Search Results (240)

This preliminary experimental study investigates mortars with partial replacement of natural sand by recycled tyre rubber (RTR) and alkali-activated fly ash as an alternative binder to Portland cement. An experimental programme was carried out on 14 mortar mixes, including cementitious mortars (CM) and alkali-activated mortars (AAM), with 5%, 10% and 20% RTR incorporation and with/without NaOH pre-treatment of rubber (saturated solution for 30 min). Fresh behaviour was assessed through flow and fresh density, while mechanical-related performance was evaluated at 28 and 56 days through compressive and flexural strength, modulus of elasticity and ultrasonic pulse velocity. Physical properties included open porosity, dry density, water absorption by immersion and capillarity. The alkali-activated reference mix achieved higher compressive strengths (46.1–53.0 MPa) than the cement reference (28.4–30.6 MPa) under the adopted mix-design and curing conditions. RTR incorporation reduced stiffness and strength in all specimens, with 20% RTR decreasing flexural strength by 26.6–51.4%, although losses were generally smaller in AAM than in CM. Under the treatment condition investigated, NaOH pre-treatment did not consistently improve mechanical-related performance, except for limited gains at 5% RTR. Overall, AAM with 5–10% RTR showed a better balance between density reduction and mechanical-related performance than CM. Full article

Construction on very soft peaty clay remains a major geotechnical challenge due to its high compressibility and low-bearing capacity. The deep mixing method (DMM) is widely adopted for in situ stabilization using cement; however, environmental concerns associated with cement production have driven the search for sustainable alternatives such as geopolymers using low-carbon materials. Existing studies predominantly rely on dried peat, processed precursors such as fly ash or calcined ground rice husk ash (RHA), and high concentrations of alkali activators such as sodium silicate (Na₂SiO₃) and sodium hydroxide (NaOH), which increase both environmental and economic burdens. This study develops a novel waste-based geopolymer incorporating untreated brick kiln-derived RHA, activated solely with low-concentration NaOH, while completely eliminating Na₂SiO₃. The avoidance of precursor pre-treatment and Na₂SiO₃ significantly reduces processing energy, cost, and associated environmental emissions. A systematic investigation was conducted to determine the optimum mixing time for maximizing strength under field-relevant conditions. Mechanical performance was evaluated using unconfined compressive strength tests considering variations in binder content, curing duration (7, 28 days), alkali concentration (6, 3 M), and alkali-to-binder ratio (0.3, 0.5, 0.7). Failure characteristics were examined, and an integrated framework combining cost analysis, life cycle assessment, and grey relation analysis was employed to optimize mix design. The optimized geopolymer achieved 2.2 times higher strength than cement-treated soil, with 25% cost reduction and more than 85% reduction in environmental impact. These findings demonstrate a scalable and sustainable solution for stabilizing highly organic soils, while promoting the valorization of supplementary cementitious materials without energy-intensive preprocessing. Full article

Spent green tea residues are an abundant lignocellulosic by-product that poses environmental disposal concerns, while its use in ruminant nutrition is constrained by low ruminal degradability associated with high fiber and phenolic contents. This study investigated the effects of gamma irradiation and solid-state fermentation using Saccharomyces cerevisiae, and their combination, on chemical composition and ruminal fermentation. Gamma irradiation reduced neutral detergent fiber (379 to 336 mg g⁻¹ dry matter), acid detergent fiber (277 to 244 mg g⁻¹ dry matter), and total phenolics (89 to 75 mg gallic acid equivalents g⁻¹ dry matter) while increasing non-fiber carbohydrates (234 to 269 mg g⁻¹ dry matter) and ash (32 to 44 mg g⁻¹ dry matter). These modifications enhanced the gas production rate (3.26 to 3.37% h⁻¹), neutral detergent fiber degradability (38.9 to 46.1%), and the acetate-to-propionate ratio (2.25 to 2.43) while reducing ammonia nitrogen (108 to 96 mg L⁻¹), crude protein degradability (55.1 to 48.8%), and increasing rumen exoglycanase activity by 11% and xylanase activity by 15%. However, the methane proportion in total gas increased from 12.4 to 13.3% and methane yield per unit of degraded dry matter increased from 36.5 to 39.2 mL g⁻¹ degraded dry matter. Solid-state fermentation using Saccharomyces cerevisiae alone did not change the chemical composition or ruminal fermentation of non-irradiated biomass. However, when applied to irradiated biomass, it increased the crude protein from 320 to 383 mg g⁻¹ dry matter and ether extract from 31 to 49 mg g⁻¹ dry matter, improved dry matter degradability (53.3 to 63.1%), organic matter degradability (55.3 to 64.3%), crude protein degradability (48.8 to 54.6%), total volatile fatty acids (49 to 57 mmol L⁻¹), and net energy for lactation (2.43 to 3.02 MJ kg⁻¹ dry matter), and maintained ammonia nitrogen at levels similar to the irradiated biomass. Although the combined treatment increased the methane yield per unit of incubated dry matter (19.2 to 23.4 mL g⁻¹ dry matter), the methane yield per unit of degraded dry matter was lower than that of the irradiated biomass alone (37.0 vs. 39.2 mL g⁻¹ dry matter degraded) and comparable to the untreated control (36.5 mL g⁻¹ dry matter degraded). Overall, the integration of gamma irradiation as a pretreatment followed by solid-state fermentation with Saccharomyces cerevisiae enhances the nutritional value of spent green tea residues, supporting its valorization as a sustainable alternative ruminant feed resource. Full article

