Search Results (6,866)

Red mud, as a by-product of alkaline regeneration of alumina, has limited application due to its strong alkalinity, fine particle size, and complex composition. In this work, red mud porous ceramics with uniform pore size distribution and high mechanical strength were prepared using a foam-gel casting method. The effects of solid loading and sintering temperature on the microstructure of porous ceramics were systematically investigated. The porosity of red mud-based porousceramics sintered at 1150 °C with a solid content of 60.4% was 33.7%, and the maximum compressive strength was 54.70 MPa, while the porousceramics prepared with a solid loading of 34.1% and sintered at 1050 °C achieved a maximum porosity of 79.7% and a compressive strength of 2.36 MPa. Increasing the solid loading reduced porosity and enhanced compressive strength, allowing for the tailoring of mechanical properties to meet specific application requirements. Higher sintering temperature promoted the formation of the liquid phase, enhanced particle bonding, and further improved the compressive strength. Additionally, toxicity leaching tests confirmed that the ceramics are environmentally safe, with leachate levels well within regulated limits. These results demonstrate the potential of foam-gel casting as an effective route for transforming red mud into value-added porous ceramics, thereby contributing to sustainable waste utilization and broadening the application prospects of red mud-based materials. Full article

Phosphogypsum (PG) stockpiles pose a persistent threat to regional water environments, yet their differential impacts on surface water and groundwater remain unclear. This study examined the pollution characteristics, sources, mechanisms, and model-predicted trends of PG-derived contaminants in both systems within a representative PG-affected region. Results showed that total phosphorus declined sharply from surface water to groundwater due to soil retention, whereas SO₄²⁻ and F⁻ remained comparable. Nitrogen species accumulated more in groundwater, indicating distinct transport and transformation processes. Arsenic was higher in surface water but rarely exceeded limits. In contrast, lead and manganese were significantly enriched in groundwater, exceeding standards by up to 27- and 11-fold, mainly due to reductive mobilization and subsurface geochemical processes. The Nemerow Index indicated heavy pollution in 35% of surface water and 43% of groundwater samples. Principal component analysis identified PG leachate as the dominant pollution source. Model predictions further suggested that increasing stockpile capacity would intensify contamination and pose long-term environmental risks. This study provided a scientific basis for understanding the distinct pollution mechanisms of PG stockpiles and offered guidance for targeted water environment management in PG-impacted areas. These findings have broader implications for regions globally facing similar challenges from industrial solid waste storage. Full article

Approximately 60% of the world’s primary energy is dissipated as waste heat, representing a critical opportunity for energy recovery in sectors such as electro-mobility and fuel cells. Commercial thermoelectric generators (TEGs), predominantly based on bismuth telluride (Bi₂Te₃), face limitations due to mechanical rigidity, toxicity, and high production costs. This study proposes graphene oxide (GO) as an emerging alternative thanks to its oxygenated functional groups and layered structure as well as GO paper facilitates’ thermal and electrical transport. However, the effective integration of this nanomaterial into solid-state systems under real operating conditions remains a technical challenge. Therefore, this work presents the development, multiphysics modeling, and experimental validation of an innovative TEG cell using GO paper as an active layer. The results demonstrate that the proposed GO-ITC achieves an average of 2.75 times higher generated voltage with a lower thermal gradient as well as an improved equivalent figure of merit (ZT) compared to Bi₂Te₃-based TEGs. This work contributes to the evaluation of GO-doped materials for voltage generation under specific thermal gradients, providing a lightweight and flexible solution for waste heat harvesting in modern power systems. Full article

