Search Results (569)

The slag from electric arc furnace (EAF) steelmaking has potential for various applications, but its safe use requires the assessment of heavy metals, such as chromium leaching, to meet environmental standards. This study investigates the microstructure of EAF slag cooled in a slag pot and its effect on Cr immobilization. Slag samples were collected at full scale using a representative sampling method, dividing the slag pot into six zones (internal and external, top to bottom). Microstructural analysis was performed using scanning electron microscopy coupled with energy dispersive spectroscopy and X-ray diffraction, followed by leaching tests on the milled samples. Thermodynamic calculations were performed using FactSage 8.4 to evaluate phase stability and composition. The results indicate that cooling conditions inferred from slag-pot location, spinel size, and spinel zoning are correlated with variations in Cr leaching under neutral conditions. Slower cooling is associated with the formation of large, reverse-zoned spinel phases that may contribute to Cr stabilization, whereas rapid cooling is associated with smaller, homogeneous spinel phases that may increase leaching risk. These findings provide insights for the environmentally safe utilization of EAF slags and inform strategies to minimize Cr release during slag valorization. Full article

Biochar, a carbon-rich material produced through pyrolysis of biomass under limited oxygen conditions, offers a potentially sustainable and cost-competitive solution (qualitative assessment; quantitative LCA and techno-economic data are beyond the scope of this review) for the removal of heavy metals from wastewater. Its high porosity, surface area, and surface functional groups enable diverse adsorption mechanisms, including complexation, ion exchange, and precipitation. Feedstock selection and production parameters critically influence biochar’s physicochemical properties and adsorption performance. Modification techniques such as chemical functionalization, metal impregnation, and composite formation enhance removal efficiency and selectivity for specific contaminants. Applications span industrial, municipal, and agricultural wastewaters, addressing multi-contaminant challenges under variable environmental conditions. Factors affecting removal efficiency include pH, temperature, contaminant concentration, and competing ions, while regeneration methods are essential for maintaining long-term functionality and are discussed. Biochar can be reused and regenerated using bases and acids, but environmental risks related to biochar use, including potential contaminant leaching and ecological impacts, require careful management and regulatory compliance. Future research should focus on novel modification strategies, scaling production for industrial use, and optimizing integration within treatment systems to meet stringent discharge standards and promote sustainable water management. Full article

Gold-mine tailings have attracted increasing interest as alternative constituents in cement-based materials, yet their use in structural concrete remains limited by the lack of multivariable approaches capable of capturing the interaction between tailing fractions with different functional roles. In this study, a tailing-derived fine aggregate and a fine tailing sludge from the Cisneros Project (Santo Domingo, Antioquia, Colombia) were jointly incorporated into structural concrete and evaluated through a response surface methodology based on a central composite design. The tailings were characterized by physical, chemical, mineralogical, and morphological analyses, while concrete mixtures proportioned according to ACI 211 were assessed in terms of 28-day compressive strength. The statistical model revealed a significant quadratic response and a strong interaction between both incorporation variables. The most favorable strength region, based solely on 28-day compressive strength, was identified at sludge contents below 20% and tailing aggregate replacement below 90%, with the latter interpreted as a preliminary mechanical threshold rather than as a practical recommendation for field application. Higher incorporation levels led to strength losses associated with the increasing fineness of the system and greater water demand. This study demonstrates that the performance of tailing-modified structural concrete depends on the coordinated dosage of fractions with distinct roles and provides preliminary mechanical incorporation limits based solely on 28-day compressive strength. Since durability and environmental safety tests, including heavy metal/cyanide leaching, permeability, shrinkage, and chemical resistance, were not conducted, these limits should not be interpreted as definitive recommendations for long-term structural application. Full article