The transition toward low-carbon cement production requires alternative fuels with improved environmental performance and resource efficiency. Refuse-Derived Fuel (RDF), produced from pre-treated non-recyclable waste streams, represents a promising alternative fuel; however, its heterogeneous and varying composition presents challenges for stable combustion and process optimization. In this study, a comprehensive physicochemical characterization of RDF was performed and compared with pet coke, a conventional, fossil cement kiln fuel. The analysis included manual sorting, particle size distribution, elemental characterization, Scanning Electron Microscopy coupled with Energy dispersive X-ray spectroscopy (SEM/EDS), X-ray Diffraction (XRD), thermogravimetric and differential scanning calorimetry (TGA/DSC), and Higher Heating Value (HHV) determination. The RDF sample exhibited a heterogeneous polymeric-mineral composition dominated by plastics, paper, textiles, and inorganic fractions. TGA revealed a broad multi-stage thermal degradation profile, while calorimetry indicated HHV of 19.2 ± 0.3 MJ/kg and ash content of 11.6 wt.%, compared with 34.57 ± 0.11 MJ/kg and 1.97 wt.% for pet coke, respectively. SEM/EDS and XRD analyses confirmed the coexistence of polymeric and mineral phases in RDF, whereas pet coke exhibited a predominantly carbonaceous and homogeneous composition. The generated dataset supports computational fluid dynamics (CFD)-based cement kiln combustion models and RDF utilization for fossil fuel substitution in the cement industry. Full article

This study presents a screening-level conceptual, stoichiometric, and scenario assessment of a pathway linking sulfur dioxide (SO₂) capture from coal-fired flue gas to sulfuric acid production and the downstream reaction of sulfuric acid with pretreated scrap aluminum. A regenerable sodium sulfite (Wellman–Lord) capture route, followed by gas polishing and drying, catalytic SO₂ oxidation, controlled SO₃ absorption, acid conditioning, and an Al–H₂SO₄ reactor, is used as the reference configuration. The sulfur balance distinguishes sulfur in coal, ash retention, gaseous SO_x, SO₃/acid mist, absorber inlet and stack slip, captured sulfur, regenerated sulfur, and sulfate purge. Under the central assumptions, 1 t of sulfur in coal yields 0.849 t of recovered sulfur equivalent, 2.599 t of H₂SO₄, 0.477 t of aluminum feed, 2.419 t of anhydrous-equivalent Al₂(SO₄)₃, 4.240 t of commercial aluminum sulfate on a 17 wt% Al₂O₃ basis, and 42.4 kg of H₂ at 80% aluminum conversion. The upstream base-energy screen is 3.3–7.2 GJth and 0.18–0.45 MWhe per tonne of sulfur in coal. Diluting the acid to the selected 0.5–1.0 M aluminum-reaction window and subsequently producing a 17 wt% Al₂O₃ product creates a minimum water-removal load of 21.6–47.6 t and a latent-heat floor of approximately 49–108 GJth/t S. Retail prices are replaced by 2024 customs unit values, and internal-acid-production and sulfuric-acid-opportunity-cost boundaries are evaluated separately. In the central opportunity-cost case, the H₂ value must reach approximately 6.9 USD/kg merely to balance material values before CAPEX, OPEX, energy, purification, transport, and environmental-compliance costs. The Afşin–Elbistan A case is treated as a full-design-throughput illustration based on an historical 18 Mt/y coal requirement, not as a measured current operating average; coal sulfur is tested over 1.0–2.5 wt%. The aluminum step is restricted to cooled and diluted 0.5–1.0 M H₂SO₄ at 40–60 °C, and direct H₂ production from 96 to 98 wt% acid is not assumed. Plant-specific capacity factor, time-matched coal assays, flue-gas flow, oxygen-corrected stack data, reaction kinetics, gas purity, and product quality remain to be verified. The integrated sustainability screening indicates conditional circular-economy potential rather than a demonstrated sustainability advantage: sulfur recovery must be weighed against energy and water demand, sulfate purge and wastewater, diversion of recyclable aluminum from remelting, hydrogen purification, and market-scale product offtake. The pathway therefore remains a research hypothesis requiring experimental validation, process simulation, techno-economic assessment, comparative life-cycle assessment, safety analysis, and market verification. Full article

