Search Results (1,136)

Aluminothermic reduction is an alternative processing route for the circular economy because Al is produced electrochemically in the Hall–Héroult process with minimal CO₂ emissions if the electricity input is sourced from non-fossil fuel energy sources. This circular processing option attracts increased research attention in the aluminothermic production of manganese and silicon alloys. The Al₂O₃ product must be recycled through hydrometallurgical processing, with leaching as the first step. Recent work has shown that the NaAlO₂ compound is easily leached in water. In this work, a suitable slag formulation is applied in the aluminothermic reduction of manganese ore to form a Na₂O-based slag of high Al₂O₃ solubility to effect good alloy–slag separation. The synergistic effect of carbon and silicon reductants with aluminium is illustrated and compared to the test result with only carbon reductant. The addition of small amounts of carbon reductant to MnO₂-containing ore ensures rapid pre-reduction to MnO, facilitating aluminothermic reduction. At 1350 °C, a loosely sintered mass formed when carbon was added alone. The alloy and slag chemical analyses are compared to the thermochemistry predicted phase chemistry. The alloy consists of 66% Mn, 22–28% Fe, 2–9% Si, 0.4–1.4% Al, and 2.2–3.5% C. The higher %Si alloy is formed by adding Si metal. Although the product slag has a higher Al₂O₃ content (52–55% Al₂O₃) compared to the target slag (39% Al₂O₃), the fluidity of the slags appears sufficient for good alloy separation. Full article

In wet flue gas desulfurization and denitrification processes, nitrite accumulation inhibits denitrification efficiency and induces secondary pollution due to its acidic disproportionation. This study developed a Mn-modified ZSM-5 zeolite catalyst, achieving efficient resource conversion of nitrite in nitrogen-containing wastewater through an O₃ + Mn/ZSM-5 catalytic system. Mn/ZSM-5 catalysts with varying SiO₂/Al₂O₃ ratios (prepared by wet impregnation) were characterized by BET, XRD, and XPS. Experimental results demonstrated that Mn/ZSM-5 (SiO₂/Al₂O₃ = 400) exhibited a larger specific surface area, enhanced adsorption capacity, abundant surface Mn³⁺/Mn⁴⁺ species, hydroxyl oxygen species, and chemisorbed oxygen, leading to superior oxidation capability and catalytic activity. Under the optimized conditions of reaction temperature = 40 °C, initial pH = 4, Mn/ZSM-5 dosage = 1 g/L, and O₃ concentration = 100 ppm, the $\mathrm{N}{\mathrm{O}}_2^{-}$ oxidation efficiency reached 94.33%. Repeated tests confirmed that the Mn/ZSM-5 catalyst exhibited excellent stability and wide operational adaptability. The synergistic effect between Mn species and the zeolite support significantly improved ozone utilization efficiency. The O₃ + Mn/ZSM-5 system required less ozone while maintaining high oxidation efficiency, demonstrating better cost-effectiveness. Mechanism studies revealed that the conversion pathway of $\mathrm{N}{\mathrm{O}}_2^{-}$ followed a dual-path catalytic mechanism combining direct ozonation and free radical chain reactions. Practical spray tests confirmed that coupling the Mn/ZSM-5 system with ozone oxidation flue gas denitrification achieved over 95% removal of liquid-phase $\mathrm{N}{\mathrm{O}}_2^{-}$ byproducts without compromising the synergistic removal efficiency of NO_x/SO₂. This study provided an efficient catalytic solution for industrial wastewater treatment and the resource utilization of flue gas denitrification byproducts. Full article

