Ions Inhibiting/Promoting the Adhesion Between Coals and Bubbles: The Effect of Ions on Hydrophobic Attraction and Electrical Repulsion

ABSTRACT Understanding the mechanism of adhesion between bubbles and particles in saline water is crucial for engineering techniques. In this work, the hydrocarbon film was selected as the coal model to investigate the adhesion mechanism between bubble and coal with AFM bubble probe in different solutions. With the increased concentration (0, 1, 100 mM) of NaCl, the decay length of hydrophobic interaction between the bubble and coal surface decreased. For the highly hydrophobic surface, it decreased from 5.39 ± 0.09 to 2.63 ± 0.09 and 0.86 ± 0.06 nm, and for the weakly hydrophobic surface, it decreased from 3.02 ± 0.07 to 2.49 ± 0.07 and 0.68 ± 0.05 nm. The critical/minimum thickness of the wetting film between the coal and bubble also decreased with increased concentration of NaCl because of the compression of the electrical double layer (EDL). Referring to the AFM images in different solutions, it indicated that the hydrophobic force (long‐range) of the coal surface might be caused by in‐plane dipole moments generated by the tilted configuration of hydrocarbon chains so that it was sensitive to the concentration of electrolytes. Our results provide insights into the effect mechanism of electrolytes on adhesion behavior between bubble and particle.