In this paper, a novel flotation technique that combines nano-scale bubbles generated by hydrodynamic cavitation (HC) and carrier flotation is proposed to promote the flotation efficiency of a high-ash (43%) ultra-fine coal sample (<45 µm). We investigated the mechanism by which cavitation bubbles enhance the separation efficiency of carrier flotation using focused beam reflectance measurements, polarizing microscopy, and extended Derjaguin-Landau-Verwey-Overbeek theory. The carrier particles (polystyrene (PS)) and fine coal were pre-treated in a venturi tube and then floated in a laboratory mechanical flotation cell. The flotation results indicate that the presence of cavitation bubbles significantly improved the carrier flotation performance of high-ash ultra-fine coal. This improvement was attributed to the presence of highly hydrophobic PS, which creates additional gas nuclei in the flotation system. The nano-bubbles, which were produced by the venturi tube and adhered to the fine coal particle surfaces, were conducive to the agglomeration of fine coal particles into large aggregates. Moreover, the nano-bubbles functioned as "bridges" of interaction between the carrier particles and large aggregates of fine coal particles. This paper mainly focused on the effect of carrier (PS) and HC on high-ash fine coal. The influence of different HC intensities on carrier (PS) flotation was discussed. Two models for the interactions between the coal particles, nano-bubbles, and PS during cavitation were proposed and were proved using the E-DLVO theory.

• Bulk micro-nanobubble solutions were prepared using a fine-bubble generator under different preparation times and aeration rates. • The dissolved oxygen contents of bulk micro-nanobubble water under different conditions were evaluated. • The bubble concentrations and sizes in bulk micro-nanobubble water under different conditions were evaluated. • The relationship between the dissolved oxygen concentration and the cavitation behaviors of bubbles was discussed.

• Homogenization, sonication, and their combination were assessed for preparing Pickering emulsions. • Optical microscopic images and chord length of emulsion droplets were evaluated. • Rotor-stator homogenizer had essential effects on emulsions when a chord length was greater than 20 μm. • Sonication method could disperse micro-scale aggregates of the nano-silica effectively. • Ultrasonic treatment was found superior over the rotor-stator homogenizer in reducing droplet size.