Search Results (76)

Sulphide soil is an organic soil characterised by high water content and poor geotechnical properties. When excavated, it oxidises and becomes an environmental hazard due to leached metals and acid drain. To avoid excavation, methods for utilizing more sulphide soil as a subgrade material are being developed. However, precise characterisation of sulphide soil is challenging, as its inherent properties make it prone to sample disturbance, introducing large scatter into geotechnical test results. To minimise the scatter in laboratory test results, a portion of the characterisation could be based on reconstituted samples. This study explores the applicability of the slurry deposition method to produce homogeneous, repeatable and representative sulphide soil samples. The reconstituted samples were assessed by comparing their initial index properties and triaxial behaviour against those of the intact samples. The index properties of the tested reconstituted samples precisely and accurately matched the average results of the intact samples. The undrained triaxial behaviour and derived critical state line of the reconstituted samples and the intact samples were found to be comparable. Neither type of sample reached critical state in drained triaxial testing. In conclusion, this study suggests that the slurry deposition method is suitable for reconstituting sulphide soil samples. Full article

This research explores the use of industrial waste as an alternative to natural raw materials, promoting a circular economy in the construction sector. It specifically investigates the manufacturing of paving blocks using blast furnace slag and recycled aggregates. Paving blocks were produced without altering typical industry conditions, entirely replacing cement with alkaline-activated blast furnace slag. The study replaced natural aggregate in three proportions (20%, 50%, and 100%) with three types of recycled aggregates: concrete recycled aggregate (CA), masonry recycled aggregate (MA), and recycled mixed aggregate (RMA), in both coarse and fine fractions. The experimental procedure analysed the impact of recycled aggregates in an alkaline-activated slag matrix through three phases: characterising physical properties (mechanical properties, water absorption, density, abrasion resistance, and slip resistance), evaluating leaching behaviour, and conducting a life cycle analysis. The results of physical characterisation were statistically analysed using principal component analysis (PCA). The results obtained show the feasibility of manufacturing paving blocks with blast furnace slag by completely replacing the natural aggregate with the coarse fraction of the three recycled aggregates used and replacing up to 20% in the case of using the fine fraction. The properties of the paving blocks manufactured with slag depend mainly on the degree of substitution of natural aggregate with the recycled aggregate. All paving blocks can be considered environmentally safe from leaching according to the Dutch Soil Quality Decree. Paving blocks made from alkali-activated ground granulated blast furnace slag and recycled aggregates generate a lower carbon footprint compared to concrete paving blocks. Full article

The management of hazardous municipal solid waste incineration (MSWI) residues represents a critical challenge for sustainable development due to their increasing generation and environmental risk. At the same time, the cement industry faces urgent pressure to reduce CO₂ emissions associated with clinker production, creating a demand for alternative supplementary cementitious materials. The aim of this study was to evaluate the feasibility of valorising hazardous municipal solid waste incineration (MSWI) air pollution control fly ash (EWC 19 01 07*) as a constituent of Portland composite cement, in line with circular economy principles and the need to reduce CO₂ emissions associated with clinker production. The investigated fly ash, originating from flue gas cleaning processes, is characterised by high alkalinity and elevated concentrations of heavy metals, which currently necessitate controlled landfilling. To enable its safe reuse, the ash was subjected to high-temperature thermal treatment following granulation and subsequently incorporated into cement formulations under semi-industrial conditions. Two Portland composite cements were produced with different ash contents, corresponding to CEM II/A-07 and CEM II/B-07, while a Portland cement manufactured from the same clinker was used as a reference material. The chemical and phase composition of the ash before and after thermal treatment was analysed using XRF and XRD, supported by SEM/EDS observations. The results demonstrate that thermal treatment at 1150 °C induces partial phase stabilisation of APC fly ash without full vitrification, allowing its integration into cement systems under semi-industrial conditions. The incorporation of ash significantly alters hydration behaviour through increased water demand governed by particle porosity, CaO-rich phase composition, and early ionic interactions in the pore solution, leading to reduced workability and mechanical performance. While immobilisation efficiencies exceeding 99.5% were achieved for most heavy metals due to precipitation and incorporation into hydration products, barium exhibited persistent leaching controlled by its solubility under highly alkaline conditions and limited incorporation into C–S–H phases. These findings define both the technological feasibility and the key environmental constraints of APC fly ash utilisation in Portland composite cement. From a sustainability perspective, the proposed approach contributes to the reduction in hazardous waste landfilling and supports clinker substitution in cement production. The results demonstrate the potential of integrating waste management and low-carbon material design within a circular economy framework while highlighting current environmental limitations related to barium leaching. Full article

