Comparative studies on the effect of mineral matter on physico-chemical properties, inherent moisture and drying kinetics of Chinese lignite

Abstract

The comparative study between the high-ash lignite (HAS) and low-ash lignite (LAS) demonstrated great effects of mineral matter on physico-chemical properties, inherent moisture and drying kinetics of Chinese lignite. The physico-chemical properties were characterized by X-ray diffraction (XRD), N2 physisorption, fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and thermoanalytical methods. Raw and treated samples (screening, dry beneficiation, and flotation) were analyzed for inherent moisture content. Drying kinetic experiments were performed by isothermal thermogravimetry in combination with thin-layer models. In comparison with LAS, HAS had less cohesive features with higher amounts of heterogeneous crystalline minerals, less quantity of O-containing functional groups, and smaller surface areas as well as lower pore volumes, as evidenced by characterization analysis. Less cohesive features could allow the moisture to move easily through the lignite, which thus resulted in a lower inherent moisture contained in HAS. On the other hand, due to higher thermal conductivity and poorer holding-moisture structures resulted from the presence of abundant minerals, HAS revealed more promising drying kinetics with lower activation energies, which were determined by the combination of isothermal experiments and Page model analyses.