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

Abstract

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 V_R band, the band at 1392 cm⁻¹ as V_L band and the band at 1540 cm⁻¹ as G_R 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.