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Concentration of Ores

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Concentration of Ores - Lesson Summary

 “Concentration of ores” one of the principal steps involved in the extraction and isolation of metals.
Most metals are found in nature in a combined state. Metals that are found in a combined state in the earth’s crust are known as minerals.
Example
Not all minerals can be used to extract metals. Only the minerals that have a relatively high concentration of metal and can be extracted in an easy and cost-effective manner are used for extraction. Such minerals are known as ores. 


Ex: bauxite is the principal ore of aluminium.

The metal is extracted from the ore after a series of procedures and techniques, known as extraction and isolation procedures. The main steps involved in the extraction and isolation of metals from ores are,
·         Concentration of the ore
·         Isolation of the metal from its concentrated ore
·         Purification of the metal
The branch of science and technology that deals with the isolation of metals from their ores is known as metallurgy.

An ore contains a metal associated with other undesired substances like sand, clay, etc. These undesired substances are collectively known as gangue (or) matrix. The process of separating gangue from an ore is known as concentration of the ore. It is also called dressing or benefaction.
Metals can be concentrated from their ores using any of these methods - hydraulic washing, magnetic separation, froth floatation or leaching.

The choice of the technique used for extraction depends upon the differences in the physical properties of the compound of the metal present and that of the gangue. The type of metal, the facilities available and environmental factors are also taken into consideration.

The name hydraulic means “operated by the pressure created by forcing water (or) another liquid”. Washing ore with water is known as hydraulic washing. Gold mines make use of the hydraulic washing technique.
 


An upward stream of running water is used to wash powdered ore. The lighter particles of the gangue are washed away and the heavier ore is left behind. This technique separates the gangue from the ore using the difference in their specific gravities. It is, also known as gravity separation.
Magnetic separation is used when either the ore (or) the impurities in it are magnetic in nature.
Ex: Separating iron from its ore hematite

 

Froth flotation separates the gangue particles from the ore, based on the fact that gangue is wetted by water, while mineral is wetted by oil.
The ore is crushed into fine powder and mixed in water. Then, collectors and stabilisers are added to the water.

A collector is a substance, such as pine oil (or) a fatty acid, which enhances the non-wettability of the ore particles.  A stabiliser is a substance like cresol which increases the stability of the froth. 
The mixture is agitated with the help of a rotating paddle. This draws air into the mixture and froth is generated. The froth is then skimmed off and is dried to recover particles of the ore.

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