Search Results (1,214)

The transition from conventional silica nanoparticle (SiNP) production based on purified alkoxysilanes and high-temperature flame hydrolysis of silicon tetrachloride to renewable and waste-derived silicon resources requires more than precursor substitution. It requires a mechanistic understanding of how feedstock mineralogy, silicon speciation, impurity chemistry, and processing history propagate through dissolution, nucleation, condensation, gelation, aging, drying, and pore evolution to determine material performance, environmental burden, and manufacturing feasibility. Although previous reviews have established the technical feasibility of producing silica from secondary resources, their predominant organization by feedstock, synthesis route, or application provides limited ability to explain why nominally similar processes generate materials with markedly different structural and functional properties. This review addresses these through a resource-pull, feedstock-to-function framework that links resource chemistry and process design to critical material attributes, application-specific specifications, sustainability, and scale-up requirements. Agricultural residues, industrial by-products, geothermal resources, waste glass, and fluorosilicate streams are critically compared according to silicon form and phase, reactivity, impurity profile, compositional variability, purification demand, and attainable product quality. Particular attention is given to waste-derived alkaline silicate systems, in which molecular, oligomeric, and colloidal silica coexist and therefore require characterization beyond bulk SiO₂ concentration. Established and emerging processing strategies, including controlled combustion and alkaline extraction, alkali fusion, ambient-pressure drying, microwave and mechanochemical activation, biogenic and biomimetic templating, and continuous processing, are evaluated according to their mechanistic effects, technological maturity, structural control, and demands for energy, reagents, water, solvents, effluent treatment, and capital. Across these routes, gelation and aging emerge as critical transfer stages through which feedstock composition is translated into network connectivity, pore architecture, shrinkage behavior, and ultimately functional performance. Evidence from secondary-source aerogels further shows that properly controlled waste-derived systems can attain BET surface areas of approximately 350–500 m² g⁻¹, within the textural range of many alkoxide-derived materials, indicating that feedstock variability, impurity management, and process control are more important constraints than an inherently lower performance ceiling. On this basis, this review proposes a minimum evidence framework comprising feedstock traceability, intermediate-speciation and colloidal characterization, silicon mass balance, gelation and aging metrics, application-specific qualification criteria, performance-normalized life cycle and techno-economic assessment, process analytical control, and staged pilot validation. Collectively, these principles provide a mechanistically grounded basis for moving sustainable silica synthesis beyond isolated proof-of-concept demonstrations toward reproducible, scalable, application-matched, and commercially credible manufacturing platforms. 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

The beneficiation of ferruginous manganese ores is limited by the intimate intergrowth of manganese-, iron-, and silicate-bearing phases. This study evaluated coal-based magnetizing roasting followed by dry magnetic separation in an externally heated chamber furnace with a charge capacity of up to 100 kg. A 0–5 mm ore fraction with an initial Mn/Fe ratio of 2.9 was roasted with Shubarkol coal. The best separation was obtained at an actual ore–coal bed temperature of 550–600 °C and an ore-to-coal mass ratio of 1:0.4. Relative to the magnetic-separation feed, 80.0–83.4% of Fe was recovered in the magnetic fraction, while 69.9–72.6% of Mn remained in the non-magnetic product. Its Fe content decreased to 3.2–3.5%, increasing the Mn/Fe ratio to 7.30–7.84. X-ray diffraction showed preferential concentration of magnetite and jacobsite in the magnetic fraction, whereas hausmannite and braunite were concentrated mainly in the non-magnetic fraction together with the gangue phases. Multipoint measurements also demonstrated a substantial difference between the combustion-zone and actual bed temperatures. The results demonstrate that controlled low-temperature roasting can generate sufficient magnetic contrast for selective iron removal from ferruginous manganese ore. Full article

