Deashing and desulfurization of subbituminous coal from the East field (Bogovina Basin, Serbia) – Insights from chemical leaching Scientific paper

Abstract

The study is focused on the determination of the most effective chemical leaching process for the simultaneous demineralization/deashing and desulfuri­zation of subbituminous coal from the Bogovina Basin. Coal was treated for 30 min, at different temperatures, using variable concentrations of hydro­chloric, nitric, acetic and citric acids; hydrogen peroxide, mixture of hyd­rogen peroxide and nitric acid (pH 2), as well as by the stepwise leaching pro­cess (nitric acid + mixture of hydrogen peroxide and nitric acid, pH 2). The changes in mineral composition, caused by the chemical leaching, are followed using X-ray diffraction, whereas alterations of coal organic matter are tracked by Fourier-transform infrared spectroscopy and the content of fixed carbon. Inorganic acid leaching, regardless of the temperature and acid concentration, enabled the successful deashing of coal, whereas the percent of desulfurization was insufficient. The organic acid leaching was not satisfactory for both, deashing and desulfurization. Leaching by H₂O₂ and H₂O₂/HNO₃ mixture (pH 2) resulted in moderate desulfurization, but the ash reduction was low. The most suitable method for the simultaneous effective ash (78 wt.%) and the sulfur (66 wt. %) removal from Bogovina coal is the two-step leaching, com­bining 10 vol. % HNO₃ and mixture of 35 vol. % H₂O₂/10 vol. % HNO₃ of pH 2 at 60 °C.