Search Results (339)

The urgent need to mitigate rising global CO₂ emissions demands the development of efficient carbon capture technologies. This study addresses the persistent challenge of sintering-induced performance degradation in CaO-based sorbents during high-temperature CO₂ capture. A novel solvent/nonsolvent synthetic strategy to fabricate CaO/CaAl-layered double oxide (LDO) composites was developed, where CaAl-LDO serves as a nanostructural stabilizer. The CaAl-LDO precursor enables atomic-level dispersion of components, which upon calcination forms a Ca₁₂Al₁₄O₃₃ “rigid scaffold” that spatially confines CaO nanoparticles and effectively mitigates sintering. Thermogravimetric analysis results demonstrate exceptional cyclic stability; the composite achieves an initial CO₂ uptake of 14.5 mmol/g (81.5% of theoretical capacity) and retains 87% of its capacity after 30 cycles. This performance significantly outperforms pure CaO and CaO/MgAl-LDO composites. Physicochemical characterization confirms that structural confinement preserves mesoporous channels, ensuring efficient CO₂ diffusion. This work establishes a scalable, instrumentally simple route to high-performance sorbents, offering an efficient solution for carbon capture in energy-intensive industries such as power generation and steel manufacturing. Full article

With the gradual depletion of high-quality iron ore resources, global steel enterprises have shifted their focus to low-grade, high-impurity iron ores. Using low-grade iron ore to produce pellets for blast furnaces is crucial for companies to control production costs and diversify raw material sources. However, producing qualified pellets from limonite and other low-grade iron ores remains highly challenging. This study investigates the mechanism by which basicity affects the consolidation and reduction behavior of high-Al₂O₃ limonite pellets from a thermodynamic perspective. As the binary basicity of the pellets increased from 0.01 under natural conditions to 1.2, the compressive strength of the roasted pellets increased from 1100 N/P to 5200 N/P. The enhancement in basicity led to an increase in the amount of low-melting-point calcium ferrite in the binding phase, which increased the liquid phase in the pellets, thereby strengthening the consolidation. CaO infiltrated into large-sized iron particles and reacted with Al and Si elements, segregating the contiguous large-sized iron particles and encapsulating them with liquid-phase calcium ferrite. Calcium oxide reacts with the Al and Si elements in large hematite particles, segmenting them and forming liquid calcium ferrite that encapsulates the particles. Additionally, this study used thermodynamic analysis to characterize the influence of CaO on aluminum elements in high-aluminum iron ore pellets. Adding CaO boosted the liquid phase’s ability to incorporate aluminum, lessening the inhibition by high-melting-point aluminum elements of hematite recrystallization. During the reduction process, pellets with high basicity exhibited superior reduction performance. Full article

Plant callus cultures are a sustainable alternative for producing bioactive secondary metabolites, but their low yields limit industrial applications. Carob (Ceratonia siliqua L.) is rich in medicinally valuable compounds, yet conventional cultivation faces challenges. To address this, we use biofortified calcium phosphate nanoparticles, which refer to CaP-NPs that have been enriched with bioactive compounds via green synthesis using Jania rubens extract, thereby enhancing their functional properties as elicitors in carob callus. CaP-NPs were green-synthesized using Jania rubens extract and applied to 7-week-old callus cultures at 0, 25, 50, and 75 mg/L concentrations. At the optimal concentration (50 mg/L), CaP-NPs increased callus fresh weight by 23.9% and dry weight by 35.1%. At 50 mg/L CaP-NPs, phenolic content increased by 95.7%, flavonoids by 34.4%, tannins by 131.8%, and terpenoids by 211.9% compared to controls. Total antioxidant capacity rose by 76.2%, while oxidative stress markers malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) decreased by 34.8% and 14.1%, respectively. Gene expression analysis revealed upregulation of PAL (4-fold), CHI (3.15-fold), FLS (1.16-fold), MVK (8.3-fold), and TA (3.24-fold) at 50 mg/L CaP-NPs. Higher doses (75 mg/L) induced oxidative damage, demonstrating a hormetic threshold. These findings indicate that CaP-NPs effectively enhance secondary metabolite production in carob callus by modulating biosynthetic pathways and redox balance, offering a scalable, eco-friendly approach for pharmaceutical and nutraceutical applications. Full article

