Search Results (280)

The southeastern Hainan Island boasts abundant hydrothermal resources, most of which are exposed as thermal springs. Analyzing the hydrochemical characteristics, hydrochemical evolutionary mechanisms, and material transition of these resources is significant for their exploitation and utilization. This study investigated the Nanping geothermal field in southeastern Hainan Island, using five groups of geothermal water samples collected in 2022, as well as seven groups of geothermal water samples, one group of shallow groundwater samples, and one group of surface water samples taken in 2023. Specifically, this study examined water–rock interactions in the geothermal field using the Gibbs model, ion ratios, chloro-alkaline indices (CAIs), and the sodium adsorption ratio (SAR). Moreover, the mineral transfer process in groundwater was analyzed using inverse hydrogeochemical simulation. The results indicate that in the study area the geothermal water temperatures range from 64 °C to 80 °C, pH values from 8.32 to 8.64, and TDS concentrations from 431 mg/L to 623 mg/L. The primary hydrochemical types of geothermal water in the study area include Cl-Na and Cl·HCO₃-Na, suggesting low-temperature, slightly alkaline geothermal water. The hydrochemical components of geothermal water in the study area are primarily affected by water–rock interactions. Besides the dissolution of silicate minerals and halite, cation exchange reactions contribute greatly to the formation of Na⁺ and K⁺ in geothermal water. Geothermal water receives recharge from the atmospheric precipitation of the Diaoluo Shan area in the northwest of the study area, with the recharge elevation ranging from 967 to 1115 m. The inverse hydrogeochemical simulation results reveal that during the water–rock interactions, silicate minerals, clay minerals, gypsum, and halite dissolve, while quartz and carbonate minerals precipitate. Additionally, these processes are accompanied by cation exchange reactions dominated by the replacement of Na⁺ in surrounding rocks by Ca²⁺ in geothermal water. This study can provide a geological basis for the exploitation, utilization, and management of the Nanping geothermal field. Full article

Proton exchange membrane fuel cells (PEMFCs) have the advantages of high efficiency, a low operating temperature, and a pollution-free reaction. Therefore, PEMFCs have emerged as a viable clean energy solution for ships to reduce their carbon emissions. When PEMFCs operate in marine salt spray environments, foreign ions entering the cathodes of fuel cells with air can cause a decline in cell performance. In this study, the effects of the cation type (K⁺, Na⁺, Mg²⁺, and Ca²⁺) and concentration (0.25 M and 0.5 M) on cell performance in terms of the polarization curve were systematically investigated using a fuel cell test system. Cell performance degradation was observed due to the existence of cations. The influence of the four cations on cell performance followed the rule of Ca²⁺ > Mg²⁺ > Na⁺ > K⁺. Meanwhile, cell performance decreased with an increase in concentration. When the fuel cell was not contaminated, the voltage was 0.645 V at a current density of 1 A/cm². When the concentration was 0.5 M, the corresponding voltages were 0.594 V, 0.583 V, 0.559 V, and 0.300 V, respectively. In addition, fuel cells contaminated by NaNO₃ and NaCl were compared. Due to the existence of Cl⁻, more severe performance degradation was observed when the fuel cells were contaminated by NaCl. Full article

Glasses exposed to soil environments are of interest across various scientific fields, from nuclear waste containment to archaeological preservation and nutrient-delivery systems for plants. While immersion experiments provide valuable insights into the ion release kinetics in root- and microbe-exuded solutions, they fail to replicate the complexities of nutrient leaching in real soil conditions. To address this, the degradation behavior of nutrient-bearing glasses (41SiO₂·6(10)P₂O₅·20K₂O·33(29)MgO/CaO/MgO + CaO) with increasing sulfate contents was investigated through a soil incubation experiment simulating Central European weather variability. A comprehensive approach, combining SEM observations and EDS semi-quantitative analysis, revealed that acidic peat strongly promoted ion exchange, where protons from the medium replaced network cations. The glass composition played a crucial role in the fracture behavior: sulfate incorporation increased the network rigidity, making the glasses more prone to mechanical degradation and accelerating the reaction front advancement. The P₂O₅ content was also a key factor in modulating the reactivity, with higher concentrations intensifying interactions with the soil medium. Limited water availability accelerated the solution saturation, leading to secondary phase precipitation and temporary nutrient immobilization. These findings demonstrate that glass reactivity can be fine-tuned through composition adjustments and highlight the dynamic nature of glass–soil interactions, including seasonal variations in nutrient release under acidic conditions. Full article

