Search Results (1,333)

The US National Academy of Sciences has reported that CO₂ mineral carbonation is among the largest, most energy-efficient CO₂ utilization technologies closest to commercial scale due to its thermodynamic favorability and end-product market size. However, the natural rate of reaction is generally slow in terms of kinetics, whereby only by dramatically increasing the CO₂ dissolution rate can a major impact on the rate of reaction for CO₂ mineral carbonation happen. Hence, despite the clear advantages of CO₂ mineral carbonation over other options in Carbon Capture and Sequestration CCS technologies, the current research gaps highlighted here should be addressed to ensure future technology deployment success. Therefore, this study investigated the feasibility of the design, operation and experimental improvement of a continuous high-pressure CO₂ reactor in producing and optimizing high-quality precipitated calcium carbonates PCC synthesized for consumer and industrial application. A novel mineral carbonation reactor is hereby proposed, in which, by incorporating the application of a high-pressure or supercritical CO₂ phase into the reactor, CO₂ diffusion can be increased into the continuously fine-sprayed aqueous reaction media within the reactor to form PCC. The effective reactor volume can be simultaneously decreased from the reduced high-pressure CO₂ volume. Next, by incorporating a backpressure regulator, a continuous flow of the liquid phase in and out of the reactor can be controlled. The initial reactor design had undergone successful start-up, but experimental improvement alone was unable to provide the anticipated particle size of the calcium carbonate precipitate PCC. Optimized design of the new reactor to limit internal dead flow zones was proven to successfully reduce the particle size of precipitated calcium carbonate PCC from an initially P50/P90 of 87/131 μm to 3.8/9.1 μm. Additionally, a continuous 100 h stable run was successfully executed to thoroughly investigate the three main factors influencing the quality of PCC synthesized, in which the reactant flow rate and feedstock concentration were found to be significant, with the exception of CO₂ gas pressure. The overall 3D surface trend of the particle size spread P50/P90 of the PCC synthesized was plotted over the experimental range and found to meet most of the industrial requirements and technical specifications, except for TiO₂ replacement which requires sub-micron quality. Instantaneous electricity power consumption was also measured at various operating points. Performance-wise, the continuous high-pressure CO₂ mineral carbonation reactor in this work was calculated to be able to process a maximum of 4200 g/h lime CaO feedstock at a lime concentration of 7 g/L and flow rate of 10 g/L, using a 40 L internal volume vessel, effectively increasing the productivity of lime CaO production by several fold from what was reported by peer studies assuming similar electricity costs were used for all productivity factors under consideration. Full article

By means of characterization techniques such as XRD, TEM, and in situ EBSD, the texture evolution, recrystallization behavior, and their modulation by the Al₃Zr phase in hot-rolled Al-Zn-Mg-Cu-Zr alloys with varied homogenization treatments were investigated. Results show that both the single-stage homogenized (SH) alloy and the double-stage homogenized (DH) alloy acquired a typical β-fiber texture after hot rolling, including brass, S, and copper orientations. The DH alloy experienced suppressed recrystallization (a recrystallization fraction of 6.05%) owing to its higher density of Al₃Zr precipitates. In contrast, the SH alloy exhibited more significant dissolution and agglomeration of Al₃Zr, leading to extensive recrystallization peaking at 78.1%. The primary recrystallization mode was identified as continuous recrystallization, characterized by the growth and coarsening of subgrains. Although dynamically recrystallized (DRx) grains formed during hot rolling could act as potential recrystallization nuclei, most of them exhibited weak growth capability, except the cube-oriented grains. During recrystallization, deformed grains with S orientation tended to transform into cube-oriented grains, while those with brass orientation prefer to convert into Goss-oriented grains. This can be attributed to the presence of highly mobile grain boundaries between these specific orientation pairs. In the DH alloy, subgrain growth and DRx grain consumption during annealing reduced orientation dispersion in deformed grains, promoting marked brass texture strengthening, with its volume fraction reaching 57.7%. Full article

