Search Results (142)

Blast furnace (BF) ironmaking remains one of the most efficient countercurrent processes; however, achieving further CO₂ emission reductions through conventional methods is increasingly challenging. Currently, BF ironmaking emits approximately 2.33 tonnes of fossil-derived CO₂ per tonne of crude steel cast. Integrating briquettes composed of biochar and in-plant fines into the BF process offers a promising short- to medium-term strategy for lowering emissions. This approach enables efficient recycling of fine residues and the substitution of fossil reductants with bio-based alternatives, thereby improving productivity while reducing energy and carbon intensity. This study investigates the reduction behavior of (i) biochar mixed with pellet fines, (ii) various in-plant residues individually, and (iii) briquettes composed of biochar and in-plant fines. The reduction rate of biochar–pellet fine mixtures was found to depend on biochar type, with pyrolyzed pine sawdust exhibiting the highest reactivity, and pyrolyzed contorta wood chips the lowest. A correlation between reduction rate and the alkali index of each char was established, although other factors such as char origin and physical properties also influenced reactivity. The effect of biochar addition (0, 5, and 10 wt.%) on the reduction of steelmaking residues was also studied. In general, biochar enhanced the reduction degree and shifted the reaction onset to lower temperatures. The produced briquettes maintained high mechanical integrity during and after reduction, regardless of biochar origin. Thermogravimetric and XRD analyses revealed that mass loss initiates with the dehydroxylation of cement phases and release of volatiles, followed by carbonate decomposition and reduction of higher oxides above 500 °C. At temperatures ≥ 850 °C, the remaining iron oxides were further reduced to metallic iron. Full article

This study investigates the potential of residual clays from a traditional ceramic-producing region in southern Portugal as raw materials for red ceramic applications. This work aims to support more sustainable ceramic practices through the local valorization of naturally available, underutilized clay resources. A multidisciplinary approach was employed to characterize clays, integrating mineralogical (XRD), chemical (XRF), granulometric, and thermal analyses (TGA/DTA/TD), as well as technological tests on plasticity, extrusion moisture, shrinkage, and flexural strength. These assessments were designed to capture both the intrinsic properties of the clays and their behavior across key ceramic processing stages, such as shaping, drying, and firing. The results revealed a broad diversity in mineral composition, particularly in the proportions of kaolinite, smectite, and illite, which strongly influenced plasticity, water demand, and thermal stability. Clays with higher fine fractions and smectitic content exhibited excellent plasticity and workability, though with increased sensitivity to drying and firing conditions. Others, with coarser textures and illitic or feldspathic composition, demonstrated improved dimensional stability and lower shrinkage. Thermal analyses confirmed expected dehydroxylation and sintering behavior, with the formation of mullite and spinel-type phases contributing to densification and strength in fired bodies. This study highlights that residual clays from varied geological settings can offer distinct advantages when matched appropriately to ceramic product requirements. Some materials showed strong potential for direct application in structural ceramics, while others may serve as additives or tempering agents in formulations. These findings reinforce the value of integrated characterization for optimizing raw material use and support a more circular, resource-conscious approach to ceramic production. Full article

Growing requirements in the field of environmental protection and waste management result in the need to search for new and effective methods of recycling various types of waste. From the perspective of technical and natural sciences, the disposal of hazardous waste, which can lead to environmental degradation, is of utmost importance. A particularly hazardous waste is asbestos, used until recently in many branches of the economy and industry. Despite the ban on the production and use of asbestos introduced in many countries, products containing it are still present in the environment and pose a real threat. This paper presents the results of research related to the process of asbestos neutralization, especially the chrysotile variety, by the thermal decomposition method. Changes in the mineralogical characteristics of asbestos waste were studied using the following methods: TG-DTA-EGA, XRD, SEM-EDS and XRF. The characteristics of the chrysotile asbestos sample were determined before and after thermal treatment at selected temperatures. The second part of the study focuses on the kinetic aspect of this process, where the chrysotile thermal decomposition process was measured by two techniques: ex situ and in situ. This study showed that the chrysotile structure collapsed at approximately 600–800 °C through dehydroxylation, and then the fibrous chrysotile asbestos was transformed into new mineral phases, such as forsterite and enstatite. The formation of forsterite was observed at temperatures below 1000 °C, while enstatite was created above this temperature. From the kinetic point of view, the chrysotile thermal decomposition process could be described by the Avrami–Erofeev model, and the calculated activation energy values were ~180 kJ mol⁻¹ and ~220 kJ mol⁻¹ for ex situ and in situ processes, respectively. The obtained results indicate that the thermal method can be successfully used to detoxify hazardous chrysotile asbestos fibers. Full article

