Photographic observations showing spreading and non-spreading of oil on gas bubbles of relevance to gas flotation for oily wastewater cleanup

Gas flotation is widely used for oily wastewater cleanup. The crux for flotation is the adhesion of the gas bubble to the oil drop. A spreading stage of oil onto the gas is vital for efficient bubble–oil rise. Thus spreading and non-spreading oils will present different fluid configurations and stabilities for bubble rise and a positive oil on a water–gas interface spreading coefficient is needed for spreading to occur. This paper provides photographic evidence of the spreading of the oil around the gas bubble. The importance of a positive spreading coefficient of the oil around the gas bubble for gas flotation is clear.