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A stable attachment between bubbles and solid particles is essential for flotation. Therefore, it is particularly necessary to study the dynamic process that occur in the attachment of bubbles to a solid surface. In this paper, Teflon and plexiglass plates were used as hydrophobic and hydrophilic solid surfaces, respectively, and solid surfaces with roughness of 0.018 μm to 5.33 μm were prepared by polishing with sandpaper. The influence of roughness on the dynamic process in bubble attachment to solid surfaces with different hydrophobicity was studied via a high-speed camera (750 frames per second). It was found that roughness played a positive role in the attachment to the hydrophobic Teflon surface while a negative role in the attachment to the hydrophilic plexiglass surface in terms of the bubble's attachment to the solid plates. For a smooth Teflon surface, the formation of three–phase contact (i.e., the drainage of wetting film) took up to 95 ms, whereas for a very rough Teflon surface it took only 5 milliseconds. On the contrary, the high roughness prevented the bubble from attaching to the hydrophilic plexiglass surface. It was concluded that the increased roughness of Teflon plates was conductive to air entrapment in surface irregularities, inducing the rapid rupture of the wetting film on a very rough Teflon surface, while the increased roughness of the plexiglass plates resulted in "water pockets" in surface grooves, making the wetting film on the plexiglass surface stable. [ABSTRACT FROM AUTHOR]

The comprehensive quality enhancement and grading of coal are crucial methods for unlocking the high value-added and low-carbon utilization of coal resources. In this work, the influence of oily bubbles on the flotation of Shendong Jurassic vitrinite-rich coal and inertinite-rich coal was studied via flotation tests, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle detection, and induction time measurements. FT-IR and XPS analyses demonstrated that the surface of inertinite-rich coal contains more hydrophilic oxygen-containing functional groups. Contact angle and induction time measurements showed that the vitrinite-rich coal is more hydrophobic than inertinite-rich coal, and that for both air and oily bubbles, the induction time on the surface of vitrinite-rich coal is shorter than that on the surface of inertinite-rich coal. In addition, rather remarkably, the induction times for both vitrinite-rich coal and inertinite-rich coal are significantly reduced by oily bubbles. Finally, a better flotation performance for oily bubble flotation of vitrinite-rich coal and inertinite-rich coal was found. It appears that oily bubble flotation is an efficient method for enhancing the recovery of vitrinite-rich coal and inertinite-rich coal. [ABSTRACT FROM AUTHOR]

The mechanism of high-intensity conditioning (HIC) has not been thoroughly revealed, and therefore this work investigates the effect of HIC on the surface hydrophobicity of coal with different particle sizes and the possible formation of particle–bubble clusters. The results show that different HIC conditions are required for coarse and fine particles. Coarse particles (+75 μm) require a higher turbulence intensity to increase collector dispersion, thereby increasing the adsorption of the collector. Fine particles (−75 μm) require a lower turbulence intensity to reduce the desorption of the collector. In this study, the optimum HIC conditions for coarse and fine particles are "2200 rpm + 1 min" and "1300 rpm + 1 min", respectively. Interestingly, it seems that the adsorption capacity between fine particles and the collector is weaker than that for coarse particles. A non-enclosed HIC system produces up to 1.78 × 104/g bubbles in coarse particle–bubble clusters, and the mean bubble diameter is approximately 87 μm. The cluster achieves pre-mineralization and increases the apparent particle size, which is expected to improve flotation. [ABSTRACT FROM AUTHOR]