Experimental study on floc-bubble interaction in the flotation of drilling wastewater at the micro-scale

Abstract

Flotation is an effective solid–liquid separation technique, in which floc-bubble interactions are crucial in determining separation efficiency. This study used polyaluminum silicate ferric (PSAF) to coagulate suspended solids (SS) in drilling wastewater, agglomerating them into flocs. The interactions between bubbles and flocs of varying sizes were observed at the micro-scale using a custom-designed system. The effects of floc size on induction time, bubble relative velocity and floc-bubble interaction force were analyzed. The results indicate that small-size flocs (=50 μm) contribute to the stabilization of the liquid film while sliding along the bubble surface. In contrast, large-size flocs (=170 μm), due to their higher settling velocities, undergo multiple ‘approach-bounce’ cycles, which significantly reduce the contact time with bubbles and impair the adhesion efficiency. As floc size increases, the induction time is markedly extended. Bubbles maintain relatively stable sliding velocities on small-size flocs, while larger flocs induce pronounced velocity fluctuations, thereby heightening the separation instability. The interaction force between the floc and the bubble increases as the deformation of the floc intensifies but subsequently decreases due to the gravity of the floc.