A review of simultaneous ultrasound-assisted coal flotation

Ultrasound can be used both simultaneously or as a pretreatment technique for flotation to produce higher combustible recoveries, higher heat values, and lower ash data from raw hard coals. The recent research works have indicated that modifying coal surfaces, especially physical surface cleaning with the help of the cavitation process created by power ultrasound at certain frequency and time intervals, might cause significant changes in flotation responses by a thorough adsorption of reagents on coal surfaces. When power ultrasound is applied to a coal slurry that makes the bubbles to collapse near a coal surface, a high-speed jet of liquid is driven into the particles, and this jet may deposit enormous energy densities at the site of impact. The simultaneous ultrasonic treatment also causes significant changes in local temperatures and pressures within the slurry containing coal and a certain number of reagents at variable dosages during flotation. This treatment improves the effectiveness of reagent molecules at coal surfaces and interfaces due to their more uniform distribution in the pulp and also enhancement of the activity of the reagents used. This paper reviews the results of the recent studies and the possible mechanism of simultaneous ultrasound-assisted coal flotation.