Search Results (1,876)

The efficient recovery of rhenium (Re), a critical metal in high-tech industries, is essential to address its growing demand and reduce reliance on primary mining. In this study, we developed novel anion-exchange resins for the selective adsorption and recovery of Re(VII) ions from acidic solutions, simulating industrial by-products. The resins were synthesized from a vinylbenzyl chloride-co-divinylbenzene copolymer modified with aliphatic, heterocyclic, and aromatic weakly basic amines, selected from among bis(3-aminopropyl)amine (BAPA), 1-(2-pyrimidinyl)piperazine (PIP), thiosemicarbazide (TSC), 2-amino-3-hydroxypyridine (AHP), 1-(2-hydroxyethyl)piperazine (HEP), 4-amino-2,6-dihydroxypyrimidine (AHPI), and 2-thiazolamine (TA). The adsorption of Re on BAPA, PIP, and HEP resins obeyed the Langmuir model, and the resins exhibited high adsorption capacities, with maximum values reaching 435.4 mg Re g⁻¹ at pH 6. Furthermore, strong selectivity for ReO₄⁻ ions over competing species, including Mo, Cu, and V, was noted in solutions simulating the leachates of the by-products of Cu-Mo ores. Additionally, complete elution of Re was possible. The developed resins turned out to be highly suitable for the continuous-flow-mode adsorption of ReO₄⁻, revealing outstanding adsorption capacities before reaching column breakthrough. In this context, the novel anion-exchange resins developed offer a reference for further Re recovery strategies. Full article

South Dongting Lake is an essential aquatic ecosystem that receives substantial water inflows from the Xiangjiang and Zishui Rivers. However, it is significantly impacted by human activities, including mining, smelting, and farming. These activities have led to serious contamination of the lake’s sediments with heavy metals (HMs). This study investigated the distribution, mobility, and influencing factors of HMs at the sediment–water interface. To this end, sediment samples were analyzed from three key regions (Xiangjiang River estuary, Zishui River estuary, and northeastern South Dongting Lake) using traditional sampling methods and Diffusive Gradients in Thin Films (DGT) technology. Analysis of fifteen HMs (Pb, Bi, Ni, As, Se, Cd, Sb, Mn, Zn, V, Cr, Cu, Tl, Co, and Fe) revealed significant spatial heterogeneity. The results showed that Cr, Cu, Pb, Bi, Ni, As, Se, Cd, Sb, Mn, Zn, and Fe exhibited high variability (CV > 0.20), whereas V, Tl, and Co demonstrated stable concentrations (CV < 0.20). Concentrations were found to exceed background values of the upper continental crust of eastern China (UCC), Yangtze River sediments (YZ), and Dongting Lake sediments (DT), particularly at the Xiangjiang estuary (XE) and in the northeastern regions. Speciation analysis revealed that V, Cr, Cu, Ni, and As were predominantly found in the residual fraction (F4), while Pb and Co were concentrated in the oxidizable fraction (F3), Mn and Zn appeared primarily in the exchangeable fractions (F1 and F2), and Cd was notably dominant in the exchangeable fraction (F1), suggesting a high potential for mobility. Additionally, DGT results confirmed a significant potential for the release of Pb, Zn, and Cd. Contamination assessment using the Pollution Load Index (PLI) and Geoaccumulation Index (Igeo) identified Pb, Bi, Ni, As, Se, Cd, and Sb as major pollutants. Among these, Bi and Cd were found to pose the highest risks. Furthermore, the Risk Assessment Code (RAC) and the Potential Ecological Risk Index (PERI) highlighted Cd as the primary ecological risk contributor, especially in the XE. The study identified sediment grain size, pH, electrical conductivity, and nutrient levels as the primary influencing factors. The PMF modeling revealed HM sources as mixed smelting/natural inputs, agricultural activities, natural weathering, and mining/smelting operations, suggesting that remediation should prioritize Cd control in the XE with emphasis on external inputs. Full article