Phosphogypsum, the primary solid waste from the wet-process phosphoric acid industry, poses significant environmental and health risks due to large-scale stockpiling. To promote its resource utilisation, this study systematically evaluated the solidification and stabilisation performance of phosphogypsum–coal fly ash cementitious material (PAC) for Cr(VI)-contaminated soil under high-chloride conditions. Phosphogypsum reactivity was enhanced via mechanical activation and high-temperature calcination. An orthogonal experimental design was employed to analyse the effects of multiple factors—including calcination temperature and duration—on compressive strength and heavy metal leaching behaviour. Results show that PAC prepared from coal ash calcined at 600 °C for 3 h exhibits excellent mechanical properties and Cr(VI) stabilisation efficacy under high-chloride conditions, achieving a maximum compressive strength of 28.75 MPa and a Cr(VI) leaching concentration as low as 15.69 μg/L. Microstructural characterisation revealed the synergistic formation of a dense framework between C–S–H gel and calcium aluminate, conferring superior mechanical strength. Substitution and chelation mechanisms of Cl⁻ ions played a key role in enhancing corrosion resistance. This study provides theoretical support and technical guidance for the high-value utilisation of phosphogypsum-based materials in remediating saline–alkali-contaminated soils. Full article

This study investigates the selective dissolution of manganese from a manganiferous iron ore using nitric acid (HNO₃) in the presence of various organic reductants. A series of leaching experiments was performed to evaluate the effects of temperature, reductant type, and leaching time on Mn recovery, with particular emphasis on biomass (horse dung) and tartaric acid as novel reducing agents. The dissolution behaviour of Fe, Mn, Mg, Ca, and Al was systematically examined, revealing that Mn extraction was strongly enhanced in the presence of reductants, while Fe dissolution remained below 10% under all conditions. The maximum Mn dissolution exceeded 90% at 90 °C using biomass and reached nearly 85%–90% with tartaric acid at elevated temperatures. Kinetic studies were conducted by applying reaction order models and the shrinking core model. The results indicated that Mn dissolution in HNO₃ medium is predominantly controlled by surface chemical reaction, with Arrhenius analysis yielding activation energies of 27.74 kJ/mol for biomass and 21.26 kJ/mol for tartaric acid. These relatively low values confirm the efficiency of organic reductants in facilitating Mn reduction and dissolution. To sum up, comparison of reductant efficiency revealed that, at the lowest concentrations, the dissolution of Mn followed the sequence glucose > sucrose > oxalic acid > tartaric acid > maleic acid > biomass > citric acid > acetic acid. At the highest concentrations, the trend shifted, with citric acid emerging as the most effective, followed by tartaric acid > oxalic acid > glucose > sucrose > maleic acid > biomass > acetic acid. Full article

Hydrochar is a carbon-rich material produced through the hydrothermal carbonization (HTC) of wet biomass such as sewage sludge. Its nitrogen content is a critical quality parameter, influencing its suitability for use as a soil amendment and its potential environmental impacts. This study develops a high-accuracy ensemble machine learning framework to predict the nitrogen content of hydrochar derived from sewage sludge based on feedstock compositions and HTC process conditions. Four ensemble algorithms—Gradient Boosting Regression Trees (GBRTs), AdaBoost, Light Gradient Boosting Machine (LightGBM), and eXtreme Gradient Boosting (XGBoost)—were trained using an 80/20 train–test split and evaluated through standard statistical metrics. GBRT and XGBoost provided the best performance, achieving R² values of 0.993 and 0.989 and RMSE values of 0.169 and 0.213 during training, while maintaining strong predictive capabilities on the test dataset. SHAP analyses identified nitrogen content, ash content, and heating temperature as the most influential predictors of hydrochar nitrogen levels. Predicting nitrogen behaviour during HTC is environmentally relevant, as the improper management of nitrogen-rich hydrochar residues can contribute to nitrogen leaching, eutrophication, and disruption of aquatic biogeochemical cycles. The proposed ensemble-based modelling approach therefore offers a reliable tool for optimizing HTC operations, supporting sustainable sludge valorisation, and reducing environmental risks associated with nitrogen emissions. Full article

