Extraction of Metals

Metals are necessarily used in our daily life. As we know, many metals are found in the Earth's crust as ores. An ore is usually a compound of the metal mixed with impurities. So how can people seperate the metal from its ore?

There are several methods of extraction:

Smeltings & refinering is one method of metal extraction. Some unreactive metals such as silver and gold can be mined from nature, but they are usually mixed with like sulphur chlorine. What people needed to do is to heat them to molten state and separate the metal from the impurities in the ore mixture to get purer metals.






Video The Process of Excavating and Refining Gold


Electrolysis is the passage of an electric current through an ionic substance that is either molten or dissolved in a suitable solvent, resulting in chemical reactions at the electrodes and separation of materials. Some metals are in the form of ionic compounds in ores. The metals can be extracted when the ionic compound are dissolved in water or in the molten state by electrolysis. Electrolysis is the most powerful extraction method, but it takes a lot of electricity and that makes it expensive. Hence, electrolysis is only used for the most reactive metals as they usually bond with other elements to form compound.


Video Electrolysis Introduction





Redox reactions are also used in metal extration. Many metals are found to be in form of oxides,so a reducing agent and heat are used to reduce the metals. The reducing agents remove oxygen from the ore to leave the metal. In industry, carbon is most commonly used as reducing agent. Besides carbon, carbon monoxide and hydrogen can be used as reducing agents.


Although it is important to extract metals, there are some negative impact on environment.For enxample, sodium metal is extracted from sodium chloride by electrolysis as the largest sourse of sodium is sodium chloride which occurs as rock salts and in sea water.
Chemical equation: 2Nacl → 2Na + Cl2
Ionic equation: NaCl → Na+ + Cl-
However, electrolysis requires a large amount of electricity.Hence,lots of fossil fuel is combusted to generate eletricity, resulting in increase of greenhouse gas such as CO2 and some harmful gases like SO2.





Many countries have realised this problem and started to take actions. In factories, cleaning facilities are installed so as to detoxify and reduce hazardous gases such as SO2. Some tried to use new resources to supply energy, these resources are usually clean like hydrogen gas. However using new resources may cost too much. Then, some people tried to use new methods of extraction, as I know, one of these new methods is to use special lens and sunlight to make laser and extract metals instead of electrolysis.

References:
http://en.wikipedia.org/wiki/Electrolysis
http://en.wikipedia.org/wiki/Smelting
http://www.scribd.com/doc/11579771/Extraction-Properties-and-Uses-of-Sodium
www.supplierlist.com/wholesale-furnace-34288.htm
www.akersolutions.com/Internet/IndustriesAndS...
http://en.wikipedia.org/wiki/Smelting
http://www.youtube.com/watch?v=apD5cPVsDjc&feature=PlayList&p=C35A673ED5D42975&playnext=1&playnext_from=PL&index=9
http://www.youtube.com/watch?v=i9xS9t-KMpc