Answer. The process of removal of gangue from the ore is technically known as concentration and the purified ore is called the concentrate. Concentration of the crushed ore is carried out by the following methods:
(a) Gravity separation
Gravity separation is based on the differences in densities of the metallic ore and the gangue particles.
In the process, the powdered heavy met
al bearing ore settles down on agitation in a stream of water, while the lighter gangue particles are carried away by the water as shown in figure below:
Water
Water +
Gangue
Concentrated
Ore
(b) Froth flotation process
Froth flotation process is based on the wetting characteristic of the ore and the gangue particles with oil and water, respectively.
The ore particles are preferentially wetted by the oil and the gangue particles by the water. Hence ore particles come to the surface in the form of a froth that can be skimmed as shown in figure below:
Fig.16.2. Froth floatation process
(c) Electromagnetic separation
Electromagnetic separation is based on the separation of magnetic ores from the non-magnetic impurities by means of electromagnets or magnetic separators. The powdered ore is dropped over a leather belt moving over two rollers, one of which is magnetic. The ore gets attracted and is collected nearer to the magnet while the nonmagnetic impurities fall further away as shown in figure below: