X-Ray Diffraction Studies of some Structurally Modified Indian Coals and their Correlation with Petrographic Parameters

In order to study the X-ray structural parameters, five coals have been chosen from different coal basins of India. These coals have been demineralized by standard HF + HCl treatment and treated with nitric acid in aqueous and glacial acetic acid media. X-ray diffraction (XRD) patterns of the samples are recorded using a slow step scan (2 s/step) over an angular range 2θ ∼ 10-90°. TOPAS software has been used to determine the structural parameters like interlayer spacing (d₀₀₂), crystallite size (L_c), aromaticity (f_a) and average number of aromatic layers (N_c). The structural parameters have been correlated with chemical as well as petrographic parameters of coals. Mean random reflectance (MR_r) of the studied coals varies between 0.44% and 0.54% and the vitrinite, liptinite and inertinite contents vary between 17.8% and 66.4%, 9.2% and 20.3% and 20.7% and 62.9% respectively. Nitration in both the media has increased d₀₀₂ values. This study also shows that d₀₀₂ and fa values are dependent on the rank of the coal, rather than only the carbon content (C_dmf, dry mineral free basis). XRD rank parameter values have been directly correlated with the petrographic rank parameters. Nitration in both the media has induced similar kind of effect on individual macerals. Behaviour of the macerals to chemical treatment is also reported in this study.