Search Results (120)

Coal gangue, a major by-product of coal mining, has long posed significant environmental and resource management challenges. With increasing global emphasis on energy transition and environmental sustainability, the comprehensive utilization of coal gangue has emerged as a critical research and policy priority. This review systematically examines the sources, characteristics, environmental impacts, and integrated utilization pathways of coal gangue. First, the formation mechanisms, mineralogical composition, and physicochemical properties of coal gangue are summarized, with particular attention to hazardous constituents and associated environmental risks, including soil and groundwater contamination, atmospheric pollution, and ecological degradation. Subsequently, current technological approaches for coal gangue management and comprehensive utilization are evaluated, including subsidence areas reclamation and underground backfilling, applications in construction materials and energy conversion, extraction of valuable chemical elements and functional materials, ecological soil engineering, and carbon sequestration. The potential contributions of these pathways to waste reduction, resource efficiency, and low-carbon development are critically discussed. Finally, key environmental, technological, and socio-economic considerations influencing sustainable coal gangue utilization are emphasized. This review provides a comprehensive synthesis of existing knowledge and identifies future research directions aimed at advancing environmentally sound, economically viable, and large-scale utilization strategies. The findings are intended to support researchers, policymakers, and industry stakeholders in promoting circular resource systems and sustainable development. Full article

Energy scarcity and subsequent global fuel market shocks have become a significant concern for the United States. Process heating in industry accounts for over half of all industrial energy usage and is almost entirely (>95%) supplied by natural gas, coal, and byproduct fuels. Many existing alternatives, technologies, and strategies can reduce dependency on this fossil fuel usage to promote energy security and competitiveness. It is expected that adoption of alternatives is limited by capital investment. A working group exploratory exercise was performed to evaluate the current barriers to alternative process heat technology adoption for the manufacturing sector. Although the working group’s findings emphasize electro-technologies due to their emergence as the central topic of discussion, we have contextualized these results by providing a fair and consistent comparison against several alternative thermal technology options. The most reported issue was the lack of financial incentives, with the second key issue for engineers and manufacturing sector decision-makers being the lack of awareness or understanding of available alternatives. This paper aims to provide an analysis of the levelized cost of heating for a variety of alternatives as part of addressing concerns from the emergent patterns reported in the exploratory exercise, as well as provide guidance on barriers to further adoption. Levelized cost of heating analysis considered the capital investment, operations and maintenance, lifespan, and fuel stream costs of various systems delivering heat to the product or process as a generalized cost per megawatt-hour delivered. The analysis indicates that biomass burners, industrial open-loop heat pumps, and central-receiver heliostat fields are at cost parity under average 2024 United States natural gas and electricity prices against well-optimized natural gas burners, though further cost reductions are necessary for consistent adoption. Full article

Finding cost-effective and eco-friendly ways to remove toxic heavy metals from wastewater remains a critical challenge for industrial sustainability. This study presents a comparative performance matrix of coal fly ash (CFA) and bone charcoal (BC) for the high-capacity remediation of Cd(II) and Pb(II) ions. This work establishes a direct cross-matrix comparison between a heterogeneous aluminosilicate phase (CFA) and a uniform calcium-phosphate structure (BC) under identical systemic boundaries. SEM/EDS, FT-IR, and complementary TG/DTG/DTA screenings confirmed that distinct material-specific functional frameworks drive a predominantly physical mechanism governed by electrostatic and van der Waals interactions. Equilibrium data fitted the non-linear Langmuir model well (R² > 0.99 at 20 °C). BC proved to be significantly more effective, achieving maximum sorption capacities (q_max of 397.55 mg/g for Pb(II) and 325.09 mg/g for Cd(II), outperforming CFA (118.22 and 105.59 mg/g, respectively). Sorption capacities decreased with temperature up to 80 °C, confirming the exothermic nature of the process, which was further substantiated by negative enthalpy values (∆H⁰ = −7.27 to −14.19 kJ/mol). Thermodynamic parameters indicated a spontaneous process (∆G⁰ < 0, −9.55 to −19.33 kJ/mol) with positive entropy changes (∆S⁰ = 5.82 to 39.09 J/(mol·K)). Adsorption kinetics followed the pseudo-second-order model, with intraparticle diffusion acting as a key rate-limiting step. Regardless of the adsorbent, Pb(II) ions were immobilized faster and more efficiently than Cd(II) due to a smaller hydration radius. In conclusion, both industrial by-products represent promising, sustainable options for heavy metal wastewater treatment, with BC demonstrating superior performance. Full article