One of the effective types of heat-resistant insulating products with an operating temperature of 1050 °C is made from calcium silicates or their hydrates. These materials are made from synthetic xonotlite and 1.13 nm tobermorite. Various wastes and by-products from other industries can be used for the synthesis of the latter compound. However, such raw materials often contain various impurities, especially Al-containing compounds, which strongly influence the kinetics of 1.13 nm tobermorite formation and its properties. Using XRD, DSC, TG, and SEM/EDX methods, it was found that at the beginning of the hydrothermal synthesis, the Al₂O₃ additive promotes the formation of 1.13 nm tobermorite; however, it later begins to inhibit the recrystallization of semi-crystalline C-S-H(I)-type calcium silicate hydrate and pure, high-crystallinity 1.13 nm tobermorite is more easily formed in mixtures without the aluminum additive. Aluminum oxide also influence the morphology of 1.13 nm tobermorite. When hydrothermally curing the CaO–SiO₂ mixture, long, thin fibers (needles) are formed within 24 h. Later, they thicken and form rectangular parallelepiped crystals. After adding alumina, the product produced by 24 h synthesis is dominated by agglomerates, the surface of which is partially covered with crystal plates. By extending the synthesis duration, amorphous aggregates are absent and the crystal shape becomes increasingly square. Full article

The flocculation-based purification of quarry wastewater continues to pose a significant challenge in mineral processing and environmental engineering, primarily due to persistent turbidity issues and inefficient floc settling behaviour. In this study, we systematically investigate the synergistic effects of organic and inorganic flocculants to reduce turbidity and improve floc settling performance. Through a series of optimised experiments using polyaluminium chloride as an inorganic flocculant, polyacrylamide as an organic flocculant, and calcium oxide as a pH regulator agent, the treatment efficiency was evaluated. Under the optimal conditions with 200 g/m³ CaO as the regulator agent and 2.5 g/m³ PAC and 12 g/m³ PAM as flocculants, the residual turbidity was reduced to 97.30 NTU, meeting stringent industrial discharge standards and enabling zero-discharge water reuse. Zeta potential measurements, optical microscopy, and DLVO theory collectively elucidated the interfacial interactions between flocculants and mineral particles, with zeta potential revealing electrostatic effects, microscopy visualising aggregation patterns, and DLVO theory modelling revealing colloidal stability, thereby mechanistically explaining the enhanced aggregation behaviour. Full article

Germanium/tin-containing silicon oxide [SiO–(GeO/SnO)] nanoclusters have been designed with different Si/Ge/Sn particles and characterized as electrodes for magnesium-ion batteries (MIBs) due to forming MgBe [SiO–GeO], MgBe [SiO–SnO], MgCa [SiO–GeO], and MgCa [SiO–SnO] complexes. In this work, alkaline earth metals of magnesium (Mg), beryllium (Be), and calcium (Ca) have been studied in hybrid Mg-, Be-, and Ca-ion batteries. An expanded investigation on H capture by MgBe [SiO–(GeO/SnO)] or MgCa [SiO–(GeO/SnO)] complexes was probed using computational approaches due to density state analysis of charge density differences (CDD), total density of states (TDOS), and electron localization function (ELF) for hydrogenated hybrid clusters of MgBe [SiO–GeO], MgBe [SiO–SnO], MgCa [SiO–GeO], and MgCa [SiO–SnO]. Replacing Si by Ge/Sn content can increase battery capacity through MgBe [SiO–GeO], MgBe [SiO–SnO], MgCa [SiO–GeO], and MgCa [SiO–SnO] nanoclusters for hydrogen adsorption processes and could improve the rate performances by enhancing electrical conductivity. A small portion of Mg, Be, or Ca entering the Si–Ge or Si–Sn layer to replace the alkaline earth metal sites could improve the structural stability of the electrode material at high multiplicity, thereby improving the capacity retention rate. In fact, the MgBe [SiO–GeO] remarks a small enhancement in charge transfer before and after hydrogen adsorption, confirming the good structural stability. In addition, [SiO–(GeO/SnO)] anode material could augment the capacity owing to higher surface capacitive impacts. Full article