The development of anode-free sodium metal batteries (AFSMBs) offers a promising pathway to achieve ultrahigh energy density and cost efficiency inherent to conventional sodium ion/metal batteries. However, irreversible Na plating/stripping and dendritic growth remain critical barriers. Herein, we demonstrate that separator engineering is a pivotal strategy for stabilizing AFSMBs. Through systematic evaluation of four separators—2500 separator (PP), 2325 separator (PP/PE/PP), glass fiber (GF), and an Al₂O₃-coated PE membrane, we reveal that the Al₂O₃-coated separator uniquely enables exceptional interfacial kinetics and morphological control. Na||Na symmetric cells with Al₂O₃ coated separator exhibit ultralow polarization (4.5 mV) and the highest exchange current density (1.77 × 10⁻² mA cm⁻²), while the anode-free AlC-NFPP full cells retain 91.6% capacity after 150 cycles at 2C. Specifically, the Al₂O₃ coating homogenizes Na⁺ flux, promotes dense and planar Na deposition, and facilitates near-complete stripping with minimal “dead Na”. This work establishes ceramic-functionalized separators as essential enablers of practical high-energy AFSMBs. Full article

This work investigated the ion exchange technique for selective separation of rare earth elements (REE) from acid mine drainage (AMD), using different column systems, pH values, and eluent concentrations. Systematic analysis of pH and eluent concentration showed that an initial pH of 6.0 and 0.02 mol L⁻¹ NH₄EDTA are the optimal conditions, achieving 98.4% heavy REE purity in the initial stage (0 to 10 bed volumes). This represents a 32-fold increase compared to the original AMD (6.7% heavy REE). The speciation of REE and impurities was determined by Visual Minteq 4.0 software using pH 2.0, which corresponds to the pH at the inlet of the fractionation column. Under this condition, La and Nd and the impurities (Ca, Mg, and Mn) remained in the fractionation column, while Al was partially retained. In addition, the heavy REE (Y and Dy) were mainly in the form of REE-EDTA complexes and not as free cations, which made fractionation more feasible. The fractionation column minimized impurities, retaining 100% of Ca and 67% of Al, generating a liquor concentrated in heavy REE. This sustainable approach adopted herein meets the critical needs for scalable recovery of REE from diluted effluents, representing a circular economy strategy for critical metals. Full article

This study focuses on the exchange of mono- and divalent metal cations in FAU-type zeolite and their behavior in gas-phase CO₂ adsorption measurements and liquid-phase methylene blue (MB) adsorption in the absence of oxidizing agents under dark conditions. Firstly, zeolites exchanged with different cations were characterized by several techniques, such as XRD, SEM, XRF, XPS, and N₂ adsorption–desorption, to reveal the impact of the cations on the zeolite texture and structure. The adsorption studies revealed a positive effect of cation exchange on the adsorption capacity of the zeolite, particularly for silver-loaded FAU zeolite. In liquid-phase experiments, Ag-Y zeolite also demonstrated the highest MB removal, with a value of 79 mg/g. Kinetic studies highlighted that Ag-Y could reach the MB adsorption equilibrium within 1 h, with its highest rate of adsorption occurring during the first 5 min. In gas-phase adsorption studies, the highest CO₂ adsorption capacity was also achieved over Ag-Y, yielding 10.4 µmol/m² of CO₂ captured. Full article

An anion exchange-assisted technique was used for the synthesis of platinum-decorated SnO₂ supports, providing nanocatalysts with enhanced activity for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). In this study, a series of SnO₂ supports, namely SnA (synthesized almost at room temperature), SnB (hydrothermally treated at 180 °C), and SnC (annealed at 600 °C), are systematically investigated, all loaded with 1 mol% Pt from H₂PtCl₆ under identical mild conditions. The chloride ions from the SnCl₄ precursors were efficiently removed via a strong-base anion exchange reaction, resulting in highly dispersed, crystalline ~5 nm cassiterite SnO₂ particles. All Pt/SnO₂ composites displayed mesoporous structures with type IVa isotherms and H₂-type hysteresis, with SP1a (Pt on SnA) exhibiting the largest surface area (122.6 m²/g) and the smallest pores (~3.5 nm). STEM-HAADF imaging revealed well-dispersed PtOx domains (~0.85 nm), while XPS confirmed the dominant Pt⁴⁺ and Pt²⁺ species, with ~25% Pt⁰ likely resulting from photoreduction and/or interactions with Sn–OH surface groups. Raman spectroscopy revealed three new bands (260–360 cm⁻¹) that were clearly visible in the sample with 10 mol% Pt and were due to the vibrational modes of the PtOx species and Pt-Cl bonds introduced due the addition and hydrolysis of H₂PtCl₆ precursor. TGA/DSC analysis revealed the highest mass loss for SP1a (~7.3%), confirming the strong hydration of the PtOx domains. Despite the predominance of oxidized PtOx species, SP1a exhibited the highest catalytic activity (k_app = 1.27 × 10⁻² s⁻¹) and retained 84.5% activity for the reduction of 4-NP to 4-AP after 10 cycles. This chloride-free low-temperature synthesis route offers a promising and generalizable strategy for the preparation of noble metal-based nanocatalysts on oxide supports with high catalytic activity and reusability. Full article