Artificial soils derived from coal combustion by-products and industrial waste have been successfully used for mine spoil reclamation; however, their ecological risk and toxic element migration in the soil–plant system have not been assessed. The objective of this study was to evaluate the ecological risks in soil substitute covers after five years of their exposition, using the ecological risk factor (ERⁱ), potential ecological risk index (PERI) and geoaccumulation index. The modified BCR-sequential extraction method was applied to determine the chemical partitioning of the most toxic heavy metals (Cd, Cr, Cu, Ni, Pb, Zn). Additionally, the bioconcentration and translocation factors were used to assess the uptake of toxic elements by Phragmites australis. Findings from PERI indicate a moderate risk (239 and 258), mainly associated with moderate and considerable ERⁱ for Cd and Hg, respectively. The other toxic metals are associated with a low risk (ERⁱ < 40). Sequential extraction results showed the lowest concentrations of heavy metals in F1 fraction (0–30%) and increased in subsequent fractions: F2 (1–43%), F3 (10–62%) and F4 (10–89%). The calculated BCF values were below 1, indicating that the concentration of toxic metals in plants was lower than that in the soil substitute. The only exception was observed for Mn and Sn (BCF > 1). The results suggest that the tested soil substitutes are suitable for the reclamation of post-mining areas and may support sustainable biomass production. However, due to industrial atmospheric deposition and ecological risk associated with selected trace elements, continued monitoring of toxic metals is recommended. Full article

The growing accumulation of industrial waste and the depletion of natural mineral resources underscore the need for sustainable approaches to producing ceramic and construction materials. Among the most promising secondary raw materials are coal combustion by-products and metallurgical slags, which are suitable for ceramic applications. This review summarizes recent advances in the use of coal ash, blast furnace and steelmaking slags, together with clay-based raw materials, for the fabrication of ceramic and composite materials. Special attention is given to the physicochemical properties of technogenic raw materials and their effects on sintering, porosity, densification, mechanical strength, and thermal stability. Modern processing methods, including pressing and high-temperature firing, are also discussed. The influence of key technological parameters, such as oxide composition, particle size distribution, firing temperature, and activation conditions, is analyzed. In addition, the review examines major challenges related to raw material heterogeneity, structural instability, thermal stress development, cracking, free CaO reactivity, and environmental risks associated with heavy metal leaching. Recent studies show that incorporating industrial waste into ceramic systems reduces waste disposal, natural resource consumption, energy use, and CO₂ emissions, while promoting sustainable and resource-efficient technologies. Ash- and slag-based ceramics therefore remain highly promising materials for construction applications. Full article

Waste materials are abundant and often act as slow environmental contaminants, creating severe ecological challenges. With rapid industrialization, electricity demand has increased substantially, and in India, coal-based thermal power plants (TPPs) remain the dominant source of power generation. Coal combustion produces two major by-products: fly ash and bottom ash (BA). While fly ash is widely utilized in blended cements due to its pozzolanic nature, BA has received comparatively limited attention despite having similar chemical characteristics. Owing to its coarser particle size, BA shows strong potential as a substitute for natural river sand, the excessive extraction of which has led to severe resource depletion and sustainability concerns. Unlike previous studies that focused on single-source BA or limited performance evaluation, this study investigates the use of BA from multiple sources to develop resource-efficient bottom ash concrete (BAC). Concrete mixes containing 0%, 20%, 35%, and 50% BA as volumetric replacements of river sand were evaluated for their fresh, mechanical, durability, and microstructural properties. The results indicate that BA significantly influences concrete performance due to its porous structure. Among the investigated mixes, 35% river sand replacement with BA showed the most favorable performance for the specific materials and sources used in this study, achieving up to 17.46% higher compressive strength and up to 16.14% higher resistance to transport-related properties at 90 days. Microstructural analysis confirmed the formation of secondary C–S–H gel, which enhanced matrix densification. However, 50% replacement resulted in reduced performance. The findings demonstrate that BA can be effectively utilized in concrete at replacement levels of up to 35% as a sustainable substitute for river sand under the investigated material conditions. Full article

