Search Results (405)

The growing demand for sustainable construction practices has driven research into self-sensing materials incorporating recycled waste for smart SHM (Structural Health Monitoring) systems. However, previous works did not investigate the influence of rheological behavior and piezoresistive properties of sustainable cementitious sensors containing red mud (RM) on the strain monitoring of concrete beams. To address this gap, this study presents an experimental analysis of the rheological, mechanical, and self-sensing performance of mortars incorporating carbon black nanoparticles (CBN) and varying levels of RM (25–100% sand replacement by volume), followed by their application in monitoring strain in a reinforced concrete beam under dynamic loading. The results showed that increasing RM content led to higher viscosity and yield stress, with a 60% reduction in consistency index. Compressive strength increased by up to 80%, while mortars with RM content higher than 50% showed high electrical conductivity and reversible resistivity changes under load cycles. Mortars containing 50–100% RM demonstrated improved piezoresistive response, with a 23% increase in gauge factor, and the best-performing sensor embedded in a concrete beam exhibited stable and reversible fractional changes in resistivity, closely matching strain gauge data during dynamic loading conditions. These findings highlight the potential of RM-based smart mortars to enhance sustainability and performance in SHM applications. Full article

Lead (Pb) is a highly toxic heavy metal frequently found in industrial wastewater, posing serious risks to both human health and the environment. In this study, a porous geopolymer synthesized from fly ash, metakaolin, and red mud was evaluated for Pb(II) removal via batch adsorption experiments under varying pH, dosage, contact time, temperature, and initial concentration. The synthesized material exhibited a favorable mesoporous structure, with a BET surface area of 42.05 m² g⁻¹ and an average pore width of 6.26 nm, making it suitable for heavy metal uptake. Adsorption kinetics followed the pseudo-second-order model (R² = 0.9993), while the Langmuir isotherm (R² ≈ 0.999) best described the equilibrium data, indicating monolayer chemical adsorption as the dominant mechanism, with a maximum capacity of 74.26 mg g⁻¹ at 318 K. Thermodynamic analyses confirmed that the adsorption was spontaneous (ΔG° < 0), endothermic (ΔH° > 0), and accompanied by increased entropy (ΔS° > 0). Desorption and regeneration tests revealed EDTA to be a more effective agent than HNO₃, maintaining a reuse efficiency of 81.35% after four cycles. These results highlight the potential of waste-derived porous geopolymers as regenerable, low-cost, and efficient adsorbents for lead removal. Full article

Red mud, fly ash, ground granulated blast furnace slag, and carbide slag are industrial byproducts posing significant environmental challenges. The synthesis of geopolymers represents a promising approach for their sustainable valorization. This study investigated the strength development mechanisms and microstructural evolution of Red Mud–Class F Fly Ash-Based Geopolymer under co-incorporation of ground granulated blast furnace slag and carbide slag through compressive strength tests, X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy–Energy Dispersive Spectrometer (SEM-EDS). Key findings include the following: (1) single incorporation of ground granulated blast furnace slag achieved a 60-day compressive strength of 11.6 MPa—6.4× higher than carbide slag-only systems (1.8 MPa); (2) hybrid systems (50% ground granulated blast furnace slag/50% carbide slag) reached 8.8 MPa, demonstrating a strength peak at balanced ground granulated blast furnace slag/carbide slag ratios; (3) the multi-source geopolymer systems were dominated by monomeric gels (C-A-H, C-S-H, C-A-S-H), crystalline phases (ettringite and hydrocalumite), and poly-aluminosilicate chains ((-Si-O-Al-Si-O-)n); (4) elevated Ca levels (>40 weight percent in ground granulated blast furnace slag/carbide slag) favored C-S-H formation, while optimal Si/Al ratios (1.5–2.5) promoted gel polycondensation into long-chain polymers (e.g., Si-O-Al-O), consolidating the matrix. These results resolve the critical limitation of low strength (≤3.1 MPa) in ambient-cured red mud–fly ash geopolymers reported previously, enabling scalable utilization of red mud (46.44% Fe₂O₃) and carbide slag (92.43% CaO) while advancing circular economy paradigms in construction materials. Full article

