Extraction of Zinc from Zinc Blende

Introduction:

Name: Zinc

Symbol: Zn

Atomic number: 30

Valency: 2

Electronic configuration: 1s2, 2s2, 2p6, 3s2, 3p6, 3d10, 4s2

Occurance: Zincite (ZnO), Zinc blende (ZnS), Calamine, Zinc Carbonate (ZNCO3) etc.

Extraction process of Zinc

The important ore of Zinc is Zinc blende (ZnS). So it is extracted from zinc blende by carbon reduction process. The following are the steps involved for the extraction process of zinc.

a. Crushing and Pulverization:

The big lumps of ore is first crushed by a jaw crusher and powered in ball mills.

b. Concentration:

The crushed and pulverized ore is concentrated by froth flotation process. This process is used for the concentration of sulphide ore. The powered ore is suspended in water and after adding pine one, it is stirred by passing the compressed air. The particles of the sulphide ore which are wetted by the oil comes to the surface along the froth (fizzy substance) which is taken out and the gangue particles remains at the bottom which are then removed.

Froth flotation process

c. Roasting:

The concentrated ore is roasted in the excess of air at a temperature of 900 degree celsius in the reverbatory furnace.
So the ore reacts with oxygen to form Zinc Sulphide (ZnS) and Sulphur dioxide (SO2) which is given by the reaction below. $$\ce{2ZnS + 3O2->[{heat}] 2ZnO + SO2}$$

Reverbatory furnace

During this process, some ore of the ZnS is also converted into zinc sulphate.$$\ce{ZnS + 2O2->ZnSO4 }$$

Above 900 degree celsius, this zinc sulphate decomposes to give Zinc Oxide.$$\ce{ZnSO4->[{>900^{\circ}C}] 2ZnO + SO2 + O2}$$

In this roasting process, the volatile impurities are also removed as their oxides.
$$\ce{C + O2->CO2 }$$
$$\ce{S + O2->SO2 }$$
$$\ce{S + O2->SO2 }$$
$$\ce{P4 + 5O2->2P2O5 }$$
$$\ce{2As + 3O2->2As2O3 }$$

d. Reduction:

The roasted ore is mixed with coke and heated strongly so that the zinc and oxides get converted into Zinc. For reduction, either Belgian process or vertical retort process is used. But vertical retort is the modern and continuous method.

Vertical retort process:

Vertical retort process

It is one of the most important, continuous and commercial technique for the reduction of zinc. Here, zinc ore is mixed with the coke in the ratio of 2:1. It is passed through the charging door. The retort is heated by the producer gas (CO + N2 ). Zinc vapour along with the carbon monoxide is led to the condenser by applying a suction and forcing producer gas from below. Following reaction takes place during reduction.
$$\ce{ZnO + C->Zn + CO}$$

Molten Zinc is taken out from the condenser time to time. The crude metal obtained is called zinc spelter which contains about 3% of other impurities.

e. Purification: The spelter zinc contains Fe, Pb, As, Sb, Cd as impurities. It is further purified by electrolysis process.

Electrolysis Process: Pure zinc is made anode and pure aluminium as anode. Zinc sulphate solution is acidified by sulphuric acid is taken as electrolyte. When electricity is passed through the electrolytic solution, pure zinc gets deposited at cathode whereas impurities remain as anode mud. Following electrolytic reaction occurs here:

At anode: $\ce{Zn – 2^e->Zn^++ }$

At cathode: $\ce{Zn + 2^e->Zn}$

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8 Responses to “Extraction of Zinc from Zinc Blende”

  1. Suman Bastola

    Thank you so much.

  2. suman manandhar

    thanks..about Nitrobenzene

  3. Anthony ogiribo

    I like the diagrammatic illustration of the purification of Zn , it’s quite explicit.

  4. Anthony ogiribo

    Pls shine more light on how the slag is formed and how Zn vapour is separated from carbon monoxide. Thank you.

  5. Ujaan Banerjee

    Thanks a lot…

  6. Luonde Simon

    Thanx a lot. tThe explanation is so clear that no one can get confused.

  7. fahimuddin azam

    Thank u so much.it is very clear explained that no one can get confused……………………..

  8. Rohit Mathur

    Extract of zinc from calamine