To investigate the carbon footprint of bamboo-based activated carbon from different manufacturing pathways, this research evaluated cradle-to-gate manufacturing emissions under a unified system boundary and allocation baseline based on primary data from a 10,000 t/year continuous industrial production line. An LCA model was constructed and verified using an allocation ratio interval scanning method. Results showed that carbon footprints of granular, powdered, and extruded activated carbons were 184.76 kg CO₂ e/t kg CO₂ e/t, 236.75 kg CO₂ e/t, and 293.36 kg CO₂ e/t. Although these products shared identical carbonization and steam activation units, the carbon footprints from milling, molding, and binder inputs accounted for 25.01%, 41.48%, and 52.77% of the total emissions. Internal thermal energy recovery via by-product gas recycling decreased emissions by 81.7%, 77.7%, and 73.8%, respectively. Compared with traditional coal-based alternatives, bamboo-based products achieved a reduction in emissions of about 95%. This study provides scientific guidance for the low-carbon production process of bamboo-based activated carbon and demonstrates the potential of biomass substitution for climate change mitigation. Full article

Coal liquefaction residues (CLRs), including both indirect (ICLR) and direct (DCLR) variants, represent industrial by-products whose conventional landfill disposal raises environmental concerns. This study comparatively analyzes ICLR and DCLR properties against limestone fine aggregates through physicochemical characterization. Results indicate that ICLR contains predominant SiO₂ crystalline phases (50.05%) with trace Fe-Ti-Al-Mg oxides, demonstrating higher Vickers hardness (615 HV vs. 246 HV for limestone) and elastic modulus (98 GPa vs. 81 GPa for limestone), while its apparent relative density (2.612) closely matches that of limestone (2.783). Conversely, DCLR features abundant carbonaceous components (75.9% C) with olefinic/aromatic structures (asphaltene content 66.2%), exhibiting lower mechanical strength (Vickers hardness 21 HV) but enhanced asphalt affinity, as indicated by strong C=C (1591 cm⁻¹) and aromatic C–H (744 cm⁻¹) absorption peaks in FTIR. Both CLRs share comparable gradation curves and micromorphological characteristics with limestone aggregates, including uniform surface scaly textures. While pore-size distributions differ minimally between CLRs, both present finer porosity than limestone and show no leachate toxicity risks, confirming their viability as sustainable alternatives to asphalt fine aggregates. Full article

Coal gangue (CG) ranks among China’s most significant industrial solid by-products. In response to China’s carbon neutrality commitments and the growing emphasis on resource recycling, finding effective ways to valorize CG has emerged as a pressing concern. Based on the mineral composition and chemical composition characteristics of CG, this study systematically investigated the enhancement effects of three alkali activators (Na₂SiO₃, NaOH, and Ca(OH)₂) on the cementitious properties of CG. Through different dosage and compressive strength tests, the efficiency ranking of the three activators was determined as follows: Na₂SiO₃ > Ca(OH)₂ > NaOH. A 10% Na₂SiO₃ dosage combined with 28-day curing was identified as the optimal condition for achieving sufficient reaction and structural densification. Under these conditions, the compressive strength of CG cementitious material reached 6.4 MPa, representing an increase of 190.9% compared to the blank group (2.2 MPa), significantly superior to Ca(OH)₂ (69.55%) and NaOH (62.27%). X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analyses revealed that alkali activators function primarily by disrupting the crystalline framework of CG, promoting the cross-linking polymerization of silicon–aluminum monomers to generate dense cementitious products, thereby improving material performance. The Na₂SiO₃ is attributed to its “dual activation effect”, providing OH⁻ to create an alkaline environment while supplying reactive silicate ions (SiO₃²⁻) to accelerate N-A-S-H gel and C-A-S-H gel formation. These findings offer guidance for optimizing CG-based cementitious formulations for formula optimization and large-scale utilization of CG cementitious materials. Full article

This study investigates the ternary co-pyrolysis behavior of Soma lignite (SL), sugar beet pulp (SBP), and hazelnut husk (HH) at four blending ratios (80:10:10, 60:20:20, 40:30:30, and 20:40:40 wt.%) using thermogravimetric analysis under a nitrogen atmosphere. Synergistic interactions were quantified through mass-based ($\Delta W$) and rate-based ($\mathrm{\Psi }$) deviation indices, and the contributions of individual pseudo-components were resolved by Gaussian deconvolution of DTG curves. Among the blends investigated, the 40:30:30 (SL:SBP:HH) composition exhibited the most consistent and intense synergistic effect across all temperature zones, with the strongest promotion concentrated in the high-temperature region associated with CaCO₃ mineral decomposition. Deconvolution analysis revealed that increasing the biomass fraction systematically shifted coal-related pseudo-component peaks to lower temperatures and enhanced the hemicellulose/pectin contribution, confirming that biomass-derived volatiles accelerate lignite devolatilization. These findings demonstrate that ternary co-pyrolysis of low-rank coal with two complementary agricultural by-products is a viable and sustainable strategy to enhance pyrolysis performance, valorize agro-industrial waste, and reduce the environmental footprint of lignite utilization, providing fundamental thermochemical data for the design of integrated lignite–biomass co-processing systems. Full article