Porcelain manufacturing technological wastewater contains many mineral particles, like kaolinite 27%, quartz 29%, calcium feldspar 15%, and mullite 12%. These particulate matters are dispersed into the wastewater from all technological steps influencing the water parameters, such as pH, electrical conductivity, total dissolved solids (TDS) and turbidity. These properties were measured and correlated with the physicochemical investigation of the collected particles. The two sample types are as follows: particles collected directly from the wastewater dispersion (WWS) and the slurry (SLR) collected from the dump. The mineral distribution was assessed by XRD correlated with mineralogical optical microscopy, revealing the relative distribution of the finest kaolinite particles with respect to quartz and feldspar boulder-like particles. Mullite was observed as a rounded inclusion occurring due to the re-circulated grounded material. It results in the presence of sodium silicate, acting as a densification binder when the samples are completely dried. Particle morphology was correlated with their elemental composition through SEM–EDX investigation. Iron hydroxide was found at about 9%. It prevents re-circulation of this wastewater slurry in porcelain production. Thus, a sustainable approach is required for its utilization as a sub-product. Therefore, the samples were subjected to thermal analysis in order to reveal its sintering behavior. Thermal analysis revealed the dehydroxylation of kaolinite between 530 and 630 °C, and a high-temperature thermal event at 994 °C (WWS) and 997 °C (SLR), which was further confirmed by DSC and attributed to mullite formation. Particle consolidation through the dehydroxylated kaolinite matrix and further mullitized mass was assessed through SEM microscopy, indicating proper densification to ensure slurry utilization for less pretentious ceramic products, allowing them to be fired at relatively lower temperature than porcelain (e.g., 600–800 °C) and ensuring a significant energy consumption saving. Full article

Reinforced concrete structures in marine environments are subjected to severe deterioration, particularly in tidal zones. The development of intrinsically hydrophobic concrete through internal modification provides a promising strategy to mitigate this challenge. This study employed sodium methyl silicate (SMS) as a hydrophobic agent to prepare recycled fine aggregate concrete (RFAC), which was subsequently subjected to accelerated indoor chloride dry–wet cycling. The deterioration behavior of RFAC and the degradation mechanism of the SMS-induced hydrophobic film during dry–wet cycling were investigated through evaluations of mechanical performance, hydrophobicity, chloride resistance, microstructure, phase composition, pore structure, chemical bonding, and functional groups. The results show that SMS improves the hydrophobicity of RFAC but inhibits its hydration process. The optimal SMS dosage for RFAC under dry–wet cycling is 9‰, which achieves a balance between hydrophobicity enhancement and pore structure optimization. Compared with ordinary RFAC, the specimen exhibits 12.9‰ and 17.6% increases in compressive strength and RDEM, respectively, after 30 cycles, accompanied by reductions of 25.8%, 52.7%, and 80.0% in peak free chloride content, chloride erosion depth, and convection zone depth, respectively. RFAC with 9‰ SMS exhibits a denser matrix with lower porosity and fewer corrosion products. SMS enhances chloride resistance mainly by reducing water transport and chloride ion ingress through hydrophobic modification. Dry–wet cycling gradually deteriorates the SMS-induced hydrophobic film through the weakening of Si-C-related structures, while the Si-O-Si framework remains relatively stable. A quantitative correlation between the contact angle and free chloride ion content is established, and the modified Lucas–Washburn equation provides a reasonable description of chloride ion penetration depth. Full article

Using ultrafine silicate cement as the cementitious material, and admixtures such as expansion agent, rapid-setting agent and water reducer as additives, a new type of composite grouting material with high early strength and high toughness was obtained by modification with nano-Al₂O₃ (NA). The influence of NA content on the mechanical properties, flowability, bleeding behavior, setting time, volume shrinkage, and microstructure was investigated for composite grouting materials. The results show that, as the NA content increases, the flowability of the paste decreases, the bleeding rate reduces, and the setting time increases first and then decreases. Appropriate NA can effectively improve the mechanical strength of the composite grouting material. Especially at the condition of 3% NA, the composite grouting material reached the highest early compressive strength and toughness. Compared with the control group, the compressive strength of the specimen increases by 39.54% and 6.83% respectively at 1 d and 21 d, and the flexural strength increased by 55.41% at 1 d. XRD, FTIR, SEM and hydration heat analysis confirm that the NA can promote the early hydration heat of ultrafine cement, and shorten the induction period. Moreover, more C-A-H gel products will be generated by consuming Ca(OH)₂ with active NA, leading to an improvement in the matrix compactness. Such an outstanding mechanical property can be mainly attributed to the triple coupling mechanism of the hydration regulation, microstructure and filling effect of superfine cement by nano-Al₂O₃ in combination with multi-component admixtures. Full article

