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Characterization of Chemical Structure with Relative Density of Three Different Ranks of Coal from India


A comparative study of coals of different ranks having different chemical structure and petrography would be desirable to gain an in-depth knowledge of Indian coals. Here, we report structural and petrographic analyses of three different coals: Coal A (coking coal), Coal B (semi-coking coal) and Coal C (non-coking coal) of Indian origin. The vitrinite reflectances of the three coals were measured to be 1.26, 1.38 and 0.46 for Coal A, Coal B and Coal C, respectively. Size fractionation (− 3.0 + 1.0 mm, − 1.0 + 0.5 mm  and − 0.5 mm) followed by density gradient separation (1.2, 1.3, 1.4, 1.6, 1.8 g/cm3) were performed for all the coal samples to study mineral matter liberation and distribution of macerals in different density fractions. Petrographic analysis of different density fractions revealed a direct proportionality of vitrinite content to swelling properties. The highest free-swelling indices (7.5 and 6.5) were observed for 1.2 density fraction of Coal A and Coal B, respectively. Fourier transform infrared spectroscopy revealed crucial information relating the degree of aromaticity and aliphaticity with observed coking properties. Specifically, aromaticity (AR1) (CHar stretching/CHal stretching, (3000–3100 cm−1)/(2800–3000 cm−1) and mean reflectance (Ro in %) were found to have a strong positive linear correlation with each other, indicative of an increase in aromaticity with coal rank.

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The authors are thankful to the Director, National Metallurgical Laboratory for permission to publish this work. The work is the part of the ongoing project sponsored by Tata Steel Ltd, Jamshedpur, India. The authors also wish to thank anonymous learned reviewers for their critical evaluation and valuable suggestions to improve the quality of paper.

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Correspondence to Sanchita Chakravarty.

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Chakravarty, S., Chakravarty, K., Mishra, V. et al. Characterization of Chemical Structure with Relative Density of Three Different Ranks of Coal from India. Nat Resour Res (2020).

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  • Indian coal
  • Petrography
  • FT-IR spectroscopy
  • Swelling index
  • Coal rank