Experimental research on the interaction behavior between particle and bubble in flotation on a micro⁃nano scale

A full understanding of the interaction process between particles and bubbles is helpful to guide the selection of surfactants and the regulation of gas⁃liquid⁃solid three⁃phase interface in practical flotation. In this paper，hydrophilic/ hydrophobic particles and solid substrates were prepared by surface modification，and the interac⁃ tion between bubbles and particles was studied by some advanced means on a micro⁃nano scale. The results show that the coating angle of hydrophilic particles is only 28.38°，but that of hydrophobic particles can reach to 168.55° at 900 s，indicating that the floatability of particles increase with the improvement of hydrophobicity. In terms of the relative motion，the center distance between the hydrophilic particle and the bubble remains unchanged dur⁃ ing the sliding process of the hydrophilic particle on the bubble surface. In contrary， the hydrophobic particles suddenly " jump in" the bubble surface during the sliding process，the liquid film between the particle and the bubble becomes thin and ruptured at this time. The thickness of the rupture liquid film is about 0.01 mm. In terms of interaction force，the adhesion force is not found between the bubble and the hydrophilic surface，which is dominated by re⁃ pulsion. The obvious “jump-in” attachment force between the bubble and the hydrophobic surface is up to 45.80 μN， and the liquid film is thinning during approaching and breaks suddenly at the moment of contact，the thickness of the rupture liquid film is about 0.02 mm (~15.16 μm). AFM results show that the thickness of liquid film between hy⁃ drophobic particle and micro bubble is 114.34 nm，which is 2 orders of magnitude less than that between particles and millimeter bubbles. It indicates that the thickness of rupture liquid film is related to the size of bubble when parti⁃ cles adhere to bubbles.