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Employing belt-like ZnSe nanoframes as colorimetric reagents, a colorimetric paper sensor based on the cation-exchange strategy has been developed for the visual determination of heavy metal ions. • A colorimetric paper sensor based on a cation-exchange strategy has been developed for the detection of heavy metal ions. • Due to Ostwald ripening, novel belt-like ZnSe nanoframes have been synthesized via a facile hydrothermal method. • Depending on the color change of the paper sensor, heavy metal ions of Ag+, Cu2+, and Hg2+ can be individually identified. A colorimetric paper sensor based on a cation-exchange strategy has been developed for the visual determination of heavy metal ions. Belt-like ZnSe nanoframes as colorimetric reagents were prepared from ZnSe·0.5N 2 H 4 hybrid nanobelts as precursors via a hydrothermal method. With the decomposition and release of N 2 H 4 ligands, the regular belt-like nanostructures of the precursors evolved into belt-like nanoframes, which consisted of numerous ZnSe nanocrystals. Inspired by the cation-exchange characteristic of chalcogenides, the as-prepared belt-like ZnSe nanoframes were employed to fabricate a colorimetric paper sensor for the detection of heavy metal ions. Owing to the color change arising from a composition change, the colorimetric paper was successfully applied to detect Ag+, Cu2+, and Hg2+ at room temperature. Depending on the color change and its intensity, heavy metal ions of Ag+, Cu2+, and Hg2+ can be individually identified and their concentrations can be determined. Particularly for Cu2+, its visually detected concentration can be down to 1 ppm. More importantly, the fabricated colorimetric paper sensor displays excellent anti-interference properties from various typical cations and anions. Considering its low cost and practicality, expectedly it can be used for practical application. [ABSTRACT FROM AUTHOR]

In this paper, the coal pillar dam body of the underground reservoir in Daliuta coal mine, along with the residual coal and the mine water present in the goaf, were taken as research subjects, and a dynamic simulation experiment device was constructed to simulate the actual process of a coal mine underground reservoir (CMUR). The composition and structure of middling coal during the experiment were determined by X-ray diffraction analysis (XRD) and X-ray fluorescence spectrometry (XRF), while changes in ion content in the mine water were assessed through ion chromatography (IC) and inductively coupled plasma emission spectrometry (ICP-OES). Based on both the composition and structure of coal as well as variations in ion concentrations in water, the interaction mechanism between coal and mine water was explored. The results showed that the water–coal interaction primarily arose from the dissolution of minerals, such as rock salt and gypsum, within coal. Additionally, coal samples in mine water exhibited adsorption and precipitation of metal ions, along with cation exchange reaction. Na+ in mine water predominantly originated from the dissolution of rock salt (sodium chloride) in coal, while Ca2+ and SO 4 2 − were released through the dissolution of gypsum and other minerals in coal. In the process of the water–coal interaction, Ca2+ in the water body was adsorbed and immobilized by the coal sample, leading to the formation and deposition of CaCO3 on the surface of the coal, thereby increasing the calcite content. These processes collectively contributed to a decrease in the concentration of Ca2+ in the water body. Moreover, the cation exchange reaction occurred between Ca2+ and Mg2+ in mine water and Na+ in the coal sample. The presence of Ca2+ and Mg2+ resulted in their displacement of Na+ within the coal matrix, consequently elevating Na+ concentration in the mine water while reducing both the Ca2+ and Mg2+ concentrations. On this basis, combined with insights from the water–rock interaction, it can be inferred that the adsorption mechanisms involving rocks played a dominant role in the decrease of Ca2+ concentration during the water–rock interactions. Meanwhile, the dissolution processes of minerals both in the water–rock and water–coal interactions predominantly contributed to the increase of Na+ and Cl− concentrations. [ABSTRACT FROM AUTHOR]

