Mineralogy and Geochemistry of organic-rich and inorganic-rich fractions of Ib valley coals, Odisha, India

Mineralogical and geochemical investigations have been carried out on organic-rich and inorganic-rich fractions of Ib Valley coal to understand the association and distribution of macerals, minerals, and the occurrence of major, minor, trace, and rare earth elements. Density fractionation was performed using heavy liquids of relative density 2.0 g/ml to generate organic-rich and inorganic-rich fractions, followed by detailed petrography, mineralogy, and geochemical analyses using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and inductively coupled plasma optical emission spectroscopy (ICP-OES). The results revealed significant differences in mineralogical composition and elemental associations between the two fractions. The inorganic-rich fraction contained mainly pyrite, siderite, hematite, and some minor sulfides minerals such as chalcopyrite, sphalerite, and galena, with enrichment of trace elements such as Mn, Co, Ni, Cu, Zn, As, Se, Mo, Cd, Sn, and Pb. The organic-rich fraction is found to host quartz, clay minerals, apatite, and Ti-oxide with elevated concentrations of Li, Sc, V, Cr, Ge, Ga, Sr, Zr, Nb, Sb, Ba, and W. The rare earth elements, including yttrium (REY), concentration of Ib Valley coal ash is higher than the average REY of global coal ash. In density separation, the REY are found to be enriched in the organic-rich fraction, suggesting their association with aluminosilicates, phosphates, and the oxide bearing phases. These findings provide insights into the mineralogical control on elemental partitioning of Ib Valley coal, with implications for its utilization, environmental impact, and resource management.