Feasibility studies of de-sulfurization and de-ashing of low grade medium to high sulfur coals by low energy ultrasonication

•A partially green method for de-sulfurization and de-ashing of low grade coals is proposed.•The removal of organic sulfur is revealed by quantitative FT-IR spectroscopy.•TG-DTG analysis shows the improvement in the combustion efficiencies of the clean coals. The present paper reports an attempt of using low ultrasonic energy (20kHz) to clean some low rank medium to high sulfur coal samples from northeast India in the presence of H2O2 solutions. The study shows satisfactory removal of all the forms of sulfur and mineral matters (ash) from the coal samples. The physico-chemical characterizations of the raw and ultrasonicated coal samples were carried out by using Fourier Transformation Infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Thermogravimetry-Derivative Thermogravimetry (TG-DTG) techniques to evaluate the final product quality. The quantitative FT-IR spectroscopic analysis demonstrated the formation of oxidized sulfur species (SO and SO2) and their subsequent removal from the coal samples during ultrasonication. The XRD profiles supported the partial removal of some minerals from the coal including their de-ashing. The TG-DTG profiles of the beneficiated coal revealed their improved quality for use in thermal plants with better combustion efficiency.