The concentration of heavy metals in soil layers has increased due to the rapid development of the industry. Lead and zinc are two frequent heavy metal contaminants in soil. This paper aims to study the effect of these types of contaminants on different fines, including kaolinite, bentonite, and zeolite mixed with sand. First, mixtures of sand and kaolinite, bentonite, and zeolite were prepared, then they were contaminated by two contaminants of lead and zinc nitrates, separately. Consolidated undrained triaxial tests, Soil Conservation Service (SCS) double hydrometer tests, scanning electron microscope (SEM), Atterberg limits, and pH determination tests were conducted on the soil samples to investigate the changes in the strength and microstructure in the presence of heavy metals. In general, triaxial test results showed that various parameters influence the strength results of these heavy metal-contaminated sandy soil samples such as type, percentage, and structure of the fine portion, type, and concentration of contaminants, bonding mechanism of fine grains, and ion exchange capacity. For instance, in the presence of kaolinite (and kaolinite-zeolite mixtures), contamination with lead decreased the strength of soil samples, but in the soil mixtures containing bentonite (and bentonite-kaolinite mixtures), an opposite trend was seen. The plasticity index of mixtures containing kaolinite and zeolite increased in the presence of heavy metal contaminants, but it decreased when the fine portion of the soil was bentonite. Heavy metal contaminants decreased the pH of all soil mixtures and made them to be acidic. The results of the SCS double hydrometer test and SEM indicated that contaminated kaolinite and zeolite soil mixtures have a dispersed structure, while bentonite soil mixtures are not dispersive. [ABSTRACT FROM AUTHOR]

The study presents a novel integrated three-compartment electrochemical continuous electrodeionization reactor that was constructed in a laboratory environment. In order to extract large amounts of carbon dioxide from naturally occurring oceanwater in the form of bicarbonate and carbonate, it develops a innovative electrolytic cation exchange process. At the same time, it produces hydrogen gas for possible hydrocarbon synthesis. The study employs the Box-Behnken experimental design approach implemented through the Design Expert software to investigate and optimize the performance of electrochemical hydrogen extraction from Ocean water from an integrated reactor. The integrated electrochemical continuous-type electrodeionization reactor comprises two cation-permeable membranes that operate as boundaries between three compartments: a central compartment and electrode compartments that house the cathode and anode, each of which may reverse polarity. These membranes are made of gel polystyrene cross-linked with divinylbenzene, which has acidic properties that allow cation transport while inhibiting anions. The integrated reactor's electrode chambers are enclosed in plexiglass end plates and contain distinct Plexiglass electrode compartments. These compartments have mesh and solid steel anode and cathode electrodes, with an electrode active area of 176.71 cm2. The influence of various factors, such as voltage and electrolyte amount, on the production of hydrogen synthesis is examined. The study results demonstrate a maximum hydrogen production rate of 2.2 mg/min and a hydrogen production efficiency of 7.82%. The lab testing was carried out using experimental equipment to determine viability. The tests included 35-min runs that measured hydrogen generation under various parameters, such as applied voltage, electrolyte concentration, and pH levels. The ocean salt solutions of 0.5M, 1M, and 2M were initially prepared and evaluated for hydrogen generation. Each concentration is assessed at a voltage range of 4–15V, with matching solution pH values ranging from 2 to 7. Optimization studies were conducted to enhance the hydrogen production rate. The results indicate that hydrogen production rises proportionally with applied voltage and electrolyte concentration but falls with pH growth. Within the Design Expert software, the statistical methods for response surface analysis and optimization are utilized accordingly. • The paper develops an integrated three-compartment system for hydrogen production. • The paper investigates the system overall efficiencies for assessment. • It discusses how varying voltage and concentration affects hydrogen production. [ABSTRACT FROM AUTHOR]

This paper demonstrates that intercalating Na+ homoionic vermiculite with Fe3+ polyhydroxy cations (1:1 molar ratio OH− to Fe3+) significantly improved the affinity of the clay mineral-based sorbent toward phosphate. Kinetic experiments revealed that adsorption is fast, approaching an equilibrium within about 200 min of contact time, and that the rate-limiting step is the intraparticle diffusion. Adsorption isotherms fitted to the Freundlich equation and a two-site Langmuir model, consistent with the heterogeneity of adsorption sites. The separation factor derived from the Langmuir constant revealed that the adsorption was favorable and even irreversible for high-affinity minor adsorption sites. The adsorption capacity was 299 ± 63 μmol g−1 (9.3 ± 2.1 mg P g−1), a value similar to several other clay-based phosphate adsorbents. Application to reservoir water spiked with 10 mg L−1 in P removed about 71% of the available phosphate. [ABSTRACT FROM AUTHOR]

N-containing heterocycles (NCHs) are largely used as precursors for pharmaceuticals and can enter the environment. Some NCHs have been shown to be toxic, persistent, and very mobile in the environment. Thus, they have received increasing attention in the past years. However, the analysis of these polar compounds in environmental samples is still a challenge for liquid chromatography. This paper investigates the use of mixed-mode liquid chromatography (MMLC), which has reversed-phase and ion exchange characteristics for measurements of NCHs in water. NCHs with low pKa (i.e., < 2.5) display mainly reversed-phase interactions (neutral species) with the stationary phase and those with higher pKa (i.e., > 5) interact by a mixture of reversed-phase/ion exchange/HILIC mechanism. It was also shown that the presented method performs well in the quantification of the majority of the selected NCHs in surface water with MDLs between 3 and 6 μg/L, a low matrix effect and recoveries in the range of 77–96% except for pyridazine exhibiting 32% were achieved. The method was successfully employed to follow the degradation of NCHs in ozonation. [ABSTRACT FROM AUTHOR]

Currently, the deep geological repository approach for spent nuclear fuel is regarded as the most dependable and secure method for permanently disposing of this kind of waste. Among its key safety components is an engineered barrier made from compacted bentonite, which isolates the encapsulated waste from the surrounding host rock. As a result, understanding how bentonites react to varying compositions of groundwater is crucial. This is where numerical modelling becomes essential. It is generally approved by the scientific community to idealise bentonite as a material structured under a double porosity system composed of the macro and microstructure. In this context, this paper illustrates the capabilities of a double-porosity reactive transport model for bentonites fully implemented in the multiphysics COMSOL platform. For this purpose, different experimental tests were simulated based on the evaluation of diffusive ion transport, mineral dissolution and cation exchange processes in MX-80 bentonite, obtaining very satisfactory results. • A new reactive transport model for bentonites was implemented in COMSOL Multiphysics. • The model includes a geochemical system composed of 14 chemical species and gypsum. • The model considers diffusive-dispersive-advective transport in double-porosity media. • The model validation was run by 3 tests set in the Task Force on Engineered Barrier. [ABSTRACT FROM AUTHOR]

Luminescent quantum dots (QDs) patterns have attracted great attention in anticounterfeiting applications because they can emit fluorescence upon excitation. Here, different from traditional luminescent patterns for anticounterfeiting purposes, a novel strategy based on the reversible cation exchange enabled Ag doped CdS quantum dots (CdS:Ag QDs) is reported to provide a higher security for anticounterfeiting. First, the reversibility of cation exchange enabled doped QDs crystal engineering have been revealed. The switch from nonluminescence to luminescence for several cycles by such a mechanism has been achieved. Second, the hydrophilic doped QDs "ink" can be prepared by surface modification, and then flexible bulk‐sized patterns can be printed on different substrates by inkjet printing technology, such as the parchment paper, PET foil, and paper currency substrates. Third, owing to the characteristic of stable crystal structure of CdS:Ag QDs, the patterns of such doped QDs on substrates can be switched by in situ cation exchange to achieve conversion of the disappearance and recovery of luminescent signals, from which a multiple dual mode anticounterfeiting verification can be provided. [ABSTRACT FROM AUTHOR]

This paper presents a stochastic model for multicomponent competitive monovalent cation exchange in hierarchical porous media. Reactive transport in porous media is highly sensitive to heterogeneities in physical and chemical properties, such as hydraulic conductivity ( K), and cation exchange capacity ( CEC). We use a conceptual model for multimodal reactive mineral facies and develop a Eulerian-based stochastic theory to analyze the transport of multiple cations in heterogeneous media with a hierarchical organization of reactive minerals. Numerical examples investigate the retardation factors and dispersivities in a chemical system made of three monovalent cations (Na, K, and Cs). The results demonstrate how heterogeneity influences the transport of competitive monovalent cations, and highlight the importance of correlations between K and CEC. Further sensitivity analyses are presented investigating how the dispersion and retardation of each cation are affected by the means, variances, and integral scales of K and CEC. The volume fraction of organic matter is shown to be another important parameter. The Eulerian stochastic framework presented in this work clarifies the importance of each system parameters on the migration of cation plumes in formations with hierarchical organization of facies types. Our stochastic approach could be used as an alternative to numerical simulations for 3D reactive transport in hierarchical porous media, which become prohibitively expensive for the multicomponent applications considered in this work. [ABSTRACT FROM AUTHOR]

