A fundamental study of flotation separation of mineral particles using ultrasound-induced bubbles

This paper describes the flotation separation of naturally hydrophobic coal particles and hydrophilic quartz particles in water (free of any reagents) using ultrasound-induced bubbles only, without any additional air supply. A laboratory-scale flow tubing system with an ultrasound transducer was designed and used. The experiments were conducted for coking coal, quartz and their mixture, respectively, over a broad range of particle size. Results showed that using ultrasound with a relatively high energy input, acoustic cavitation occurred in water and on the surface of coal particles, and different behaviours of coal particles and quartz particles under this condition were observed: coal particles formed larger aggregates and most of them were trapped in the slurry or floated to the surface of the slurry, while quartz particles had very slight aggregation and settled down. This difference enabled good separation of coal particles from quartz particles, with high combustible recoveries and product grade over a broad particle size range tested (including 250–500 µm for coal particles). When the energy input of ultrasound was relatively low, however, no cavitation bubbles were visible, with slight aggregation and trapping of coal and quartz being observed and explained by the acoustic radiation force.