First of all lets know definitions of terms used in metallurgical operations.
Minerals
The solid natural materials found beneath the Earth's surface, which contains compounds of metals in the combined state along with earthly impurities, are called minerals.
Ores
Those minerals from which the metals are extracted commercially at a comparatively low cost with minimum effort are called ores of the metals. For example: ores of copper are; copper glance and chalcopyrite . Hence, all ores of the metals are minerals, but all minerals are not ores.
Interesting Information
The colour of hair is caused by the presence of transition metal compounds in the hair. Brown hair contains iron or copper compounds, blonde hair contains compounds of titanium and redhead hair is because of the presence of molybdenum compounds.
Gangue
The earthly and other impurities associated with the minerals are known as gangue.
Metallurgy
The process of extraction of a metal in a pure state on a large scale from its ore by physical or chemical means is called metallurgy.
The processes involved in metallurgy for extraction of a metal in the pure state from its ore are:
(i) concentration of the ore; (ii) extraction of the metal, and (iii) refining of the metal.
(i) Concentration of the Ore
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 metal 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 16.1.
Diagram image pending upload by Admin.
(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 oil and the gangue particles by water. The whole mixture is agitated with compressed air. Hence, oil coated ore particles being lighter come to the surface in the form of froth that can be skimmed as shown in figure 16.2.
Diagram image pending upload by Admin.
(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 non- magnetic ore falls first and the magnetic ore gets attracted and falls farther away as shown in figure 16.3.
Diagram image pending upload by Admin.