Mechanically improved polymeric membranes with high ionic conductivity (IC) and good permeability are highly desired for next-generation anion exchange membranes (AEMs) in order to reduce Ohmic losses and enhance water management in alkaline membrane fuel cells. To move towards the fabrication of such high-performance membranes, the creation of hydrophilic ion-conducting double gyroid (DG) nanochannels within block copolymer (BCP) AEMs is a promising approach. However, this attractive solution remains difficult to implement due to the complexity of constructing a well-developed ion-conducting DG morphology across the entire membrane thickness. To deal with this issue, water permeable polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) membranes with ion-conducting DG nanochannels were produced by combining a solvent vapor annealing (SVA) treatment with a methylation process. Here, the SVA treatment enabled the manufacture of DG-forming BCP AEMs while the methylation process allowed for the conversion of pyridine sites to N-methylpyridinium (NMP⁺) cations via a Menshutkin reaction. Following this SVA-methylation method, the IC value of water-permeable (~384 L h⁻¹ m⁻² bar⁻¹) DG-structured BCP AEMs in their OH⁻counter anion form was measured to be of ~2.8 mS.cm⁻¹ at 20 °C while a lower IC value was probed, under the same experimental conditions, from as-cast NMP⁺-containing analogs with a non-permeable disordered phase (~1.2 mS.cm⁻¹). Full article

Sustainable soil management through the use of an appropriate tillage system can positively change the edaphic parameters. The aim of the present study was to compare the effects that reduced tillage (RT) and conventional tillage (CT) systems have on changes in selected physical and chemical properties and enzymatic activity in various soil types. The study included the following soil types: Eutric Fluvisol, Mollic Fluvisol, Haplic Chernozem, Haplic Luvisol, Eutric Regosol, Eutric Gleysol, and Stagnic Planosol. Soil samples were collected in the Danubian Lowland and Eastern Slovak Lowland. The following parameters were determined in the soil samples: soil texture, pH, hydrolytic acidity and the sum of basic exchangeable cations, the contents of carbon (TOC), nitrogen (TN), and dissolved organic carbon (DOC), and the activities of dehydrogenases (DEH), catalase (CAT), peroxidases (PER), alkaline phosphatase (AlP), acid phosphatase (AcP), proteases, and β-glucosidase (BG). The reaction of the analysed soils, in the RT and CT cultivations alike, ranged from acidic to neutral, and the sorption properties differed between individual soil types. The TOC ranged from 16.53 to 42.07 g kg⁻¹ for conventional cultivation and from 15.51 to 38.90 g kg⁻¹ for reduced tillage. The values of enzymatic soil quality indices values correlated with TOC, DOC, and TN, as well as with pH, the sum of exchangeable base cations, cation exchange capacity, and degree of base saturation of the sorption complex. The tillage system determined changes in the activity of the studied enzymes, but the intensity and direction of these changes depended on the soil type. Based on the enzyme activity results, soil quality indices such as GMea and TEI were calculated. TEI proved to be a more sensitive indicator than GMea. It was shown that, of all studied soil types and regardless of the cultivation system, Eutric Gleyosols had the most variable properties. For conventional tillage, Haplic Luvisol and Eutric Regosol were characterised by the greatest uniformity. In general, the edaphic properties of soils under conventional tillage differed from those of soils under simplified tillage. Full article

Magnesium sulfate leaching of ionic rare earth ores is generally characterized by a smooth outflow curve, a long leaching time, and a high impurity content in the leach liquor. To reveal the leaching law of rare earth cations and impurity aluminum ions in the leaching process of ionic rare earth ores in magnesium sulfate, equilibrium leaching and leaching kinetics experiments were carried out using ore samples of five particle sizes (<0.10, 0.10–0.25, 0.25–0.50, 0.50–1.00, and >1.00 mm). Furthermore, prediction models of equilibrium constants and rate constants were constructed based on ion-exchange theory. The results show that the equilibrium constants of the rare earth and aluminum ion-exchange reactions decrease gradually with the increase in the magnesium ion concentration, the decrease in the temperature, and the increase in the surface area of the particles. Moreover, the equilibrium constant prediction models of rare earth and aluminum with magnesium sulfate were constructed using data fitting. From the leaching kinetics experiment, there is a significant relationship between the reaction rate constant of ion exchange and the surface area of the particles: the larger the particle size, the smaller the reaction rate constant. Based on the kinetic test data and the Arrhenius equation, the frequency factors and activation energies of the ion-exchange reactions were inversely analyzed through the Chemistry Reaction Module of COMSOL. The reaction activation energy for rare earth and aluminum leaching is 10,743 J/mol and 10,987 J/mol, respectively. The rate constant prediction model was obtained by fitting the analyzed rate constant data. The rare earth and aluminum leaching results for the full-grade ores are in high agreement with the predictions of the constructed model, which verifies the validity of the proposed model. This study can provide theoretical support for the improvement of the leaching efficiency of rare earths and the optimization of the magnesium sulfate leaching process. Full article