The study examines the biosorption potential of Ulva intestinalis (UI) and calcium oxide-modified Ulva intestinalis (CaO-UI) for the environmentally favorable removal of cadmium (Cd²⁺), nickel (Ni²⁺), and lead (Pb²⁺) from aqueous solutions. This research addresses the critical need for sustainable water treatment solutions by developing a green-synthesized biosorbent that combines renewable biomass with enhanced adsorption properties. The adsorption properties of the biomass were improved by preparing calcium oxide (CaO) using Ulva intestinalis extract by green synthesis. Langmuir, Freundlich, and Temkin isotherms were employed to model the results of adsorption experiments that were conducted under a variety of conditions, such as contact time, biosorbent dose, and initial metal ion concentration. Langmuir (R² = 0.999) and Freundlich (R² = 0.999) models both provided an exceptionally well-fitted model for the adsorption isotherms, suggesting a hybrid mechanism that integrates monolayer chemisorption at CaO-active sites and multilayer adsorption on the heterogeneous algal matrix. Key findings demonstrate that the maximum adsorption capacity (qm) of CaO-UI was substantially higher than that of UI, with values of 571.21 mg/g for Cd²⁺, 665.51 mg/g for Ni²⁺, and 577.87 mg/g for Pb²⁺, respectively, in comparison to 432.47 mg/g, 335.75 mg/g, and 446.65 mg/g for UI. The adsorption process was dominated by pseudo-second-order (PSO) chemisorption, as evidenced by kinetic studies (R² = 0.949–0.993). CaO-UI exhibited substantially higher rate constants (k₂ = 9.00–10.15 mg/mg·min) than raw UI (k₂ = 4.72–5.71 mg/mg·min). The green synthesis of calcium oxide has resulted in an increase in surface area, porosity, and functional group density, which is responsible for the enhanced performance of CaO-UI. The adsorption efficacy of Pb²⁺ was the highest, followed by Cd²⁺ and Ni²⁺, which was indicative of the differences in metal ion affinity and hydration energy. These results underscore the potential of CaO-UI as a biosorbent that is both cost-effective and sustainable for the removal of heavy metals in wastewater treatment applications. Full article

The selective catalytic reduction (SCR) of NO_x emissions by hydrocarbons (HCs) using a silver (Ag)-based catalyst offers significant advantages over conventional SCR systems that rely on ammonia reductants and vanadium-based catalysts. However, the conversion rate of SCR is influenced by several factors, among which catalyst poisoning is a major concern. Toxic metals such as sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca) can degrade catalyst activity and lead to deactivation. Poisoned catalysts suffer from reduced conversion rates and premature deactivation before reaching their intended operational lifespan. In particular, calcium poisoning results in the formation of CaO (calcium oxide), which reacts to produce a CaWO₄ compound that severely impairs SCR performance. This study investigates the role of antimony (Sb) in mitigating Ca-induced deactivation in HC-SCR of NO_x. Five catalysts with varying Sb loadings were prepared and tested to evaluate Sb’s effect on NO_x conversion rate at a space velocity of 30,000 h⁻¹. The results demonstrate that Sb effectively suppresses Ca deactivation, enhancing the conversion rate across all engine test conditions. The highest NO_x conversion rate (95.88%) was achieved using a catalyst with 3% Sb. Full article

Powders with phase composition including quasi-amorphous phases and calcium carbonate CaCO₃ in the form of calcite or aragonite and sodium halite NaCl as a reaction by-product were synthesized from 0.5M aqua solutions of sodium silicate and 0.5M aqua solutions of calcium and/or magnesium chlorides. Starting solutions were taken in quantities which could provide precipitation of hydrated calcium and/or magnesium silicates with molar ratios Ca/Si = 1 (CaSi), Mg/Si = 1 (MgSi) or (Ca+Mg)/Si = 1 (CaMgSi). Hydrated calcium and/or magnesium silicates, hydrated silica, magnesium carbonate, hydrated magnesium carbonate or hydrated magnesium silicate containing carbonate ions are suspected as components of quasi-amorphous phases presented in synthesized powders. Heat treatment of synthesized powders at 400, 600, 800 °C and pressed preceramic samples at 900, 1000, 1100 and 1200 °C were used for investigation of thermal evolution of the phase composition and microstructure of powders and ceramic samples. Mass loss of powder samples under investigation during heat treatment was provided due to evacuation of H₂O (m/z = 18), CO₂ (m/z = 44) and NaCl at temperatures above its melting point. After sintering at 1100 °C, the phase composition of ceramic samples included wollastonite CaSiO₃ (CaSi_1100); enstatite MgSiO₃, clinoenstatite MgSiO₃ and forsterite Mg₂SiO₄ (MgSi_1100); and diopside CaMgSi₂O₆ (CaMgSi_1100). After sintering at 1200 °C, the phase composition of ceramics CaSi_1200 included pseudo-wollastonite CaSiO₃. After heat treatment at 1300 °C, the phase composition of MgSi_1300 powder included preferably protoenstatite MgSiO₃. The phase composition of all samples after heat treatment belongs to the oxide system CaO–MgO–SiO₂. Ceramic materials in this system are of interest for use in different areas, including refractories, construction materials and biomaterials. Powders prepared in the present investigation, both via precipitation and via heat treatment, can be used for the creation of materials with specific properties and in model experiments as lunar regolith simulants. Full article

