Ultrasonic-assisted flotation of fine coal: A review

Abstract

This review is to highlight the application of ultrasound in cavitation bubbles, reagent emulsification, coal slime pretreatment and simultaneous ultrasonic flotation. Ultrasonic cavitation is considered as the most predominant phenomena to improve flotation performance of fine coal. The cavitation can disperse reagents to form uniform and steady emulsion in coal slurry, which results in the reduction of reagents dosage and therefore, their consumption. The mechanical effects produced by ultrasonic cavitation remove the clay and oxide layer from the coal surface to restore the hydrophobic surface of coal particles, resulting in an increase in flotation selectivity. The chemical effect caused by ultrasound can be usually utilized to improve desulfurization performance in coal flotation. However, prolonged ultrasonic treatment re-oxidizes the coal surface, resulting in a decrease in floatability of coal fines and an increase of desulfurization rate. In addition, the use of simultaneous ultrasound in coal flotation process produces a large number of cavitation micro-bubbles in the pulp, which can further stabilize the froth layer and improve flotation efficiency. This critical review will provide some guidance for more efficient use of ultrasonic technology in flotation of fine coal.