During the thermal treatment of kaolinite, the main mineral phase in kaolin rock, dehydroxylation occurs, forming metakaolin through a process that has significant industrial applications. This study experimentally analyzed dehydroxylation in two kaolinite samples: a well-crystallized reference sample from the Clay Mineral Society and a locally sourced, industrial kaolin sample. The mechanism and kinetic parameters were evaluated from a series of thermogravimetric measurements. Non-isothermal kinetic analysis revealed that dehydroxylation followed a third-order (F3) reaction mechanism, with activation energies ($E_a$) ranging from 35 to 60 kcal/mol. Additionally, theoretical calculations based on Density Functional Theory were performed on four systems in which a water molecule was removed by combining OH group and H atom vacancies in the kaolinite unit cell. These models represented the onset of dehydroxylation and provided values for the reaction energy Q from first-principles calculations, which served as reference values for $E_a$. The results confirm that water molecule formation involving both OH at the kaolinite outer surface and inner surface are energetically competitive and highlight the crucial role of structural relaxations following water removal to determine Q values in the range of 30–50 kcal/mol, in very good agreement with the experiments. Full article

The crystal–chemical behavior of two layered titanosilicate minerals with porous crystal structures, kupletskite, K₂NaMn₇²⁺Ti₂(Si₄O₁₂)₂O₂(OH)₄F, and kupletskite-(Cs), Cs₂NaMn₇²⁺Ti₂(Si₄O₁₂)₂O₂(OH)₄F, was investigated under high-temperature conditions using single-crystal and powder X-ray diffraction; infrared and optical absorption spectroscopy and electron-microprobe analysis. Both minerals undergo topotactic transformation to dehydroxylated and oxidized high-temperature (HT) modifications at temperature above 500 °C while maintaining the basic bond topology of the astrophyllite structure-type. The high-temperature structures show contraction of the unit-cell parameters similar to that of Fe²⁺-dominant astrophyllite, indicating that Mn²⁺ oxidizes along with Fe²⁺ in M(2)–M(4) sites. The oxidation of Mn²⁺ is confirmed by the increase of the Mn³⁺-related absorption (in optical spectra) that is inversely correlated with the intensity of O–H bands in the infrared spectra. The Fe,Mn-oxidation is also evident by the contraction of the M(2), M(3), and M(4)O₆ octahedra. The M(1)–O bond length increases slightly, indicating a preference for mono- and divalent cations to occupy the M(1) site in the heated structure; this may be due to site-selective oxidation and/or migration of unoxidized cations (as previously shown for lobanovite) to this site. The role of extra framework A-site cations (K, Cs) in thermal expansion of these minerals is discussed. Full article

