Geochemical and mineralogical evaluations of coal, shale, and mine waste overburden from Makum coalfield of the Northeast India

The Cenozoic-age Makum coal from northeastern India offers numerous research opportunities because of its diverse geochemical and geological characteristics. Due to its high sulfur content, the coal has been found to be less useful for industrial purposes. It can, however, serve as a hub for ongoing research on coal-based derivative products. The aim of this research work is to investigate the mineralogical and geochemical compositions of the coal, mine overburden (MOB) and shale samples taken from the Makum coal field and also on establishing a mutual relationship between them. To characterize the geochemical controlling factors of the Makum coal field, the study employs coal petrography, FTIR, mineralogical, and geochemical analysis. According to X-ray diffraction analysis, the major minerals like quartz, kaolinite, haematite, illite, pyrite, and calcite are present in coal and MOB. Pyrite is observed by SEM–EDS analysis as cubic-shaped particles that are smaller than a few µm in size. The presence of sulfide minerals represents a phase of pyrite mineralization. The petrography study was used to better understand the environment that existed during the formation of the plant material, which aids us in determining the quantity of detrital mineral sediment contained in the coal. According to the ICP-MS analysis, the samples indicate significant levels of rare earth elements including yttrium. The present study reveals higher concentrations of potential hazardous elements in the coal samples, with V, Cr, Ni, Cu, and Zn content in coal being considerably enriched compared to world-average concentrations. The correlation analysis reveals that the potential hazardous elements like Co, Ni, As, and Cu are associated with pyrite as they have strong affinity towards pyrite. Thus, numerous minerals and rare earth elements (REEs) exist, opening up a fresh avenue for more research in the area. This study also assists researchers in understanding the significance of Makum coal and provides numerous ideas for coal characterization.