A geosynthetic clay liner (GCL) was exhumed from a composite liner (geomembrane over GCL containing granular sodium bentonite) in the base of a landfill cell after 12 years of atmospheric exposure. The GCL was altered appreciably during exposure, despite being overlain by a geomembrane. Water content, hydration, and bentonite erosion varied considerably along the slope. GCL samples from the top of the slope were dry, with visible bentonite granules comparable to those in a virgin GCL as if the bentonite had not hydrated. No substantial change in exchange complex or swell index (SI) occurred in samples from the top of the slope, and hydraulic conductivity of these samples to water was low (≈10−11 m/s). GCL samples from the toe of the slope varied considerably, from moist and soft to dry and cracked, but all had undergone hydration, and had low SI, a small mole fraction of monovalent cations in the exchange complex, and high hydraulic conductivity (10−8 m/s or higher). Bentonite in GCL samples from midslope had a cracked structure commonly observed in GCLs that have undergone wet–dry cycling. Midslope GCLs typically had hydraulic conductivity greater than 10−7 m/s. A sample from the top of the slope from a location near a GCL panel separation was comparable to other samples from the top of the slope. GCL samples from the anchor trench differed considerably, being very permeable or having low hydraulic conductivity. Hydraulic conductivity was strongly correlated with SI; GCL samples with SI<15 mL/2 g were highly permeable, and those with SI>15 mL/2 g were comparable to a virgin GCL. The variation in SI was related directly to replacement of sodium by calcium in the exchange complex of the bentonite. Hydraulic conductivity also was affected by the thinning of the GCL. [ABSTRACT FROM AUTHOR]

Interactions at the oil/brine/rock interfaces play a pivotal role in the mobility of crude oil within reservoir matrices. Unraveling the microscopic mechanisms of these interactions is crucial for ion-engineered water flooding in secondary and tertiary oil recovery. In this study, the occurrence and transport behavior of crude oil in kaolinite nanopores covered with thin brine films was investigated by molecular dynamics simulation. There is an apparent interface layered phenomenon for the liquid molecules in slit pores and the polar oil components primarily concentrate at the oil/brine interfacial region and form various binding connections with ions. The interfacial interactions between the polar oil components and brine ions exhibit an inhibitory effect on the transport of crude oil through nanopores. The interaction mechanism between acetic acid molecules and hydrated ions was elucidated by interaction modes and interaction intensity, which was proved to illustrate the flow difference in different brine film systems. Moreover, a strategy of exchanging the binding sites of divalent cations with acetic acid molecules by monovalent cations with a higher concentration was proposed. The cation exchange scheme was further validated, demonstrating an enhancement in the oil mobility within nanopores. These findings deepen our understanding of oil/brine/rock interfacial interactions and provide a significant molecular perspective on ion-engineered water flooding for enhanced oil recovery. [ABSTRACT FROM AUTHOR]

Salt stress seriously hinders the normal growth of plant seedling roots. Magnesium, as one of the essential medium elements for plant growth, can effectively alleviate the damage of salt stress to plant roots, but the key genes involved and their mechanism are still unclear. The purpose of this study was to explore the related molecular mechanism of exogenous magnesium regulating cation homeostasis in peanut seedlings under salt stress. Firstly, according to plant physiology experiments, it was found that exogenous magnesium treatment significantly improved the tolerance of peanut seedlings to salt stress. After that, the transcriptome data were integrated, and further gene expression analysis showed that the expression of genes such as CNGC1, NCLs, and NHX7 was regulated under exogenous magnesium treatment, which effectively reduced the accumulation of sodium ions in cells. At the same time, exogenous magnesium also regulates the expression of genes such as ACAs and POTs and maintains the homeostasis of calcium and potassium ions in cells. These results reveal the molecular mechanism of exogenous magnesium regulating the cation homeostasis of peanut seedlings under salt stress, which provides an important reference for further revealing the key genes of salt tolerance in plants. [ABSTRACT FROM AUTHOR]