Geothermal silica has emerged as a promising and underutilised precursor for silicon-based lithium-ion battery anodes. Geothermal silica can be recovered from brines, scales, and solid residues generated during geothermal energy production, creating an opportunity to valorise existing waste streams while mitigating silica-scaling problems. This review examines the formation, availability, and material characteristics of geothermal silica, with particular emphasis on its high silica content, commonly reported in the range of ~50–98 wt% in solid geothermal residues, as well as its generally amorphous nature and porous structure. It then evaluates the main processing steps required to convert geothermal silica into battery-relevant silicon, including extraction, purification, and silica-to-silicon reduction, with particular focus on magnesiothermic reduction. Among the available routes, methods that provide improved impurity control while preserving porous or amorphous precursor structures appear most relevant for achieving favourable electrochemical performance. Recent comparative findings indicate that geothermal silica can, in some cases, be competitive with biomass-derived silica sources in terms of purity, composition, and morphology, although these advantages are not universal and depend on source-specific chemistry, impurity profile, and processing conditions. Reported electrochemical studies further show that geothermal-silica-derived silicon and silica-based composites can deliver electrochemically relevant capacities, in some cases exceeding the theoretical capacity of graphite (~372 mAh g⁻¹), although performance varies significantly across studies. In addition, specific surface areas of ~50–150 m² g⁻¹ reported for some geothermal silica materials may support further silicon processing and influence electrochemical behaviour. Overall, geothermal silica represents a technically relevant and sustainability-oriented pathway toward silicon-based anode materials; however, further work is needed on source consistency, impurity management, structural control, long-term cycling stability, and scalable production. Full article

The transition toward low-carbon and circular Municipal Solid Waste (MSW) systems requires integrated evaluation approaches that consider environmental performance, technological maturity, and governance capacity. This study presents a structured, systematic review of MSW disposal and treatment practices published between 2018 and 2026, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines. A total of 71 studies were included and analyzed. Due to heterogeneity in methodologies, system boundaries, and reported indicators, no formal meta-analysis was conducted. Instead, the review provides a comparative and qualitative synthesis of key environmental indicators and structural determinants. Results indicate a transition from open dumping toward engineered landfills and advanced treatment technologies, including waste-to-energy and biological processes. Open dumping is consistently associated with high greenhouse gas emissions and environmental risks, while engineered systems improve containment and enable partial resource recovery. The findings highlight that environmental performance is not determined solely by technology but by the interaction between infrastructure design, operational quality, governance capacity, and economic conditions. The proposed analytical framework supports context-sensitive waste management strategies aligned with circular economy principles and climate mitigation objectives. Full article

A rapid accumulation of plastic waste has created an urgent need for efficient and sustainable recycling technologies. Among various approaches, pyrolysis stands out as promising method of thermochemical recycling of plastic waste; however, the process needs optimization and further research to make it more energy-efficient and sustainable. The conventional approaches for optimization focus on the enhancement of yield, only overlooking efficiency and system-level sustainability. In this study, a machine learning-enabled surrogate-assisted multi-objective artificial intelligence (AI) optimization framework is developed for plastic pyrolysis to maximize product recovery and minimize energy consumption. The model integrates energy return on investment (EROI) and higher heating value (HHV) into process design. A curated dataset of 312 experimental cases covering polyolefins, PET, nylon, and mixed plastics was used to train multiple machine learning algorithms, such as polynomial regression, Gaussian process regression, and Random Forest models. The Random Forest algorithm demonstrated superior predictive robustness across oil yield, HHV, char formation, and EROI. Pareto front analysis using NSGA-II revealed that moderate reaction severities (400–450 °C, 40–70 min) maximize net energy performance while minimizing solid residues. The conditional variational autoencoder as a GenAI model was incorporated to work as a generative proposal engine, which enhances the exploration of chemically feasible operating regions under uncertainty-aware active learning. The integration of techno-economic and life-cycle assessment demonstrates that energy-positive configurations outperform high-yield scenarios, achieving IRR > 15%, energy intensity < 10 MJ kg⁻¹, and CO₂ reductions up to 47% relative to incineration. The proposed framework establishes a data-driven methodology for aligning polymer pyrolysis optimization with circular economy and energy sustainability objectives. Full article

