Rare earth elements geochemistry, mineral hosts and recovery potential from Singrauli coalfield, India

Abstract

The geochemical behavior and mineralogical associations of critical and rare earth elements plus yttrium (REY) in the Singrauli Coalfield, India, were investigated. Representative samples were analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES) and X-ray fluorescence (XRF) to determine REY concentrations and their correlations with major oxides (SiO₂, Al₂O₃, Fe₂O₃). Total REY concentrations ranged from 79 to 136 ppm (coal basis), with Ce, Nd, and La being the most abundant. Critical REY, such as Nd and Y, exceeded global averages for coal. Light rare earth elements (LREEs: La, Ce, Nd) showed strong positive correlations with SiO₂ and Al₂O₃. Scandium also displayed a high affinity for alumino-silicate phases, consistent with its known geochemistry. In contrast, heavy rare earth elements (HREEs: Lu, Yb) correlated positively with Fe₂O₃, suggesting incorporation into iron-bearing minerals like hematite or goethite. Erbium exhibited a distinct pattern, with a strong positive correlation to Al₂O₃ and a pronounced negative correlation with Fe₂O₃, potentially due to redox-sensitive fractionation. Field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy (FE-SEM-EDX) of coal ash revealed REY (Ce, Nd) within glassy Si–Al–P phases. Higher-magnification observations identified ferromanganese minerals, zirconium silicates, and potential monazite or xenotime associations. The study concludes that the distribution and host phases of REY in the Singrauli Coalfield, particularly from the Krishnashilla and Kakri mines, indicate significant potential for secondary recovery.