Advance of the research on the technologies for intensification of nanobubble flotation process

Froth flotation process is a effective means for separation and upgrading of low-grade ore and low-rank coal. However, the process faces challenging problems in separation of micro-fine materials. Nanobubble flotation process proves to be an important approach for tackling the bottleneck. Nevertheless, numerous fundamental and scientific issues regarding intensification of this process still remain unresolved. With an aim to promote the development of the said process intensification technologies, a study is made in the paper with emphasis centered on the following three aspects: selective nucleation kinetics of interfacial nanobubbles, mechanism of exceptionally long-time stability of interficial nanobubbles, and the micro-mechanical mechanism of nanobubble-enhanced particle - bubble capture efficiency. Meanwhile, an introduction is made to the latest achievements of the work on enhancement of nanobubble flotation process obtained by the co-workers. As revealed by study results, selective nucleation of nanobubbles is a crucial factor contributing to process intensification while the stability of nanobubbles serves in this case as a prerequisite for effecting the intensification process; the mechanism of the process intensification lies in mainly promotion of formation of flocs of particles and cutting of induction time while the intrinsic mechanism of action comes into effect due to synergistic effect of long-range hydrophobic attraction force and boundary slip of nanobubbles. Though the study, the energy mechanism of selective nucleation of nanobubbles at the solid-liquid interface is brought to light; the stability mechanism of nanobubbles based on automatic compensation of high-density gas layers at the solid-liquid interface is proposed; and the mechanism that the action of interface in enhancing nanobubble flotation process is boosted by micronano mechanics - boundary slip combined effect is defined. The work made in the paper further enriches and develops the up-to-date basic theory of flotation process and provides a certain guidance for the development of the technology for effecting enhancement of nanobubble flotation process in separation of micro-fine particles.