Surface modification for low-rank coal with poor hydrophobicity is critical to its efficient flotation. In the present study, induction time and flotation results were employed to evaluate the coal sample's flotability in the pickling process, while the changes in coal surface properties were comprehensively investigated by various surface analysis technologies. The results suggested that the induction time between coal particles and bubbles decreased from 115 ms to 13 ms with increases in the concentration of hydrochloric acid, and the combustible matter recovery correspondingly exhibited an evident increase from 31.98 to 59.22%. Additionally, after pickling, a significant increase in the liberation of gangue minerals from coal particles was observed by XRD and SEM measurements. Furthermore, the XPS results indicated that the hydrophilic oxygen-containing functional groups of coal sample decreased after the pickling process. Consequently, the enhanced flotation performance could be attributed to the changes in surface chemical functional groups and increased liberation of gangue minerals from coal particles in the pickling process. (C) 2019 Elsevier B.V. All rights reserved.