The sustainability, crop production, and food safety of agriculture are increasingly challenged by microplastic pollution, as agricultural soils are the largest reservoirs and may serve as points of contact for plastic particles in the food chain. This review provides a comprehensive overview of plant materials, fate and uptake pathways, detection techniques, and the possible risks of microplastics in agriculture. Agroecosystems are also a source of microplastics, such as plastic mulch films, sewage sludge, compost and manure additives, wastewater irrigation, polymer-coated fertilizers, greenhouse materials, atmospheric deposition, and decomposition of discarded agricultural plastics. Their distribution and mobility in soil are controlled by polymer composition, particle size, morphology, density, surface ageing, soil texture, organic matter content, tillage practices, runoff, leaching, and soil biota. Recent data show that microplastics, especially smaller microplastics and nanoplastics, can attach to root surfaces, penetrate plants via cracks in roots, areas of lateral root development, and apoplastic pathways, and eventually move to tissues aboveground. Plant tissue detection is often accomplished by digestion of the sample, density separation, visual and fluorescence microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, pyrolysis–gas chromatography mass spectrometry, and electron microscopy, but standardization of these methods remains a significant challenge. Microplastics can disrupt seed germination, root structure, nutrient absorption, photosynthesis, oxidative homeostasis, biomass buildup, yield development, and quality. Further, their capacity to transport additives, plasticizers, heavy metals, and persistent organic pollutants raises concerns about the transfer of contaminants to edible plant parts and their potential transfer to human diets. Further studies are needed focusing on field-realistic exposure conditions, long-term crop–soil interactions, nanoplastics behaviour, standardised analysis procedures, uptake and translocation pathways, edible crop risk assessments, and sustainable mitigation approaches to reduce microplastics in agroecosystems. Full article

The sustainable recovery of high-value metals from wastewater has garnered significant attention in light of the circular economy and environmental preservation. Because of its appealing characteristics, membrane separation technology is essential for the sustainable and effective recovery of valuable metals from wastewater, in contrast to conventional methods, which are chemical- or energy-intensive. In this study, a rational design approach was utilized to synthesize a metal–organic framework (MOF) using a deep eutectic solvent (DES) as a mediating medium to control the reaction of framework formation and particle properties. While DESs have been widely used for the physical modification of materials, their role as a chemically modifying medium during MOF synthesis for structural tailoring remains less explored. This synthesized MOF (DM-Zn-PDC@MOF) was further introduced as filler in polysulfone (PSf)-based mixed matrix membranes (MMMs). The performance of DM-Zn-PDC@MOF within the polymer matrix was examined. Several characterization techniques were used to thoroughly analyze the morphological, chemical, and physical characteristics of the MMMs and DM-Zn-PDC@MOF. The addition of the filler material significantly enhanced the membrane characteristics, including pure water flux, hydrophilicity, porosity, surface roughness, pore size, and heavy metal resource recovery in comparison with the pristine membrane. Stable incorporation of the filler within the membrane matrix was indicated by much less filler leaching (<5%) at all concentrations. With DM-Zn-PDC@MOF loading, the pure water flux increasedmore than nine times from 102.8 L/m²h (M-0) to 971.5 L/m²h (M-4). The functionalized membranes showed better flux retention in high-value heavy metal resource recovery using simulated wastewater: 871.8 L/m²h when filtering a Pb(II) ion solution (compared to M-0 with flux 120.6 L/m²h) and 526.8 L/m²h when filtering a Cr(III) ion solution (compared to M-0 with flux 97.1 L/m²h). These values represented approximately 7-fold and 5-fold improvements, respectively. Overall, Pb⁺² > Cr⁺³, but the rejection of Cr(III) ions was also improved, when compared with M-0. The high flux of the membrane makes it easier to process large volumes and concentrate metals in the retentate, turning diluted contaminated streams into a concentrated feedstock for subsequent recovery procedures. 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

The massive generation of coal-based solid wastes (CBSWs) poses severe environmental challenges globally, while widespread soil degradation threatens food security and ecosystem stability. This review critically evaluates the technical feasibility and agro-ecological benefits of valorizing CBSWs—including coal gangue, fly ash, gasification slag, and desulfurization gypsum—as soil amendments within a circular economy framework. We systematically examine the physicochemical characteristics of major CBSW types, analyze modification methods that enhance their performance and safety, and assess their multifaceted effects on soil physical structure, chemical properties, nutrient dynamics, heavy metal immobilization, and microbial communities. A dedicated section addresses environmental risks, particularly toxic element leaching, and outlines integrated control strategies from source selection to post-application monitoring. Critical knowledge gaps persist regarding long-term contaminant stability under climate change scenarios, molecular-scale immobilization mechanisms, and economic scalability. Future research must prioritize advanced low-energy modification technologies, robust long-term field studies, and harmonized international regulations. We conclude that with scientifically guided modification and stringent risk management, CBSWs can be transformed into safe, multifunctional soil conditioners, simultaneously addressing industrial waste management and contributing to global restoration of degraded soil health. Full article