Garden pruning waste from Cynodon sp. is a lignocellulosic resource with high lignin content, which limits anaerobic digestion efficiency. White-rot fungi degrade biomass through solid-state fermentation (SSF). The efficacy of these organisms, however, depends on the balanced removal of lignin and the subsequent preservation of fermentable carbohydrates. The present study evaluated the effect of SSF durations (8, 21, and 36 days) with Trametes hirsuta on enzymatic activity and subsequent biogas production. Laccase activity increased progressively, reaching 983.84 U/L at 36 days, while manganese and versatile peroxidases peaked at 21 days. Fungal-pretreated samples exhibited reduced methane yields, with a maximum of 225.32 NmL/gVS at 8 days, compared with untreated biomass (381.66 NmL/gVS). The total lignin content increased across treatments, suggesting the formation of pseudo-lignin during autoclave sterilization, while glucose and xylose decreased. These results underscore the complexity of optimizing fungal pretreatment and highlight the need to balance fermentation time to preserve carbohydrates while modifying lignin structure. Full article

Abundant non-medicinal byproducts of Polygonatum sibiricum and Gentiana scabra are severely underutilized, resulting in resource waste and environmental burden. A previous study confirmed that triple-microbial co-fermentation enhances their antibacterial activity, yet the temporal metabolic mechanism and optimal process parameters remain unclear due to endpoint-only metabolomics limitations. This study aimed to optimize the staged solid-state fermentation (SSF) system for maximum antibacterial activity, verify the triple-microbial consortium’s synergistic enhancement effect, and elucidate the dynamic metabolic mechanism via time-series metabolomics. A staged SSF strategy was established: Aspergillus niger monoculture (0–48 h) followed by Bacillus subtilis and Saccharomyces cerevisiae co-culture (48–72 h). Key parameters were optimized via single-factor experiments and a Box–Behnken design. Under optimal conditions, inhibition zones against Staphylococcus aureus and Escherichia coli reached 20.8 ± 0.3 mm and 17.6 ± 0.2 mm, respectively, with a 17.5% increase in S. aureus inhibition and markedly improved E. coli inter-batch consistency. Time-series untargeted LC-MS/MS metabolomics (2681 identified metabolites) revealed a three-stage metabolic relay model driving antibacterial enhancement: 0–48 h shikimate pathway activation for phenolic precursor accumulation; 48–60 h dipeptide conversion and ABC transporter enrichment initiating antibacterial synthesis; 60–72 h metabolic flux redirected to indole alkaloid biosynthesis for complex antibacterial compound accumulation. This work provides a mechanistic paradigm for the high-value valorization of herbal byproducts, with applications in natural antibacterial agents and functional feed additives. Full article

The complexity of physicochemical properties in iron ore tailings has led to extensive and varied study avenues. Moreover, changes in these features resulting from source discrepancies have complicated the identification of consistent patterns in study findings, thereby hindering the standardization and advancement of resource exploitation technologies. This paper provides a comprehensive analysis of the utilization pathways for iron tailings. It identifies the mainstream recovery processes for rare earth minerals, a relatively less-researched direction. It also describes research progress on the use of iron tailings for the preparation of fertilizers and soil conditioners, as well as their application as cementitious materials or aggregates in building materials and mine backfilling engineering. It incorporates various activation methods for the preparation of cementitious materials from iron tailings into a unified comparative framework and quantifies the key performance indicators of different activation pathways through a summary table. It also summarizes studies on the ecological reclamation of tailings ponds based on bioremediation techniques. The essential physicochemical properties of iron deposits are meticulously analyzed, and this is followed by a specialized overview of the principal treatment techniques, critical performance indicators, and their foundational mechanisms. The current application of various technical approaches is examined to identify key problems, and future development opportunities are outlined. Full article