This study evaluates the potential of biomass fuels (10 wt% and 20 wt%) as partial coal replacements in combustion and their effects on clinker performance. Cement was produced by co-grinding clinker with gypsum, and hydration products were analyzed. Potassium and sodium carbonates were introduced to create highly alkaline conditions, thereby simulating the effect of alkali metals in biomass-derived fuel ash on the mineral phases of clinker under high substitution ratios. The results showed biomass fuels’ low ignition point and high volatile matter content improved mixed fuels combustion, increasing the average combustion rate by 0.52%~2.28% and reducing the ignition temperature by up to 56 °C. At low substitution levels, biomass ash did not adversely affect clinker mineral composition or cement properties. However, the highly alkaline environment suppressed the formation of tricalcium silicate (C₃S) in the clinker, resulting in an increased content of free calcium oxide(f-CaO). Simultaneously, it promotes the formation of sulfates (K₂SO₄, Na₂SO₄) and sodium silicate (Na₂Si₂O₅). Full article

This study demonstrated the effectiveness of using autoclaved aerated concrete AAC waste as a low-cost filtering material for removing hydrogen sulfide (H₂S) from gas streams. A long-term experiment (89 days) was conducted in a packed bed reactor to purify synthetic biogas composed of N₂, CO₂, H₂S, and O₂. Optimal H₂S removal efficiencies, reaching up to 100%, were achieved under highly acidic conditions (pH ≈ 1–3) and low oxygen concentrations (<1%). In the presence of oxygen, calcium oxides in the AAC waste react with H₂S to form gypsum (CaSO₄ 2H₂O). The simultaneous removal of both oxygen and H₂S by AAC waste, following an approximate 2:1 molar ratio, may be particularly beneficial for biogas streams containing unwanted traces of oxygen. The transformation and lifespan of AAC waste were monitored through sulfur accumulation in the material and pressure drop measurements, which indicated structural changes in the AAC waste. At the end of its lifespan, the AAC waste exhibited an H₂S removal capacity of 185 g_H2S kg_AAC⁻¹. This innovative and sustainable process not only provides a cost-effective and environmentally sound solution for the simultaneous removal of H₂S and O₂ from biogas, but also promotes waste valorization and aligns with circular economy principles. Full article

Milk of lime (MOL), a suspension of calcium oxide and calcium hydroxide, is vital in the purification of sugar beet and cane juices. This study evaluates the application of Fourier Transform Near-Infrared (FT-NIR) spectroscopy combined with chemometric models—Partial Least Squares (PLS) and Principal Component Regression (PCR)—for rapid, non-destructive assessment of key MOL parameters: density, total lime content, calcium oxide availability, and sucrose content. Ninety samples were analyzed using both wet chemistry and FT-NIR. The predictive performance was assessed using the coefficient of determination (R²). High predictive accuracy was observed for density (PLS: R² = 0.8274; PCR: R² = 0.8795) and calcium oxide availability (PLS: R² = 0.9035; PCR: R² = 0.9115). Total lime content showed moderate accuracy (PLS: R² = 0.7748; PCR: R² = 0.7983), while sucrose content exhibited low predictive power (PLS: R² = 0.2312; PCR: R² = 0.3747). The weak performance was noted for %CaO (PLS: R² = 0.4893; PCR: R² = 0.2409), likely due to spectral overlap and matrix complexity. Despite these challenges, FT-NIR remains a viable, reagent-free method for monitoring MOL, with the potential to enhance process control in the sugar industry. Future work should focus on refining calibration strategies and addressing spectral interferences to improve predictive accuracy for complex matrices. Full article