This study investigates a karst bauxite deposit from NE Spain with a dual objective incorporating the novel aspect of directly linking genetic processes to industrial ceramic performance. First, the bauxite is mineralogically and texturally characterized using X-ray diffraction and field emission scanning electron microscopy. Second, the mineralogical and textural transformations of the bauxite during firing at 1000, 1200 and 1300 °C are analyzed, together with their effects on the physical properties of the fired products. The Lower Cretaceous bauxite is autochthonous, shows a pisolithic structure, and formed in situ under tropical monsoon conditions through intense chemical weathering involving dissolution–crystallization processes. For ceramic testing, the bauxite was mixed with illitic–kaolinitic clays in a 90/10 proportion. During firing, kaolinite and illite destabilize and transform into mullite, initially by solid-state reactions at 1000 °C and subsequently by crystallization from a vitreous phase at higher temperatures, producing larger crystals and composition closer to the empirical mullite formula. The formation of vitreous phase and mullite leads to reduced porosity and increased density and linear shrinkage, particularly between 1000 and 1200 °C. Specimens fired at 1300 °C show higher mechanical strength, related to higher mullite content and a larger size of its crystals. The results demonstrate the potential interest of these bauxites for ceramic manufacturing. Full article

p-Nitrophenol (PNP), a highly toxic and recalcitrant organic pollutant prevalent in industrial wastewater, poses severe challenges to traditional Fenton treatment technologies. In this study, a novel nanoporous catalyst is synthesized via a combined annealing–dealloying strategy. Annealing at 550 °C and 600 °C induces partial crystallization, generating α-Fe and Fe₂B phases that serve as preferential corrosion sites during chemical dealloying. This process results in a three-dimensionally interconnected nanoporous structure, which significantly increases the specific surface area of the catalyst to 2.642 m²/g. The optimized nanoporous catalyst exhibits excellent degradation performance, achieving complete removal of PNP within 30 min under room temperature reaction conditions. Notably, kinetic analysis reveals a degradation mechanism involving adsorption and Fenton-like catalysis. The high specific surface area provides abundant active sites for PNP adsorption, while the enhanced Fe²⁺ dissolution synergistically accelerates the degradation. The adsorption kinetic follows a pseudo-second-order model, and the degradation kinetic conforms to a first-order model, with activation energy analysis further confirming a surface-reaction-controlled process. This work provides a feasible approach and technical reference for designing efficient porous catalysts based on amorphous alloys for advanced treatment of refractory organic wastewater. Full article

Titanium alloys are widely used as bone graft materials due to their excellent corrosion resistance and biocompatibility. Implant failure can result from long-term exposure to body fluids and inflammation-induced pH decreases, both of which compromise the material’s corrosion resistance and mechanical stability. To address this issue, porous Ti-6Al-4V alloy was selected in this work. Immersion tests were conducted in Hank’s solution with different pH values (3, 5, and 7) for 90 days to simulate the in vivo microenvironment under various physiological conditions. The degradation behavior of porous Ti-6Al-4V alloy during the 90-day immersion period was systematically investigated using a combination of characterization techniques. The results indicated that TiO₂, Ca₃(PO₄)₂, and Ca(H₂PO₄)₂ phases were formed on the surface of the after 90 days of immersion. Massive dissolution of TiO₂ was observed in solutions with high H⁺ concentration (low pH). Ion release tests revealed that the concentration of titanium ions released was significantly higher in acidic solutions, suggesting that the passive film formed on porous Ti-6Al-4V alloy was unstable and prone to dissolution under acidic conditions. Consequently, a large amount of corrosion products accumulated on the specimen surfaces immersed in acidic solutions for a long duration. Moreover, the compression properties of the samples deteriorated after immersion. Specifically, the compressive strength decreased by 12.68 MPa, 11.67 MPa, and 5.84 MPa for sample immersed in solutions with pH = 3, 5, and 7, respectively. The significant reduction in compressive performance of the alloy in high H⁺ concentration solutions was attributed to the decreased compactness caused by ion release. The fracture mode of the porous Ti-6Al-4V alloy after immersion was identified as a mixed mode of ductile and brittle fracture. Full article

This study investigates the synergistic effects of an electropulsing (EP) and ultrasonic impact treatment (UIT) hybrid process on the mechanical and corrosion properties of D36 low-carbon steel. Conventional UIT has been shown to enhance surface hardness and induce compressive residual stress but is limited by a shallow affected depth and potential for increased surface roughness, which can exacerbate corrosion. In this work, we integrate high-energy electropulsing with UIT to overcome these limitations. The EP-UIT process leverages the combined effects of acoustoplasticity, thermal softening, and electroplasticity to achieve a significantly deeper hardened layer, extending beyond 2 mm, which is an order of magnitude thicker than that obtained by UIT alone. Microstructural analysis reveals that the process induces continuous dynamic recrystallization (CDRX), resulting in a gradient nanostructured layer with equiaxed grains near the surface and submicron ferrite grains at greater depths. Additionally, cementite dissolution and reprecipitation lead to a dual-phase microstructure comprising a supersaturated ferrite matrix and spheroidized Fe₃C particles. The EP-UIT treatment also forms a dense oxide scale composed primarily of magnetite (Fe₃O₄) and hematite (α-Fe₂O₃), significantly enhancing corrosion resistance. Potentiodynamic polarization tests demonstrate that EP-UIT reduces the corrosion current density by 68% compared to UIT-treated samples, while electrochemical impedance spectroscopy confirms the improved barrier properties of the oxide layer. This innovative approach offers a promising strategy for significantly extending the service life of welded marine structures by concurrently enhancing their mechanical properties and corrosion resistance. Full article

