Demineralization of coal by stepwise bioleaching: a comparative study of three Indian coals by fourier transform infra red and X-ray diffraction techniques

Abstract

A method was devised for the removal of deleterious minerals and metals from high ash-containing Indian coals. A selective enriched mixed culture developed for this purpose was used for stepwise aerobic bioleaching of two high ash Indian bituminous coals (Topa coal and Godavari coal) and Neyveli lignite. The process of bioleaching resulted in the removal of more than 50% of the mineral matter in five repeated steps and thus produced relatively demineralized, clean coal. Various parameters were optimized for bioleaching in order to maximize the removal of mineral matter. Based on the above studies a two-step pilot experiment was conducted under optimum conditions. The results obtained indicated removal of 75% of the mineral matter from one of the coals. The changes in mineral matter composition of these coals were evaluated using Fourier Transform Infra Red (FTIR) spectroscopy and X-ray diffraction (XRD) techniques. The results indicated a decrease in the intensity of many peaks when seen in combination with the amount of mineral matter removed from the bioleached coals. The mechanism of the bioleaching process is discussed and many uses of the clean coal produced are suggested.