Investigation on secondary dewatering characteristics and kinetics of fine-grained bituminous clean coal during microwave heating

Fine clean coal often had excessive moisture after mechanical dewatering, failing to meet industrial demands. This study investigated microwave secondary dewatering of fine and coarse clean coal from Xiezhuang and Zhongxin coal preparation plants. A laser particle size analyzer, X-ray diffractometer, scanning electron microscope, and BET pore structure analyzer characterized coal samples. Results revealed that flotation clean coal from Zhongxin had a finer particle size (D50 = 24.65 μm), larger specific surface area (2.487 m2/g), and total pore volume (0.01 cm3/g), along with more clay minerals, leading to higher water retention capacity. The weight loss of coal samples was positively correlated with microwave power, heating time and initial moisture content, but negatively correlated with sample mass. Raising microwave power could significantly improve dewatering efficiency. The Two-term Exponential model achieved the best fitting for Zhongxin coal. At 357 W microwave power, it obtained an R2 of 0.994 and an RMSE of 0.020. And, the quadratic model and modified page model exhibited the best fitting performance for Xiezhuang coal. These differences stemmed from pore structure and water migration mechanisms. This work verified microwave technology was feasible for deep dewatering of bituminous clean coal and provided theoretical and technical support for field applications.