The influence of ultrasound treatment on the hydrophobic flocculation of lignite

Abstract

Ultrasonic energy has mostly been investigated for the flotation process in coal fines, but its application to agglomeration is extremely limited. Therefore, the effect of ultrasound on the process of hydrophobic flocculation was investigated in this study. In addition, the effect of using ultrasound at the flocculation stage and/or at the pretreatment stage on the combustible matter recovery and the ash content was determined. In this regard, the use of ultrasound at the pretreatment stage improved the hydrophobic flocculation of coal, but the use of ultrasound at the flocculation stage, in other words, the use of ultrasound during the entire process, reduced the recovery of the combustible matter. Also, the power of ultrasound and the time of treatment affected the success of flocculation, and the best values were achieved at a power of 150 watt of ultrasound and a treatment time of 3 min. In addition, the ultrasonic treatment reduced the zeta potential negativity of coal particles. Moreover, ultrasound pretreatment led to higher contact angle values, resulting in more successful flocculation. As a result, coal with an ash content of 26.02% was enriched with an ash content of 10.81% and an efficiency of 78.12 by using ultrasound pretreatment.