Presently, geothermal resources have been globally recognized as an indispensable component of the energy system due to their sustainability. However, previous studies on geothermal reservoirs focus primarily on single reservoirs, lacking a systematic investigation of composite geothermal reservoirs. The geothermal reservoirs in the northwestern Shandong geothermal area in China are primarily of sandstone and karst types, characterized by extensive distributions, shallow burial depths, high water temperatures, and high water abundance, holding considerable potential for exploitation. This study explored the hydrochemical, isotopic, and circulation characteristics of geothermal fluids in the composite geothermal reservoirs in the study area using methods like hydrogeochemistry and geothermal geology. The purpose is to determine the geochemical differences in geothermal fluids across the composite geothermal reservoirs and provide scientific support for subsequently efficient and sustainable exploitation and utilization of geothermal resources in the study area. The composite geothermal reservoirs in the study area are composed of porous sandstone geothermal reservoirs (also referred to as sandstone reservoirs) in the upper part and karst-fissured geothermal reservoirs (also referred to as karst reservoirs) in the lower part. The results show that the geothermal fluids in the sandstone and karst reservoirs are primarily of Na-Cl-SO₄ and Na-Ca-Cl-SO₄ types, respectively. The hydrochemical composition of geothermal fluids in the karst reservoirs is principally influenced by the precipitation–dissolution equilibrium of carbonate and sulfate minerals, while that in the sandstone reservoirs is predominantly influenced by the precipitation–dissolution equilibrium of carbonate and silicate minerals, as well as cation exchange reactions. The temperatures of the karst reservoirs were calculated at 52.9–82.09 °C using geothermometers. Given the cold-water mixing ratios range from 89% to 96%, the corrected reservoir temperatures vary from 200 to 225 °C. In contrast, the temperatures of the sandstone reservoirs were calculated at 60.54–85.88 °C using geothermometers. These reservoirs exhibit cold water mixing ratios ranging from 85% to 90%, and their corrected reservoir temperatures vary from 150 to 200 °C accordingly. The circulation depths of geothermal fluids in the karst and sandstone reservoirs range from 1107.28 to 1836.69 m and from 1366.60 to 2102.29 m, respectively. The study area is primarily recharged by meteoric water from Mount Tai and the Lushan and Yishan mountains (collectively referred to as the Tai-Lu-Yi mountains) to the southeast of the study area. Investigating the differences in geochemical characteristics of geothermal fluids in composite geothermal reservoirs in the study area is significant for balancing the exploitation and supply of geothermal resources, optimizing the exploitation and utilization modes, and promoting the efficient and sustainable exploitation and utilization of geothermal resources in the study area. Full article

Montmorillonite (Mont) is a natural two-dimensional material with a 2:1 layered silicate crystal structure. It possesses abundant surface groups, cation exchange capacity, and adsorption performance. In addition, it has other advantages such as abundant reserves, environmental friendliness, strong mechanical stability, and a large specific surface area. As such, it shows excellent potential for application in environmental remediation. In the following paper, we focus on the removal of TCS (triclosan) from an aqueous environment by utilizing montmorillonite-supported bimetallic Fe/Ag particles. We use scanning electron microscopy, X-ray diffraction patterns, Fourier-transform infrared spectra, and specific surface area to analyze the structure, morphology, and composition of these nanocomposites. The effects of the pH, different materials, contact time, and different initial concentrations on the degradation efficiency of TCS were studied systematically. Based on the results of our study, montmorillonite-supported bimetallic Fe/Ag nanoparticles (Fe/Ag-Mont) should be categorized as a type of mesoporous material of high uniformity because the pore size of all its catalysts ranges from 10 to 20 nm, and they are well-distributed. The Si-O stretching vibrations of montmorillonite can be changed by adding Fe/Ag. We found that Fe or Ag combined with -O to form a new bond and interacted with Si-O, and the incorporation of Fe/Ag-Mont nanoparticles removed TCS with better reduction rates. By enhancing reduction capacity, the pH was below 4 due to H• species generation by Fe/Ag. H• was the main factor enhancing the redox reaction in reducing TCS. The pH controlled the competition between Fe corrosion and silver formation, which enabled the system to self-regulate. In addition, this study provided a suitable method of efficiently synthesizing clay-supported bimetallic nano-system materials for reduction. Full article

