Amit Karmakar

The escalating demand for critical elements (CEs), particularly rare earth elements and yttrium (REY), driven by their indispensability in modern green technologies, electronics, and defence, emphasises the urgency for identifying secure and sustainable alternative sources. This review broadly evaluates the viability of coal and its by‐products, fly ash, bottom ash, and slag, as promising reservoirs for these strategic elements. Key findings reveal that REYs are significantly enriched in coal combustion residues, with fly ash demonstrating higher concentrations than bottom ash, while certain volatile elements partition into the flue gas. The occurrence and enrichment of CEs are governed by coal rank and maceral composition, with elements like gallium associated with collodetrinite and cobalt with inertinite. Critically, REYs are primarily hosted within amorphous aluminosilicate glass and specific mineral phases, such as haematite in fly ash, whose disordered atomic structures facilitate element incorporation. The distribution patterns of REY in power plants consistently show a hierarchy, lowest in raw coal, medium in slag, and highest in fly ash. While acknowledging the technological and economic challenges in extraction, this review synthesises and proposes an integrated recovery flowchart that synergises physical separation, acid/alkali leaching, and purification techniques to enhance efficiency. The recovery of critical elements from coal and its combustion by products holds significant strategic implications for India's long term resource security. As global supply chains for rare earths and other strategic metals remain highly concentrated, domestic extraction from coal based sources could help reduce import dependence and enhance supply resilience. Leveraging India's vast coal reserves for secondary recovery of elements such as REEs, Ga, Ge, and U align with the objectives of the National Critical Minerals Mission, supporting both industrial diversification and clean energy transitions. This approach also offers a dual benefit addressing environmental concerns related to coal waste management while advancing self‐reliance in critical mineral supply.

Air pollution poses a significant public health risk, as pollutants, emitted from both natural and anthropogenic sources, can penetrate deep into the respiratory system, leading to a wide range of respiratory diseases. While numerous studies have examined the role of meteorological factors in modulating air quality, limited research has focussed specifically on their effectiveness in regions characterized by intensive mineral extraction activities, particularly coal mining zones where emission loads remain persistently high. In this context, the concentration levels of PM₁₀, PM_2.5, SO₂, and NO₂ were continuously monitored for one year using an automated ambient air quality monitoring system to investigate their seasonal behaviour and meteorological interactions. The recorded concentration ranged from 17.49 to 393.40 µg/m³ for PM₁₀, 5.45 to 231.53 µg/m³ for PM_2.5, 12.3 to 62.05 µg/m³ for NO₂, and 11.59 to 182 µg/m³ for SO₂. The pollutant concentrations peaked during winter and declined during summer and monsoon seasons. The trend analysis using Theil–Sen estimator revealed significant negative trends for all four pollutants PM₁₀ (− 181.79 units), PM_2.5 (− 106.11 units), SO₂ (− 22.76 units), and NO₂ (− 29.89 units). The linear regression analysis demonstrated a strong correlation between PM₁₀ and PM_2.5 (R² = 0.89), whereas a weak association (R² = 0.01) was observed between NO₂ and SO₂. Nonlinear regression further indicated temperature as a key influencing factor, showing a strong inverse relationship with NO₂ (− 13.218) and a moderate negative impact on PM_2.5 (− 1.517). Overall, the findings of this study underscore highlight the seasonal vulnerability of coal mining regions to pollutant accumulation and highlights the limitations of mechanisms under elevated emission scenarios. Furthermore, this study establishes temperature as a boundary-layer control variable and emphasizes that effective air-quality management in coal-mining regions must integrate real-time meteorological forecasting with emission scheduling for sustainable air-quality compliance.

The beneficiation of indigenous high ash bituminous coal is crucial for optimizing its suitability for Pulverized Coal Injection (PCI) in the steel industry. This study investigates the impact of size and density-based beneficiation on key coal properties, including proximate and ultimate analysis, calorific value, organic petrography, swelling index and thermal analysis. The raw coal, with an initial ash content of 28.73%, volatile matter of 19.43%, and fixed carbon of 51%, goes through density separation into fractions ranging from 1.3 to 1.8 kg/m³. The < 1.44 kg/m³ fraction shows a significant reduction in ash content average 16.23% in all sizes with total recovery of 32.58%, which attracted investigations to assess its utilisation potential as PCI coal after blending it with very low ash imported non-coking coal. Furthermore, beneficiated coal with a density of < 1.44 kg/m³ reveals an optimal volatile matter content of 21.62% and fixed carbon above 61.46%, aligning with PCI specifications. Our study also magnifies the importance of maceral composition and vitrinite reflectance (Ro%), with low-density fractions (< 1.44 kg/m³) containing 62.4–77.8% vitrinite, enhancing combustion efficiency. Ultimate analysis endorses that the < 1.44 kg/m³ density fraction, with an average carbon content of 73.46% and minimal sulphur < 0.42%, ensures efficient energy transfer. Gross Calorific Value (GCV) unveils that this fraction consistently provides energy outputs between 6642 and 8355 kcal/kg, making it the most suitable for PCI applications. Thermal analysis (DSC-TGA-DTG) of the beneficiated coal samples revealed combustion profiles closely aligned with imported PCI coal, confirming their compatibility with significant recovery yield (32.58%), and the successful blending strategy that brings the final ash content to within PCI specifications (9.59%). The potential for synergistic effects in blended combustion further reinforces their suitability for efficient PCI application. This study accentuates the strategic advantage of beneficiation in reducing dependency on imported PCI coal, enhancing domestic resource utilization, and promoting cost-effective steel production.