Mafic mine tailings are highly resistant to bioleaching due to their silicate-rich composition, low sulfide content, and strong buffering capacity. This study aimed to assess the potential use of heterotrophic bioleaching to promote the release of metals from mafic tailings by evaluating the organic acid production and leaching capabilities of indigenous bacterial isolates and a known lactic acid producer, Lactiplantibacillus plantarum ATCC 8014. Indigenous acid-producing heterotrophic bacteria were isolated from a vanadium-titanium-bearing magnetite tailings in Québec, Canada, and screened for organic acid production in various culture media. The most active bacteria were L. plantarum and two isolates identified by their 16S rRNA gene as Enterococcus (CBGM-1C) and Acetobacter (BL-F) sp. They produced significant quantities of lactic acids, followed by acetic, citric, and gluconic acids during glucose metabolism, through fermentative or oxidative pathways. A two-step bioleaching process was implemented, consisting of an initial organic acid production phase followed by tailings leaching at 5% pulp density over 10 days at 30 °C. Metal solubilization and mineralogical analyses demonstrated strain-dependent and metal-specific mobilization, with zinc being the only element efficiently leached (up to ~74% recovery by L. plantarum). XRD analyses confirmed partial dissolution and reduced crystallinity of key silicate phases without secondary mineral formation. These findings indicate that heterotrophic leaching can selectively mobilize more labile metals such as Zn from alkaline, silicate-rich tailings, although its overall efficiency for refractory elements remains limited under the tested conditions. Full article

In this study, 3 wt.% Re/Inconel 718 composite was fabricated by laser powder bed fusion (LPBF), and the effects of aging treatments on the microstructure and properties of the Re/Inconel 718 composite were systematically investigated. This study aims to elucidate the synergistic optimization of microstructure and properties in LPBF Inconel 718, achieved through Re alloying and subsequent heat treatment. Results demonstrated that the samples undergo recrystallization and precipitate numerous fine strengthening phases after heat treatment. Concurrently, heat treatment promotes the diffusion of Re within the material, leading to a significant reduction in its concentration in locally enriched regions. The addition of Re improves the mechanical properties and corrosion resistance of the Inconel 718 alloy through synergistic strengthening mechanisms, including dispersion strengthening, solid solution strengthening, and dislocation strengthening. When the two-stage aging is 720 °C × 8 h (FC × 2 h) + 620 °C × 8 h (AC), the optimum mechanical properties are observed. The dissolution of Laves phases, simultaneous precipitation of both γ″ and γ′ phases, and homogenization of microstructure are responsible for the enhancement of the material’s mechanical properties. However, the extensive precipitation of strengthening phases also promotes the formation of numerous microscopic corrosion cells, which accelerates the corrosion rate and leads to a marked reduction in corrosion resistance of the material. This study provides new insights into the laser additive manufacturing of high-performance nickel-based composites. Full article

The formation and evolution of secondary phases, such as sigma (σ), chi (χ), Laves, carbides (M₂₃C₆), and nitrides (Cr₂N), have a fundamental impact on the corrosion resistance of stainless steels. These stages alter the matrix’s local chemistry, compromise the passive film’s quality, and promote micro-galvanic interaction, which enhances localized corrosion issues. The thermodynamic stability, precipitation kinetics, and corrosion consequences of secondary phases in austenitic, ferritic, duplex, and lightweight (Fe–Mn–Al–C) stainless-steel systems are thoroughly reviewed and discussed in this paper. Advances in high-resolution characterization techniques, such as TEM, EBSD, atom-probe tomography, and in situ synchrotron techniques, have made it possible to map corrosion problems caused by secondary phases at the nanoscale. Computational thermodynamics (CALPHAD, DICTRA, TC-PRISMA) and emerging machine-learning models now provide quantitative prediction of phase formation and dissolution. Strategies for mitigation through alloy design, thermal treatment, and surface engineering are summarized, together with additive-manufacturing approaches for microstructural tailoring. Finally, this review highlights the integration of multi-scale modeling and sustainable alloy design to ensure phase-stable, corrosion-resistant stainless steels that enhance asset integrity and infrastructure reliability as per Sustainable Development Goals. Full article