A novel strategy has been developed for extracting value-added resources from iron-lean, high-alumina- and -silica-containing red muds (RMs). With little or no recycling, such RMs are generally destined for waste dumps. Detailed results are presented on the carbothermic reduction of 100% RM (29.3 wt.% Fe₂O₃, 22.2 wt.% Al₂O₃, 20.0 wt.% SiO₂, 1.2 wt.% CaO, 12.2 wt.% Na₂O) and its 2:1 blends with Fe₂O₃ and red mill scale (MS). Synthetic graphite was used as the reductant. Carbothermic reduction of RM and blends was carried out in a Tamman resistance furnace at 1650 °C for 20 min in an Ar atmosphere. Reduction residues were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), elemental mapping and X-ray diffraction (XRD). Small amounts of Fe₃Si alloys, alumina, SiC and other oxide-based residuals were detected in the carbothermic residue of 100% RM. A number of large metallic droplets of Fe–Si alloys were observed for RM/Fe₂O₃ blends; no aluminium was detected in these metallic droplets. A clear segregation of alumina was observed as a separate phase. For the RM/red MS blends, a number of metallic Fe–Si droplets were seen embedded in an alumina matrix in the form of a cermet. This study has shown the regeneration of alumina and the formation of alumina-based cermets, Fe–Si alloys and SiC during carbothermic reduction of RM and its blends. This innovative recycling strategy could be used for extracting value-added resources from iron-lean RMs, thereby enhancing process productivity, cost-effectiveness of alumina regeneration, waste utilization and sustainable developments in the field. Full article

Diverging from conventional dephosphorization approaches, this study employs a novel pre-reduction and smelting separation (PR-SS) to efficiently co-recover iron and phosphorus from high-phosphorus oolitic iron ore, directly yielding Fe–P alloy, and the Fe–P alloy shows potential as feedstock for high-phosphorus weathering steel or wear-resistant cast iron, indicating promising application prospects. Using oolitic magnetite concentrate (52.06% Fe, 0.37% P) as feedstock, optimized conditions including pre-reduction at 1050 °C for 2 h with C/Fe mass ratio of 2, followed by smelting separation at 1550 °C for 20 min with 5% coke, produced a metallic phase containing 99.24% Fe and 0.73% P. Iron and phosphorus recoveries reached 99.73% and 99.15%, respectively. EPMA microanalysis confirmed spatial correlation between iron and phosphorus in the metallic phase, with undetectable phosphorus signals in vitreous slag. This evidence suggests preferential phosphorus enrichment through interfacial mass transfer along the pathway of the slag phase to the metal interface and finally the iron matrix, forming homogeneous Fe–P solid solutions. The phosphorus migration mechanism involves sequential stages: apatite lattice decomposition liberates reactive P₂O₅ under SiO₂/Al₂O₃ influence; slag–iron interfacial co-reduction generates Fe₃P intermediates; Fe₃P incorporation into the iron matrix establishes stable solid solutions. Full article

Chromium slag sites pose severe environmental risks due to hexavalent chromium (Cr(VI)) contamination, characterized by high mobility and toxicity. This study focused on chromium-contaminated soil from a historical chromium slag site in North China, where long-term accumulation of chromate production residues has led to serious Cr(VI) pollution, with Cr(VI) accounting for 13–22% of total chromium and far exceeding national soil risk control standards. To elucidate Cr(VI) transformation mechanisms and elemental linkages, a combined approach of macro-scale condition experiments and micro-scale analysis was employed. Results showed that acidic conditions (pH < 7) significantly enhanced Cr(VI) reduction efficiency by promoting the conversion of CrO₄²⁻ to HCrO₄⁻/Cr₂O₇²⁻. Among reducing agents, FeSO₄ exhibited the strongest effect (reduction efficiency >30%), followed by citric acid and fulvic acid. Temperature variations (−20 °C to 30 °C) had minimal impact on Cr(VI) transformation in the 45-day experiment, while soil moisture (20–25%) indirectly facilitated Cr(VI) reduction by enhancing the reduction of agent diffusion and microbial activity, though its effect was weaker than chemical interventions. Soil grain-size composition influenced Cr(VI) distribution unevenly: larger particles (>0.2 mm) in BC-35 and BC-36-4 acted as main Cr(VI) reservoirs due to accumulated Fe-Mn oxides, whereas BC-36-3 showed increased Cr(VI) in smaller particles (<0.074 mm). μ-XRF and correlation analysis revealed strong positive correlations between Cr and Ca, Fe, Mn, Ni (Pearson coefficient > 0.7, p < 0.01), attributed to adsorption–reduction coupling on iron-manganese oxide surfaces. In contrast, Cr showed weak correlations with Mg, Al, Si, and K. This study clarifies the complex factors governing Cr(VI) behavior in chromium slag soils, providing a scientific basis for remediation strategies such as pH adjustment (4–6) combined with FeSO₄ addition to enhance Cr(VI) reduction efficiency. Full article