Wastewater-derived microplastics (WW-MPs) are increasingly recognised as reactive vectors for aromatic organic contaminants (AOCs), yet their role in contaminant fate remains insufficiently constrained. This review synthesises current knowledge on the transformation of microplastics in wastewater treatment plants, including fragmentation, oxidative ageing, additive leaching, and biofilm formation, and links these processes to changes in sorption capacity toward phenols, PAHs and their derivatives, and organochlorine pesticides (OCPs). We summarise the dominant adsorption mechanisms-hydrophobic partitioning, π-π interactions, hydrogen bonding, and electrostatic and, in some cases, halogen bonding-and critically evaluate how wastewater-relevant parameters (pH, ionic strength, dissolved organic matter, temperature, and biofilms) can modulate these interactions. Evidence in the literature consistently shows that ageing and biofouling enhance WW-MP affinity for many AOCs, reinforcing their function as mobile carriers. However, major gaps persist, including limited data on real wastewater-aged MPs, lack of methodological standardisation, and incomplete representation of ageing, competitive sorption, and non-equilibrium diffusion in existing isotherm and kinetic models. We propose key descriptors that should be incorporated into future sorption and fate frameworks and discuss how WW-MP-AOC interactions may influence ecological exposure, bioavailability, and risk assessment. This critical analysis supports more realistic predictions of AOC behaviour in wastewater environments. Full article

Geopolymers are inorganic aluminosilicate binders formed by alkali activation of reactive powders, offering a sustainable, low-carbon alternative to Portland cement. Their rapid setting and chemical durability make them well-suited for additive manufacturing (AM) in demanding environments, including underwater construction, where chemical stability is essential for both structural integrity and environmental safety. This study evaluates two metakaolin-based formulations designed for underwater extrusion, differing in activator chemistry and rheology control. Standardized leaching tests revealed alkaline but stable leachates with strong immobilization of most ions; major anions and total dissolved solids remained within regulatory thresholds. Limited exceedances were observed—soluble organic carbon in the NaOH-activated mix and arsenic/selenium in the waterglass–sand system—highlighting specific areas for mix improvement rather than fundamental limitations of the material. Complementary radioactivity screening confirmed activity concentration indices well below the regulatory limit, with measured radionuclide activities falling comfortably within exemption ranges. Together, the leaching and radioactivity results demonstrate that both formulations provide robust matrix integrity and environmental compatibility, while highlighting clear opportunities for mix design improvements to further minimize ecological risks. Full article

Lead (Pb(II)) contamination in water poses severe environmental and health risks due to its toxicity and persistence. This study compares almond shell-derived biochars produced by slow pyrolysis (SP) and microwave pyrolysis (MW), with and without KOH activation, focusing on structural properties and Pb(II) adsorption performance. Biochars were characterized by proximate and elemental analysis, BET surface area, FTIR spectroscopy, and adsorption experiments including pH dependence, kinetics, and equilibrium isotherms. Non-activated SP exhibited the highest surface area (S_BET = 693 m²·g⁻¹), pronounced mesoporosity (≈73% of total pore volume), and the largest observed equilibrium capacities. KOH activation increased surface hydroxyl content but degraded textural properties; in MW samples, it induced severe pore collapse. Given the very fast uptake, kinetic modeling was treated cautiously: for non-activated biochars, Elovich adequately captured the time-course trend, whereas activated samples returned non-physical kinetic constants (e.g., negative k₂) likely due to high post-adsorption pH (>11) and probable Pb(OH)₂ precipitation. Equilibrium data (fitted over 50–500 mg·L⁻¹) were better captured by the Freundlich and Redlich–Peterson models, indicating a mixed adsorption behaviour with contributions from heterogeneous site distribution and site-specific interactions. Optimal Pb(II) removal occurred at pH 4, with no measurable leaching from the biochar matrix. Overall, non-activated SP biochar is the most effective, sustainable and low-cost option among the tested materials for Pb(II) removal from water, avoiding aggressive chemical activation while maximizing adsorption performance. Full article

