The Effect of Bubble Size Distribution on the Flotation of Coal Fines

Bubbles serve carriers for mineral particle flotation, and bubble-particle interaction directly affects flotation efficiency. Using flotation tailings from a Guizhou coal preparation plant as feed, a laboratory-scale flotation column with adjustable bubble size was used to study the effects of bubble size and the combination of conventional bubbles and nanobubbles on flotation. The experimental results indicate that bubble size has a substantial impact on the yield and ash content of the clean coal. Smaller bubbles contribute to an increase in clean coal yield, while larger bubbles are more conducive to reducing the ash content. The introduction of nanobubbles into the flotation system further enhances the yield of the coal fines and reduces the consumption of collector and frother. This demonstrates that the combined use of bubbles of different sizes is beneficial for improving clean coal yield and reducing its ash content. For feed with 56.90% ash, a "one roughing-one cleaning" process-using 10 μm bubble generators for roughing and 80 μm for cleaning-produced qualified clean coal with 11.05% ash and 29.84% yield. The combined use of bubble generators with different pore sizes results in a more dispersed bubble size distribution in the flotation system, thereby balancing both the yield and ash content of the concentrate. Measurements reveal that small bubbles correspond to shorter induction time, thus improving bubble-particle adhesion efficiency. This study provides new insights into fine coal flotation via bubble size control, supporting deep coal cleaning and efficient utilization.