Growing municipal solid wastes, environmental deterioration, and the world’s increasing energy demand highlight the urgent need for effective, sustainable energy recovery solutions. Uncontrolled municipal solid wastes contribute explicitly to the global crises of climate change, pollution, and biodiversity loss. Food and organic waste are converted into value-added products using biochemical and thermochemical techniques. Anaerobic digestion (AD) is a versatile, multi-phase waste-to-energy technology that transforms organic waste into renewable energy in an oxygen-free environment. AD uses microorganisms to break down waste, yielding biogas (mostly methane and carbon dioxide) and digestate, a nutrient-fortified by-product. Compared with traditional Single-Stage Anaerobic Digesters (SSAD), Two-Stage Anaerobic Digesters (TSAD) offer notable benefits by separating hydrolysis–acidogenesis from acetogenesis–methanogenesis. These include increased methane yield, improved process control, increased microbial stability, and resistance to inhibitory substances. According to the literature, TSAD systems have been shown to increase methane yield by about 10–30% compared to SSAD. This article covers the dynamics of the microbial population at various stages, the impact of operational factors (HRT, OLR, pH, and temperature), and novel reactor designs with modular and multi-state functions. In line with Oman’s Vision 2040, this study discusses the continuous operation of a two-phase AD co-digestion process and the in-depth techno-economic feasibility of decentralized waste management through optimized biogas production. Optimizing the carbon-to-nitrogen (C/N) ratio within the range of 20–30 in co-digestion systems significantly enhances microbial activity and methane production. The potential of recent developments, such as microbial immobilization, biogas generation techniques, and hybrid integration with photobioreactors or electrochemical systems, to enhance the scalability and efficiency of bioconversion is addressed in a TSAD system. In addition to encouraging circular economy principles through efficient organic waste valorization, this review identifies TSAD as a promising approach to achieving the SDGs related to sustainable cities, clean energy, and responsible consumption. Full article

Palm kernel cake (PKC), a byproduct of palm kernel oil extraction, is processed into palm kernel meal (PKM), which contains hemicellulose rich in mannose, a versatile sugar with applications in the pharmaceutical and food industries. However, its association within the lignin–cellulose matrix is a challenge for industrial extraction. This study proposes an optimized enzymatic hydrolysis method utilizing mannanase to maximize the mannose content from PKM powder to produce palm kernel mannose syrup. A 3³ Box–Behnken design within a response surface methodology coupled with a desirability function method was used to optimize hydrolysis parameters to maximize mannose and solids content while minimizing enzyme concentration and hydrolysis time. The optimal conditions for enzymatic hydrolysis were established as a reaction time of 16 h, 5% (w/v) solids, and 5% (w/w) enzyme, resulting in 4.325 g/L of mannose and a mannose yield of 24.33 ± 0.5%. The palm kernel mannose syrup was evaluated, resulting in a moisture content of 15.85 ± 0.07%, water activity of 0.6918 ± 0.003, and a pH of 4.05 ± 0.282, demonstrating shelf-life stability. These findings demonstrate the technical feasibility of valorizing PKC and PKM into a stable, mannose-rich syrup, offering a sustainable and scalable pathway for converting agro-industrial waste into high-value ingredients for multiple value-added applications. Full article

In developing countries, final disposal sites exhibit different levels of operational control, which influence their environmental performance. This study evaluated the environmental performance of four types of final disposal sites in Mexico: sanitary landfill with energy recovery (SLF+ER) and sanitary landfill with gas flaring (SLFGF), controlled site (CS), and open dump (OD), using life cycle assessment for 1 t of municipal solid waste. Biogas generation was estimated using the Mexican Biogas Model 2.0, and Ecoinvent processes were adapted to local conditions; six impact categories were assessed, and a sensitivity analysis was conducted. The SLF+ER scenario showed the lowest impact in global warming, followed by SLFGF and CS, while OD recorded the highest impact, mainly associated with biogas management. In contrast, scenarios with gas capture and treatment showed higher contributions in categories related to combustion processes. Normalized results indicated that freshwater eutrophication and human carcinogenic toxicity are the dominant impact categories. The sensitivity analysis confirmed the influence of the organic fraction on CH₄ generation without altering the relative ranking among scenarios. Overall, increasing the level of environmental control reduces impacts from fugitive emissions but introduces trade-offs across other impact categories, highlighting the need for comprehensive assessments to support decision-making. Full article