This study aims to explore the preparation process and properties of unburned lightweight aggregate using red mud synergistically with fly ash, granulated blast-furnace slag, and other multi-source solid wastes. Curing regimes and alkali-activated systems were controlled. Their effects on physical properties and environmental safety of lightweight aggregate were systematically evaluated. Results show that curing temperature and alkali activator exert significant synergistic effects on physical properties of lightweight aggregates. Steam curing performs better than standard curing. Performance improves with increasing steam temperature. Sodium silicate solution with a modulus of 1.0 is determined as the optimal activator. Under 90 °C steam curing, Sample D2 achieves the best overall performance. Its cylinder compressive strength reaches 6.92 MPa. 1 h water absorption is 14.8%. Softening coefficient is 0.93. Porosity is as low as 31.07%. Microscopic analysis reveals that higher curing temperature significantly accelerates the hydration reaction of the RMLWA system. It promotes the formation of abundant cementitious products such as C-S-H gel. These products fully fill internal pores and microcracks of the aggregate. A dense three-dimensional network skeleton structure is finally formed. For environmental safety, heavy metal leaching concentrations of steam-cured samples are generally lower than those of standard-cured samples. This study realizes high-value resource utilization of industrial solid wastes. It also provides a new technical route for the development of green building lightweight aggregate. Full article

Municipal solid waste incineration fly ash (MSWI FA) represents a significant environmental challenge due to its high content of toxic heavy metal (HM) and large-scale generation. This study demonstrates the feasibility pathway for converting hazardous MSWI FA into well-crystallized layered double hydroxide nanosheets (LDH-FA). Sodium dimethyl dithiocarbamate (SDD) was incorporated as a chelating stabilizer to enable synergistic HM immobilization during acid leaching and crystallization. High-resolution transmission electron microscopy (HRTEM) confirmed the characteristic two-dimensional nanosheet morphology with interlayer spacings consistent with LDH structures, while elemental mapping revealed homogeneous distribution of Pb and Zn within the nanosheet matrix. SDD dosages higher than 1.0 wt% effectively suppressed HM leaching, and Pb concentrations were controlled below 0.1 mg/L and Zn maintained at minimal levels. BCR sequential extraction analysis further demonstrated that SDD treatment effectively transformed HMs from bioavailable acid-soluble fractions to stable forms. This investigation establishes an innovative approach to MSWI FA resource utilization and provides mechanistic insights into HM stabilization within LDH nanostructures, offering a scientific basis for safer applications of waste-derived nanomaterials. Full article

In situ leaching is increasingly used for rare earth element (REE) extraction because of its operational efficiency; however, acidic and chemically reactive leaching solutions may generate substantial environmental risks in riverine systems. This study evaluated water contamination and screening-level ecological risk following a cyanide leakage incident associated with a pilot REE mining operation in Houaphanh Province, northern Lao PDR. Surface water samples were collected from 12 downstream monitoring locations between February and April 2024. Physicochemical parameters, free cyanide (CN⁻), and dissolved metals, including arsenic (As), lead (Pb), copper (Cu), manganese (Mn), aluminum (Al), zinc (Zn), and iron (Fe), were analyzed using portable multiparameter probes, colorimetric cyanide determination, and ICP-OES. Contamination severity was interpreted using Pollution Index (PI) and Hazard Quotient (HQ) indicators based on Lao national standards and international guideline values. Results showed severe downstream contamination, with free cyanide and several dissolved metals substantially exceeding permissible thresholds. Observed elevated concentrations of As (30.29 mg/L), Pb (10.38 mg/L), Cu (14.97 mg/L), and CN⁻ (0.51 mg/L) indicated elevated ecological risk conditions, while acidic pH conditions may have enhanced metal mobilization and downstream transport. Descriptive spatial observations indicated apparent downstream contaminant dispersion within affected downstream river communities reliant on river water for domestic use, irrigation, and fisheries. Field observations additionally documented fish mortality, reduced irrigation usability, and deterioration of river water quality conditions in affected downstream communities. The findings suggest the potential vulnerability of Mekong-connected river systems to chemically intensive REE extraction activities and highlight the importance of preventive environmental governance, continuous monitoring, and operational risk management in emerging rare earth mining regions. Full article

