This study was conducted to investigate the mechanisms of enhanced microfine flake graphite (MFG) flotation by nanobubbles generated based on the principle of hydrodynamic cavitation. The effects of nanobubbles on graphite surface properties were characterized in terms of the flotation kinetics, collector adsorption behavior, Zeta potential, IR spectra, contact angle, etc. The results show that the surface nanobubbles increased the hydrophobic attraction and reduced the electrostatic repulsion between the graphite particles and collector molecules, significantly improving the flotation selectivity and the kinetic flotation rate and promoting the agglomeration of MFG.

Effects of nanobubbles on fine coal column flotation and underlying mechanisms have been investigated under different operating parameters including frother dosage, collector dosage, feed flow rate, air flow rate and wash water flow rate with a Chinese sub-bituminous coal sample. Experimental results show that the use of nanobubbles significantly improved the column flotation efficiency with fine coal particles. The collector dosage was reduced by almost one half in the presence of nanobubbles as a result of nanobubbles playing a role as a secondary collector and a similar reduction in the frother dosage was observed due to distinctly different mechanisms of nanobubble generation as compared to traditional bubble formation methods. Nanobubbles generated based on the hydrodynamic cavitation mechanism also reduced required air dosage and improved carrying capacity. The aggregation effect of fine coal particles caused by the preferential formation of nanobubbles on the surface of hydrophobic coal particles in the flotation system improves the rate of mineralization of bubbles. The flotation efficiency enhancement by nanobubbles is a result of multiple benefits to flotation processes brought by nanobubbles that form directly on the surface of coal particles.