In this work, the development of Al-based metal matrix composites (MMCs) is achieved using hybrid SiC and ZrO₂ reinforcement particles for automotive applications. Powder metallurgy (PM) is employed with various combinations of important process parameters for the fabrication of MMCs. MMCs were characterized using scanning electron microscopy (SEM), X-ray diffractometry (XRD), and a microhardness study. All XRD graphs adequately exhibit Al, SiC, and ZrO₂ peaks, indicating that the hybrid MMC products were satisfactorily fabricated with appropriate mixing and sintering at all the considered fabrication conditions. Also, no impurity peaks were observed, confirming high composite purity. MMC products in all the XRD patterns, suitable for the desired applications. According to the SEM investigation, SiC and ZrO₂ reinforcement components are uniformly scattered throughout Al matrix in all produced MMC products. The occurrence of Al, Si, C, Zr, and O in EDS spectra demonstrates the effectiveness of composite ball milling and sintering under all manufacturing conditions. Moreover, an increase in interfacial bonding of fabricated composites at a higher sintering temperature indicated improved physical properties of the developed MMCs. The highest microhardness value is 86.6 HVN amid all the fabricated composites at 7% silica, 14% zirconium dioxide, 500° sintering temperature, 90 min sintering time, and 60 min milling time. An integrated Particle Swarm Optimization–Support Vector Machine (PSO-SVM) model was developed to predict microhardness based on the input parameters. The model demonstrated strong predictive performance, as evidenced by low values of various statistical metrics for both training and testing datasets, highlighting the PSO-SVM model’s robustness and generalization capability. Specifically, the model achieved a coefficient of determination of 0.995 and a root mean square error of 0.920 on the training set, while on the testing set, it attained a coefficient of determination of 0.982 and a root mean square error of 1.557. These results underscore the potential of the PSO-SVM framework, which can be effectively leveraged to optimize process parameters for achieving targeted microhardness levels for the developed Al-SiC-ZrO₂ Composites. Full article

Aluminum nitride (AlN) thin films were deposited on SiO₂ substrates by RF-magnetron sputtering at varying powers (110–140 W) and subsequently subjected to thermal annealing at 450 °C under nitrogen atmosphere. A comprehensive multi-technique investigation—including X-ray reflectometry (XRR), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), optical profilometry, spectroscopic ellipsometry (SE), and electrical measurements—was performed to explore the physical structure, morphology, and optical and electrical properties of the films. The analysis of the film structure by XRR revealed that increasing sputtering power resulted in thicker, denser AlN layers, while thermal treatment promoted densification by reducing density gradients but also induced surface roughening and the formation of island-like morphologies. Optical studies confirmed excellent transparency (>80% transmittance in the near-infrared region) and demonstrated the tunability of the refractive index with sputtering power, critical for optoelectronic applications. The electrical characterization of Au/AlN/Al sandwich structures revealed a transition from Ohmic to trap-controlled space charge limited current (SCLC) behavior under forward bias—a transport mechanism frequently present in a material with very low mobility, such as AlN—while Schottky conduction dominated under reverse bias. The systematic correlation between deposition parameters, thermal treatment, and the resulting physical properties offers valuable pathways to engineer AlN thin films for next-generation optoelectronic and high-frequency device applications. Full article