Direct air capture (DAC), as a complementary strategy to carbon capture and storage (CCS), offers a scalable and sustainable pathway to remove CO₂ directly from the ambient air. This study presents a detailed evaluation of the amine-functionalised metal-organic framework (MOF) sorbent, mmen-Mg₂(dobpdc), for DAC using a temperature–vacuum swing adsorption (TVSA) process. While this sorbent has demonstrated promising performance in point-source CO₂ capture, this is the first dynamic simulation-based study to rigorously assess its effectiveness for low-concentration atmospheric CO₂ removal. A transient one-dimensional TVSA model was developed in Aspen Adsorption and validated against experimental breakthrough data to ensure accuracy in capturing both the sharp and gradual adsorption kinetics. To enhance process efficiency and sustainability, this work provides a comprehensive parametric analysis of key operational factors, including air flow rate, temperature, adsorption/desorption durations, vacuum pressure, and heat exchanger temperature, on process performance, including CO₂ purity, recovery, productivity, and specific energy consumption. Under optimal conditions for this sorbent (vacuum pressure lower than 0.15 bar and feed temperature below 15 °C), the TVSA process achieved ~98% CO₂ purity, recovery over 70%, and specific energy consumption of about 3.5 MJ/KgCO₂. These findings demonstrate that mmen-Mg₂(dobpdc) can achieve performance comparable to benchmark DAC sorbents in terms of CO₂ purity and recovery, underscoring its potential for scalable DAC applications. This work advances the development of energy-efficient carbon removal technologies and highlights the value of step-shape isotherm adsorbents in supporting global carbon-neutrality goals. Full article

Esterification is a key transformation in the production of lubricants, pharmaceuticals, and fine chemicals. Conventional processes employing homogeneous acid catalysts suffer from limitations such as corrosive byproducts, energy-intensive separation, and poor catalyst reusability. This review provides a comprehensive overview of heterogeneous catalytic systems, including ion exchange resins, zeolites, metal oxides, mesoporous materials, and others, for improved ester synthesis. Recent advances in membrane-integrated reactors, such as pervaporation and nanofiltration, which enable continuous water removal, shifting equilibrium and increasing conversion under milder conditions, are reviewed. Dual-functional membranes that combine catalytic activity with selective separation further enhance process efficiency and reduce energy consumption. Enzymatic systems using immobilized lipases present additional opportunities for mild and selective reactions. Future directions emphasize the integration of pervaporation membranes, hybrid catalyst systems combining biocatalysts and metals, and real-time optimization through artificial intelligence. Modular plug-and-play reactor designs are identified as a promising approach to flexible, scalable, and sustainable esterification. Overall, the interaction of catalyst development, membrane technology, and digital process control offers a transformative platform for next-generation ester synthesis aligned with green chemistry and industrial scalability. Full article

To date, one of the main problems associated with the engineering application of metallic materials is corrosion protection. To increase their durability and reduce damage, a variety of protection methods have been studied and applied. In recent decades, coating techniques have become increasingly important. Among these coatings, Layered Double Hydroxides (LDHs) have shown unique properties, such as ion exchange, high adhesion, and hydrophobicity, particularly useful for biomedical applications. In this review, after a detailed exposition of the LDHs’ synthesis processes, the most recent corrosion protection methods are illustrated. Intercalation of corrosion inhibitors and release kinetics of intercalates are presented. Although this work is mainly focused on laboratory-scale investigations and fundamental research, the problems inherent to large-scale industrial manufacturing and application are outlined and briefly discussed. Full article

