Simple procedure for an estimation of the coal rank using micro-Raman spectroscopy

An alternative way for an estimation of coal rank, based on micro-Raman spectroscopy, is presented. Raman spectra and mean random reflectance percentage (%R-r,) were measured from 170 vitrinite grains, with %R-r in the range from 0.18 to 4.67, representing 35 coals within a broad range of rank (peat to anthracite). The spectral region between 850 cm(-1) and 1840 cm(-1) of the Raman spectra was fitted with two Lorentzian functions and a linear inclined baseline. It was found that the width of the graphitic band (G near 1580 cm(-1)) and both width and position of the disordered band (D near 1340 cm(-1)) monotonously decreased with the increase of %R-r of the grains. Due to the high reproducibility of these parameters, when calculated from Raman spectra obtained on different spots of the same grain, as well as the clearly pronounced Raman parameters-reflectance dependences, they can be used for an estimate of the coal rank. The correlation between Raman parameters and random reflectance of the vitrinite grains was expressed with empirical formulae. (C) 2014 Elsevier B.V. All rights reserved.