Diffuse Reflectance Spectra of Coals in the UV-Visible and Near-IR Regions

Abstract

Chemical leaching of sub-bituminous coal with inorganic and organic leachants has been monitored by the UV-Visible and Near-IR spectra with the diffuse reflectance method. The shape and intensity of the observed absorption bands changed with leaching, reflecting the solubilization of the aromatic molecules and the degree of the intermolecular interaction between organic and inorganic phases. The absorption maximum of benzene-oxygen system was found between 235-270 nm and is showing a red shift with leaching. The characteristic naphthalene ring systems (220 & 280 nm) are masked by the absorption regions of monoaromatic rings; indicating the content of napthalenoid hydrocarbon is very low. The bands observed in the visible region (450nm) is attributed to S0₂ in the sample and with leaching this band is showing a red shift. The weak bond of the 680 nm is attributed to the ∏-∏* electronic transitions of the polynuclear aromatic hydrocarbons which shows red shift with leaching.