Although low-carbon geopolymers incorporating construction and demolition waste (CDW) offer a promising circular economy pathway, the synergistic mechanisms between pretreated recycled fine aggregates (RFA) and geopolymer binders have not been systematically elucidated. This study investigated the comprehensive performance of geopolymer mortar containing recycled powder (RP) incorporating RFA; 50% Fly ash, 25% slag, and 25% RP were incorporated as precursor for the production of geopolymer binders, while the replacement ratios (0%, 20%, 40%, 60%, 80%, 100%) and the pretreatment methods (carbonation and prewetting) of RFA were taken as experimental parameters. The effect of these parameters on the fluidity, setting time, water absorption, compressive strength, and microstructure of recycled geopolymer mortar (RGM) and recycled cement mortar (RCM) was analyzed. Results showed that as the RFA replacement ratio increases, the measured properties generally decline. However, pretreating the RFA, particularly through carbonation, effectively mitigates these drawbacks. The use of 60% carbonated RFA enhanced the compressive strength of RGM by 12% compared to untreated RFA at equivalent replacement ratio. A comparative evaluation of the performance variations between RGM and RCM revealed that geopolymer mortar exhibited lower fluidity, faster setting time, and higher compressive strength. The microstructure analysis by SEM showed that the geopolymerization reaction between adherent cement paste in RFA and geopolymer binders significantly enhanced the microstructural compactness compared to RCM. Furthermore, carbonation and prewetting treatments can mitigate cracks and pores in the mortar. The results demonstrate that RGM prepared with carbonated RFA offer an estimated 76% reduction in net CO₂ emission and 14.3% reduction in total cost relative to conventional cement mortar. This study established a framework that compares the mechanisms of RFA pretreatment and equip engineers with validated pretreatment strategies for upcycling CDW into construction materials. Full article

The growing demand for granular materials in transportation infrastructure increases the extraction of natural aggregates and the environmental impacts of the construction sector. At the same time, large volumes of municipal solid waste incineration bottom ash (IBA) and mine tailings (MTs) are generated and stored, posing environmental and geotechnical challenges. This review critically evaluates the potential of these waste streams as alternative materials for transportation infrastructure embankments, including zoned embankment approaches, that may enhance sustainability. The analysis integrates evidence on physical, geotechnical, and environmental performance, including compaction, compressibility, shear strength, permeability, bearing capacity, chemical composition, leaching, and ecotoxicity. IBA generally exhibits favourable engineering properties, although its performance depends on ageing and pre-treatment. MTs show greater variability, with behaviour largely controlled by mineralogy, particle-size distribution, and contaminant mobilisation potential. Environmental assessment should consider total chemical composition alongside leaching behaviour, ecotoxicity, and exposure conditions. Overall, the safe use of IBA and MTs requires an integrated evaluation of geotechnical and environmental performance, enabling their selective placement within functional embankment zones. Such approaches can support circular resource use and more sustainable transportation infrastructure without compromising technical performance. Full article