To conserve natural resources and reduce waste generation, the effective valorization of industrial waste and byproducts in engineering applications is becoming increasingly important. Among these materials, aluminum production residues (APRs) offer a promising and sustainable solution for road pavement applications. Unlike previous reviews, this paper uniquely examines recent research on the use of various APRs in bituminous materials across multiple scales, with particular attention to their roles as additives and fillers. The APRs examined included red mud (RM), aluminum dross (AD), and spent pot lining (SPL) residues, as well as secondary aluminum waste (SAW). These materials have been employed as additives in asphalt binders (microscale), as fillers in asphalt mastics (mesoscale), and as additives or fillers in asphalt mixtures (macroscale). Overall, this review indicates that adopting appropriate treatment approaches for APRs as asphalt modifiers can enhance their dispersion, thermal stability, rheological behavior, and leaching performance. In particular, the use of RM has been shown to improve thermal stability, tensile strength, intermediate-temperature cracking resistance, and rutting resistance, largely due to the increased stiffness it imparts to asphalt mastic and mixture phases. However, there is no clear consensus among researchers regarding other properties, as performance outcomes depend strongly on multiple factors, particularly the physicochemical characteristics of the RM, filler–binder ratios, testing methods, and reference filler types. Other APRs—such as AD, SPL, and SAW—have also shown beneficial effects on the performance of asphalt mixtures. There is still limited research on the influence of APRs physicochemical variability on asphalt–filler interactions and the performance of bituminous materials. For the safe and large-scale adoption of APRs, it is essential to establish standardized characterization procedures, testing methods, and application guidelines while considering diverse climatic conditions. Comprehensive assessments of cost and environmental impacts should also be incorporated to support informed decision-making by engineers and industrial stakeholders. Full article

This study developed a sustainable high-strength coal gangue backfill material for underground mining applications using coal gangue, fly ash, and cement as primary raw materials, with red mud (RM) as an alternative alkali activator. The mechanical properties of the backfill material were systematically optimized by adjusting coal gangue particle size and alkali activator dosage. The optimized formulation (coal gangue/fly ash/cement = 5:4:1, 3–6 mm coal gangue particle size, 5% RM, which named BF-6-5RM) achieved superior compressive strengths of 8.23 MPa (7 days) and 10.5 MPa (28 days), significantly exceeding conventional backfill requirements and outperforming a CaO-activated reference system (coal gangue/fly ash/cement = 5:4:1, 3–6 mm coal gangue particle size, 2% CaO, which named BF-6-2CaO). Microstructural and physicochemical analyses revealed that both formulations produced calcium silicate hydrate gels (C-S-H gels) and ettringite (AFt) as key hydration products, though BF-6-5RM exhibited a denser microstructure with well-developed ettringite networks and no detectable portlandite (CH), explaining its enhanced early-age strength. Environmental assessments confirmed effective heavy metal immobilization via encapsulation, adsorption, precipitation and substitution, except for arsenic (As), which exceeded Class III groundwater thresholds (DZ/T 0290-2015) due to elevated raw material content, displaying “surface wash-off, diffusion and depletion” leaching behavior. The findings confirm that red mud-based alkali activation is a viable technology for underground backfilling, provided it is coupled with arsenic control strategies like chemical stabilization or the selection of low-arsenic raw materials. This approach not only enables the resource utilization of hazardous industrial waste but also facilitates the production of backfill materials that combine both mechanical strength and environmental compatibility, thereby delivering dual economic and ecological benefits for sustainable mining practices. Full article

