Influence of Air Solubility on the Flotation Performance of Low-Rank Coal

Low-rank coal (LRC) contains large amounts of harmful impurities that must be processed before utilization. Flotation is an effective means for separating fine particles, which can be influenced by air solubility in water. In this work, deaerated water (DW), ordinary water (OW), and pressurized water (PW) were prepared to research the underlying mechanism of the effect of air solubility on the flotation performance of LRC. The results show that PW dissolves the greatest amount of air in the three kinds of water (DW, OW, and PW). The flotation performance of LRC in different water types is directly proportional to air solubility in aqueous solutions. In addition, the induction time of LRC in PW (600 ms) is significantly shorter than those in OW (1200 ms) and DW (4000 ms). Atomic force microscopy (AFM) studies reveal that typical interfacial nanobubbles (NBs) only form on a highly oriented pyrolytic graphite (HOPG) surface in PW due to the supersaturated air in water. Furthermore, the interaction between LRC particles and HOPG in PW is significantly stronger than those in both OW and DW, which is attributed to the capillary force of rgw nanobubble bridge formed between particles. The hydrophobic interaction enhanced by NBs is critically important for the attachment of LRC particles to macrobubbles in flotation. Overall, air solubility in water has a great effect on LRC flotation performance, and PW flotation technology can be extended to LRC purification.