LI Kuo, LIU Qin-Fu*, ZHANG Shuai, YUAN Liang
(College of Geoscience and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China)
Abstract: Coaly graphite is an important non-metallic mineral resource. It was transformed from coal by the metamorphism of the coal-bearing stratum which was intruded by the large scale magma. In this paper, the typical coaly graphite samples from the Loudi and Chenzhou areas of Hunan Province have been studied by using coal petrological methods, X-ray diffraction (XRD), micro-Raman spectroscopy, and scanning electron microscopy (SEM). A comparative study has also been undertaken among anthracite samples from the Loudi area of Hunan Province, coked coal from the Illinois basin, coked bitumen from the Colorado Trinidad coalfield, and crystalline graphite from Sri Lanka. It was found that cryptocrystalline graphite with microcrystal size of about 0.35 μm is the main component of the coaly graphite (>80% by volume), with a small amount of pyrolytic carbon, needle graphite, and flake graphite, as well as occasionally residual vitrinite and inertinite. The rough surface of cryptocrystalline graphite observed under the reflecting light microscope could cause the scatter of incident light to result in the relatively low measured reflectance values of 3%-5% for the coaly graphite. The narrow (002) peak in the XRD spectrum of coaly graphite is obviously different to the broad banded peaks of anthracite and natural coke, so, full widths at half maximum (FWHM) height of (002) peaks in the XRD spectra of coaly graphite, anthracite and natural coke can be used as main parameters to distinguish coaly graphite from anthracite and coke. The sharp G band and a weak D band shown in the first order region and the relatively strong 2D band and an additional 2450 cm-1 peak shown in the second order region of the Raman spectra of coaly cryptocrystalline graphite suggest that its structural evolution occurred in the process of graphitization. However, there is weak 2D band and no 2450 cm-1 peak in the Raman spectra of anthracite, meta-anthracite, and natural coke, suggesting that their structural evolutions occurred in the process of carbonization.
Keywords: Coaly graphite; cryptocrystalline graphite; optical features; micro-Raman; micro component
ACTA MINERALOGICA SINICA Vol. 41, No.1, 2021, page 101