Q.Explain the extraction of zinc from zinc blende.

Zinc is extracted from its sulphide ore (zinc blende) via concentration, roasting, reduction and refining.

Step 1 – Concentration (Froth Flotation):

Zinc blende (ZnS) is a sulphide ore, so it is concentrated by the froth flotation process. The powdered ore is mixed with water, a collector (e.g. pine oil/xanthate) and a frothing agent; air is blown through the mixture, and the sulphide mineral particles (preferentially wetted by the oil) rise with the froth to the top, while the gangue (rock impurities) settle at the bottom.

Step 2 – Roasting:

The concentrated ore is roasted in excess air at about 1200 K, converting zinc sulphide to zinc oxide:

$2ZnS + 3O_2 \xrightarrow{\Delta} 2ZnO + 2SO_2\uparrow$

The SO2 gas released is used to manufacture sulphuric acid.

Step 3 – Reduction:

Zinc oxide is reduced with coke (carbon) at about 1673 K in a fire-clay retort (the 'Belgian process'):

$ZnO + C \xrightarrow{1673\text{K}} Zn + CO$

Zinc vapour distils over and is condensed and collected; this is also called the distillation process for zinc.

…

Zinc blende ZnS is roasted to ZnO (2ZnS + 3O2 -> 2ZnO + 2SO2), then reduced by coke (ZnO + C -> Zn + CO), and the zinc is refined.

Zinc blende (sphalerite) is zinc sulphide, ZnS. Extraction of zinc from it involves these steps:

1. Concentration of ore: The powdered ore is concentrated by the froth flotation process, which separates the sulphide ore from the gangue.

2. Roasting: The concentrated sulphide ore is heated strongly in a regular supply of air (roasting), converting it to zinc oxide:

   2 ZnS + 3 O2 -> 2 ZnO + 2 SO2.

   (Roasting is preferred for sulphide ores; the SO2 by-product is used to make sulphuric acid.)

3. Reduction (smelting): The zinc oxide is mixed with powdered coke and heated to about 1673 K in a furnace. Carbon reduces the oxide to zinc metal:

   ZnO + C -> Zn + CO.

   …