Investigation of adhesion behavior between reactive oily bubble and low-rank coal

Abstract

Reactive oily bubble, defined as air bubble covered with a thin layer of diesel oil containing surfactants, was used in low-rank coal flotation. Both the cationic surfactant dodecyl amine (DDA) and the anionic surfactant palmitic acid (HPa) were used to generate the reactive oily bubble. The strengthening mechanism of the reactive oily bubble was investigated by a series of flotation tests and the adhesion force measurements. The results showed that at low concentrations (0.5, 2.5, and 5.0 mM), the effect of the reactive oily bubble with DDA to enhance adhesion and promote separation was not significant. When the concentration of DDA increased to 50 mM, the coalescence of bubbles deteriorated separation. In addition, the competitive adsorption between oil and DDA (reverse orientation) reduced the hydrophobicity of the coal surface and weakened the adhesion force between the bubble and coal surface. While for HPa, the synergistic adsorption between HPa and diesel oil played an important role in promoting separation and the concentration of HPa in the oily bubble and the flotation efficiency was positively correlated. The values of normalized contact line (x) could be used to represent the expansion of the three-phase contact line which indicated that the reactive bubble containing HPa could squeeze more water out from grooves of coal surface than that of bubble containing DDA. These findings suggest that using the reactive oily bubble is conducive to promoting the separation efficiency only when proper concentration and type surfactant is used to generate the reactive oily bubble.