Question

Explain the extraction of Zinc from its chief ore.${{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}$

Answer 1

Hint: There are two common ores of Zinc, they are Calamine and Zinc blende. Out of these two ores one is considered as the chief ore. We need to identify the chief ore and write the extraction process accordingly.

Complete step by Step answer:

The main core of zinc is zinc blende. The processes involved in the extraction of zinc are:

1. Concentration – the zinc ore is crushed and is concentrated by the froth-floatation method.
2. Roasting – the concentrated ore is roasted at a temperature of about 1200K in the presence of excess air. The chemical equation involved in the process is:
   $\text{2ZnS + 3}{{\text{O}}_{\text{2}}}\xrightarrow{\text{ }\\!\\!\Delta\\!\\!\text{ }}\text{ 2ZnO + 2S}{{\text{O}}_{\text{2}}}$
3. Reduction – Zinc oxide is heated to 1673K in the presence of powdered coke, in a fire clay retort. There, it is reduced to zinc metal. The chemical equation involved in the process is:
   $\text{ZnO + C }\xrightarrow{\text{1673K}}\text{ Zn + CO}$
4. Purification – Zinc is purified by electrolytic refining. This process involves impure zinc as anode and thin sheet of pure zinc as cathode. The electrolyte present is $\text{ZnS}{{\text{O}}_{\text{4}}}$ solution containing a small amount of dilute ${{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}$, which on passing electric current through, deposits pure zinc at the cathode.

Note:

Froth flotation is a process for selectively separating hydrophobic material from hydrophilic. This is used in mineral processing, paper recycling and waste water treatment industries.
Froth flotation process is based on the principle that the metallic sulphide particles of ore are preferentially wetted by oil and the gangue particles by water. Collectors attach themselves by polar groups to grains of minerals which then become water repellent and thus, pass on into the froth.