Slime coating, defined as a layer of fine or ultrafine hydrophilic particles coated on the larger value mineral surface, has been recognized to have an important effect on froth flotation. These slimes on the mineral surface prevent value mineral particles from contacting with collectors and/or air bubbles, consequently resulting in a lower flotation recovery. It is demonstrated that the high intensity conditioning is an effective way to improve flotation performance. However, the relative significance of its mechanisms on high intensity conditioning still needs to be explored, especially the surface cleaning. In this work, the role of surface cleaning in high intensity conditioning was investigated by carrying out a series of tests including conditioning-flotation, microscope visualization, laser particle size analysis and Focused Beam Reflectance Measurement. The combustible matter recovery is employed to evaluate the flotation performance. The results show that the high intensity conditioning greatly improves the hydrophobicity of coal surface by producing a complete clean surface and consequently enhances the adhesion between coal and collector, which results in a significant increase of the combustible matter recovery no matter with or without the collector. It is also found that surface cleaning is an important factor in the reduction of the reagent consumption. In addition, it is noted that surface cleaning is the internal driving force for the significantly increased recovery of the coarse coal particles. Based on the findings in this work, a prospective high intensity conditioning-flotation process is presented. (C) 2017 Elsevier B.V. All rights reserved.