Large‐scale coal mining in India produces vast overburden (OB) waste, contributing to land and environmental issues. This study is the first to evaluate OB from the Bhowra and Dhansar mines (Jharia Coalfield) as a sustainable alternative to conventional coarse aggregates in concrete. Five tons of OB were collected, processed, and subjected to comprehensive geotechnical, mineralogical, and mechanical characterization per Indian Standard methods. OB‐based mixes (25%–100% replacement) demonstrated specific gravity (2.77–2.52), water absorption (1.02%–2.21%), and bulk density (1.61–1.38 kg/L), with aggregate crushing and impact values meeting IS:383‐1970 guidelines. M‐30 concrete with Bhowra OB retained a compressive strength of 48 MPa at 56 days for 100% replacement, suitable for construction use. Mineralogical analysis identified primarily quartz, kaolinite, gypsum, hematite, and calcite, with high SiO ₂ content and low hazardous metals. Microscopy and spectroscopic analyses confirmed mineral stability and absence of deleterious phases. The results show Bhowra OB is particularly effective at ≤ 50% replacement, providing strong mechanical performance and minimal strength loss. The findings present OB as a viable, environmentally responsible aggregate, potentially reducing the use of natural aggregates by 30%–50%, cutting mining waste by 5–10 Mt/year, and supporting circular economy goals in the construction industry.

This study investigates the structural and thermal evolution of lignite from the Barmer Basin, Rajasthan, India, using Raman spectroscopy and organic petrology. Lignite samples were collected from active mines in Kapurdi, Giral, and Sonari and analyzed through proximate and ultimate analyses, petrography and Raman spectroscopic techniques to assess their rank and structural characteristics. Vitrinite reflectance measurements, ranging from 0.24% to 0.38%, to assess maturation of organic matter. The volatile matter, a conventional maturity parameter, ranges from 38.5% to 46.5%, indicating low rank and limited thermal evolution. Ash yield values vary from 2.32% to 28.24%. Petrographically, the lignite’s are rich in huminite, ranging from 58.0% to 77.4%, with inertinite content between 3.6% and 13.6% and liptinite concentration from 5.4% to 13.0%. The maceral composition suggests carbonaceous materials in an early diagenetic phase. Raman spectroscopy reveal the presence of D and G bands, typical spectral signatures of carbon-rich natural materials. The Raman shift for the D band ranges from 1343 to 1391 cm⁻¹ and for the G band, from 1565 to 1588 cm⁻¹. The intensity ratio of the I_D/I_G band ranged from 0.71 to 0.97, while the (G-D1) parameter varied from 187 to 238 cm⁻¹, indicating sample heterogeneity. However, the AD₁/A_G ratio shows an irregular pattern, with values between 1.19 and 2.74. The study demonstrates that integrating Raman spectroscopy with Vitrinite reflectance (VRo) provides insights into the structural attributes of immature kerogen which denotes organic matter that has not yet undergone sufficient thermal evolution to generate oil or gas, which is typical of low-rank coals like lignite. The petrological, proximate and ultimate analyses collectively confirm the carbonaceous, coaly material in its early coalification stages. This study emphasizes the use of Raman spectroscopy and Organic petrology as a proxy to evaluate lignite thermal evolution, enhance the interpretation of carbon structural disorder (e.g., D/G band ratios) and offer deeper insights into the aromaticity, maturity and heterogeneity of lignite, comparing its results with traditional maturity indicators.

The mining industry plays a crucial role in global economic growth and technological advancement, faces persistent challenges in managing mining tailings pose significant environmental and societal risks. Mine tailings are primarily composed of finely milled rock, water, and extraction chemicals, often lead to soil and water contamination, atmospheric pollution, and ecological disruption when improperly managed. Recent advancements have transformed mining tailings from waste into valuable resources for synthesizing nanomaterials (NMs) through sustainable extraction processes. Emerging extraction methods, including acidic and alkaline treatments and chemical reduction, enable the recovery of metals like copper, iron, nickel, and gold in nanoparticulate forms. These NMs exhibit exceptional properties enhanced reactivity, tunable optical and mechanical behaviors and support diverse applications in catalysis, environmental remediation, medicine, and energy storage. NMs derived from mining tailings align with circular economic principles, addressing global resource shortages while offering economic and environmental benefits. Their production not only mitigates waste management challenges but also reduces dependence on primary resources. Despite promising advancements, challenges such as process optimization, toxicity management, scalability, and regulatory gaps remain. We emphasize the necessity of life cycle assessments, green chemistry practices, and policy frameworks to ensure safe and efficient industrial integration. This review provides a comprehensive insight into current technologies, applications, risks, and future research directions, underscoring the transformative potential of mining tailings for sustainable development.