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

Concentration removes gangue; roasting in excess air converts the sulphide ore to the oxide while releasing SO$_2$ (used for sulphuric acid); reduction with carbon at high temperature (in a fire-clay retort, the Belgian process) or via electrolysis of $ZnSO_4$ solution then gives metallic zinc, which is refined by distillation (zinc's low boiling point, 1180 K, allows it to be distilled off and condensed as …

Step 1 – Concentration

Zinc blende (ZnS) ore is first concentrated by froth flotation, which removes the earthy/siliceous gangue and leaves a concentrate rich in ZnS.

Step 2 – Roasting

The concentrated ore is roasted, i.e. heated strongly in a plentiful supply of air, converting the sulphide to the oxide and releasing sulphur as sulphur dioxide (a valuable by-product used to manufacture sulphuric acid):

Step 3 – Reduction

Zinc oxide is then reduced to the metal. This can be done in two ways:

• Carbon (coke) reduction, typically in a fire-clay retort (the "Belgian process"), at about 1673 K:

Zinc vapour produced is collected and condensed (zinc boils at 1180 K, well below the reduction temperature, so it distils off directly).

• Electrolytic reduction: the roasted oxide is leached with dilute sulphuric acid to give a $ZnSO_4$ solution, which is then electrolysed between an aluminium cathode and a lead anode, depositing high-purity zinc at the cathode. This is the more modern, higher-purity route.

Step 4 – Refining …

Follow the standard four-stage metallurgical sequence for zinc — concentrate (froth flotation) → roast (sulphide to oxide) → reduce (carbon or electrolysis) → refine …

• Omitting the roasting step's balanced equation or forgetting that SO$_2$ is a useful by-product, not just waste gas. …