Explain the froth flotation method of concentration of ores with a labelled diagram. For which type of ores is it used ?

Answer: Froth flotation is used to concentrate sulphide ores (e.g. zinc blende, ZnS); it works because ore particles are wetted by oil and gangue particles are wetted by water.

Diagram to draw and label: a large tank containing water; a rotating stirrer (agitator) at the centre; a pipe that blows compressed air into the mixture; a layer of froth at the top carrying ore particles, with the froth overflowing into a side channel; gangue (soil, sand) settled at the bottom of the tank.

1. The finely powdered ore is put in a large tank with water and a little pine oil (or eucalyptus oil).
2. Compressed air is blown through the mixture and it is stirred. Froth (foam) is formed.
3. The particles of the sulphide ore get wetted by the oil and rise with the froth to the surface; the froth is removed and dried to obtain the concentrated ore.
4. The gangue particles get wetted by water, become heavy and settle at the bottom of the tank.