High ash andsss urea formaldehyde (UF) resin contents in particleboard sanding powder (SP) have restricted the effective resource utilization of SP and make it a hazardous biomass material for particleboard enterprises. To achieve high-value resource utilization of SP while addressing its hazardous disposal issues, different HCl concentration-oriented deashing pretreatments of SP coupled with fast pyrolysis was proposed for producing value-added pyrolytic sugar levoglucosan (LG) and high-quality pyrolytic char. The results show that H⁺ ions released from HCl solution could effectively remove structural ash, likely by disrupting the chemical linkages between the structural ash and lignocellulosic matrix. An amount of 2 mol/L HCl could achieve an over 95% removal rate of alkali and alkaline earth metals (AAEMs) in the ash while maintaining a low loss of polysaccharides. This considerably facilitated the glycosidic cleavage of cellulose into levoglucosan (LG), with the LG yield increasing from 2.18% of raw SP to 13.69% of 2 mol/L HCl deashed SP. Interestingly, it was found that HCl washing of SP facilitated the co-production of value-added platform chemical acetic acid via acid-catalyzed hydrolysis of acetyl groups in UF resin attached to the xylose unit, with the yield increasing from about 7% of raw SP to over 11% of HCl deashed one. Specifically, 2 mol/L HCl deashing pretreatment of SP significantly improved the quality of pyrolytic char with the ash content decreasing from 7.24% to 2.39% and fixed carbon content lifting from 54.08% to 76.04%, thus drastically improving the higher heating value (HHV) from 24.66% of raw SP-derived char to 30.05% of deashed SP-derived char. Moreover, the pyrolytic char CO₂ gasification reactivity increased from 0.027 min⁻¹ of raw SP-derived char to 0.034 min⁻¹ of that derived from 2 mol/L HCl deashed SP, approaching that of the widely used industrial charcoal fuel. Pyrolysis kinetic analysis indicates that deashing pretreatment of SP makes the formation of value-added platform chemicals and high-quality carbonaceous fuel proceed more easily at a lower activation energy (214.39 kJ·mol⁻¹) than that of raw SP (245.81 kJ·mol⁻¹). This study offers a novel approach for the synergistic production of value-added chemicals and high-quality carbonaceous fuel from biomass waste materials with high contents of ash and UF resin, providing a feasible strategy for the clean and high-value resource utilization of wood-based industrial residues. Full article

The efficient utilization of natural resources and agricultural wastes aligns well with the UN Sustainable Development Goals. Sunflower seed husks are an affordable and renewable source of cellulose that can be used as an alternative to wood-based resources. However, the yield and quality of cellulose are affected by the presence of components such as phytomelanin, hemicellulose, and lignin. In this study, cellulose pulp (CP) was extracted from untreated, water-treated, and water and alkali-treated SFH. The optimal peroxyacetic acid (PAA) to biomass ratio was established to assess the influence of pre-treatment on CP properties. Water and alkali pre-treatments significantly increased CP yield and reduced residual lignin, hemicellulose, and ash compared to untreated samples. The optimal yield of CP for SFH-NaOH was 55.73%. All microcrystalline cellulose (MCC) types exhibited comparable α-cellulose content, confirmed by the IR band at 1430 cm⁻¹. XRD showed lower crystallinity in untreated CP-SFH relative to pre-treated samples. SEM revealed porous fibrous structures across all MCCs. Pre-treatment also improved the thermal stability and ζ-potential of cellulose nanocrystals (CNCs) obtained from MCC, without altering morphology. CNC yields were determined for all three CP variants. The CP-SFH-NaOH sample had the maximum CNC yield of 52.12%. Phytomelanin with admixture of lignin was recovered from alkaline extracts (8.56%) and fully characterized. Overall, the findings demonstrate the potential of integrated SFH utilization to produce high-quality cellulose derivatives and phytomelanin with admixture of lignin. Full article

