Effect of nanobubbles (NBs) on the decarbonization behavior of fly ash flotation

Based on the flotation kinetics of nanobubbles (NBs) on fly ash in this study, a systematic investigation was conducted to explore the mechanism of the enhanced flotation and decarbonization of fine-grained fly ash by NBs by particle size analysis, Zeta potential testing, contact angle testing and foam stability testing. Flotation kinetics studies show that the decarbonization rate of NBs flotation is significantly higher than that of conventional flotation, the loss on ignition (LOI) and unburned carbon removal rate (UCRR) are 0.62 and 1.09 percentage points higher than those of conventional flotation, respectively. Particle size analysis indicates that the presence of NBs effectively agglomerates unburned carbon particles based on the capillary bridging effect between NBs, increasing the average particle size of the pulp by 33.8 μm to enhance the flotation probability of bubbles-unburned carbon and reduce the lower limit of unburned carbon recovery particle size from 0.9 μm to 0.3 μm. More importantly, the presence of NBs effectively enhances the particle size recovery (PSR) of ultrafine particles smaller than 10 μm. Mechanism studies shows that NBs not only cause a significant positive shift in the Zeta potential on urburned carbon surface, but also work in synergy with collectors to amplify the hydrophobicity of urburned carbon surface. In addition, NBs significantly reduce the pulp surface tension and the drainage rate, meanwhile greatly extend the bubble half-life, enhancing the stability and load-bearing capacity of the foam layer. This study confirmed the advantages of NBs in reducing the lower limit of fine particle flotation and enhancing the recovery of unburned carbon to prove a theoretical basis for the efficient decarbonization and resource utilization of fly ash.