In response to the pressing environmental challenges posed by electrolytic manganese residue (EMR) and red mud (RM), this study proposes an innovative cementitious material technology for the synergistic co-utilization of these industrial wastes. By employing steel slag (SS) as a calcium-rich skeleton, the system effectively immobilizes sulfates from EMR and alkalinity from RM, converting hazardous wastes into value-added construction materials. Through orthogonal experimentation, an optimal mix proportion was established—30% RM, 20% EMR, and 50% SS at a water-to-binder ratio of 0.28—which achieved a 28-day compressive strength of 20.40 MPa, meeting relevant industry standards for auxiliary cementitious materials. Microstructural analysis unveiled a multi-stage alkali-sulfate synergistic activation mechanism: (1) the high alkalinity derived from RM rapidly activates the dissolution of aluminosilicate phases in both SS and EMR; (2) sulfate ions released from EMR promote extensive formation of ettringite (AFt), enhancing early-age structural integrity; and (3) calcium ions from SS facilitate the development of a dense C-S-H gel matrix, which serves as the primary binding phase. More profoundly, this process exemplifies a self-stabilizing waste-to-resource conversion mechanism, whereby harmful constituents (sulfates and free alkalis) are constructively incorporated into stable hydration products. This work not only elucidates a coherent scientific framework for the safe and efficient reclamation of multi-source solid wastes, but also demonstrates a scalable and ecologically viable pathway for million-ton-scale valorization of EMR and RM. Furthermore, it presents feasibility insights for the application of high-dosage steel slag-based material systems, thereby unifying significant environmental and economic advantages. Full article

Red mud, a by-product of aluminum production, leads to significant environmental challenges due to its alkalinity and presence of soluble compounds. This study explores its valorization through agglomeration with blast furnace sludge as a reducing agent to form self-reducing briquettes. Five C/Fe₂O₃ ratios (0.131, 0.262, 0.523, 0.840 and 1.000) were tested to determine the most effective reducing condition, with 0.840 emerging as optimal based on thermal analysis (mass loss of 27.44 wt.% at 1200 °C and iron formation specific energy of 450 J g⁻¹). Briquettes prepared with three agglomeration methods varying in water content (water/starch ratios of 6:1, 12:1 and 18:1) were evaluated through drop, compression and abrasion tests. The agglomeration method with a 12:1 water/solid ratio, involving both starch gelatinization and red mud water absorption, produced the most mechanically resistant briquettes (19.210 MPa). The mechanical and metallurgical properties of the 0.840-2W briquettes after reduction at 700, 950, 1200 and 1450 °C (temperature maintenance for 15 min) were assessed to define the best compromise between the reduction degree and mechanical strength. While reduction at 950 °C led to the weakest structure (0.449 MPa) but poor metallization, 1450 °C ensured the highest degree of reduction (94%) with adequate brittleness to facilitate a possible subsequent magnetic separation. Full article

Mineral expansive from FDG—flue-gas desulfurization—blended with calcium aluminate cement CAC was analyzed as mitigation shrinkage of alkali-activated residual mortars AAM. The AAM mortars were composed of red mud (RM) and bottom ash (BA), as precursors of a metakaolin MK-based system. MK replacement (0, 50, 70%) in alkaline solution (10M) and ratio 1:2 (binder/sand) was studied. Engineering properties were performed, and included mechanical strength, setting times, and dry shrinkage (HR 60%), as well as the microstructure formed at 7 d and 28 days. A total of 10% CAC-FGD dosage was the most efficient, reducing drying shrinkage by 23% and autogenous shrinkage by up to 30%. The findings showed that this addition also improved mechanical strength by approximately 16% at 28 days. Under the addition of CAC-FGD, the results suggest the presence of aluminosilicate gels of the (Na,C)-(A)-S-H type and the formation of ettringite, which are possibly responsible for ensuring good performance and a controlled expansion that, in turn, compensates for the shrinkage of the activated mortars. Full article