The severe slagging caused by high-alkali coals restricts the utilization of Xinjiang coal resources in China. This study investigates the mineral composition, geochemical characteristics, modes of occurrence, and controlling factors of alkali and alkaline earth metals in high-alkali coals from the Dananhu Coalfield, Turpan–Hami Basin. The investigated coals are classified as lignite, characterized by low ash yield, extra low sulfur, and medium–high alkali contents. Quartz and kaolinite are dominant, with accessory calcite, K-feldspar, pyrite, gypsum, siderite, celestite, and Ba-bearing celestite. Compared to average Chinese coals, Na, Mg, Ca, and Cl are enriched, with the shallowest No. 3 coal seam showing the highest enrichment. Based on the correlation analysis, K is likely associated with K-bearing aluminosilicates (e.g., K-feldspar and illite), while Ca, Mg, and Na probably exhibit both organic and inorganic affinities. Sequential extraction results indicate that Na is predominantly water-soluble and ion-exchangeable, whereas Ca and Mg are largely ion-exchangeable and HCl-soluble. The abundant cell cavities and oxygen-containing functional groups in lignite provide both binding sites and accommodation space for Ca, Mg, and Na. Despite a continental freshwater depositional setting, tectonic isolation and persistent arid conditions potentially promoted epigenetic enrichment of Na, Mg, and Ca. Closed hydrogeological units formed by tectonic movements restricted leaching and enhanced evaporation, concentrating these elements in the coal seams. Future research should focus on implementing economically feasible dealkalization pretreatment processes for the clean utilization of high-alkali coals. Full article

Marine by-products, including fishery discards, seafood-processing residues, aquaculture wastes, crustacean shells, and seaweed-derived side streams, are heterogeneous feedstocks rich in proteins, lipids, minerals, chitinous materials, polysaccharides, and bioactive compounds. This review examines insect-mediated bioconversion as a controlled biorefinery strategy for transforming these unstable marine residues into functional aquafeed ingredients and value-added bioproducts. We compare major marine feedstock classes and industrially relevant insects, with emphasis on substrate–insect matching, moisture control, salinity, lipid and ash load, texture, spoilage risk, and safety. Particular attention is given to how marine substrates can tailor insect meal, insect oil, chitinous fractions, hydrolysates, frass, and functional feed additives. The review further summarizes aquafeed applications of insect-derived products, including fishmeal and fish-oil replacement, protein and amino acid quality, lipid enrichment, gut health, immunity, and disease resistance in aquatic animals. Microbiome-assisted strategies, such as fermentation, enzymatic pretreatment, and gut or substrate microbial management, are discussed as tools to improve substrate stability, digestibility, and product quality. Finally, safety, regulation, scale-up, life cycle assessment, and techno-economic issues are considered. Overall, marine insect biorefineries should be optimized not only for biomass yield, but also for product quality, traceability, and application-specific safety. Full article

The growing global population has increased energy and food demand, leading to a higher production of waste streams such as fly ash from the energy sector and wastewater from food and beverage industries. Without proper treatment, these wastes pose significant environmental concerns. One promising strategy is to repurpose industrial byproducts for wastewater treatment. Winery wastewater, for instance, contains acidic organic compounds and alcohol that are difficult to remove using conventional methods, while large amounts of fly ash remain underutilized. This study, therefore, examines a hybrid system that combines fly ash-assisted Fenton oxidation with membrane filtration for winery wastewater treatment. The process involved sequential Fenton pre-treatment followed by lab-scale nanofiltration using a 1 kg/mol ceramic membrane (13.1 cm²). A Design of Experiments approach was applied to evaluate system performance under varying H₂O₂ dosages (10–30 mL/L), fly ash loadings (1–3 g/L), and membrane fluxes (40–80 LMH). Filtration was performed through multiple constant-flux cycles, with energy requirements ranging from 400 to 800 kWh/m³ for the flux variations calculated from the lab-scale pump operating at a constant power supply. The hybrid method showed strong performance, achieving 70% TOC removal and 90% reduction of color and iron. However, considerable membrane fouling was observed, likely due to increased retention and deposition of organic matter, iron, and fly ash during filtration. Full article

