Minerals are naturally occurring chemical substances in the earth’s crust obtainable by mining.
Out of many minerals in which a metal may be found, only a few are viable to be used as sources of that metal. Such minerals are known as ores. Examples: Galena, PbS, etc.
It is usually contaminated with earthly or undesired materials known as gangue. The extraction and isolation of metals from ores involve the following major steps:
• Concentration of the ore,
• Isolation of the metal from its concentrated ore, and
• Purification of the metal. It is also called ‘Refining’.
Stages of extraction of metals:
After the concentration of the ore is done, there are two main steps or stages in extractive metallurgy. They are:
Conversion of the ore into Metal oxide or metal compound.
Extraction of crude metal from metal from metal compound.
Concentration of ores:
Removal of the unwanted materials (e.g., sand, clays, etc.) from the ore is known as concentration, dressing or benefaction. It involves several steps and selection of these steps depends upon the differences in physical properties of the compound of the metal present and that of the gangue.
Principle: Concentration is done mainly to increase the percentage of pure metal.
It is of 3 types.
1. Gravity separation (Hydraulic washing)
2. Froth floatation
3. Magnetic separation.
This method has been in use for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water. To it, collectors and froth stabilizers are added. Collectors (e. g., pine oils, fatty acids, xanthates, etc.) enhance non-wettability of the mineral particles and froth stabilizers (e. g., cresols, aniline) stabilize the froth. The mineral particles become wet by oils while the gangue particles by water. A rotating paddle agitates the mixture and draws air in it. As a result, froth is formed which carries the mineral particles. The froth is light and is skimmed off. It