Fe-oxyhydroxides can incorporate toxic metals during the formation of mineral phases in soils and sediments, thereby potentially altering the environmental reactivity of metals and impacting the microbial communities. In this study, isothermal microcalorimetry has been used to monitor the metabolic activity of Pseudomonas putida KT2440 exposed to pure ferrihydrite and to Pb-, Cd-, and As-bearing ferrihydrites under oxygen-limited conditions. Calorimetric measurements of the integral heat released during the exponential growth were combined with the analysis of dissolved iron and heavy metals, as well as the glucose uptake, to understand how heavy metal incorporation modifies mineral reactivity and microbial heat output. Pure ferrihydrite decreased the integral heat by about 45%, primarily due to glucose and phosphate depletion, Fe(III) leaching, and mineral–cell aggregation. Heavy metal dopants were found to modulate nutrient availability, surface charge, and Fe solubilization, which, in turn, influenced the integral heat. Pb-Fh generated the highest ferrihydrite dissolution and metabolic heat, with a maximum effect at intermediate substitution levels. As-Fh induced moderate Fe release and metabolic activity, consistent with the enhanced phosphate sorption and lowered surface charge. Cd-bearing Fh showed minimal reactivity and yielded the lowest heat output. Microcalorimetry was proven useful for unraveling microbe–mineral interactions in complex contaminated environments. Full article

Interfacial reactions between Sn-based solders and Au/Pd/Ni metallization were investigated at 260 °C, with particular emphasis on the effects of Pd and Sn thicknesses. Au/Pd/Ni substrates with Pd layers of approximately 70 nm, 200 nm, and 1 µm were reacted with Sn layers of about 50, 20, and 10 µm. Additionally, Sn-Pd and Sn-3Ag-Pd solders containing 0.1–1 wt.% Pd were reacted with Ni substrates. In the Sn/Au/Pd/Ni reactions, rapid dissolution of the Pd layer and partial Ni dissolution at the early stage promoted the formation of large amounts of faceted (Pd,Ni)Sn₄. With increasing reaction time, continuous Ni diffusion enriched the interfacial region, leading to the nucleation and growth of Ni₃Sn₄. Once the Ni solubility limit in (Pd,Ni)Sn₄ was exceeded, this phase gradually transformed into the thermodynamically more stable Ni₃Sn₄. In addition to phase evolution, Pd was found to significantly influence the interfacial grain morphology. Minor Pd additions enhanced the Ni₃Sn₄ nucleation, resulting in refined and columnar grains. In the Sn-Pd/Ni reactions, low Pd contents led to the rapid replacement of (Pd,Ni)Sn₄ by Ni₃Sn₄, whereas higher Pd contents significantly enhanced the stability and interfacial retention of (Pd,Ni)Sn₄. These results reveal that increasing Pd thickness or Pd content in the solder significantly enhances the stability of (Pd,Ni)Sn₄, whereas reducing Sn thickness markedly accelerates interfacial reactions and phase transformation. The experimental observations can be consistently interpreted using a local interfacial equilibrium hypothesis based on the Sn-Pd-Ni phase diagram. Full article

Experimental results are compiled to show apparent hysteresis seen in hydride thermal precipitation–dissolution cycling in zirconium alloys using X-ray diffraction, dynamic elastic modulus techniques, and differential scanning calorimetry (DSC). Gibbs’ phase rule is used to justify a description of a stable hydride in the H-Zr system in terms of a control volume with a hydride at its core, surrounded by a stress gradient that produces a stabilizing gradient of hydrogen in the solution. The conditions for a stable hydride are derived when the flux of hydrogen in solid solution is zero. DSC heat flow curves are analyzed with a thermodynamic model that predicts concentrations of hydrogen in a solution during temperature cycling and a description of experimental results that show how concentrations evolve at a constant temperature to the same final state when cycling is paused, from which hysteresis is deemed an illusion. The control volume is supported by previous energy calculations, performed with density functional theory. Implications of replacing the order parameter for phase field methods with the gradient of the yield stress are discussed. A practical method for forming a stable hydride is presented. Full article