Yttrium is one of the lesser-known critical elements, but it has recently gained significant market attention due to a dramatic price increase of up to 1400% in Europe. Although its primary application is in phosphors (e.g., in LEDs), modern society heavily depends on these technologies, making yttrium indispensable. However, the limited availability of yttrium raises concerns about its long-term supply. Therefore, there is a need for efficient techniques to recover yttrium from secondary materials to ensure a stable supply. While the wastes contain only trace amounts of yttrium and often have complex elemental compositions, they are more readily available than primary sources. The yttrium content ranges from a few percent in spent phosphors to several hundred ppm in red mud, around a few dozen ppm in phosphogypsum, and up to several ppm in coal and coal fly ashes. Although conventional hydrometallurgical methods are commonly used, they lack selectivity for yttrium recovery. In contrast, unconventional solvometallurgical and bioleaching approaches currently play a relatively minor role in recovery applications. This review discusses a range of methods investigated for yttrium recovery from different types of secondary resources, including pretreatment (where applicable), leaching, and subsequent yttrium recovery from the resulting leachates. Although the chemical and phase compositions of yttrium-bearing waste materials differ substantially, necessitating tailored treatment strategies, acid leaching remains the predominant extraction route and is most commonly followed by solvent extraction and/or oxalate precipitation. Most studies reported to date have been conducted at the laboratory scale. Despite progress and the development of promising recovery concepts, the efficient separation of high-purity yttrium from other rare earth elements and co-existing impurities continues to represent the key obstacle to commercial-scale application. Full article

Flue gas torrefaction is an emerging biomass pretreatment technology that utilizes industrial flue gas as a reactive medium to replace inert atmospheres. However, the intrinsic complexity of biomass and the catalytic interference of ash hinder mechanistic elucidation. This study investigated the torrefaction behavior of demineralized poplar wood under N₂, CO₂, dry flue gas (DFG), and wet flue gas (WFG) at 300 °C for 5–20 min. Thermogravimetric analysis combined with kinetic modeling (FWO, KAS, and CR methods) revealed that the apparent activation energy (E_α) varied non-monotonically with atmosphere oxidizability. Under N₂, the average E_α was 177 kJ/mol following the three-dimensional diffusion model (D5). CO₂ gave the highest average E_α (314 kJ/mol) with the Avrami–Erofeev nucleation model (A₁/₄). DFG and WFG significantly reduced the average E_α to 133 and 128 kJ/mol, respectively, both following the A₁/₃ model. Consistently, WFG yields the lowest char and the highest gas yield. XPS and FTIR analyses indicated that flue gas atmospheres, especially WFG, promoted deeper deoxygenation and aromatization of biochar. Tar composition underwent a noticeable transition from ketones to aldehydes and saccharides under flue gas conditions, with the most remarkable variation observed under WFG. Gaseous products were dominated by CO₂ under N₂ and by CO under CO₂, while DFG and WFG produced moderate and stable gas compositions. These findings demonstrate that flue gas torrefaction, particularly under WFG, effectively enhances biomass effectively upgrades biomass quality by regulating pyrolysis kinetics and product distribution, and demineralized biomass is a suitable intermediate model for mechanistic investigation. Full article

This review evaluates pretreatment strategies for blending the organic fraction of municipal solid waste (OFMSW) with agricultural residues to recover fermentable sugars. Three mechanistic benefits have been hypothesized for such blends: ash-mineral pH buffering, endogenous protein reduction of non-productive cellulase–lignin binding, and inhibitor dilution. These mechanisms are inferred from analogous lignocellulosic systems rather than measured directly in OFMSW–agricultural residue combinations, and their translation into saccharification gains remains substrate- and pretreatment-specific. A synergy index framework with a four-tier classification (true synergy, additive, substitution, and process complementarity) is applied to reclassify the available evidence, alongside an assessment of pretreatment chemistry, enzymatic hydrolysis outcomes, and techno-economic feasibility. Integrated sequential pretreatment, particularly acid-catalyzed steam explosion and deacetylation with mechanical refining, proved most robust for heterogeneous feeds. The strongest Tier I synergy is found for SO₂-catalyzed steam explosion of hybrid poplar–wheat straw (SI 1.29–1.33; 22% monomeric sugar gain). OFMSW combined with organosolv beechwood cellulose at 35–45% OFMSW reached 58–68% saccharification (44–46 g sugar L⁻¹), a Tier III–IV outcome. Matched-control saccharification data for OFMSW–agricultural residue blends specifically have not been reported. Co-processing corn stover with wet organic waste reduced CO₂ mitigation cost from $236 to $67 per ton CO₂-eq under bio-CNG upgrading. Formal synergy quantification, blend-specific inhibitor profiling, and high-solids process intensification are the central prerequisites for commercial translation. Full article