Carbonaceous materials (CMs) have gained great attention as heterogeneous catalysts in water treatment because of their high efficiency and potential contribution to achieving carbon neutrality. Expanded graphite (EG) is ideal for studying CMs because the reactivity in CMs largely depends on graphitic structures, and most surface of EG is exposed, minimizing mass transfer resistance. However, EG is poor in adsorption and catalysis. In this study, EG was modified by simple thermal treatment to investigate the effects of characteristics of graphitic structures on reactivity. Tetracycline (TC) removal rate via activating peroxydisulfate (PDS) by the EG treated at 550 °C (EG550) was more than 10 times that of EG. The thermal modification did not significantly increase surfaces but led to increases in damaged, rough surfaces, graphitization degree, C content, defects, and C=O. Radical and non-radical pathways, such as SO₄^•−, O₂^•−, ¹O₂, and electron transfer, were involved in TC removal in EG550+PDS. TC degradation in EG550+PDS was initiated by hydroxylation, followed by demethylation, dehydroxylation, decarbonylation, and ring-opening. The ions ubiquitous in water systems did not significantly affect the performance of EG550+PDS, except for H₂PO₄⁻ and HCO₃⁻, suggesting the high potential of practical applications. This study demonstrated that graphitic structure itself and surface area are not detrimental in the catalytic reactivity of CMs, which is different from previous studies. Rather, the reactivity is governed by the characteristics, i.e., defects and functional groups of the graphitic structure. It is thought that this study provides valuable insights into the development of highly reactive CMs and the catalytic systems using them. Full article

Rare earth-doped phosphate glasses have found widespread application in the field of solid-state and fiber laser technologies. Nevertheless, the fabrication of high-quality rare earth-doped phosphate glasses with minimal residual hydroxyl groups remains a significant challenge. To address this, a two-step melting process was utilized in this work to synthesize Er³⁺-Yb³⁺ co-doped phosphate glasses with low residual hydroxyl group content and improved optical quality. When re-melted under a N₂ atmosphere at 900 °C for 12 to 16 h, the hydroxyl absorption coefficient (α_-OH) decreased to ~1 cm⁻¹. The structural and compositional characteristics of the glass remained essentially unchanged throughout the re-melting process. The weak broadband absorption in the visible range and the red-shift of the ultraviolet absorption edge were attributed to the reduction in residual hydroxyl group content rather than carbon contamination. The dehydroxylation mechanism was governed by the physical diffusion of hydroxyl groups within the glass matrix. Full article

Bile acids (BAs) are important signaling molecules in the gastrointestinal (GI) tract and are associated with health and disease in humans and animals. Intestinal bacteria transform BA through deconjugation, dehydroxylation, and epimerization reactions, producing various isoforms, many of which have not been investigated in companion animal diseases. We aimed to develop and analytically validate a novel liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the quantification of 30 BAs in dog feces, with a simple extraction procedure and on-line solid-phase extraction. Validation demonstrated good accuracy, precision, sensitivity, spiking recovery, dilution, and stability for 29 BAs. The method was applied to fecal samples from healthy dogs (H; n = 121) and dogs with chronic enteropathy (CE; n = 58). The immediate and downstream products of bacterial 7α-dehydroxylation reactions with cholic acid were lower in concentration in dogs with CE when compared to healthy dogs (deoxycholic acid, 3-oxo-deoxycholic acid, and 12-oxo-lithocholic acid; q < 0.001). Across all fecal samples, the products of hydroxysteroid dehydrogenase (including oxo- and iso-BA) made up an average of 30% of the total measured fecal BA pool (glycine-BA, 0.1%; taurine-BA, 2.2%; unconjugated BA, 53%). Full article

Clostridium scindens is a commensal gut bacterium capable of forming the secondary bile acids as well as converting glucocorticoids to androgens. Historically, only two strains, C. scindens ATCC 35704 and C. scindens VPI 12708, have been characterized to any significant extent. The formation of secondary bile acids is important in the etiology of cancers of the GI tract and in the prevention of Clostridioides difficile infection. We determined the presence and absence of bile acid inducible (bai) and steroid-17,20-desmolase (des) genes among C. scindens strains and the features of the pangenome of 34 cultured strains of C. scindens and a set of 200 metagenome-assembled genomes (MAGs) to understand the variability among strains. The results indicate that the C. scindens cultivars have an open pangenome with 12,720 orthologous gene groups and a core genome with 1630 gene families, in addition to 7051 and 4039 gene families in the accessory and unique (i.e., strain-exclusive) genomes, respectively. The pangenome profile including the MAGs also proved to be open. Our analyses reveal that C. scindens strains are distributed into two clades, indicating the possible onset of C. scindens separation into two species, as suggested by gene content, phylogenomic, and average nucleotide identity (ANI) analyses. This study provides insight into the structure and function of the C. scindens pangenome, offering a genetic foundation of significance for many aspects of research on the intestinal microbiota and bile acid metabolism. Full article

