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Occurrence and Enrichment of Ores

Most of the metals are reactive and hence they do not occur free in nature. The earth’s crust is the major source of metals. The various compounds of metals, which occur in nature and are obtained by mining, are called minerals. Ores are minerals from which metals can be extracted profitably. The processes used for removing the gangue from the ores are based on the differences between the physical or chemical properties of the gangue and the ore. The various methods used for the

Enrichment of ores are:
  1. Hydraulic Washing or Gravity Separation
  2. Froth Floatation Process
  3. Electromagnetic Separation
  4. Hydraulic Washing or Gravity Separation
  1. Hydraulic Washing or Gravity Separation
    In hydraulic washing, the powdered ore is added to a stream of flowing water. The lighter particles are carried away with the flowing water, while the heavier particles of the ore are left behind. The method makes use of the difference in the densities and the impurities of the ore. It is also called the gravity separation method.


  1. Froth Floatation Process
    Copper pyrite, a sulphide ore of copper is concentrated by froth flotation process. The froth floatation process is generally used for concentration of sulphide ores like ZnS (zinc blende), PbS (galena), CuFeS2 (copper pyrites), etc.
    The principle of the method is that ore particles are made wet more readily by pine oil while the gangue particles are made wet by water.

The crushed ore is treated with pine oil (or eucalyptus oil) and water in a tank. It is then agitated with air. Froth is formed at the top of the tank. This froth takes the ore particles away with it. The gangue is left behind at the bottom. The froth is then collected, which is the concentrated form of the ore.

  1. Electromagnetic Separation
    Magnetic ores like haematite, chromite, etc., are concentrated by the magnetic separation method.

The powdered ore is allowed to fall on the moving belt of a magnetic separator. The magnetic ore is attracted by the magnetic roller of the separator and falls nearer, while the non-magnetic impurities are thrown away and form a separate heap. In this way, magnetic ores are separated from non-magnetic gangue and become concentrated.

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