Arsenic (As) accumulation in rice (Oryza sativa L.) is considered a major environmental and food safety concern, particularly in flooded agroecosystems where reducing conditions mobilize As from soils. Portugal is one of Europe’s rice producers, especially in the Tejo, Almansor, and Sorraia valleys. As such, this study evaluates As pathways across 5000 ha of rice fields in the Tagus, Sorraia, and Almansor alluvial plains by combining soil, water, and plant analyses with a geostatistical approach. The soils exhibited consistently elevated As concentrations (mean of 18.9 mg/kg), exceeding national reference values for agricultural soils (11 mg/kg) and forming a marked east–west gradient with the highest levels in the Tagus alluvium. Geochemical analysis showed that As is strongly correlated with Fe (r = 0.686), indicating an influence of Fe-oxyhydroxides under oxidizing conditions. The irrigation waters showed low As (mean of 2.84 μg/L for surface water and 3.51 μg/L for groundwater) and predominantly low sodicity facies, suggesting that irrigation water is not the main contamination vector. In rice plants, As accumulation follows the characteristic organ hierarchy roots > stems/leaves > grains, with root concentrations reaching up to 518 mg/kg and accumulating progressively in the maturity phase. Arsenic content in harvested rice grains was 266 μg/kg (with a maximum of 413.9 μg/kg), being close to EU maximum limits when considering typical inorganic As proportions, assuming 60 to 90% inorganic fraction. Together, the findings highlight that a combined approach is essential, and identify soil geochemistry (and not irrigation water) as the primary source of As transfer in those agroecosystems, due to the flooded conditions that trigger the reductive dissolution of Fe oxides, releasing As. Additionally, the results also identified the need for targeted monitoring in areas of elevated As content in soils and support future mitigation through As speciation analysis, cultivar selection, improved fertilization strategies, and water-management practices such as Alternate Wetting and Drying (AWD), to ensure the long-term food safety. Full article

This study investigates the as-cast Mg-8Gd-1Y-2Sm-1.2Zn-0.5Mn (wt.%) alloy with high rare-earth content. Solution treatments were conducted at 480 °C, 520 °C, and 560 °C for 6–10 h. Microstructure and mechanical properties were characterized using OM, XRD, SEM-EDS, and compression testing. The as-cast alloy shows a dendritic structure with continuous grain-boundary phases (Mg₅RE, W, and LPSO), exhibiting a compressive yield strength of 145 MPa, ultimate strength of 238 MPa, and fracture strain of 12.66%. Solution temperature has a critical influence on phase dissolution and grain refinement. Notably, the overall plasticity of the material did not show a significant dependence on the specific solution temperature or holding time within the studied range. Treatment at 520 °C produces the most balanced microstructure: clear grain boundaries, extensive phase dissolution, refined grains, and enhanced solid-solution strengthening. Specifically, 520 °C for 10 h results in the finest and most uniformly distributed residual phases, a homogeneous matrix, the highest compressive strength, and suitable conditions for subsequent aging, thus being identified as optimal. Fractography reveals a transition from quasi-cleavage in the as-cast state toward enhanced ductility after solution treatment. However, small cleavage facets after 10 h are attributed to stress concentrations from rare-earth-rich regions and reduced deformation compatibility due to retained LPSO phases. Full article

In this work, a method for leaching black mass from spent Li batteries using oxalic acid was developed and experimentally verified with the objective of selectively separating lithium and cobalt. Oxalic acid proved to be an efficient and selective leaching agent. Under 1 M C₂H₂O₄, 120 min, L:S = 20, 80 °C and 300 rpm, a lithium yield of 90% was achieved, while cobalt dissolution remained low at 1.57%. Subsequently, cobalt spontaneously precipitated from the leachate within several hours, and the solid phase was fully separated after 24 h. The leachate contained minor amounts of accompanying metals, with dissolution yields of 0.5% Mn, 8% Fe and 1.4% Cu. These impurities were removed from the leachate by controlled pH adjustment using NaOH at ambient temperature and 450 rpm, with complete precipitation at pH 12. This procedure generated a purified lithium-rich leachate, which was converted into lithium oxalate by crystallisation at 105 °C. Subsequent calcination of the resulting solid at 450 °C for 30 min produced Li₂CO₃ with a purity of 91%. Based on the experimental findings, a conceptual technological process for selective lithium leaching using oxalic acid was proposed, demonstrating the potential of this method for sustainable lithium recovery. Full article