Why do zinc sulfide particles attach to air bubbles during flotation?

In the process of flotation, zinc sulfide particles attach to air bubbles because their surfaces are chemically altered to become hydrophobic, or water-repellent.1

During the concentration process, the ore is ground into a fine slurry and mixed with specific chemical reagents, such as oils or other collectors. These chemicals adsorb onto the surface of the zinc sulfide particles, preventing them from being wetted by water. Because the particles remain unwetted, they readily adhere to the air bubbles introduced into the flotation cell. These clinging bubbles decrease the effective density of the mineral particles, allowing them to rise to the surface and form an oily froth that can be skimmed off, effectively separating the valuable zinc minerals from the unwanted gangue, which remains wetted and sinks.2314