Insight into the influence of surface wettability on flotation properties of solid particles - Critical contact angle in flotation

Bubble-particle attachment is a fundamental element of the flotation process, and its occurrence depends on the stability of the thin liquid film separating these objects. In this study, the effect of surface wettability on the stability of liquid film and subsequent attachment was investigated by flotation of glass microspheres (70-110 mu m) with controlled contact angles (9-89 degrees) in a Hallimond tube. Additionally, pH was varied to determine the electrostatic interactions between the bubble and particles. The results showed that for the flotation process to take place, the minimum (critical) value of the contact angle must be exceeded. This value was found to be ca. 25 degrees when the electrostatic interactions were either attractive or weakly repulsive and as high as 62 degrees for strong repulsive electrostatic interactions. These findings highlight the role of attractive hydrophobic interactions, whose importance increases with increasing surface contact angle in the context of stability of thin liquid films.