This experimental study analyses the extent of chemo-mineralogical changes that occur when a building stone encounters a cycling isothermal treatment at 600 °C. Four carbonate and two silicate European building stones were analysed in their fresh quarried and thermally treated conditions by means of colour measurements, in situ X-ray diffraction (XRD), and optical microscopy. Furthermore, powdered samples were characterised by Fourier-transform infrared spectroscopy, simultaneous thermal analysis, and cycling thermogravimetry (TG). The in situ XRD spectra revealed a surface-limited phase transformation of solid calcite and dolomite under isothermal conditions during the first 10 min at 600 °C and 500 °C, respectively. The onset of thermal decomposition and extent of phase transformation were governed by the microstructure of the solid samples. Inter- and intragranular microcracks are induced to varying degrees, and their incidence depended on the stone’s microstructure. Discolouration indicated a transformation of minor elements across the entire analysed sample volumes. Kaolinite was preserved even after three hours of thermal treatment at its dehydroxylation temperature due to its sheltering in confined pore spaces. Mass loss was more pronounced when cyclic treatment was employed compared to a non-periodic treatment, as determined by a TG analysis performed at same time intervals. Examining the chemo-mineralogical and microstructural changes caused by heat treatment allows us to study how and if regaining mechanical strength and restoring physical properties are possible for purposes of heritage restoration after fire damage. Full article

Flavonoids represent a class of natural plant secondary metabolites with multiple activities including antioxidant, antitumor, anti-inflammatory, and antimicrobial properties. However, due to their structural characteristics, they often exhibit low bioavailability in vivo. In this review, we focus on the in vivo study of flavonoids, particularly the effects of gut microbiome on flavonoids, including common modifications such as methylation, acetylation, and dehydroxylation, etc. These modifications aim to change the structural characteristics of the original substances to enhance absorption and bioavailability. In order to improve the bioavailability of flavonoids, we discuss two feasible methods, namely dosage form modification and chemical modification, and hope that these approaches will offer new insights into the application of flavonoids for human health. In this article, we also introduce the types, plant sources, and efficacy of flavonoids. In conclusion, this is a comprehensive review on how to improve the bioavailability of flavonoids. Full article

This study examines the effects of thermal (1000 °C), hydrothermal (100 °C), mechanochemical (ambient T), and microwave (~100 °C) treatments on three types of Chinese vermiculites, one with lower potassium content than the others. The goal was to obtain materials with enhanced properties related to specific surface areas. The response of the vermiculites to treatments and their physicochemical properties were analyzed using X-ray diffraction (XRD), thermal analysis (TG and DTG), and textural characterization via the BET method. XRD analyses showed similar mineral composition in treated and untreated samples, but the treatments affected the intensity and width of phase reflections, altering crystallinity and structural order, as well as the proportions of vermiculite, hydrobiotite, and phlogopite. Thermogravimetric analysis revealed two mass loss stages: water desorption (from 25 °C to about 250 °C) and recrystallization or dehydroxylation (above 800 °C). The isotherms indicated mesoporous characteristics, with hydrothermally CO₂-treated samples having the highest specific surface area and adsorption capacity. The samples with vermiculite, hydrobiotite, and phlogopite generally showed moderate to high specific surface area (S_BET) values, and mechanochemical treatments significantly increase S_BET and pore volume (V_p) in the vermiculite and hydrobiotite samples. Crystallinity affects S_BET, average V_p, and average pore size, and its monitoring is crucial to achieve the desired material characteristics, as higher crystallinity can reduce S_BET but improve mechanical strength and thermal stability. This study highlights the influence of different treatments on vermiculite properties, providing valuable insights into their potential applications in various fields (such as thermal insulation in vehicles and aircraft, and the selective adsorption of gases and liquids in industrial processes, improving the strength and durability of building materials like cement and bricks). Full article

