Investigation On The Structural Ordering Of Natural Coaly Graphite From Xinhua,Hunan Province,China

In the current study,mineralogy,petrology,coal petrography,coal geology,geochemistry and other theoretical knowledge were used to study the structural evolution of natural graphitized coal that associate with pluton intrusion,including coal macerals transformation,geochemical evolution,ordering of the C atoms in coal macromolecule,the temperature of different graphitization degree coals have undergone,finally the naturally graphitization models for macro process and micro process were proposed,and the mechanism of coal graphite formation was discussed.(1)A series of Carboniferous coals located at the Hanpo'ao mining area,central Hunan Province,China,were graphitized to varying degrees by the Tianlongshan Granitic pluton intrusion.For the samples JZS-3 and LX-3 collected far away from the intrusion(Rr=4.3-4.7%),it mainly consist of vitrinite and inertinite,whereas the microcrystalline graphite becomes the dominate components in the most graphitized samples,concurrently some new components formed including pyrolytic carbon,needle graphite,and flake graphite,suggesting vitrinite and inertinite can transform into graphite,the graphitizing ability of different kind coal components:collotelinite and collodetrinite>degradofusinite>pyrofusinite.The reflectance of microcrystalline graphite is fairly low,only 3-5%,can not reflect the real metamorphic degree of graphitized coal.(2)Micro-Raman and micro-FTIR spectroscopy were applied to analysis on the different components in graphitized coals;results show that although vitrinite and inertinite macerals still preserve some of their original morphological features,micro-Raman and micro-FTIR data show that differences of maceral structure in the same sample diminish with increased rank at the anthracite stage.The presence of microcrystalline graphite and vitrinite in the same samples,components that have distinctly different Raman spectra,confirms the compositional and structural heterogeneity of highly graphitized coals.Based on Raman spectral data,the structural evolution of metamorphosed coal ranging between anthracite and coal graphite can be divided into two phases:carbonization for the vitrinite and graphitization for the microcrystalline graphite.Micro-FTIR may not provide clear structural information for coals with Rr>5.9%,but the sharp peak at 870 cm-1 shows up in the FTIR spectra of graphite components may used as identify components in graphitized coals.The microcrystalline graphite and coal macerals in the partly graphitized coal can be separate by DGC technique.(3)Rather than use a single parameter as a measure of rank,both reflectance and(002)FWHM used to group samples with different metamorphic levels was proposed in this paper.For the anthracite and meta-anthracite samples,they have broad(002)XRD peaks,and the reflectance(Rr and Rmax)of these samples increases approaching the intrusion;for the partly graphitized samples and microcrystalline graphite,metamorphic degree is indicated more clearly with XRD data than reflectance.(4)The trend seen in a plot of VM versus Rr suggests a similarity between graphitized coals and other intruded coals.However,van Krevelen and Seyler diagrams suggest that the elemental evolution in graphitized coals differs from both intruded coals and coals matured by normal burial maturation.These results suggest the maturation pathway of graphitized coals may be different from either coals that have undergone normal burial maturation or have been affected by small-scale intrusions.Hydrogen is more readily removed from coals that have undergone natural graphitization than normal burial coals and previously reported intruded coals.The appearance of different maturation pathways associated with magmatic intrusion is probably related to the scale of the intrusion events.(5)According to the mineralogy and coal petrology analysis on graphitized coal,combing with Raman geothermometer and artificial synthetic graphite analysis,the temperature of JZS and LX mines was confined at 250-260?,CM mine was confined at 320-350?,SL mine was confined at 370-390?,BC mine was confined at 440-460?,SHL mine was confined at 470?.The temperature that graphitized coals have undergone is relatively low,cannot provide enough activation energy for graphitization.(6)The stress effect on graphitized coal can be observed by tectonic characters,micro-structure in coal macerals,and HRTEM images,suggesting that pressure has important effect on the graphitization of coal.The catalytic graphitization phenomenon was also observed for natural graphitized coals by HRTEM observation,and the main inorganic element is Si.(7)Combing with the magma and tectonic activities analysis and the coal graphitization process,the graphitization models for macro process and micro process were proposed.Only under high temperature treatment,carbonization is the main process for coal structural evolution,C atoms were connected by sp2 bonding forming local ordering molecular domain,but still disorder,whereas under high temperature and shear stress treatment,the nanopores in anthracite were broken,the disordered local ordering molecular domains reorient and join together,finally forming nanoscale polycrystalline graphite.The coupling effect of igneous and tectonic is the key point for the graphitization of coal,only the pressure take effect when the igneous temperature still on,can the graphitization of coal happen.