Investigation into sliding behavior of bubbles on a hydrophilic surface containing discretely distributed hydrophobic patches

Flotation of coarse particles with poor mineral liberation, aiming at gangue rejection at early stage, has attracted great attentions. Bubble detaching probability ultimately determines the coarse particle separation efficiency. To date, the bubble detaching behavior from the surface of coarse particles with poor liberation remains unclear. In this study, three sizes of bubbles (650 μm, 900 μm and 1200 μm) were generated to comparatively study their sliding behavior on a hydrophilic quartz substrate containing discretely distributed hydrophobic dots with a diameter of 100 µm and an edge distance of 400 µm. It was found that bubbles experienced stretching phase and sliding phase during the process. The initial three-phase contact line before sliding increased over the bubble size, resulting in greater force required to initialize bubble sliding. During the sliding process, the three-phase contact line remained the same for the bubble of 650 μm, while it exhibited a stepwise increase for the bubbles of 900 μm and 1200 μm, indicating that the sliding could stabilize bubble attachment to some extent for larger bubbles by strengthen the adhering force. Further study showed that the enhanced bubble attaching stability was only valid with the Reynolds number below 6222. The finding indicates that bigger bubbles may be able to benefit coarse particle flotation in a tranquil flow by providing stronger lifting force for particle ascending. It is believed that the outcomes of this study could facilitate the optimization of coarse particle flotation.