The feasibility of using brick aggregates for the preparation of aluminosilicate “glass-ceramic” forms as a novel cementitious composite capable of immobilizing radioactive elements was examined. Raw brick was initially activated with sodium hydroxide. X-ray diffraction analysis (XRD) confirmed zeolites (Na-A and Na-P), illite, and sand (quartz) as major phases. Thermal analysis showed several successive events: dehydration/dehydroxylation of illite, followed by degradation of illite and zeolites. Upon heating to 1000 °C, scanning electron microscopy and XRD provided evidence of the presence of novel crystalline aluminosilicate forms (analcime and leucite in the form of solid solutions). Then, upon heating to 1150 °C, the thermal process led to the additional formation of mullite and an amorphous silica-rich phase. The latter resulted from silica melting taking place, owing to the involvement of low-melting-point components on sand grains. Alkali-brick particles were then doped with Cs⁺, Rb⁺, Ca²⁺, and Sr²⁺ ions (individually) and subsequently heated at different temperatures. The corrosion resistance of the heated materials was examined in a hydrochloride acid solution. The aim was to highlight (i) the enhanced cationic-immobilization capacity of crystalline aluminosilicate phases embedded inside amorphous silica, and (ii) the role of sand in the creation of brick-based glass ceramics. Full article

Kaolin-based graphitic carbon nitride (g-CNx) composite photocatalysts were synthesized from a urea precursor using a commercial kaolin. Structural characterization by X-ray diffraction and infrared spectroscopy (FTIR) verified the successful thermal polycondensation of g-CNx along the thermal dehydroxylation of kaolinite to metakaolin at 550 °C. The g-CNx content of the composites were estimated by thermogravimetry and CHN analysis, ranging from ca. 87 m/m% to ca. 2 m/m% of dry mass. The addition of kaolin during the composite synthesis was found to have a significant effect: the yield of in situ formed g-CNx drastically decreased (from ca. 4.9 m/m% to 3.8–0.1 m/m%) with increasing kaolin content. CHN and FTIR indicated the presence of nitrogen-rich g-CNx, having a specific surface area of 50 m²/g, which synergistically increased after composite synthesis to 67–82 m²/g. Estimated optical band gaps indicated the affinity to absorb in the visible light spectrum (λ < 413 nm). Photocatalytic activity upon both UV and artificial sunlight irradiation was observed by hydroxyl radical evolution, however, without the synergistic effect expected from the favorable porosity. Full article

Montmorillonite is a layered clay mineral whose modification by pillaring, i.e., insertion of oxide nanoclusters between the layers, yields porous materials of great potential in sorption and catalysis. In the present study, an unrefined industrial bentonite from Kopernica (Slovakia), containing ca. 70% of montmorillonite, was used for the preparation of Ti-, Zr-, and mixed [Ti,Zr]-pillared clay sorbents. The pillared samples were characterized with X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and N₂ adsorption at −196 °C and tested for the capacity of CO₂ sorption at 0 °C and 1 bar pressure. The experiments revealed that pillared samples sorbed at least four times more CO₂ than the parent bentonite. Of the materials tested, the sample pillared with mixed [Ti,Zr] oxide props showed the best performance, which was attributed to its superior microporosity. The results of CO₂ adsorption demonstrated that the cost-effective use of crude industrial bentonite as the sorbent precursor is a viable synthesis option. In another experiment, all pillared montmorillonites were subjected to 24 h exposure at room temperature to a flow of dry CO₂ and then tested using simultaneous thermal analysis (STA) and the mass spectrometry (MS) analysis of the evolving gases (STA/QMS). It was found that interaction with dry CO₂ reduces the amount of bound carbon dioxide and affects the processes of dehydration, dehydroxylation, and the mode of CO₂ binding in the pillared structure. Full article