Concentration of an ore is the process of removal of impurities from the ore.This process is based on the difference in the physical or chemical properties between the ore and gangue particles.
Physical Methods of Concentration
Hydraulic Washing (Hydraulic Classifier)
When the ore particles are poured over a vibrating sloped table with grooves and a jet of water is allowed to flow over it, the denser ore particles settle in the grooves while the lighter gangue particles are washed away.
Difference in the densities of the ore and gangue particles.
Concentration of heavy oxide ores of lead, tin, iron etc.
Powdered ore is spread over a sloping wooden platform which vibrates continuously.Small wedge shaped obstacles are fixed on the platform. A strong jet of water is passed over the platform. Lighter gangue particles are washed away while the heavier ore particles are left behind.
Difference in the wetting properties of the ore and gangue particles.
Sulphide ores only.
- A mixture of water, pine oil, detergent and powdered ore is taken in a tank
- A blast of compressed air is blown through the pipe of a rotating agitator to produce froth
- Sulphide ore particles wetted and coated by pine oil rise up along with the froth (froth being lighter)
- Gangue particles wetted by water sink to the bottom of the tank (water being heavier)
- Froth containing the sulphide ore is transferred to another container, washed, and dried.
Note : Sulphide being more electronegative attracts the covalent oil molecules. The gangue being less electronegative is attracted by the water.
Difference in the magnetic properties of the ore and gangue particles.
Magnetic ores like pyrolusite (MnO2) and chromite (FeO.Cr2O3)
- Powdered ore is dropped over a conveyor belt running over two rollers, one of which is magnetic.
- The magnetic ore particles get attracted to the magnetic roller and run along with the conveyor belt for a little longer than the non magnetic gangue.
- Gangue particles drop down first forming a heap.
- Then, the magnetic ore particles drop down forming a separate heap.
- Thus, two separate heaps of ore and gangue particles are formed.