Designing phosphate adsorbents is often hindered by trial-and-error optimization that overlooks nonlinear coupling between preparation parameters and operational conditions. Here we present a unified, explainable machine-learning framework that links red mud modified biochar bead (RM/CSBC) preparation (red mud dosage, biomass dosage, and pyrolysis temperature) to operating variables (initial pH, reaction temperature, contact time, and initial phosphate concentration) and directly guides condition selection. Using 95 independent experiments, six regressors were trained and compared. Random Forest (RF) model demonstrated strong prediction accuracy, with R² values of 0.916 for the training set and 0.892 for the test set. Support Vector Regression (SVR) model showed superior performance, achieving R² values of 0.984 and 0.967 for training and test sets, respectively, with low RMSE (0.068 and 0.083) and PBIAS (5.41% and 6.86%). Feature importance analysis revealed red mud and biomass doses positively influenced phosphate adsorption, with surface active sites and phosphate concentration gradient playing significant roles. Experimental verification confirmed RF and SVR models provided accurate predictions under three representative conditions, with deviations between predictions and measurements of +0.66, +0.19, and −0.69 mg·g⁻¹ for SVR and −1.08, −0.79, and −1.15 mg·g⁻¹ for RF, offering reliable guidance for phosphate removal in wastewater using RM/CSBC. This work highlights the potential of using machine learning to optimize waste-based adsorbent materials for wastewater treatment, significantly reducing time and experimental costs. Full article

This study investigates the use of preliminary thermochemical activation in a NaHCO₃ solution under elevated pressure and temperature to modify the chemically stable and hard-to-process phase composition of various mineral raw materials and improve the recovery of valuable components. The method was tested on various types of mineral raw materials, including slag from the reductive smelting of red mud from alumina production prior to acid leaching, ash before chemical beneficiation, gibbsite–kaolinite bauxite prior to gravity separation, and nephelines, for which the sintering process was replaced with chemical beneficiation. The slag from the reductive smelting of red mud was also tested before acid leaching. The activation of slag enhanced tricalcium silicate formation lead to leaching recoveries of ~96% for rare earth elements, ~92% for TiO₂, ~98% for CaO and Al₂O₃, and 50% for Fe₂O₃, compared to much lower values without activation. With ash, activation eliminated the sillimanite and hedenbergite phases, increased mullite and free silica, and formed calcite, resulting in a 15–20% higher silica recovery. With gibbsite–kaolinite bauxite, activation altered kaolinite, siderite, quartz, and hematite contents; eliminated calcium silicate; and improved the silicon modulus of the sand fraction by 35.9% during gravity beneficiation. For nepheline ore, activation promoted the formation of albite and hydrosodalite, eliminated corundum and andradite, and increased silica recovery from 33.58% to 59.6%. These results demonstrate that thermochemical activation effectively transforms mineral structures and significantly improves the efficiency of subsequent beneficiation processes. Full article

In this study, red mud (RM) was utilized as an iron and aluminum source, and reed biomass served as a carbon precursor to prepare red mud-modified biochar beads (RM/CSBC) via the gel-calcination method. Under a pyrolysis temperature of 900 °C and an RM/biomass dosage of 3 g each, RM/CSBC exhibited an optimal balance between adsorption performance and cost. Within typical pH range of 6–9 in wastewater, RM/CSBC maintained effective adsorption performance, while metal ion leaching (Fe ≤ 0.3 mg·L⁻¹, Al ≤ 0.2 mg·L⁻¹) complied with Class II surface water standards in China. Kinetic data were well fitted by the pseudo second-order model, supported by the Elovich model, indicating the involvement of both chemical and physical adsorption mechanisms. Isotherm results showed that the Langmuir model provided the best fit, indicating monolayer adsorption, with a maximum capacity of 85.16 mg·g⁻¹ at 25 °C. XPS analysis revealed the formation of AlPO₄ and FePO₄ precipitates, confirming chemical precipitation as a key mechanism, along with electrostatic attraction and physical sorption. This study highlights the feasibility of RM/CSBC as an efficient and low-cost phosphate adsorbent and provides a theoretical basis for phosphorus removal and recovery from wastewater using waste-derived materials. Full article

