Question

Write chemical reactions taking place in the extraction of zinc from zinc blende.

Answer 1

We know that zinc blende is the chief ore of zinc. Zinc blend has the formula . Pure zinc metal is extracted from its ore zinc blende. The various steps in the process of extraction are concentration, roasting, reduction and purification.

Complete step by step answer:
We know that the extraction of pure zinc metal from its ore zinc blende involves four steps:
i) Concentration: In this step, the ore zinc blende is crushed. The crushed ore is then concentrated using the froth flotation process.
ii) Roasting: In this step, the concentrated ore is roasted in the presence of excess of air at about a higher temperature of $1200{\text{ K}}$. The chemical reaction that occurs during the concentration of ore is as follows:
$2{\text{ZnS}} + 3{{\text{O}}_2}\xrightarrow{{{\text{Heat}}}}2{\text{ZnO}} + {\text{2S}}{{\text{O}}_2}$
iii) Reduction: In this step, zinc oxide is mixed with powdered coke and heated at $1673{\text{ K}}$. The reduction occurs in fine clay retort. During reduction, zinc oxide is converted to pure zinc metal. The chemical reaction that occurs during the reduction of zinc oxide is as follows:
${\text{ZnO}} + {\text{C}}\xrightarrow{{{\text{Heat}}}}{\text{Zn}} + {\text{CO}}$
iv) Purification: In this step, purification of zinc is done using electrolytic refining process. In the process of electrolytic refining, pure zinc metal is transported from the impure sample at anode to cathode. The metal which is more basic remains in the electrolytic solution while the less basic metal present as impurity precipitates out as anode mud. The reactions occurring at anode and cathode are as follows:
Anode: ${\text{Zn}} \to {\text{Z}}{{\text{n}}^{2 + }} + 2{{\text{e}}^ - }$ (From anode)
Cathode: ${\text{Z}}{{\text{n}}^{2 + }} + 2{{\text{e}}^ - } \to {\text{Zn}}$ (From electrolyte)

Note: The other ores of zinc are calamine or smithsonite. In these ores, zinc is found in the form of zinc carbonate $\left( {{\text{ZnC}}{{\text{O}}_{\text{3}}}} \right)$. Zinc blende contains zinc sulphide along with calcite, dolomite and fluorite.