Effects of 20 kHz ultrasound on coal flotation: The roles of cavitation and acoustic radiation force

Abstract

Cavitation and acoustic radiation force are two main effects of ultrasound. In this study, ultrasonic pretreatment (UPT) and simultaneous treatment (UST) methods were applied to coal flotation. The ultrasonic effects were analyzed by measuring changes in ash content and yield of concentrate with or without ultrasound treatment. The decrease in ash content after UPT or UST was due to the cleaning effect of ultrasound. This effect is generated by the collapse of tiny bubbles trapped on the rough coal surfaces, as seen in images obtained by scanning electron microscopy (SEM). An improvement in recovery was only seen with the UST method. Properties of large bubbles, specifically their aggregation and shape, were influenced by ultrasound through the oscillation behavior and acoustic radiation force in the sound field, respectively. This work is expected to provide a novel perspective to the study of ultrasound-assisted flotation.