In high-concentration tailings backfilling, the stability of the backfill largely depends on the slurry’s self-weighted siltation behavior. Red mud—the strongly alkaline by-product of the Bayer process and a mixture of coarse and fine particles—requires a clear understanding of its self-weight settling–consolidation mechanisms to ensure safe and efficient backfilling. In this study, red mud slurry was selected as the research object, and a multi-scale approach combining sedimentation column tests and microstructural image analysis was employed to reveal the intrinsic relationships among the sediment layer height, sedimentation rate, and pore structure changes during self-weighted siltation. The results show that the flocculated structure of red mud slurry exhibits distinct stratification during self-weighted siltation, including a clarified layer, a structural transition layer, and a dense sediment layer. During the siltation process, the sediment layer height, sedimentation rate, and floc structure of red mud evolve nonlinearly. The addition of flocculants significantly enhances the formation rate of flocculated structures but increases the porosity of the sediment body. At the macroscopic level, this results in a shortened self-weighted siltation time and increased final sediment layer height. To describe the regulatory effect of flocculants on red mud floc structure, a macro–micro predictive model for the sediment layer height was established by introducing a structural enhancement coefficient, considering the effect of flocculants. The model achieved a prediction error within 16%. These findings provide theoretical support for structural control technologies and process optimization of high-concentration fine tailings backfilling, thereby contributing to the sustainable utilization of red mud and the development of environmentally responsible backfilling practices. Full article

The escalating global water crisis, coupled with the unsustainable accumulation of industrial and urban waste, demands innovative solutions that align with circular economy principles. This review explores the transformative potential of waste-derived ceramic membranes as a sustainable strategy for water purification, simultaneously addressing waste valorization and clean water scarcity. Ceramic membranes, traditionally fabricated from high-purity inorganic materials, are renowned for their superior chemical resistance, thermal stability, and durability. Recent advances demonstrate that industrial byproducts, such as red mud, coal fly ash, blast furnace slag, coal gangue, and kiln roller waste, can be effectively repurposed into cost-effective, high-performance filtration materials. This paper critically examines fabrication techniques, material properties, and performance metrics of waste-derived ceramic membranes. By transforming industrial waste into functional filtration materials, this approach not only mitigates environmental pollution but also contributes to sustainable water security. Full article

Infrastructure construction is a major contributor to carbon emissions, primarily due to the extensive use of mineral materials such as cement and aggregates, which release significant amounts of carbon dioxide during production and use. While existing research has predominantly centered on the applications of concrete, the present study extends the investigation to encompass inorganic–organic composites, alloy materials, and wastewater treatment systems, with particular attention to bridging the gap between theoretical potential and practical implementation. This study identifies China, the USA, and India as leaders in this field, attributing their progress to abundant material resources and sustained policy support. Key findings reveal that while geopolymers can fully replace cement, substitution rates of less than 50% are optimal for high-performance concrete to maintain structural integrity and decarbonization benefits. Aggregate replacements using materials such as air-cooled blast furnace slag show 50–100% feasibility. This review further highlights the multifunctional potential of red mud, rice husk ash, fly ash, and blast furnace slag as cement replacements, aggregates, reinforcers, catalysts, adsorbents, and composite fillers. However, challenges such as unstable raw material supply, lack of standardization, and insufficient international collaboration persist; these issues have often been overlooked in prior research and viable solutions have not been proposed. To address these barriers, a triple-objective framework is introduced in this study, integrating sustainable infrastructure, resource recycling, and environmental remediation, supported by optimized production processes and policy models from leading nations. Future research directions emphasize comprehensive life cycle assessments and enhanced global cooperation to bridge the divide between resource-rich and resource-scarce regions. By synthesizing cross-disciplinary applications and actionable solutions, this work advances the transition toward sustainable infrastructure systems. Full article

The use of mining by-products in bitumen and asphalt mixture modification has drawn a lot of interest lately since it can improve pavement performance while advancing the goals of the circular economy and environmental sustainability. Mining by-products such as steel slag, red mud, silica fume, and fly ash have demonstrated good results as sustainable materials for improving the chemical, mechanical, durability, and rheological properties of asphalt binders and mixtures while also reducing the environmental degradation brought about by the disposal of these by-products. This study reviews research efforts on mining by-products (specifically steel slag, silica fume, red mud, and fly ash) in asphalt concrete pavement construction, analyzing the existing research, with emphasis on their various applications in asphalt concrete, their benefits as sustainable asphalt concrete materials, and limitations connected to their use. This review concludes by providing future directions in the utilization of these mining by-products in asphalt concrete production. This review contributes to the development of cost-effective, eco-friendly, and high-performance road construction materials, helping the transition to sustainable infrastructure. Full article