Sunday, September 2, 2012

Extraction of Zinc from Zinc Blende


What is "Ore"?

It is a naturally source of a metal, and the metal can be extracted from it. Ore is commonly the oxides of metals (e.g. bauxite is hematite is Al2O3, hematite is Fe2Oand rutile is TiO2) or the sulfides (e.g. pyrite is FeSand chalcopyrite is CuFeS2). By nature, it contains lots of impurities.

What is "Zinc Blende"?


Zinc blende is the ore of zinc and is made up of zinc sulfide and a high percentage of iron.

 Zinc blende, also known as "sphalerite" or "black-jack", has a structure that is relatively similar to that of a diamond. It crystallizes in a cubic crystal system.

How to extract Zinc?

There are 2 steps to the extraction: concentration and reduction.

“Concentration”
It is the process of removing any impurities from the oxide or sulfide of the metal.       

Firstly, zinc blende is combusted in oxygen, resulting in the as follow reaction:
2ZnS (s) + 3O2 (g) --> 2ZnO (s) + 2SO2 (g)

The product of the reaction is then added to a solution that causes ZnO to be hydrophobic and float to the surface.


“Reduction”
A reducing agent is added to the metal oxide to cause it to reduce to the metal.

In the extraction of zinc, carbon monoxide is used to reduce zinc oxide to zinc:
ZnO (s) + CO (g) --> Zn (s) + CO2 (g)



However, in other cases, reduction by electrolysis can be done. During the process, electrons are added to the metal ions directly, producing very pure metals.

Problems

Mining for ores results in removal of underground materials and clearing of natural habitats. This results in threats to living organisms and also affect the geography of Earth. Mining can cause sinkholes and land collapses.

The process of extraction of ores can pollute water and air. Carbon dioxide, carbon monoxide and many other toxic materials are produced during the process. This is a threat not only to wildlife's but also humans, especially the indigenous people.

Many governments are controlling the rate of mining and also made laws to ensure proper purification and disposal of waste materials. However, it is the company's responsibility to ensure that they play a part to ensure the world remains a clean place.

Credits

http://en.wikipedia.org/wiki/Sphalerite
http://www.chemguide.co.uk/inorganic/extraction/introduction.html
http://wiki.answers.com/Q/How_does_the_mining_of_metal_ores_and_the_extraction_of_metals_affect_the_environment