The application of oxygen-deficient perovskites (ODPs) has attracted interest as anode materials for lithium-ion batteries for their unique properties. One such material, CaSrFe_0.75Co_0.75Mn_0.5O_6-δ, has been studied extensively. The structure of CaSrFe_0.75Co_0.75Mn_0.5O_6-δ was investigated using various techniques, including Rietveld refinements with X-ray diffraction and neutron diffraction. Additionally, iodometric titration and X-ray photoelectron spectroscopy were employed to study the oxygen-deficiency amount and the transition metal’s oxidation states in the material. As an anode material, CaSrFe_0.75Co_0.75Mn_0.5O_6-δ exhibits promising performance. It delivers 393 mAhg⁻¹ of discharge capacity at a current density of 25 mAg⁻¹ after 100 cycles. Notably, this capacity surpasses both the theoretical graphite anode capacity (372 mAhg⁻¹) and that of the calcium analog reported previously. Furthermore, the electrochemical performance of CaSrFe_0.75Co_0.75Mn_0.5O_6-δ remains highly reversible across various current densities ranging from 25 to 500 mAg⁻¹. This suggests the material’s excellent stability and reversibility during charge–discharge cycles, showing its probable application as an anode for lithium-ion batteries. The mechanism of lithium intercalation and deintercalation within CaSrFe_0.75Co_0.75Mn_0.5O_6-δ has also been discussed. Understanding this mechanism is crucial for optimizing the battery’s performance and ensuring long-term stability. Overall, this study highlights the significant potential of oxygen-deficient perovskites, particularly CaSrFe_0.75Co_0.75Mn_0.5O_6-δ, for applications as an anode material for lithium-ion batteries, offering enhanced capacity and stability compared with traditional graphite-based anodes. Full article

Despite the increasing adoption of machine learning and data-driven models for predicting regional groundwater potential (GWP), exploration geoscientists have recognized that these models still face various challenges in their predictive precision. For instance, the stochastic uncertainty associated with incomplete groundwater investigation inventories and the inherent non-transparency characteristic of machine learning models, which lack transparency regarding how input features influence outcomes, pose significant challenges. This research constructs a bagging-based learning framework that integrates Positive–Unlabeled samples (BPUL), along with ex-post interpretability, to map the GWP of the Lijiang River Basin in China, a renowned karst region. For this purpose, we first aggregated various topographic, hydrological, geological, meteorological, and land conditional factors. The training samples were enhanced with data from the subterranean stream investigated in the study area, in addition to conventional groundwater inventories such as wells, boreholes, and karst springs. We employed the BPUL algorithm with four different base learners—Logistic Regression (LR), k-nearest neighbor (KNN), Random Forest (RF), and Light Gradient Boosting Machine (LightGBM)—and model validation was conducted to map the GWP in karst regions. The findings indicate that all models exhibit satisfactory performance in GWP mapping, with the hybrid ensemble models (RF-BPUL and LightGBM-BPUL) achieving higher validation scores. The model interpretation of the aggregated SHAP values revealed the contribution patterns of various conditional factors to groundwater distribution in karst zones, emphasizing that lithology, the multiresolution index of valley bottom flatness (MRVBF), and the geochemical element calcium oxide (CaO) have the most significant impact on groundwater enrichment in karst zones. These findings offer new approaches and methodologies for the in-depth exploration and scientific prediction of groundwater potential. Full article

Calcium acetate lactate (CAL) was rapidly synthesized for the first time using the reaction between the scallop shell-derived calcium carbonate (CaCO₃) and the binary phase of acetic and lactic acids. Calcium acetate (CA) and calcium lactate (CL) synthesized from the reaction of scallop shell-derived CaCO₃ with each acid by similarity routes are compared with the obtained CAL product. The production yields are 88.24, 79.17, and 96.44%, whereas the solubilities are 93.77, 90.18, and 95.08% for CA, CL, and CAL, respectively. All the synthesized CA, CL, and CAL samples were characterized and confirmed by X-ray fluorescence (XRF) to examine the calcium main element and other impurities of minor elements, X-ray diffraction (XRD) to investigate the crystallography, Fourier transform infrared (FTIR) to characterize the vibrational characteristics of the functional groups, scanning electron microscope (SEM) to observe the sample morphologies, and the thermogravimetric analysis (TGA) to investigate the thermal decomposition processes of samples. The experimental results pointed out that the synthesized CA, CL, and CAL were the monohydrate, pentahydrate, and dihydrate forms with chemical formulae of Ca(CH₃COO)₂·H₂O, Ca(CH₃CHOHCOO)₂·5H₂O, and Ca(CH₃COO)(CH₃CHOHCOO)·2H₂O, respectively. The final thermal decomposition product of all calcium compounds was calcium oxide (CaO). The CAL sample’s vibrational characteristics, crystal phases, and morphologies show the binary acetate and lactate anion phases, confirming the new binary anionic calcium acetate lactate obtained. In conclusion, this research proposes an easy and low-cost technique to prepare a new valuable CAL compound using scallop shell waste as a cheap and renewable calcium source. Full article