This study investigates the damage evolution mechanism affecting the fracture-bearing performance of fly ash cement paste under low-temperature curing conditions. Pre-cut cement paste specimens with fly ash contents of 0%, 15%, and 25% were prepared and subjected to both standard curing and low-temperature curing at 5 °C for 28 days. Three-point bending tests combined with acoustic emission (AE) monitoring were conducted to analyze peak flexural load, AE ring count, cumulative energy, RA-AF crack classification, and b-value evolution. Additionally, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were employed to characterize micromorphology and relative changes in hydration product content. The results indicate that both fly ash incorporation and low-temperature curing significantly reduce the flexural bearing capacity of pre-notched specimens. Under low-temperature curing, the peak loads of LF15 and LF25 decrease by 34.83% and 47.19%, respectively, compared to LF0. At the same fly ash replacement level, all low-temperature-cured specimens exhibited lower peak loads than those cured under standard conditions. Overall AE activity was reduced in low-temperature-cured specimens, with crack propagation instability occurring at lower load levels. The addition of fly ash shifted the fracture mode toward a tensile-dominated type, whereas low-temperature curing increased the proportion of shear-type AE events. Fly ash incorporation increased the relative content of calcium silicate hydrate (C-S-H) gel and decreased that of calcium hydroxide (CH); however, this did not result in improved peak flexural load. This outcome is attributed to the insufficient reactivity of fly ash at low temperatures, leading to residual unreacted spherical particles, dilution of clinker, and inadequate interfacial bonding, which collectively weaken the continuous load-bearing skeleton of the matrix. This paper establishes a multi-scale interpretation of the damage mechanisms affecting the low-temperature fracture-bearing performance of fly ash cement paste by correlating macroscopic bearing response, AE damage evolution, crack types, and hydration product composition. Full article

This study focuses on loess in the Lanzhou region and employs a self-developed LM-1 ionic cementitious curing agent (mainly sodium silicate) combined with cement for loess improvement. Through mechanical tests, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) analysis, the mechanical properties, microstructure, and mineralogical evolution of composite-improved loess were systematically investigated, with emphasis on revealing the reinforcement mechanism. The results show that combining LM-1 and cement significantly enhances the unconfined compressive strength (UCS) of loess. The optimal proportion of 1.5% LM-1 + 10% cement achieves 7-day and 28-day UCS values of 3.43 MPa and 4.12 MPa, representing increases of 69.0% and 54.7% over 10% cement alone, and outperforming 12% cement-only specimens. This formulation develops a uniform, dense C-S-H gel network with optimized pore structure and reduced microcracks. LM-1 generates hydrated silicate products through alkali-activated reactions, which together with cement hydration C-S-H gel form a dual-gel cementation system, while effectively accelerating cement hydration. This provides a theoretical basis and technical support for balancing cement reduction and performance enhancement in subgrade reinforcement and slope protection in loess regions. Full article

The history of steel rail manufacturing at the Hanyang Iron Works in China is briefly summarized first in this paper. The chemical composition, microstructure, inclusions, and mechanical properties of the manufactured rails were then systematically analyzed. The progress of manufacturing process evolution and the enhancement of product quality are elucidated through this study. The chemical composition of steel rails produced by Hanyang Iron Works in its initial stage (before 1904) was characterized by low carbon content (0.13–0.22 wt.%) and high phosphorus levels (P ≥ 0.15 wt.%). Inclusions were primarily identified as sulfides (MnS) and composite inclusions of sulfides and silicates (MnS·SiO₂). The microstructure consisted of a large amount of ferrite and pearlite. Following the technical transformation from 1905 to 1908, dephosphorization was achieved and the composition control of the steel rails was optimized. The carbon content of the rails was increased to above 0.48 wt.%, while the phosphorus content was significantly reduced (P ≤ 0.10 wt.%). The inclusions were identified as sulfides (MnS) and composite inclusions consisting of sulfides and aluminum oxides (MnS·Al₂O₃). The microstructure was transformed into a combination of a small amount of proeutectoid network ferrite and pearlite. The mechanical performance of the steel rails was substantially improved via the implementation of technological upgrades at the Hanyang Iron Works. A tensile strength of 800 MPa grade was achieved in some rails, which constitutes a 200 MPa increment over the strength of rails from the early production period. A transition in the fracture morphology of tensile specimens was observed, shifting from large and shallow dimples with a small amount of cleavage fracture to small, shallow dimples combined with predominant cleavage fracture. Full article