This study investigates the concentrations and geochemical behaviour of strategic elements—including Li, Co, Ni, Cu, Ga, Ge, rare earth elements (REEs), and yttrium (Y)—in bottom ash samples from the Afşin–Elbistan thermal power plant, Türkiye. Thirty bottom ash samples were analysed, revealing average ∑LREE and ∑HREE concentrations of 86.3 µg/g and 3.3 µg/g, respectively, resulting in an L/H ratio of 24.9, indicating pronounced enrichment in light REEs. The total ∑REE + Y concentration (111 µg/g) is comparable to the background value for coal but approximately 1.5 times lower than those reported for average Chinese coals and the upper continental crust (UCC). REE contents significantly exceed those of sedimentary (5.36 µg/g), mafic (16.77 µg/g), and felsic (3.60 µg/g) rocks. Elevated Li (30.5 µg/g) and Ni (114.4 µg/g) concentrations point to a mafic magmatic source, whereas Cu (28.7 µg/g) likely originates from basic volcanic rocks such as those of the Dağlıca Complex and the Kemaliye Formation. Chondrite-normalised REE patterns show Dy depletion relative to mafic rocks and Ho depletion compared to sedimentary rocks. Positive δEu anomalies (>1) support a mafic or UCC provenance, while slightly positive δCe values indicate hydrothermal leaching influences. The co-precipitation of Ce with Ca–Mg hydroxides and clay minerals in coal-bearing lacustrine sediments is suggested. Ga enrichment is attributed to aluminium-rich clay minerals and organic matter. Overall, these geochemical signatures reflect combined inputs from hydrothermal leaching and volcanic weathering within a coal-bearing lacustrine environment. Full article

The extraction of DNA from biological samples precedes many research and commercial applications. This study compares surface treatments of cellulose (a low-cost binding matrix) to enhance binding and elution of DNA to paper-based dipsticks. Cellulose paper was modified with poly-L-lysine, silica, or guanidine, as well as subjected to TEMPO-based oxidation. Subsequently, binding and elution behaviour of fragmented salmon sperm DNA to dipsticks was evaluated. Qubit fluorimetry and agarose gel electrophoresis measurements indicated that TEMPO-based oxidation significantly increased the binding of DNA and its elution from dipsticks, while silica modifications bound DNA efficiently, but strongly retained it. Leaching of select modifiers (guanidine, silica and poly-L-lysine) was indicated by UV/Vis spectroscopy, indicating that further optimization of attachment processes is required. This study is the first to compare multiple cellulose surface treatments for their influence on DNA binding and elution, especially the use of TEMPO-based oxidation for this purpose, and highlights some means of identifying leaching of modifiers during DNA capture at these surfaces and subsequent elution. While TEMPO-based oxidation proves a promising treatment to enhance DNA elution, further refinement of the approach is needed to ensure compatibility with molecular biology techniques. Full article