Alkali-activated cementitious materials (AACMs) are recognized as promising green building materials and a viable alternative to traditional cement due to their low carbon footprint, high durability, and superior mechanical properties. These materials primarily utilize industrial by-products such as coal gangue, steel slag, and gasification slag. The alkali activation process offers an environmentally friendly pathway for the construction industry. To address the need for the large-scale utilization of bulk solid wastes, this study established a ternary solid waste synergy system comprising coal gangue, steel slag, and gasification slag. The preparation and performance optimization of AACMs based on this system were investigated. An optimal mix proportion was identified through orthogonal experiments, and the influence of various factors on the mechanical properties at different curing ages was analyzed. The results indicate that the fluidity of all AACMs meets the requirements for general backfilling applications. Among the alkali activators, Na₂SO₄ had the smallest effect on fluidity. Under single-activator conditions, sodium silicate (water glass) and sodium hydroxide exerted a greater influence on strength development compared to anhydrous sodium sulfate. For the composite activator system, the significance of parameters affecting compressive strength followed the order: silicate modulus > alkali activator content. The maximum 28-day unconfined compressive strength reached 7.653 MPa with a mix proportion of 55% coal gangue, 45% steel slag, and 5% gasification slag, as well as a silicate modulus of 1.2 and a water glass content of 8%. This represents increases of 540.95% and 299.25% compared to the non-activated group and single-activator groups, respectively. Microstructural analysis revealed that the enhanced integrity and strength of AACMs are attributed to pore-filling by hydration products, predominantly C–S–H and C–A–S–H gels. This study successfully developed high-performance AACMs based on a coal gangue–steel slag–gasification slag ternary system, elucidating the critical regulatory role of silicate modulus in composite activators and the underlying microstructural strengthening mechanisms. The findings provide a theoretical foundation and technical support for the high-value, large-scale utilization of bulk industrial solid wastes in building materials. Full article

Within a waste biorefinery framework, integrating agro-industrial by-products into the circular economy requires a detailed understanding of the thermochemical conversion behaviour of low-grade carbonaceous materials. This study evaluates the co-pyrolysis characteristics of Soma lignite (SL) and pectin-rich sugar beet pulp (SBP) as a sustainable route for upgrading these resources into clean energy carriers. Interactions between the two feedstocks were analysed by thermogravimetric measurements, triple-region kinetic modelling, and quantitative synergy indices at six mixing ratios, including the pure samples (100:0, 80:20, 60:40, 40:60, 20:80, and 0:100 wt% SL:SBP). The Reactivity Index ($R_{\mathrm{m}}$) increased from 0.97 × 10⁻⁴ s⁻¹K⁻¹ for pure SL to 8.65 × 10⁻⁴ s⁻¹K⁻¹ for the 20:80 blend, showing that SBP acts as a highly reactive biomass component that accelerates devolatilisation in the main pyrolysis region. Synergy analysis indicated a shift from inhibitory behaviour in coal-rich blends to slightly positive synergy in SBP-rich mixtures, with the onset of positive $\Delta TC$ around 60 wt% SBP under the present single-heating-rate, non-replicated TGA conditions. This tentative threshold-like behaviour suggests that a critical level of literature-supported, hypothesised hydrogen-donating biomass radicals may be required to overcome the structural resistance of the coal matrix. Within these experimental limitations, the apparent macro-kinetic deviations and first-order Arrhenius parameters suggest that SL/SBP co-pyrolysis follows a complex, non-additive pathway that should be further validated by multi-heating-rate and product characterisation studies in future work. The primary contribution of this work lies in proposing this distinct threshold-like biomass fraction at the macro-kinetic level that governs the transition from heat-transfer-limited antagonism to radical-influenced synergy in low-rank coal and pectin-rich biomass blends. Overall, the combined $\Delta TC$, $\Delta E$ and $R_{\mathrm{m}}$ descriptors provide useful macro-kinetic benchmarks for guiding the optimisation of thermochemical processes for low-grade carbonaceous resources. Full article

