Question

Describe the extraction of zinc metal from its sulphide ore (zinc blende). Write equations of the reactions involved.

Answer 1

Roasting is the process in which a sulphide ore is strongly heated in the presence of air to convert it into a metal oxide.

Zinc is found as a sulphide in the ore zinc blende (ZnS). To extract zinc metal from zinc sulphide, it must first be transformed into zinc oxide. This is obtained through roasting. Upon strongly heating of zinc blende ore (zinc sulphide) in the presence of air (roasting), zinc oxide and sulphur dioxide are produced.

\[\ce{\underset{(Zinc blende or)}{\underset{Zinc sulphide}{2ZnS_{(s)}}} + \underset{(From air)}{\underset{Oxygen}{3O2_{(g)}}} ->[Roasting] \underset{Zinc oxide}{2ZnO_{(s)}} + \underset{Sulphur dioxide}{2SO2_{(g)}}}\]

Thus, roasting converts zinc sulphide into zinc oxide.

Zinc metal is extracted by the reduction of its oxide with carbon (or coke). Thus, when zinc oxide is heated with carbon, zinc metal is produced.

\[\ce{\underset{Zinc oxide}{ZnO_{(s)}} + \underset{(Reducing agent)}{\underset{Carbon}{C_{(s)}}} -> \underset{Zinc metal}{Zn_{(s)}} + \underset{Carbon monoxide}{CO_{(g)}}}\]