Explain the concentration of ore by Magnetic Separation.

(N/A) Principle: This method is based on the difference in magnetic properties of the ore components (ore or gangue).
Procedure: The powdered ore is dropped over a conveyor belt which moves over a magnetic roller.
Mechanism: If either the ore or the gangue particles are magnetic,they are attracted towards the magnetic roller and fall closer to it,while the non-magnetic particles fall further away,forming a separate heap.
Example: This method is used for the concentration of iron ores like magnetite $(Fe_3O_4)$ and hematite $(Fe_2O_3)$.