Fig. 1. Near-infrared spectra of different coals

Fig. 2. (a) The near-infrared spectroscopy of lignite (YNH, FH), bituminous coal (AY, MY) and anthracite (EWY, CWY); (b) The relationship between the absorbance at 10 001 cm^-1 and the fixed carbon content

Fig. 3. (a) The XRD spectra of lignite (YNH, FH), bituminous coal (AY, MY) and anthracite (EWY, CWY); (b) Gaussian fitting curve of γ peak and 002 peak of EWY coal sample in 2θ range of 10°~35°

Fig. 4. (a) The relationship between the f_a and the H/C; (b) The relationship between the spectral slope and the f_a

Fig. 5. (a) Cumulative contribution rate of PCs; Loading plot of (b) PC1 (98.11%), (c) PC2 (1.708%)

Fig. 6. (a) Discriminant function (F₁, F₂) decentralized point map; (b) Correlation coefficient of each variable in the discriminant function (F₁, F₂)