Iron-rich bauxite residue (red mud) is a hazardous alkaline solid waste produced during the production of alumina from high-iron bauxite, which poses severe environmental challenges due to its massive stockpiling and limited utilization. In this study, metallic iron was recovered from high-iron red mud using the smelting reduction process. Thermodynamic analysis results show that an increase in temperature and sodium oxide content, along with an appropriate mass ratio of Al₂O₃ to SiO₂ (A/S) and mass ratio of CaO to SiO₂ (C/S), contribute to the enhancement of the liquid phase mass fraction of the slag. During the smelting reduction process of high-iron red mud, iron recoveries for low-alkali high-iron red mud and high-alkali high-iron red mud under optimal conditions were 98.14% and 98.36%, respectively. The metal obtained through reduction meets the industrial standard for steel-making pig iron, which is also confirmed in the pilot-scale experiment. The smelting reduction process of high-iron red mud can be divided into two stages, where the reaction is predominantly governed by interfacial chemical reaction and diffusion control, respectively. The apparent activation energy of high-alkali high-iron red mud is lower than that observed for low-alkali high-iron red mud. The reduced slag can be used as a roadside stone material or cement clinker. This proposed method represents a sustainable process for the comprehensive utilization of high-iron red mud, which also promotes the minimization of red mud. Full article

This study investigates the thermally induced phase transformation of Ni-exchanged LTA zeolite as a dual-purpose method for nickel immobilization and the synthesis of stable ceramic pigments. The process describes a cost-effective and sustainable alternative to conventional pigment production, aligning with circular economy principles. Upon thermal treatment at temperatures ranging between 900 °C and 1300 °C, Ni-exchanged LTA zeolite undergoes a transformation to NiAl₂O₄ spinel, confirmed by XRPD, FTIR, and thermal analysis. Initially, NiO is formed, but as the temperature increases, it dissolves and transforms into NiAl₂O₄. Colorimetric studies revealed intensified blue pigmentation with increasing temperature, correlating with crystallite growth and structural evolution. SEM analysis showed morphological changes from cubic particles to sintered agglomerates, enhancing pigment stability and hardness. The Ni-LTA sample calcined at 1300 °C showed the highest hue angle, which was consistent with the formation of over 99 wt.% of the nickel aluminate crystalline phase at this temperature. The results demonstrate that Ni-LTA zeolite can be effectively transformed into durable greenish-blue pigments suitable for application in porcelain. This transformation is especially evident at 1300 °C, where a spinel phase (NiAlSi₂O₄) forms, with colorimetric values: L = 58.94, a* = –16.08, and b* = –15.90. Full article

To investigate the corrosion resistance of 60Si2MnA spring steel coated with Zn-Al in a domestic atmospheric environment containing harmful salts, the corrosion environmental factors (temperature, humidity, deposited salts, and pH) were obtained through field research. The deliquescence and weathering behavior of harmful salts were studied using impedance methods to establish their characteristic curves. Additionally, a self-designed salt deposition test apparatus was employed to conduct accelerated atmospheric corrosion tests under constant salt deposition (10 g/m²) and controlled temperature and humidity conditions (20 °C/75% RH and 40 °C/75% RH) over different corrosion periods. The results show that noticeable red rust appeared on the samples after one month of corrosion. As the temperature increased, the consumption of the coating accelerated. XRD and Raman analyses reveal that the main corrosion products of the coating materials were ZnO, Zn(OH)₂, and Zn₅(CO₃)₂(OH)₆, while the red rust primarily consisted of iron oxides and hydroxides. In the early stages of corrosion, the self-corrosion current density was relatively low due to the protective effects of the coating and the corrosion product layer, indicating good corrosion resistance. However, in the later stages, the integrity of the coating and the corrosion product layer deteriorated, leading to a significant increase in the self-corrosion current density and a decline in corrosion resistance. This study provides a data foundation for understanding the corrosion behavior of Zn-Al-coated spring steel in atmospheric environments and offers theoretical insights for developing more corrosion-resistant coatings and optimizing anti-corrosion measures. Full article

