Chemical Leaching of High-Ash Indian Coals for Production of Low-Ash Clean Coal

Abstract

It is difficult to reduce the ash content in Indian coals below a certain level by conventional physical beneficiation techniques due to their poor washability characteristics. In the present work, the effect of aqueous alkali leaching at elevated temperature, followed by acid washing on the removal of mineral matter, was evaluated for different captive coals of Tata Steel. The research study revealed that the ash content of all these coals could be reduced by more than 50% using this method. The degree of demineralization improved by increasing the reaction time, alkali concentration, and temperature, and by reducing the coal particle size. No significant change was observed in the alkali content, whereas silica, alumina, and phosphorous content reduced significantly after the final acid treatment. The mechanism of demineralization was evaluated by analyzing the coal samples before and after the alkali and acid treatments using X-ray diffraction (XRD) techniques. Overall, this study provides an insight into possible alternative methods of beneficiation for removal of ash from physically beneficiated high-ash Indian coals.