Effects of simultaneous ultrasonic treatment on the separation selectivity and flotation kinetics of high-ash lignite

Abstract

The purpose of this study was to investigate the effects of conventional flotation and simultaneous ultrasonic flotation in the pulp/froth zones on the separation selectivity and kinetics of high-ash lignite flotation. Particularly, the mechanism of ultrasonic flotation in the froth zone, which improved the flotation performance of lignite, was elucidated. Flotation tests, wet screening, SEM, and froth layer observation tests were employed to reveal the mechanism by which simultaneous ultrasonic flotation improved lignite flotation. The flotation results indicated that the lowest concentrate ash content was obtained using ultrasonic flotation in the pulp zone, while the highest concentrate yield and water recovery were achieved using ultrasonic flotation in the froth zone. The wet screening and SEM results indicated that ultrasonic flotation in the pulp zone afforded the best surface cleaning on the coal surface, which significantly improved the flotation selectivity of lignite. Ultrasonic treatment in the froth zone produced large bubbles and a thin froth layer due to ultrasonic cavitation and oscillation, thereby improving the recovery of fine particles by water entrainment. However, simultaneous ultrasonic treatment in the froth zone did not improve the separation selectivity of lignite flotation. In addition, the second-order model with rectangular distribution of floatability provided the best fit with the experimental data of all the flotation types, based on the analysis of the model fit and stability. Notably, the flotation rate constants of ultrasonic flotation in the froth and pulp zones were 1.8981 min−1 larger and 1.476 min−1 smaller, respectively, than those of conventional flotation.