A SiO₂-Al₂O₃-B₂O₃-CaO-MgO-Na₂O glass-based protective lubricant coating was developed for Ti-6Al-4V alloy forging, featuring a fully non-toxic formulation. The coating consisted of a composite glass matrix formed by blending two phases with distinct softening temperatures, extending its operational window to 700–950 °C. The composite glass showed initial softening at 700 °C and complete melting at 800 °C, with contact angle measurements confirming superior wettability (θ < 90°) across the forging range (800~950 °C). With an increase in temperature, the surface tension of the composite glass melt decreased, and subsequently, the wettability of the composite glass melt was significantly improved. XRD revealed that the uncoated Ti-6Al-4V formed a 22 μm thick rutile TiO₂ scale with a porous structure and interfacial cracks, while the coated sample retained an amorphous glass layer with no TiO₂. Cross-sectional SEM showed a crack-free, poreless interface with strong metallurgical bonding, in contrast to the uncoated sample’s spalled oxide layer. EDS showed minimal oxygen diffusion of the glass coating into the substrate. Ring upsetting tests showed that the coating reduced friction from 0.5–0.7 to 0.3 (50–57% decrease). Collectively, the glass protective lubricant coating showed good performance in terms of protection and lubrication. Full article

Olive mill wastewater (OMW) is a highly polluting effluent rich in organic pollutant compounds derived from olive oil production. In this work, the steam reforming reaction of OMW (OMWSR) was performed in a traditional reactor at 400 °C and different pressures (1–4 bar) to treat and valorize this effluent. A commercial catalyst (Rh/Al₂O₃) was used as a reference sample and several new catalysts were prepared (Ni-Ru/Ce-SiO₂) using different preparation methods to study their effect on the activity and stability. The best-performing catalysts were also subjected to long-term operation experimental tests (24 h). It was observed that the preparation method used for the catalysts synthesis influenced the catalytic performance of the samples. In addition, temperature-programmed oxidation (TPO) analysis of the used catalyst showed the presence of carbon deposits: the results showed that periodic oxidative regeneration improved the catalyst stability and sustained H₂ production. Finally, it was verified that the Ni-Ru/Ce³ catalyst stood out during the experimental tests, exhibiting high catalytic activity along the stability test at 400 °C and 1 bar: H₂ yield always over 7 mol_H2·mol_OMW⁻¹ and total organic carbon (TOC) conversion always higher than 94%. Despite these promising results, further research is needed to assess the economic feasibility of scaling up the process. Additionally, future work could explore the development of catalysts with enhanced resistance to deactivation by carbon deposition. Full article

Microwave dielectric ceramics are indispensable in modern communication technologies, playing a pivotal role in components such as filters, oscillators, and antennas. Among these materials, ZnAl₂O₄ ceramics have garnered attention for their excellent quality factor (Q × f) and low dielectric constant (ε_r). However, their high sintering temperature (~1650 °C) limits practical applications. This study investigates ZnAl_2-x(Zn_0.5Si_0.5)_xO₄ (ZAZS) (x = 0.1–0.9) ceramics, where [Zn_0.5Si_0.5]³⁺ substitutes Al³⁺, to reduce sintering temperature while maintaining high-performance microwave dielectric properties. ZAZS ceramics were synthesized via the solid-state reaction method and characterized for their structural, morphological, and dielectric properties. X-ray diffraction analysis confirmed the formation of a single-phase solid solution up to x = 0.8, with minor secondary phases appearing at x = 0.9. The substitution increased lattice parameters and enhanced material densification, as observed through SEM and relative density calculations. Microwave dielectric measurements showed that ZAZS ceramics achieved a maximum Q × f of 20,200 GHz and a τ_f value reduced to −62 ppm/°C at x = 0.8, while ε_r decreased from 7.90 to 6.98. Bond-valence calculations reveal that the reduction of the average Al/Zn/Si–O bond valence weakens octahedral rigidity, systematically tuning τ_f toward zero. These results demonstrate that ZAZS ceramics, with a reduced sintering temperature of 1400 °C, exhibit excellent potential for application in low-loss microwave devices. Full article