The utilization of industrial solid waste is crucial for sustainable development. This study developed a novel composite cementitious material (OSSC-GGBS) using oil shale semi-coke and slag as cement substitutes. A multi-objective optimization method was employed to determine the optimal formulation of OSSC-GGBS. Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM-EDS), Thermogravimetric Analysis (TG-DTG-DSC), and pH testing. Finally, the synergistic effects of oil shale semi-coke and slag on the mechanical properties of this composite material were thoroughly investigated. Results indicate that the composite cementitious material exhibits optimal performance when the mass ratio of oil shale semi-coke to slag is 3:7, cement content is 15%, water glass modulus is 1.4, and water glass content is 10%. Microscopic analysis revealed that the synergistic interaction between oil shale semi-coke and slag optimized the microstructure of OSSC-GGBS. Its hydration products primarily consisted of C-S-H gel, Ca(OH)₂, and AFt, forming a dense and stable microstructure. Simultaneously, under alkali-activated conditions, oil shale semi-coke and slag synergistically participated in hydration reactions and secondary pozzolanic reactions. This significantly promoted the formation of cementitious products such as calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H). These products filled internal pores to form a network skeleton, thereby optimizing the microstructure. Full article

Silicon fertilization has been reported to improve crop performance under different environmental conditions; however, information regarding the efficiency of different foliar silicon sources under subtropical field conditions remains limited, particularly for soybean. This study evaluated the effects of different foliar silicon sources on silicon accumulation in leaves and seeds and their association with soybean yield under subtropical conditions in southern Brazil. A field experiment was conducted using five treatments consisting of different silicon sources applied during the reproductive stage. Silicon concentrations in leaves and seeds and seed yield were determined, and Pearson’s correlation analysis was performed to investigate the relationships among these variables. Foliar silicon accumulation differed according to the fertilizer source, with potassium silicate resulting in the greatest silicon concentration in leaves, whereas silicon oxide promoted the highest silicon accumulation in seeds. Silicon-containing thermophosphate was associated with the highest seed yield; however, because this fertilizer also supplied nutrients other than silicon, this response cannot be attributed exclusively to silicon. Significant positive correlations were observed between silicon accumulation and seed yield, particularly for seed silicon concentration. Overall, the results indicate that the agronomic efficiency of foliar silicon fertilization depends on the fertilizer source, with different formulations exhibiting distinct responses for silicon accumulation and productivity. These findings provide useful information for selecting foliar silicon fertilizers according to specific agronomic objectives, since no single silicon source simultaneously maximized foliar silicon accumulation, seed silicon concentration, and seed yield. Full article

There exist multiple conflicting challenges in dryland agricultural production: excessive chemical fertilizer input contrasts with low utilization efficiency of maize straw resources, and long-term over-fertilization triggers continuous degradation of farmland soil fertility. To explore the soil improvement and growth-promoting potential of silicon-modified biochar-based fertilizers, this study conducted relevant preparation and pot experiments. This study used maize stover as feedstock to investigate the effects of pyrolysis temperature and silica modification on the structural characteristics of biochar. Raw biochar was pyrolyzed at 400–600 °C and subsequently modified with sodium silicate. Biochar-based fertilizers were then produced using modified biochar as the carrier, and their influences on soil physicochemical properties, soil enzyme activities, and foxtail millet growth were analyzed via pot experiments. The results indicate that 500 °C is the optimal pyrolysis temperature for maize straw biochar. After sodium silicate modification, the specific surface area of modified biochar increased by 18.84% relative to unmodified raw biochar, accompanied by a more developed surface pore structure. The application of biochar-based fertilizers significantly reduced soil pH and increased soil carbon stocks and available nutrient content. All biochar-based fertilizer treatments significantly improved foxtail millet growth, among which the BF3 treatment showed the strongest growth-promoting performance. Compared with the sole chemical fertilizer (CF), BF3 increased plant height by 63.72% and total biomass by 54.27%, while stem diameter decreased by 11.41%. In summary, sodium silicate-modified biochar-based fertilizer pyrolyzed at 500 °C can effectively improve soil quality and promote millet growth, with a biochar-to-fertilizer ratio of 1:3 being the optimal formulation for dryland millet cultivation. This study provides a direct basis for the compatibility evaluation of biochar-based fertilizers in dryland foxtail millet cultivation. Full article