The urgent need to reduce greenhouse gas emissions, particularly carbon dioxide (CO₂), has led to intensive research into novel techniques for synthesizing valuable chemicals that address climate change. One technique that is becoming increasingly important is the electrochemical reduction of CO₂ to produce carbon monoxide (CO), an important feedstock for various industrial processes. This comprehensive review examines the latest developments in CO₂ electroreduction, focusing on mechanisms, catalysts, reaction pathways, and optimization strategies to enhance CO production efficiency. A particular emphasis is placed on the role of ion exchange membranes, including cation exchange membranes (CEMs), anion exchange membranes (AEMs), and bipolar membranes (BPMs). The review explores their advantages, disadvantages, and the current challenges associated with their implementation in CO₂ electroreduction systems. Through careful analysis of the current literature, this report aims to provide a comprehensive understanding of state-of-the-art methods and their potential impact on sustainable CO production, with a special focus on membrane technologies. Full article

In recent years, there has been increasing concern regarding the widespread occurrence of dyes in aquatic environments, due to their harmful effects on both water quality and human health. This investigation uses bauxite residue as a cost-effective sorbent to eradicate the hazardous reactive blue (RB) dye from aqueous solutions. The reusability potential of bauxite residue was also evaluated. The bauxite residue was characterized by X-ray diffraction, Cation Exchange Capacity, Chemical analysis, FTIR, and Analysis of particle size and particle distribution. The RB dye adsorption parameters revealed that the removal efficiency and adsorption capacity of bauxite residue was 100% and 186.01 mg/g, respectively, under the following adsorption conditions: adsorbent dosage of 0.5 mg/L, initial pH of 2, dye concentration of 50 mg/g, and reaction temperature of 25 °C. Furthermore, the adsorption of RB dye on bauxite residue followed the pseudo-second-order kinetic and Freundlich isotherm models. After one adsorption cycle, the adsorption capacity of bauxite residue for reactive RB removal reached 186.01 mg/g. The regeneration study revealed that the bauxite residue remained 99% of its original condition following the water regeneration cycle. Full article

Background: N-succinimidyl-[¹⁸F]fluorobenzoate ([¹⁸F]SFB) is commonly prepared through a three-step procedure starting from [¹⁸F]fluoride ion. A number of methods for the single-step radiosynthesis of [¹⁸F]SFB have been introduced recently, including the radiofluorination of diaryliodonium salts and the Cu-mediated ¹⁸F-fluorination of pinacol aryl boronates and aryl tributyl stannanes, but they still have the drawbacks of lengthy product purification procedures. In the present work, two approaches for the direct labeling of [¹⁸F]SFB from diaryliodonium (DAI) salt (4) and pinacol aryl boronate (6) are evaluated, with a major focus on developing a fast and simple SPE-based purification procedure. Methods: DAI salt precursor 6 was labeled employing the common “minimalist” approach with a two-step reaction heating sequence. The Cu-mediated radiofluorination of 4 was accomplished using Bu₄NOTf as a phase transfer catalyst for the elution of [¹⁸F]fluoride, followed by radiofluorination in the same solvent. Several types of SPE cartridges were tested in the elution and SPE procedures. Results: The Cu-mediated ¹⁸F-fluorination of the pinacol aryl boronate precursor afforded a higher RCC of 56 ± 3% (n = 7), making it better suited for the one-pot synthesis of [¹⁸F]SFB. SPE-based purification was achieved using cation exchange and reverse-phase polymer resin cartridges, connected in series. In a full-batch test, [¹⁸F]SFB was obtained with an RCY of 30% (n. d. c.), RCP > 99%, A_m 96–155 GBq/µmol, and a synthesis time of ≤35 min. Conclusions: Compared to other published methods, [¹⁸F]SFB production via the Cu-mediated radiofluorination of pinacol aryl boronate precursor provides significant time and cost savings, coupled with an ease of implementation. Full article

Electrodialysis (ED) has already been applied to recover nickel in galvanizing processes, allowing nickel recovery and the production of a treated effluent with demineralized water quality. However, the growth in ED use is still limited by the production and commercialization of ion-selective membranes, currently limited to a few large companies. Therefore, this paper presents the development of homogeneous cationic and anionic membranes made from poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) for ED use. Cationic membranes were prepared by the sulfonation reaction of PPO under different experimental conditions (PPO:H₂SO₄ molar ratio and reaction time). Anionic membranes were prepared by the bromination reaction of PPO, followed by the amination reaction. The membranes were characterized for their chemical and electrochemical properties, including ion exchange capacity, conductivity, thermal stability, and surface morphology. The optimal conditions for cationic membrane sulfonation were achieved with a 1:4.4 PPO:H₂SO₄ molar ratio, and a reaction time of 0.5 h. For anionic membranes, the best results were obtained with bromination, with a PPO:NBS (N-Bromosuccinimide) molar ratio of 1:0.5, followed by 14 days of amination. Overall, 91.8% chloride, 90.9% sulfate, and 85.5% nickel ion extraction was achieved, highlighting PPO as a promising polymer for the development of anionic and cationic ion-selective membranes for ED. Full article

