Aggregates Characterizations of the Ultra-Fine Coal Particles Induced by Nanobubbles

Particle aggregates induced by nanobubble (NB) bridging has been recognized as one of the main contributors to improve the flotation performance of minerals in NBs-associated flotation. Despite the numerous investigations in particle-NB interaction, scarce research on revealing the properties of aggregates induced by NBs has been conducted, severally limiting the further understanding of the NB-assisted mineral flotation. In this study, NBs were first produced based on the principle of hydrodynamic cavitation. The aggregates of ultra-fine coal particles with different hydrophobicity induced by these tiny bubbles was investigated, with the size distribution, structure, and strength features of the aggregates systematically explained accordingly. In this study, NBs remained stable in the aqueous solution for more than one hour, and the size of these bubbles expanded from 240 to 650 nm within this period. The aggregates of coal particles was significantly enhanced, especially for the more hydrophobic ones, which could be well reflected by the right-shifted particle-size distribution curve, the newly formed chain-structure aggregates, and larger apparent viscosity and shear yield stress of the coal pulp. Moreover, the flotation performance (both flotation recovery and flotation kinetics) of ultra-fine coal particles was remarkedly improved in the presence of NBs, confirming that NBs did benefit the ultra-fine coal aggregates.