Generally, for which of the following ores, froth floatation method is used for concentration?
Froth floatation is mainly used for sulphide ores. But it can be applied for non-sulphide ores as well! The process takes advantage of the difference in the wetting properties of the ore and the gangue particles.
Here, only cinnabar is a sulphide ore.
Sulphide ore particles are wetted by oil.
Gangue particles are wetted by water.
Thus froth carries the ore particles (to the top) where it can be skimmed away from gangue.