Coal gangue (CG) and iron tailings (ITs) are major industrial solid wastes, and their high-value reuse is crucial for sustainable construction materials. This study explores the feasibility of fabricating sintered porous bricks using CG and ITs as primary constituents, with shale as an auxiliary component. To evaluate durability in cold regions, laboratory freeze–thaw (F-T) cycling experiments were conducted. A degradation assessment framework based on the Wiener stochastic process was developed to predict frost-resistance service life by integrating experimental data with regional climatic conditions. Results show that the fabricated bricks exhibit satisfactory initial properties, with a compressive strength of 10.6 MPa and water absorption of 13.3%. With increasing F-T cycles, compressive strength decreases significantly, accompanied by increased mass loss and water absorption. Stress–strain analysis reveals progressive stiffness reduction and a transition from brittle to ductile failure. Microstructural observations confirm degradation of the glassy phase, pore expansion, and enhanced interconnectivity. The Wiener process-based model effectively describes the stochastic accumulation of F-T damage. By establishing equivalence between laboratory and natural F-T cycles, the long-term service life of coal gangue–iron tailing sintered porous bricks (CG-IT SPBs) in cold regions is theoretically evaluated. This work provides an integrated understanding of F-T damage behavior and establishes a scientific foundation for durability-oriented design and application of such bricks in extremely cold environments. Full article

Coal gangue is one of the most abundant solid wastes generated during coal mining. The use of coal gangue for underground backfilling is widely recognized as an effective approach to reducing waste accumulation and promoting sustainable utilization. To further investigate the bearing and deformation behavior of underground gangue filling materials, combined with the underground occurrence conditions of crushed gangue in goaf, a self-designed loading apparatus for crushed gangue was employed to perform lateral compression experiments on crushed gangue. The compaction deformation, fractal dimension, and acoustic emission evolution characteristics of crushed gangue under the influence of lithology, water content state, particle size distribution, and axial pressure were analyzed. The results indicate that higher rock strength, lower moisture content, smaller particle size range, and lower axial pressure significantly enhance the bearing capacity and reduce axial strain. The fractal dimension increases with decreasing rock strength, increasing moisture content, and increasing axial pressure, reflecting intensified particle fragmentation. The acoustic emission response exhibits three different stages, corresponding to void compaction, void filling, and structural adjustment. Axial pressure has been identified as the main factor controlling acoustic emission energy release, while water content significantly suppresses acoustic emission energy and event frequency. The key roles of particle sliding, rotation, and torque-driven rearrangement in controlling overall deformation were elucidated. These findings provide theoretical support for the mechanical behavior of gangue filling in the goaf and the sustainable disposal and resource utilization of mining waste. Full article

Using solid waste as supplementary cementitious materials (SCMs) is an effective strategy for promoting low-carbon construction development. However, single or binary systems often exhibit mismatched reaction kinetics, thereby limiting their performance at high cement replacement rates. This study focuses on a novel low-carbon concrete designed based on reaction sequence coordination, containing recycled brick powder (RBP), ground granulated blast-furnace slag (GGBS), and self-combusting coal gangue (SCCG). The effects of RBP, GGBS, and SCCG on the hydration process and microstructure of the novel low-carbon concrete with different replacement levels have been studied by testing compressive strength, workability, and durability and observing microstructural changes. The results showed that an optimized ternary composition with an RBP:GGBS:SCCG ratio of 4:3:1 achieves a cement replacement level of 30% while exhibiting a 28-day compressive strength of 38.26 MPa, representing a 14.2% increase compared with plain cement mortar. Microstructural analyses indicate that this enhanced performance results from a time-dependent reaction sequence, in which GGBS contributes predominantly at early ages by supplying calcium, whereas RBP and SCCG mainly participate through delayed pozzolanic reactions and pore refinement at later ages. Consequently, the optimized ternary mortar exhibits a water absorption of 11.12% and a 27.2% reduction in electrical flux. This study aims to provide practical strategies for enhancing the performance of low-carbon cementitious materials through a reaction sequence coordination design approach, thereby improving the utilization efficiency of solid waste in the production of low-carbon building materials. Full article