Composite impeller system delivering high local shear and bulk circulation for pulp conditioning of high-ash fine coal

High-ash fine coal flotation is critically limited by the persistent adhesion of ultrafine clay minerals to particle surfaces, which reduces hydrophobicity and impairs bubble–particle interactions. Conventional pulp conditioning with uniform shear fields fails to simultaneously achieve effective localized high-shear surface cleaning and global slurry circulation, particularly in such complex systems. In this study, a multi-stage conditioning strategy featuring a coupled shear–mixing flow field was developed, integrating serrated shear discs for localized surface cleaning with parabolic blade turbines for controlled axial mixing. Numerical simulations and experimental analyses demonstrate that this engineered flow field generates hierarchical turbulence, enabling microscale shear-driven clay detachment while sustaining bulk slurry circulation for enhanced reagent dispersion and particle suspension. The results show that significant improvements in slurry rheology and particle surface hydrophobicity were achieved, as evidenced by increased shear stress and enhanced bubble-particle attachment dynamics. The optimized conditioning process markedly improved flotation performance, promoting selective recovery across both coarse and fine particle fractions. This work provides new mechanistic insights into the design of advanced shearmixing conditioning strategies and offers a promising pathway for process intensification in fine coal flotation.