Two mineral-based solid residues, namely coal gangue (CG) and phosphorus tailings (PT), two of the largest solid waste streams in the mining industry, were used as the sole metal feedstocks to fabricate a novel MgCaFeAl layered double hydroxide (LDH-GT) via a 700 °C calcination, acid leaching and hydrothermal coprecipitation route, with simultaneous synthesis of white carbon black from the reaction byproducts. Under optimized conditions (total metal load is 150 mg kg⁻¹, LDH-GT dose is 0.09 g, pH from 6 to 7), the synthesized material achieved concurrent immobilization efficiencies of 76.28%, 99.96%, and 99.95% for Cr (VI), Cd (II) and Ni (II), respectively, within a 24 h reaction period. TCLP leachability decreased by 82 to 91% relative to the untreated soil. After three wetting, drying and freeze–thaw cycles, the leached concentrations of all three metals remained below 0.3 mg L⁻¹, confirming excellent long-term stability. Mechanistic analyses revealed that Cr (VI) was mainly sequestered through interlayer anion exchange and surface complexation, whereas Cd (II) and Ni (II) were immobilized via isomorphic substitution into the LDH lattice, precipitation as carbonates, and incorporation into Fe/Mn oxides. A 7-day mung bean bioassay showed that LDH-GT amendment increased seed germination from 50% to 73%, enhanced root and shoot biomass by 1.1- to 1.6-fold, and decreased plant Cr, Cd, and Ni contents by over 80%. The 16S rRNA sequencing further demonstrated that LDH-GT reversed the decline in microbial α diversity induced by heavy metal stress, restored aerobic chemoheterotrophic and sulfur cycling functional guilds, and reduced pathogenic signatures. This study provides the demonstration of a waste-to-resource LDH that achieves efficient, durable remediation of multi-metal-contaminated soils, offering a scalable route for coupling solid waste valorization with in situ site restoration. Full article

Fly ash (FA), a major by-product of coal combustion, has long been regarded as a challenging industrial solid waste. Its inherent abundance of alkaline-earth oxides positioned it as a promising candidate for CO₂ sequestration through mineral carbonation. This study systematically investigated the effects of key operational parameters, including time, stirring rate, ultrasonic treatment, and solid-to-liquid ratio, on the leaching efficiency of calcium ions and subsequent CO₂ fixation. Ultrasonic treatment, a solid-to-liquid ratio of 1:7, a stirring speed of 600 rpm, and 7% monoethanolamine (MEA) collectively enhanced the calcium leaching efficiency (χ_e) to 16.7%, thereby supplying a substantial reservoir of calcium ions for CO₂ fixation. Additionally, the CO₂ injection into fly ash slurry and the slurry spraying into CO₂ gas were investigated to optimize reactor configurations. The latter method demonstrated superior performance, attaining a CO₂ fixation efficiency of 7.23%. This corresponds to a carbonation conversion efficiency (ηc) of approximately 44.5%, indicating that nearly half of the leached calcium ions were successfully converted into stable carbonates. Advanced characterization techniques (SEM-EDS, XRD, FTIR) confirmed the formation of stable carbonates and highlighted the role of additives in enhancing reactivity. The environmental benefit of this approach is addressing fly ash wastes and transforming fly ash into a CO₂ fixation material. These findings provided critical insights for calcium leaching and CO₂ fixation of fly ash. Full article

Coal gangue, as a predominant solid byproduct of the global coal industry, poses severe environmental challenges because of its massive accumulation and low utilization rate. This review systematically synthesizes and analyzes published experimental and analytical studies on the dual-pathway utilization of coal gangue in concrete, including Pathway 1 (aggregate substitution) and Pathway 2 (cementitious activity activation). While the application of coal gangue aggregates is traditionally limited by their inherent high porosity and lower mechanical strength than those of natural aggregates, this review demonstrates that performance barriers can be effectively overcome. Through multiscale modification strategies—including surface densification, biological mineralization (MICP), and matrix synergy—the interfacial defects are significantly mitigated, allowing for feasible substitution in structural concrete. Conversely, for the mineral admixture pathway, controlled thermal activation is identified as a key process to optimize the phase transformation of kaolinite, thereby significantly enhancing pozzolanic reactivity and long-term durability. According to reported studies, the partial replacement of natural aggregates or cement with coal gangue can reduce CO₂ emissions by approximately tens to several hundreds of kilograms per ton of coal gangue utilized, depending on the substitution level and activation strategy, highlighting its considerable potential for carbon reduction in the construction sector. Nevertheless, challenges related to energy-intensive activation processes and variability in raw gangue composition remain. These limitations indicate the need for future research focusing on low-carbon activation technologies, standardized classification of coal gangue resources, and long-term performance validation under realistic service environments. Based on the synthesized literature, this review discusses hierarchical utilization concepts and low-carbon activation approaches as promising directions for promoting the sustainable transformation of coal gangue from an environmental liability into a carbon-reduction asset in the construction industry. Full article