Geochemistry and mineralogy of coal mine overburden (waste): A study towards their environmental implications

Abstract

Open-cast mining of coal generates waste material, including rock and soil with different minerals, and traditionally dumped as waste over the valuable lands worldwide. Overburden (OB) is devoid of actual soil characteristics, low micro and macronutrient content, and a sufficient amount of rare earth elements, silicate, sulphate, and clay minerals. This study aimed to determine the geochemistry and mineralogy of OB samples collected from Makum coalfield, Margherita of Northeast (NE) India. The geochemical and mineralogical analyses of overburden (OB) were carried out by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), High resolution-inductively coupled plasma mass spectrometer (HR-ICP-MS), Field-emission scanning electron microscopy (FE-SEM) techniques. This study shows potentially hazardous elements (PHEs), including Pb, Co Cu, Cr, Ni, and Zn, and their association with minerals observed in OB samples. The major oxides (SiO₂, Al₂O₃, Fe₂O₃, MgO, CaO, K₂O, and Na₂O) are present in all the overburden samples analyzed by the X-ray fluorescence (XRF) technique. Various minerals such as quartz, kaolinite, gypsum, melanterite, rozenite, hematite, and pyrite were identified. The overburden samples contain considerable amounts of rare earth elements and yttrium (REY; as received basis) with an average of 26.3 (ppm). The presence of abundant minerals and REY opens up a new avenue for the gainful and sustainable utilization of such waste materials.

Keywords: Ecological risk (Er); Geochemistry; Mineralogy; Open-cast mining; Overburden (OB); Principal component analysis (PCA); Rare earth elements and yttrium (REY).