Influence of oil film on the interaction between bubble and bubble/lignite particle

The floatability of low-rank coal is poor because of its low metamorphosis, and the oily bubble flotation is an effective means to collect coal particles. In this paper, adhesion angles and forces between watery/oily bubbles and coal surfaces were measured to analyze the influence of oil film on adhesion behavior between bubble and particle. The properties of watery/oily bubbles were analyzed by dynamic foam analyzer (DFA) to reveal the influence of oil film on the bubbles further. The results showed that in the dynamic environment, the maximum adhesion angle of the oily bubble was 36.55 degrees, while the angle of the watery bubble was 31.29 degrees, and the adhesion kinetic constant for oily bubble-particle and watery bubble-particle were 0.0295 and 0.0174, respectively. The measured maximum adhesion forces of the watery bubble and oily bubble were 19.2 mu N and 86.8 mu N, respectively, indicating that oily bubbles were more prone to attach to the coal surface and were beneficial to flotation. The calculated normalized contact line indicated that the oil film could squeeze a lot of water out from the coal surface, increasing the actual contact area and strengthening the attachment. The results of DFA showed that with the oil film, the oily bubbles could be more stable with a smaller size and lower liquid content than the watery bubbles. The results of the above study show that the oil film covering the watery bubble could improve the adhesion between bubble and particle and reduce the bubble size, which is conducive to promoting the sorting efficiency and thus enhancing the flotation of lignite.