Nanobubble column flotation of fine coal particles and associated fundamentals

• Nanobubbles were successfully produced using cavitation tube.
• Nanobubbles were two orders of magnitude smaller than conventional sized bubbles.
• Nanobubbles improved combustible recovery by 5 to 50 absolute percentage points.
• Nanobubbles also reduced reagent and air consumption by one third to half.
• Nanobubble flotation fundamentals were provided.

Froth flotation is a widely used, cost effective particle separation process. However, its high performance is limited to a narrow particle size range between approximately 50 to 600 μm for coal and 10 to 100 μm for minerals. Outside this range, the efficiency of froth flotation decreases significantly, especially for difficult-to-float particles of weak hydrophobicity (e.g., oxidized coal).This study was aimed at enhancing recovery of an Illinois fine coal sample using a specially designed flotation column featuring a hydrodynamic cavitation nanobubble generator. Nanobubbles that are mostly smaller than 1 μm can be formed selectively on hydrophobic coal particles from dissolved air in coal slurry. Results indicate that the combustible recovery of a − 150 μm coal increased by 5–50% in the presence of nanobubbles, depending on process operating conditions. Nanobubbles also significantly improved process separation efficiency. Other major advantages of the nanobubble flotation process include lower frother dosage and air consumption since nanobubbles are produced from air naturally dissolved in water, thereby resulting in considerably lower operating costs.