Research on the role of nanobubbles in coal slime flotation

To address the technical challenge of efficiently separating fine, difficult-to-wash coal slime using traditional flotation methods, a study was conducted using coal slime from the Guandi Coal Preparation Plant as the sample. A self-developed nanobubble flotation system was employed to investigate the stability of hydrodynamic cavitation-generated nanobubbles and their impact on flotation performance, while also analyzing the mechanism by which nanobubbles enhance fine particle separation. The results indicate that after more than 5 minutes of cavitation treatment, nanobubble size stabilized within the range of 175～225 nm, maintaining high stability even after one hour of standing. In the presence of nanobubbles, a frother dosage of 0.3 kg/t achieved a combustible recovery rate of 91%, representing a 25% reduction in frother consumption compared to conditions without nanobubbles. When the aeration rate ranged from 0.4 cm/s to 1.6 cm/s, the combustible recovery rate in the nanobubble-containing slurry system remained around 90%. However, the ash content of the product increased with higher aeration rates, attributed to nanobubbles enhancing the hydrophobicity of coal particles while simultaneously increasing the probability of attachment of less hydrophobic mineral particles. Nanobubbles exhibit excellent stability and significantly enhance coal slime flotation through multiple mechanisms, including promoting the aggregation of fine particles, capillary bridging, and destabilizing liquid films. This provides a new pathway for the efficient separation of fine-grained coal.