Enhanced fine coal column flotation using cavitation concept

Flotation tests with a difficult-to-float coal sample have been performed using a 5-cm in diameter flotation column to demonstrate the effectiveness of cavitation nanobubbles. Nanobubbles are characterized by an inherently high probability of collision with particles, a high probability of attachment, and a low probability of detachment, etc. Major flotation process parameters were examined individually to investigate their effects on flotation recovery and concentrate grade. The results show that the median diameter of nanobubbles produced by hydrodynamic cavitation was about 300 and 800 nm in the presence of 100 and 10 ppm MIBC, respectively. Use of nanobubbles significantly increased flotation recovery and separation efficiency under various conditions. For example, at 0.5 cm/s air velocity, the recovery was almost 30% higher in the presence of nanobubbles. The use of nanobubbles increased recovery by about 25-40% at different collector dosages. The separation performance curve suggests that the combustible recovery was 12-21% higher at different product ash values when nanobubbles were employed. A 28-32% increase in combustible recovery was produced at different frother dosages. Flotation product size analysis shows that nanobubbles were most effective in improving the flotation performance of ultrafine (< 0.08 mm) and relatively coarse particles (>0.4 or 0.5 mm).