Green roofs offer significant potential for urban stormwater management, yet their capacity to improve runoff water quality is constrained by the limited pollutant retention of conventional substrates and inherent nutrient leaching risks. This critical review synthesizes recent advances in substrate engineering and phytoremediation to establish an integrated framework for transforming green roofs into active bio-filtration systems. Our analysis reveals that amending conventional substrates with waste-derived biosorbents substantially enhances heavy metal and nutrient retention through complementary mechanisms of surface complexation, ion exchange, and microprecipitation. When strategically coupled with hyperaccumulator plant species and rhizospheric microbial communities, these amended substrates significantly reduce contaminant loads in urban runoff while maintaining hydraulic functionality. We critically evaluate standard growing media versus substrates amended with targeted biosorbents: biochar, which enhances heavy metal retention and hydraulic conductivity via surface complexation; seaweed biomass, which provides superior water retention and cation exchange while reducing synthetic fertilizer dependence; and chitin-rich crab shell waste, which promotes microprecipitation of metals and phosphates while valorizing marine waste. The novelty resides not in the materials themselves, but in their synergistic combination and the systematic comparative analysis of their retention mechanisms under green roof hydrological conditions. This review further identifies critical engineering trade-offs, including biosorbent-induced hydraulic conductivity reductions and long-term adsorption site saturation, and provides actionable design thresholds for amendment dosing, substrate depth, and species selection. Ultimately, this work establishes a mechanistic and practical roadmap for next-generation green roofs that simultaneously optimize stormwater retention, runoff quality, and circular economy valorization, highlighting priority research directions for long-term field validation and climate-adaptive standardization. Full article

Vanadium tailings-based ceramsite (VT-Ceramsite), a type of porous ceramsite synthesized from vanadium tailings, was employed for the adsorption of fluoride ions from high-fluoride wastewater. This approach not only mitigates environmental pollution caused by industrial solid waste but also effectively removes fluoride contaminants from wastewater. The effects of vanadium tailings content, sintering temperature, and sintering time on the adsorption performance of the VT-Ceramsite were systematically investigated. Comprehensive characterizations via XRD, SEM, BET, and adsorption modeling reveal that fluoride sequestration by VT-Ceramsite is governed by the synergy between physical diffusion and chemical interactions. While the porous architecture provides essential transport pathways, the chemically active sites facilitate stable bonding. Future research will prioritize surface functionalization and tailoring strategies to augment the density of these active sites, thereby maximizing the adsorption potential for treating complex industrial effluents. The optimal preparation conditions were determined to be a ratio of 6.5:2.5:1 for vanadium tailings, fly ash, and kaolin, with a preheating temperature of 300 °C for 20 min and a sintering temperature of 900 °C for 20 min. In these conditions, the adsorption capacity for fluorine ions can reach 43.59 mg/g. VT-Ceramsite exhibited a specific surface area of 3.61 m²/g, hydrochloric acid solubility of 1.2%, and a void fraction of 48.68%, all parameters met national industrial standards. In addition, the leaching concentrations of heavy metals were found to be well below the limits specified in CJ/T 299-2008, indicating that the material poses no risk of secondary pollution. The study provides an economical, safe, and environmentally friendly route for the utilization of solid waste, and it offers a promising adsorbent for treating high-fluoride wastewater. Full article

