Break-up in formation of small bubbles: Comparison between low and high frother concentrations

Abstract

Frothers are widely used in flotation to help generate small bubbles, with coalescence prevention generally considered the predominant mechanism. However, recent studies have demonstrated that the presence of frothers also reduces the size of bubbles at the initial formation stage. One possible explanation is that frothers introduce a surface tension gradient-driven stress, which increases instabilities along the air/water interface: increasing the number of instabilities along the surface of a finite-volume air mass means that more small bubbles will break away. The magnitude of surface tension gradient, and thus number of instabilities, is related to frother concentration. This paper investigates the effect of increasing frother concentration on the size of bubble formed. The hypothesis tested is that while low concentration may sustain gradients, at high concentration mass transfer may be sufficient to damp them. The finding is that with an increase in frother concentration the bubble size initially decreased to a minimum then increased supporting the hypothesis.