To elucidate the geochemical features of produced water in coalbed methane (CBM) wells of the Gujiao Block and their indicative significance for production, systematic testing of ion composition and total dissolved solids (TDS) of produced water from ten CBM wells was conducted through five discrete sampling campaigns over an 18-month period. Combined with production performance data, the spatiotemporal evolution patterns, controlling factors, and the response relationship with productivity were analyzed. The results show that the water chemistry type of produced water in the study area is mainly identified as the Na-HCO₃ type. The TDS averages 1716.62 mg/L. The hydrochemical characteristics are primarily controlled by water/rock interactions, with Na⁺ and K⁺ mainly derived from silicate mineral weathering and dissolution, coupled with cation exchange processes. The Na/Cl ratio suggests that halite dissolution contributes to both Na⁺ and Cl⁻, whereas the excess Na⁺ relative to Cl⁻ likely reflects cation exchange or dissolution of Na-bearing silicate minerals. As drainage proceeded, Na⁺ and K⁺ concentrations increased, Ca²⁺ decreased, Cl⁻ increased, and SO₄²⁻ first increased and then decreased. Spatially, TDS increases from north to south, with the central-southern region representing a stagnant groundwater zone. Productivity response analysis reveals that Na⁺, HCO₃⁻, and TDS all show a trend of initially slow increase followed by rapid increase with increasing gas production. A negative trend is observed between gas production and the concentrations of Cl⁻, Ca²⁺, Mg²⁺, and SO₄²⁻. The productivity response index for the Gujiao Block ranges from 3.75 to 42.43, with an average of 17.78. As the productivity response index increases, gas production initially decreases and then increases. The findings clarify the geochemical evolution mechanisms of produced water in the Gujiao Block, providing a scientific basis for productivity evaluation of CBM wells. Full article

This study used silicate cement as the base material and nano-silica, fly ash, and bentonite as the composite modification components. Through laboratory tests, the engineering characteristics and impermeability and drying shrinkage properties of the modified slurry were systematically investigated. The results showed that the verification test mix proportion of the slurry was a water–binder ratio of 0.7, a nano-silica content of 2%, a fly ash content of 40%, and a bentonite content of 6%. This ratio of the slurry had the best comprehensive performance. Compared with pure cement slurry, the water loss rate decreased by 61.90%; the 3d, 7d, and 28d compressive strengths increased by 30.60%, 36.08%, and 20.08% respectively; the fluidity decreased by 6.38%; and the initial setting time decreased by 9.77%. The anti-seepage pressure of the verification test mix proportion slurry group reached 1.05 MPa, which was 43.84% higher than the pure cement reference group and was superior to each single addition group. Combined incorporation of nano-silica, fly ash, and bentonite remarkably improved the impermeability. The 56d drying shrinkage rate was 1257 × 10⁻⁶, which was 19.16% lower than that of the reference group. Based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests, the microstructure was analyzed, and the hydration mechanism was discussed. The composite modification did not change the type of hydration products but significantly improved the microstructure. Nano-silica reacted with the hydration product Ca(OH)₂ in the early stage of hydration, accelerating the hydration process and promoting the interwoven coating of the hydration product on the calcium aluminosilicate crystals, thereby improving the compactness of the matrix. Fly ash participated in the pozzolanic reaction in the later stage of hydration, adhering to the secondary hydration products on the surface and gradually consuming them, further filling the pores and optimizing the interface structure. Combined with bentonite, nano-silica and fly ash jointly densified the matrix, refining the microstructure of modified samples and forming a continuous integrated hydration product network inside the grout. Full article

Thermal treatment of clay minerals induces a sequence of dehydration, dehydroxylation, and recrystallization reactions that control the properties of ceramic materials, calcined clays, and other high-temperature products. This review examines how vibrational spectroscopic techniques, particularly Fourier-transform infrared (FTIR), Raman, and infrared emission spectroscopy (IES), have advanced the molecular-level understanding of these transformations. Unlike conventional thermal analysis methods, these techniques directly monitor changes in hydroxyl groups, interlayer water, silicate frameworks, and newly formed phases during heating, providing real-time insight into reaction pathways and intermediate structures. The thermal behavior of major clay mineral groups, including kaolinite-group minerals, serpentines, smectites, illite, palygorskite, sepiolite, and mixed-layer clays, is compared in terms of their characteristic spectroscopic responses to increasing temperature. Particular attention is given to band shifts, intensity variations, band disappearance, and the appearance of new vibrational features associated with structural reorganization and phase development. The reviewed studies demonstrate that thermal stability is primarily governed by octahedral composition, cation–OH bond strength, vacancy distribution, and crystallinity. Integration of spectroscopic observations with complementary diffraction and thermal analysis data provides a unified framework for understanding clay mineral transformations and for optimizing thermal processing in ceramic manufacture and calcined clay applications. Full article