heat in the excess of air is called roasting.
3. Sulphide ores are first converted into their oxides during the process of extraction.
4. Now, these obtained oxides are further converted to their respective metals, which is a much easier process.
5. Instead of using impure metal a more reactive metal is used in the extraction process.
6. The reaction involved in the process of roasting is represented as follows:
7. Conversion of Zinc sulphide $\left(\mathrm{ZnS}\right)$ to Zinc oxide$\left(\mathrm{ZnO}\right)$ in the presence of excess air:
   $2\mathrm{ZnS}\left(\mathrm{s}\right)+3{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2\mathrm{ZnO}\left(s\right)+2{\mathrm{SO}}_2\left(\mathrm{g}\right)$
8. The obtained Zinc oxide is further heated with the more reactive element Carbon, which displaces the Oxygen to form Carbon monoxide and yields the Zinc metal.
9. The chemical reaction is represented as:
   $\mathrm{ZnO}\left(s\right)+\mathrm{C}\left(s\right)\to \mathrm{Zn}\left(\mathrm{s}\right)+\mathrm{CO}\left(\mathrm{g}\right)$