Question

Write a short note on the three major steps involved in extraction of a metal after its ore is mined.

Answer 1

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1. Crushing and Grinding
First of all, ores are crushed into a fine powder in big jaw crushers and ball mills. This method is called pulverization.
2. Concentration (Dressing) of ores
The technique of removing gangue, the rocky impurities like Sio2 present in an ore, is called concentration of an ore or ore dressing and the purified ore is called concentrated ore.
Concentration of the crushed ore is done by the following methods:

a) Hydrolytic method

The principle of the hydrolytic method is based on the difference in the densities of the ore and the gangue.

In this method, the ore is poured over a sloping and vibrating corrugated table with grooves and a jet of water is allowed to flow over it. The denser ore particles settle down in the grooves and lighter gangue particles are washed down by water.

b) Magnetic Separation

The Principle of magnetic separation is magnetic properties of the ores.

In this process, the crushed ore is placed over a conveyer belt, which rotates around two metal wheels, one of which is magnetic. The magnetic particles are attracted to the magnetic wheel and fall separately apart from the non magnetic particles. Due to this separation occurs and process is called magnetic separation.

c) Froth floatation

This technique depends on the prefential wettability of the ore with oil(pine oil)and the gangue particles by water. The ore (crushed) is taken in a large tank containing oil and water and agitated with a current of compressed air. The ore is wetted by the oil and thus gets separated from the gangue in the form of froth. As the ore is lighter, it comes on the surface with the froth and impurities are left behind.

d) Chemical Method or leaching:

The ore is treated with a reagent (that may be acid, base or some other reagent) and the ore is soluble in it but the impurities are not. Then the impurities are removed by filtration. The solution of the ore that is the filtrate is treated with a suitable reagent which precipitates the ore.