Phosphorylated cellulose is proposed as a bio-resin for the removal of heavy metals, as a substitute for synthetic polymer-based materials. Phosphorylation is carried out using kraft pulp fibers as the cellulose source, with phosphate esters and urea as reactants to prevent significant fiber degradation. Herein, phosphorylated fibers, with three types of counterions (sodium, ammonium, or hydrogen), are used in adsorption trials involving four individual metals: nickel, copper, cadmium, and lead. The Langmuir isotherm model is applied to determine the maximum adsorption capacities at four different temperatures (10, 20, 30, and 50 °C), enabling the calculation of the Gibbs free energy (ΔG), entropy (ΔS), and enthalpy (ΔH) of adsorption. The results show that the adsorption capacity of phosphorylated fibers is equal or even higher than that of commercially available resins (1.7–2.9 vs. 2.4–2.6 mmol/g). However, the nature of the phosphate counterion plays an important role in the adsorption capacity, with the alkaline form showing a superior ion exchange capacity than the hybrid form and acid form (2.7–2.9 vs. 2.3–2.7 vs. 1.7–2.5 mmol/g). The thermodynamic analysis indicates the spontaneous (ΔG = (-)16–(-)30 kJ/mol) and endothermic nature of the adsorption process with positive changes in enthalpy (0.45–15.47 kJ/mol) and entropy (0.07–0.14 kJ/mol·K). These results confirm the high potential of phosphorylated lignocellulosic fibers for ion exchange applications, such as the removal of heavy metals from process or wastewaters. Full article

To address the issue of excessive chemical fertilizer use in agricultural production, this study conducted a pot experiment with four treatments: CK (no fertilization), T1 (the application of potassium magnesium sulfate fertilizer), T2 (the application of slow-release fertilizer equal to T1), and T3 (the application of slow-release fertilizer with the same fertility as T1). The effects of these treatments on garlic seedling yield, growth quality, chlorophyll content, photosynthetic characteristics, and the soil environment were investigated to evaluate the feasibility of replacing conventional fertilizers with slow-release formulations. The results showed that compared with CK, all three fertilized treatments (T1, T2, and T3) significantly increased the plant heights and stem diameters of the garlic sprouts (p < 0.05). Plant height increased by 14.85%, 17.81%, and 27.75%, while stem diameter increased by 9.36%, 8.83%, and 13.96%, respectively. Additionally, the chlorophyll content increased by 4.34%, 7.22%, and 8.05% across T1, T2, and T3, respectively. Among the treatments, T3 exhibited the best overall growth performance. Compared with those in the CK group, the contents of soluble sugars, soluble proteins, free amino acids, vitamin C, and allicin increased by 64.74%, 112.17%, 126.82%, 36.15%, and 45.43%, respectively. Furthermore, soil organic matter, available potassium, magnesium, and phosphorus increased by 109.02%, 886.25%, 91.65%, and 103.14%, respectively. The principal component analysis indicated that soil pH and exchangeable magnesium were representative indicators reflecting the differences in the soil’s chemical properties under different fertilization treatments. Compared with the CK group, the metal contents in the T1 group slightly increased, while those in T2 and T3 generally decreased, suggesting that the application of slow-release fertilizer exerts a certain remediation effect on soils contaminated with heavy metals. This may be attributed to the chemical precipitation and ion exchange capacities of phosphogypsum, as well as the high adsorption and cation exchange capacity of bentonite, which help reduce the leaching of soil metal ions. In summary, slow-release fertilizers not only promote garlic sprout growth but also enhance soil quality by regulating its chemical properties. Full article