To enhance both the environmental performance and mechanical properties of phosphate solid waste backfill materials, this study examines the effects of corn straw fibre (CS), rice straw fibre (RS), and jute fibre (JF), each at five lengths (3–15 mm) and five dosages (0.1–0.5 wt%), on the rheological behaviour, mechanical strength, and microstructural characteristics of the backfill slurry. The experimental results showed that the incorporation of natural fibres markedly improved both the compressive and tensile strengths of backfill materials. For example, incorporating CS at a length of 12 mm and a dosage of 0.2 wt% increased the compressive and tensile strengths by 144.4% and 18.8%, respectively. Likewise, RS at 3 mm and 0.2 wt% increased the strengths by 68.3% and 11.9%, while JF at 12 mm and 0.5 wt% enhanced them by 108.2% and 14.9%, respectively. Ion leaching experiments and XPS analyses confirmed that the incorporation of natural fibres effectively adsorbed and immobilized phosphorus and fluorine in phosphogypsum. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses revealed that the improved mechanical strength was primarily attributed to fibre-bridging effects and enhanced fibre–matrix bonding. Furthermore, nuclear magnetic resonance (NMR) analysis demonstrated that incorporating natural fibres reduced the porosity of backfill materials (from 12.9% to 8.14%) while increasing their density. This study provides an experimental foundation for optimizing backfill materials and recommends a 12 mm CS fibre length at a dosage of 0.2 wt% to improve the stability and safety of mine fill structures. Full article

Moringa (Moringa oleifera Lam.) is widely recognised as a multipurpose crop suitable for human and animal consumption, medicinal, and industrial purposes, making it attractive for introduction into new ranges. Its extracts have been found to have beneficial impacts on various crop species and biological activity against multiple weeds, making their use in agriculture promising. However, concerns have also been raised about moringa’s potential to negatively impact the growth and development of other cultivated and non-cultivated plant species, especially in areas where it has been introduced outside its native range. To understand the positive and negative interactions between moringa and other plants, it is essential to investigate its allelopathic potential. Allelopathy is a biological activity by which one plant species produces and releases chemical compounds that influence the reproduction, growth, survival, or behaviour of other plants with either beneficial or detrimental effects on the receiver. Plants produce and release allelochemicals by leaching, volatilisation, or through root exudation. These biochemical compounds can affect critical biological processes such as seed germination, root and shoot elongation, photosynthesis, enzymatic activities, and hormonal balance in neighboring plants. Therefore, allelopathy is an important driver of plant composition and ecological interactions in an ecosystem. This review explores the positive and negative allelopathic effects of moringa extracts on other plant species, which may help to inform decisions regarding its introduction into new biogeographical regions and incorporation into existing farming systems, as well as the use of moringa plant extracts in agriculture. Full article

This work focuses on the design of concrete for the construction of winemaking tanks, as well as coating behaviour and stability of the systems in wine immersion. More specifically, alternative laboratory concrete mixtures were investigated by replacing cement with natural pozzolan and using silicate aggregates and quartz sand as filler in order to obtain self-compacting concrete of strength class C 20/25. The optimal mixture was selected and further tests were carried out on the mechanical properties of permeability, durability and thermal conductivity. Three coatings and plain concrete were tested for their leachability of heavy metals in wine. The results show that the selected composition with 20% cement replacement by natural pozzolan has the desired workability and strength and is comparable to a reference concrete without natural pozzolan. The leachability tests show that heavy metals do not leach out upon contact with wine, but only calcium and potassium oxide, which can be easily addressed by coating or treating the surface of the concrete. Also, the optimum coating did not influence the pH of the wine. Full article

The presence of persistent contaminants in soils is of growing concern around the world. Contaminated soils can affect numerous ecological environments and lead to significant health risks to humans, affecting soil biodiversity, structure and geomechanical behaviour and agricultural sustainability. Additionally, soil contaminants can also leach into water flows, which is another concern. In general, soil contamination can be attributed to natural sources or to anthropogenic sources associated with human activity. Soil contaminants are usually classified in the following categories: biological, radioactive, organic and inorganic contaminants. State of the art information regarding some of the most common persistent soil contaminants, including possible sources and prevalence, and monitoring approaches and information about their effects on soil characteristics, including usability, as well as information on possible mobility to other environmental media is presented in this review paper. Finally, a comprehensive overview of remediation strategies which are being developed, including the more traditional ones as well as novel strategies that have been proposed lately by the scientific community, is provided. This includes physicochemical and biological technologies, as well as mixed remediation technologies aimed at enhancing remediation efficiency. Full article