Describe the method of froth flotation used for concentrating sulphide ores.

Froth flotation is a metallurgical process used for concentrating sulphide ores. The finely powdered ore is mixed with water, a frothing agent (like pine oil), and a collector (like potassium ethyl xanthate). 

Air is then blown into the mixture through a rotating paddle. The frothing agent creates a stable froth, and the collector selectively adheres to the sulphide ore particles, making them water-repellent (hydrophobic) and oil-attracting.

These oil-coated ore particles become lighter and rise with the froth to the surface, which is then skimmed off. The gangue (impurities) particles, being hydrophilic, settle down at the bottom.