Soil acidification, salinization, and heavy metal pollution pose serious threats to global food security and sustainable agricultural development. Biochar, with its high porosity, large surface area, and abundant functional groups, can effectively improve soil properties. However, due to variations in feedstocks and pyrolysis conditions, it may contain potentially harmful substances. Industrial wastes such as fly ash, steel slag, red mud, and phosphogypsum are rich in minerals and show potential for soil improvement, but direct application may pose environmental risks. The co-application of biochar with these wastes can produce composite amendments that enhance pH buffering capacity, nutrient availability, and pollutant immobilization. Therefore, a review of biochar-industrial waste composites as soil amendments is crucial for addressing soil degradation and promoting resource utilization of wastes. In this study, the literature was retrieved from Web of Science, Scopus, and Google Scholar using keywords including biochar, fly ash, steel slag, red mud, phosphogypsum, combined application, and soil amendment. A total of 144 articles from 2000 to 2025 were analyzed. This review summarizes the physicochemical properties of biochar and representative industrial wastes, including pH, electrical conductivity, surface area, and elemental composition. It examines their synergistic mechanisms in reducing heavy metal release through adsorption, complexation, and ion exchange. Furthermore, it evaluates the effects of these composites on soil health and crop productivity, showing improvements in soil structure, nutrient balance, enzyme activity, and metal immobilization. Finally, it identifies knowledge gaps as well as future prospects and recommends long-term field trials and digital agriculture technologies to support the sustainable application of these composites in soil management. Full article

This study investigates the effects of NaCl activation on the structural and chemical properties of kaolin for the adsorption of Zn²⁺ from solution. Kaolin was treated with NaCl solution at varying concentrations (0.5, 1.0, 2.0, and 4.0 M), and ultrasonication was used as a means of agitation. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and dynamic light scattering (DLS) were employed to characterize the physical and chemical effects of the NaCl activation and its subsequent influence on the kaolin’s heavy metal removal efficiency. The kaolin activated with 0.5 M NaCl solution yielded the optimal performance with a 13% increase in Zn²⁺ removal compared to the unmodified clay. The adsorption data best matched the pseudo-second-order kinetic model and the Langmuir isotherm. This indicates a monolayer adsorption on a homogeneous surface, with chemisorption as the dominant adsorption mechanism. Thermodynamic analysis also revealed that the adsorption process was endothermic and spontaneous. Furthermore, NaCl activation slightly enhanced the microstructural properties of the kaolin and moderated the surface charge, creating a more favorable electrostatic environment for improved heavy metal ion adsorption. The findings further highlight the potential of NaCl activation to introduce exchangeable Na⁺ onto the kaolin surface in a pH-neutral environment and promise a clean, mechanistically clear, and practical route for ion exchange with heavy metals such as Zn²⁺. Full article

As in the case with other metals, tungsten is an element with a number of uses in different fields, which is why its recovery from both primary and secondary materials continues to be of great interest. Various hydrometallurgical processes, considered as unit operations, can be used for the recovery, separation and concentration of tungsten from any source, with ease of scaling-up a potential factor when considering the best process for practical use. The present work reviewed investigations into the use of such unit operations for the recovery of tungsten which were published during 2024 and the first half of 2025. Because most if not all of these investigations were conducted on a laboratory scale, there is still much room for improvement before deciding on the best option for tungsten recovery. In all cases, however, this recovery is based on a series of steps from leaching to separation technologies (ion exchange resins, liquid–liquid extraction, etc.) to the tungsten end-product. Full article

Biodiesel, a renewable and environmentally friendly alternative to fossil fuels, has attracted significant attention due to its potential to reduce greenhouse gas emissions. However, high production costs and complex processing remain challenges. Heterogeneous catalysts have shown promise in overcoming these barriers by offering benefits, such as easy separation, reusability, low-cost raw materials, and the ability to reduce reaction times and energy consumption. This review evaluates key classes of heterogeneous catalysts, such as metal oxides, ion exchange resins, and zeolites, and their performance in transesterification and esterification processes. It highlights the importance of catalyst preparation methods, textural properties, including surface area, pore volume, and pore size, activation techniques, and critical operational parameters, like the methanol-to-oil ratio, temperature, time, catalyst loading, and reusability. The analysis reveals that catalysts supported on high surface area materials often achieve higher biodiesel yields, while metal oxides derived from natural sources provide cost-effective and sustainable options. Challenges, such as catalyst deactivation, sensitivity to feedstock composition, and variability in performance, are discussed. Overall, the findings underscore the potential of heterogeneous catalysts to enhance biodiesel production efficiency, although further optimization and standardized evaluation protocols are necessary for their broader industrial application. Full article