Question

While ZnS is roasted, the temperature is consistently maintained above
${860}^{0}C$ while the influx of air is controlled – True or False?

• A. True
• B. False

Answer 1

The correct option is A

True

This is to prevent the oxidation of ZnS to $ZnS{O}_4$ which again converts back into ZnS during the smelting-Carbon Reduction step

Above ${860}^{0}C$ and under a controlled blast of air, ZnS + $1.5O_2$ $\to$ ZnO + $S{O}_2$ $\uparrow$

With excess air and temperature lower than ${860}^{0}C$

ZnS + $2O_2$ $\to$ $ZnS{O}_4$

During smelting,

$ZnS{O}_4$+ 4C $\to$ ZnS + 4CO $\uparrow$