Ultrasonic-assisted coal beneficiation: A review

Limited availability and large industrial demands of high-grade coals have forced many coal-dependent industries to shift their preference towards low-grade coals to meet the feedstock requirements. The low-grade coals due to their poor washability nature do not respond efficiently toward existing coal beneficiation techniques, making the cleaning process challenging. Inefficient cleaning of such coals could potentially lead to environmental problems such as solid waste generation and gaseous emissions during combustion. Therefore, it is important to upgrade the existing coal beneficiation techniques for improving the clean coal quality, and simultaneously enhance the efficiency of the process. In the past few decades, many techniques have been developed to improve existing coal beneficiation techniques. Among them, ultrasound technology has gained significant attention due to its ability to enhance the process performance. The incorporation of ultrasound can significantly increase the clean coal yield under the substantial effect of cavitation and streaming. In this paper, an overview on the recent development in ultrasonic-based coal beneficiation techniques and the role of ultrasound in improving the efficiency of various coal beneficiation techniques are discussed. This includes a critical review of the ultrasound mechanism in enhancing coal demineralization, desulphurization, grindability, slurryability and dewatering.