The influence mechanism of micron surface roughness on slime coating and bubble attachment on coal surface

Abstract

Surface roughness has significant influence on the hydrophobicity of particle surface and bubble attachment process. To date, there is scarce research concerned the influence of roughness on surface hydrophobicity when the surface is contaminated by slime, which is inevitable in actual process involving heterogeneous suspension. In this work, the influence of micron surface roughness on the slime coating between quartz particles and coal surface was studied. In addition, the bubble attachment process before and after slime coating was also analyzed. The coal surfaces with root mean square (RMS) roughness Ra of 2.50 to 6.02 μm were obtained by polishing a lump coal by sandpaper of different meshes. The slime coating process was observed by an in-situ particle vision and measurement (PVM) probe and quantified by image processing. It was found that slime coating became more severe with the decrease of Ra. The non-contact van der Waals and the elastic contact interaction between quartz particle and coal surface of different roughness was analyzed. It indicates that high roughness could mitigate slime coating due to the larger elastic contact interaction. The attachment of a rising bubble on coal surface immersed in water was observed by a high-speed camera. A reduced contact angle and prolonged contact time was found for coal surface with Ra = 2.50 μm after slime coating. For coal surfaces with Ra ≥ 3.60 μm, the contact angle did not change profoundly, however, the contact time decreased slightly after slime coating, which may be attributed to the filling of the grooves between asperities and the decrease of surface roughness caused by the coating of quartz particles.