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

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.

Shifts in composition and function of soil fungal communities and edaphic properties during the reclamation chronosequence of an open-cast coal mining dump

The diversity, composition and ecological guilds of soil fungal communities in relation to revegetation were assessed during an open-cast mining dump reclamation chronosequence of the soil <1, 5, 10, 15 and 20 years after the start of reclamation. Soil pH and electrical conductivity, total nitrogen (TN), soil organic carbon (SOC), available potassium (AK), and available phosphorus (AP) contents, and soil phosphatase (Pha), urease (U) and invertase (INV) activities were measured. Using high-throughput sequence analysis on internal transcribed spacer (ITS) sequences, 1059 soil fungal operational taxonomic units (OTUs) were identified belonging to 64 orders and these were further categorized by ecological guild. Soil fungal diversity indices were significantly different between the early (<1 year) and later reclamation communities. Nonmetric multidimensional scaling (NMDS) analysis indicates that the composition and ecological guilds of soil fungal communities were significantly different early in the process and at the end of reclamation (P < 0.05). Co-occurrence network and structural equation model analyses show that soil fungal community structure and ecological guilds were correlated with edaphic properties and had an indirect effect on soil available nutrients through direct action on soil enzymes. Overall, the data suggest that soil fungal community composition and function within an open-cast coal mining dump reclamation chronosequence changed during the period following artificial re-vegetation, with interactions between edaphic properties and soil fungal communities associated with these changes.

Modeling of air pollutant concentrations in an industrial region of Turkey

The hourly SO₂ and PM₁₀ concentrations in ambient air of the Kutahya city located at the western part of Turkey have exceeded the air quality limits in winter months since several years. The region has major industrial plants including lignite-fired power plants and open-cast mining activities, residential areas, and traffic sources. To obtain and quantify the sector-wise anthropogenic emissions and spatial distribution of the major pollutants including SO₂, NO _x , PM₁₀, and CO, a comprehensive emission inventory with 1-km spatial resolution was prepared for the year of 2014, and the AERMOD dispersion model was used to predict ambient air concentrations in a domain of 140 km by 110 km. Validation of the model results was also done referring to in situ routine measurements at two monitoring stations located in the study area. Total emissions of SO₂, PM₁₀, NO _x , and CO in the study area were calculated as 64,399, 9770, 24,627, and 29,198 tons/year, respectively. The results showed that industrial plants were the largest sources of SO₂, NO _x , and PM₁₀ emissions, while residential heating and road traffic were the most contributing sectors for CO emissions. Three major power plants in the region with total annual lignite consumption of 10 million tons per year were main sources of high SO₂ concentrations, while high PM₁₀ concentrations mainly originated from two major open-cast lignite mines. Major contributors of high NO _x and CO concentrations were traffic including highways and urban streets, and residential heating with high lignite consumption in urban areas. Results of the dispersion model run with the emission inventory resulted in partially high index of agreement (0.75) with SO₂ measured in the urban station within the modeled area.