Impact of ultrasonic pretreatment on the flotation of lignite particles of different size fractions

Abstract

ABSTRACT The purpose of this study was to investigate the impacts of ultrasonic pretreatment on flotation of lignite particles of different size fractions. Wet-screening, laser particle size analyzer, energy dispersive spectrometer (EDS), mercury porosimeter, attachment time and flotation tests were employed to reveal the changes of particle size, surface properties and floatability of different size fraction lignite before and after ultrasonic pretreatment. Flotation results show the combustible matter recovery of coarse particles (0.25–0.125 and 0.125–0.074 mm size fractions) after ultrasonic pretreatment was significantly improved whereas that of fine particles (0.074–0.045 and −0.045 mm size fractions) was decreased. Wet-screening and laser particle size analyzer results reveal that more breakage occurred in 0.125–0.074 mm size fraction using ultrasound than in other size fractions. In addition, coarse particles were crushed to fine particles using ultrasound benefitting improvement of the flotation performance. EDS and mercury porosimeter results indicate ultrasonic pretreatment removed some high ash minerals embedded in lignite surface through surface cleaning and cracking to reduce some pore/cracks of all size fractions except −0.045 mm, which made an increase in the hydrophobicity and floatability of lignite. Therefore, ultrasonic pretreatment was an efficient method to enhance flotation performance of 0.25–0.074 mm size fractions lignite.