Microstructural, mechanical and qualitative phase identification of durable mullite-based ceramics obtained by utilization of waste clay–diatomite has been studied. Mullite-based ceramics were fabricated using waste clay–diatomite from the Baroševac open-cast coal mine, Kolubara (Serbia). The raw material consists mainly of SiO₂ (70.5 wt%) and a moderately high content of Al₂O₃ (13.8 wt%). In order to achieve the stoichiometric mullite composition (3Al₂O₃-2SiO₂), the raw material was mixed with an appropriate amount of Al(NO₃)₃·9H₂O. After preparing the precursor powder, the green compacts were sintered at 1300, 1400 and 1500 °C for 2 h. During the process, rod-shaped mullite grains were formed, measuring approximately 5 µm in length and a diameter of 500 nm (aspect ratio 10:1). The microstructure of the sample sintered at 1500 °C resulted in a well-developed, porous, nest-like morphology. According to the X-ray diffraction analysis, the sample at 1400 °C consisted of mullite, cristobalite and corundum phases, while the sample sintered at 1500 °C contained mullite (63.24 wt%) and an amorphous phase that reached 36.7 wt%. Both samples exhibited exceptional compressive strength—up to 188 MPa at 1400 °C. However, the decrease in compressive strength to 136 MPa at 1500 °C is attributed to changes in the phase composition, the disappearance of the corundum phase and alterations in the microstructure. This occurred despite an increase in bulk density to 2.36 g/cm³ (approximately 82% of theoretical density) and a complete reduction in open porosity. The residual glassy phase (36.7 wt% at 1500 °C) is probably the key factor influencing the mechanical properties at room temperature in these ceramics produced from waste clay–diatomite. However, the excellent mechanical stability of the samples sintered at 1400 and 1500 °C, achieved without binders or additives and using mined diatomaceous earth, supports further research into mullite-based insulating materials. Mullite-based materials obtained from mining waste might be successfully used in the field of energy-efficient refractory materials and thermal insulators. for high-temperature applications Full article

The Karamaili Granite Belt (KGB) in the southern margin of the Eastern Junggar is the most important tin metallogenic belt in the southwestern Central Asian Orogenic Belt. The plutons in the western part have a close genetic relationship with tin mineralization. The zircon U-Pb ages of the Kamusite, Laoyaquan, and Beilekuduke plutons are 315.1 ± 3.4 Ma, 313.6 ± 2.9 Ma, and 316.5 ± 4.6 Ma, respectively. The plutons have high silica (SiO₂ = 75.53%–77.85%), potassium (K₂O = 4.43%–5.42%), and alkalis (K₂O + Na₂O = 8.17%–8.90%) contents and low ferroan (Fe₂O₃^T = 0.90%–1.48%), calcium, and magnesium contents and are classified as metaluminous–peraluminous, high-potassium, calc-alkaline iron granite. The rocks are enriched in Rb, Th, U, K, Pb, and Sn and strongly depleted in Ba, Sr, P, Eu, and Ti. They have strongly negative Eu anomalies (δEu = 0.01–0.05), 10,000 Ga/Al = 2.87–4.91 (>2.6), showing the geochemical characteristics of A-type granite. The zircon U/Pb ratios indicate that the above granites should be I- or A-type granite, which is generally formed under high-temperature (768–843 °C), low-pressure, and reducing magma conditions. The high Rb/Sr ratio (a mean of 48 > 1.2) and low K/Rb ratio (53.93–169.94) indicate that the tin-bearing plutons have undergone high differentiation. The positive whole-rock εNd(t) values (3.99–5.54) and the relatively young Nd T_2DM model ages (616–455 Ma) suggest the magma is derived from partially melted juvenile crust, and the underplating of basic magma containing mantle materials that affected the source area. The results indicate the KGB was formed in the tectonic transition period in the late Carboniferous subduction post-collision environment. Orogenic compression influenced the tin-bearing plutons in the western part of the KGB, forming highly differentiated and reduced I, A-type transition granite. An extensional environment affected the plutons in the eastern sections, creating A-type granite with dark enclaves that suggest magma mixing with little evidence of tin mineralization. Full article