Chemical leaching of an Indian bituminous coal and characterization of the products by vibrational spectroscopic techniques

High volatile bituminous coal was demineralized by a chemical method. The vibrations of the “aromatics” structure of graphite, crystalline or non-crystalline, were observed in the spectra at the 1600 cm−1 region. The band at 1477 cm−1 is assigned as VR band, the band at 1392 cm−1 as VL band and the band at 1540 cm−1 as GR band. Graphite structure remains after chemical leaching liberates oxygenated functional groups and mineral groups. The silicate bands between 1010 and 1100 cm−1 are active in the infrared (IR) spectrum but inactive in the Raman spectrum. Absorption arising from C-H stretching in alkenes occurs in the region of 3000 to 2840 cm−1. Raman bands because of symmetric stretch of water molecules were also observed in the spectrum at 3250 cm−1 and 3450 cm−1. Scanning electron microscopy analysis revealed the presence of a graphite layer on the surface. Leaching of the sample with hydrofluoric acid decreases the mineral phase and increases the carbon content. The ash content is reduced by 84.5wt% with leaching from its initial value by mainly removing aluminum and silicate containing minerals.