Heavy metal pollution from coal gangue severely degrades mine soil structure and threatens landscape ecological stability. Particularly, γ-polyglutamic acid (γ-PGA), a green biopolymer, offers potential applications for pollution remediation while supporting ecological restoration. To evaluate γ-PGA’s efficacy in immobilizing Pb, Cd, and Zn in gangue-based soil and clarify its regulatory mechanism for landscape-friendly remediation, soil samples from a 3-year-weathered gangue hill in the Liupanshui mining area were subjected to indoor leaching experiments with different γ-PGA doses, combined with material characterization and Density Functional Theory (DFT) simulations. The results showed that the optimal γ-PGA dose was 6 g/kg, achieving 93.25% Pb immobilization and reducing Cd/Zn migration risk by over 30%; γ-PGA acted via carboxyl-amide dual-site chelation and hydrogen-bonded agglomeration, forming stable aggregates that inhibited metal migration. DFT calculations confirmed strong chelation for Cu²⁺ (−59.54 kcal/mol, BSSE-corrected: −57.23 kcal/mol), while Pb²⁺ and Cd²⁺ showed weaker binding (−8.32 kcal/mol and −5.67 kcal/mol, BSSE-corrected: −6.15 kcal/mol and −3.89 kcal/mol, respectively), indicating multi-pathway immobilization mechanisms. This study provides a theoretical basis for applying γ-PGA in mine landscape ecological restoration. Full article

Heavy metal contamination in soil and the resulting groundwater pollution are common at many brownfield sites. Soil washing, which dissolves contaminants into a washing solution to separate them from the soil matrix, has emerged as a promising remediation strategy. This study assessed the feasibility of applying soil washing to Pb-contaminated soil collected from an industrial area within the Trieste Port Authority (Italy) through a series of leaching tests. Batch tests were conducted using ethylenediaminetetraacetic acid (EDTA)-based extractants combined with various reducing agents to identify the most effective and environmentally sustainable washing solution. The results show that coupling EDTA with hydroxylamine hydrochloride or sodium dithionite significantly enhanced Pb solubilisation compared with EDTA alone, with dithionite emerging as the most suitable reducing agent due to its lower toxicity and reduced environmental impact. Sequential extraction tests revealed that up to 50% of total Pb could be removed after repeated washing cycles. Column leaching tests further confirmed the high efficiency of the EDTA–sodium dithionite system, achieving Pb removal rates of approximately 70% under continuous flow conditions. Overall, the results demonstrate that EDTA combined with low-dose sodium dithionite provides an effective and practical remediation strategy for heavily polluted industrial soils. Full article

Sustainable management of industrial solid waste is critical for a circular economy. This study presents a novel approach for valorizing blast furnace slag (BFS) into NaA zeolite through selective acetic acid leaching followed by hydrothermal crystallization. The leaching step selectively extracts Ca²⁺ and Mg²⁺ while efficiently retaining silicon and aluminum in the solid residue, producing a reactive aluminosilicate precursor that facilitates zeolite nucleation and growth. The effects of the silicon-to-aluminum molar ratio (n(Si)/n(Al)), crystallization temperature, and duration on the phase evolution and morphology were systematically investigated. The results demonstrate that phase-pure NaA zeolite with high crystallinity and a uniform cubic morphology can be obtained from precursor gels with n(Si)/n(Al) ratios of 0.5–1.25. Optimal synthesis conditions were identified as n(Na):n(Si):n(Al):n(H₂O) = 6:1:1:240 at 373 K for 8 h. The resulting zeolites exhibit a BET specific surface area of 52.1 m²/g, a micropore volume of 0.016 cm³/g, an average adsorption pore size of 4.7 nm, and an external specific surface area of 12.8 m²/g. It achieved near-complete removal of Cu²⁺ and high adsorption efficiencies for Pb²⁺ (77.78%) and Ni²⁺ (71.79%) from 250 mg/L solutions at 298 K with a dosage of 4.0 g/L, following the affinity sequence Cu²⁺ > Pb²⁺ > Ni²⁺, with all pairwise differences statistically significant at p < 0.001, using one-way ANOVA and Tukey’s HSD tests. The adsorption of three metal ions was most accurately described by the Freundlich isotherm and pseudo-second-order kinetic models, indicating heterogeneous multilayer chemisorption. The theoretical maximum monolayer adsorption capacities (q_max) were 307.67 mg/g for Cu²⁺, 246.09 mg/g for Pb²⁺, and 173.79 mg/g for Ni²⁺, whereas the kinetic equilibrium adsorption capacities (q_e) reached 62.69, 48.85 and 41.69 mg/g, respectively. This study demonstrates a value-added strategy for valorizing BFS into a micro-mesoporous adsorbent, advancing both circular resource utilization and environmental remediation. Full article