Improving saline soils’ properties by incorporating limes is a practical technique, generally due to cation exchange, pozzolanic reaction, and carbonation. This study explores how soil salinity, measured by electrical conductivity, affects untreated and lime-treated saline soils. An Algerian sebkha soil (from Ain M’lila) with an original high salinity (ECe3 = 23.2 dS.m⁻¹) was used. The same soil was washed to create medium (ECe2 = 8.3 dS.m⁻¹) and low (ECe1 = 2.32 dS.m⁻¹) salinity soil samples. The results of this study indicate that salinity influenced the shape of the particle size distribution curve, particularly in the silt range. Salinity also had a significant effect on carbonate content (CaCO₃) and unconfined compressive strength (UCS). For the untreated soil, when salinity decreased, the UCS and CaCO₃ content increased. However, when salinity decreased for the treated soil, the UCS increased, while the CaCO₃ content decreased. X-ray diffraction (XRD) analysis of untreated soils showed halite (NaCl) disappearance and gypsum (CaSO₄ 2H₂O) reduction with decreasing salinity in ECe1. In treated soil at ECe3, these mineral phases remained constant. While XRD detected no new cementitious phases in treated ECe3 or ECe1 samples, thermogravimetric analysis confirmed the presence of portlandite in both. As Ain M’lila sebkha is a chloride–sulfate soil, the dissolution of the halite and gypsum phases released more Cl⁻ and SO₄²⁻ ions into the interstitial solution. In a low fraction of clay, these ions obstructed and slowed the pozzolanic reaction in the ECe3 soil. Identifying the season when this type of soil has lower salinity can be beneficial for treatment from a technical, economic, and environmental point of view. Full article

The industrial processes used to produce paper and cellulose generate many lignocellulosic residues. These residues are usually burned to produce heat to supply the energy demands of other processes, increasing greenhouse gas emissions and resulting in a high environmental impact. Instead of burning these lignocellulosic residues, they can be converted into saccharides, which are feedstock for high-value products and biofuels. Keggin heteropolyacids are efficient catalysts for obtaining saccharides from cellulose and hemicellulose and converting them into bioproducts or biofuel. Furfural, 5-hydroxymethylfurfural, levulinic acid, and alkyl levulinates are important platform molecules obtained from saccharides and raw materials in the biorefinery processes used to produce fine chemicals and biofuels. This review discusses the significant progress achieved in the development of the processes based on heteropolyacid-catalyzed reactions to convert biomass and their residues into furfural, 5-hydroxymethylfurfural, levulinic acid, and alkyl levulinates in homogeneous and heterogeneous reaction conditions. The different modifications that can be performed to a Keggin HPA structure, such as the replacement of the central atom (P or Si) with B or Al, the doping of the heteropolyanion with metal cations, and a proton exchange with metal or organic cations, as well as their impact on the catalytic activity of HPAs, are detailed and discussed herein. Full article

We examined the effectiveness of metal-exchanged phosphomolybdic acid salts in converting levulinic acid, derived from biomass, into valuable products (alkyl levulinate). We prepared salts of phosphomolybdic acid using different metals (Fe³⁺, Al³⁺, Zn²⁺, Cu²⁺, Mn²⁺, Ni²⁺, and Co²⁺). The influence of metal cations on the conversion and selectivity of the reactions was assessed. We found that the salts prepared with iron and aluminum phosphomolybdate were the most effective catalysts for the esterification of levulinic acid with methanol, with the conversion and selectivity tending towards 100% after 6 h of reaction at a temperature of 323 K. The effect of catalyst loading and its recovery and reuse was evaluated; the results from the reaction using aluminum phosphomolybdate remained similar for four cycles of use. The influence of temperature on conversion and selectivity was investigated between 298 and 353 K. The reactivity of different alcohols with a carbon chain size of C1-C4 was assessed and conversions above 65% were obtained for all alcohols tested under the conditions evaluated, except for tert-butyl alcohol. These catalysts are a promising alternative to the traditional soluble and corrosive Brønsted acid catalysts. The superior performance of these catalysts was ascribed to the higher pH decline triggered by the hydrolysis of these metal cations. Full article