Montmorillonite (Mt) is a ubiquitous swelling clay mineral and major component of soft rocks, sediments, and soils with an inherent capability to sorb metal cations. This unique feature renders Mt important for the enrichment and mobilization of environmentally important metal cations, retardation of heavy metals and radionuclide ions, the evolution of clay mineral itself, soils and sediments, and other geological processes. Understanding the interfacial interactions of Mt with metal cations at the molecular level is of fundamental importance in all these processes, but still remains elusive, due to the chemical and structural complexity of Mt surfaces and the diverse chemistries of metal cations. In this Review, we aim to provide the reader with a comprehensive overview of the adsorption modes of metal cations on basal and edge surfaces of Mt, local chemical environments of the cation binding sites, the driving forces for metal sorption, and factors influencing the dynamics of cation uptake onto Mt surfaces. Various surface complexation models [i.e., nonelectrostatic model (NEM), constant capacitance model (CCM), diffuse layer model (DLM), and triple-layer model (TLM)], advanced spectroscopic techniques (i.e., NEM, CCM, DLM, and TLM), and atomistic simulation methods (i.e., MD, DFT, and FPMD) have been used in conjunction with macroscopic adsorption experiments to gain detailed insights into the interfacial interactions of metal cations on Mt. Mt adsorbs metal cations via three independent pathways: (1) cation exchange; (2) surface complexation; and (3) nucleation and surface precipitation. The principal driving force for cation exchange is electrostatic interaction, while chemical bonding governs the two other mechanisms that depend on the basal and edge surface properties of Mt. The siloxane cavities on the tetrahedral basal plane exhibit the strongest adsorption sites for cation exchange and are greatly affected by the the degree of Al3+/Si4+ tetrahedral substitutions. At the amphoteric edge surfaces bearing hydroxyl groups, metal cations could form mono/multidentate surface complexes on Mt [010] and [110] edges. Ionic strength, pH, the presence of competing cations, temperature, and layer charge have been shown to affect the adsorption mechanisms and quantity of adsorbed cations. The updated information on the interfacial interactions of metal cations with Mt basal and edge surfaces presented in this review provides an improved understanding of the enrichment of metals, formation of metal ores, and natural biogeochemical cycles, as well as may promote technological and engineering applications of this important clay mineral in environmental remediation, geological repository, petroleum exploration and extraction, and extraterrestrial research. [ABSTRACT FROM AUTHOR]

The desert of eastern Libya forms one of the most arid regions of the Sahara. Libya suffers from a shortage in water resources due to its arid climate. On the other hand, Libya has large resources of good-quality groundwater distributed in six basin systems beneath the Sahara. In order to deal with the shortage of water in most coastal cities, the Libyan government established the Great Man-Made River Project to transport millions of cubic meters of water a day from desert wellfields to the coastal cities, where over 80% of the population lives. In this paper, a hydrogeochemical study is presented for the Nubian Sandstone Aquifer in Tazerbo Wellfield, SE Libya, based on chemical analyses and physical parameters for 108 wells. Samples were collected from 108 borewells of the Nubian Aquifer (Akakus Formation) from depth range between 280 m in the north and 500 m in the south. This study is the first hydrochemical investigation in Tazerbo and also in the whole Sahara, which introduces the importance of considering the end members and the synsedimentary influence for the interpretation of the groundwater hydrochemistry. The results of the analyses indicate soft to moderately hard, lowly mineralized, slightly alkaline groundwater, with Mg as the main cation and HCO as the main anion. The major hydrogeochemical processes that affect the quality of water in sediments of the Nubian system at Tazerbo have been identified; the water type is mostly fresh MgHCO while NaHCO and KHCO are also found for some wells. These water types indicate that groundwater chemistry is changed by cation exchange reactions during flushing of the aquifer by freshwater from the south. [ABSTRACT FROM AUTHOR]

This paper studies the addition (0-40% w/w) of natural zeolite (NZ, 84% clinoptilolite) in blended cements made with Portland cement (PC) with low and medium CA content. The isothermal calorimetry was used to understand the effect of NZ on the early cement hydration. For low CA cement, the addition of NZ produces mainly a dilution effect and then the heat released curve is similar to plain cement with lower intensity. For medium CA cement, the curve shows the CS peak in advance and a high intensity of third peak attributed to CA hydration. The high cation fixed of NZ reduces the ions concentration (especially alkalis) in the mixing water stimulating the PC hydration. The flowability decreases when the NZ replacement level increases. Results of Fratini's test show that NZ with both PCs used presents slow pozzolanic activity. At early age, XRD and FTIR analyses confirm that hydration products are the same as that of the corresponding PC and the CH is progressively reduced after 28 days and some AFm phases (hemi- and monocarboaluminate) appear depending on the NZ percentage and the PC used. For low replacement levels, the compressive strength is higher than the corresponding PC from 2 to 28 days. For high replacement levels, the early compressive strength is lower than that of corresponding plain PC and the pozzolanic reaction improves the later compressive strength of blended cements. [ABSTRACT FROM AUTHOR]

This paper reports the effect of surface modification on the mechanical and morphological properties of palygorskite (PAL) filled natural rubber (NR) nanocomposite. NR/PAL nanocomposites were prepared by co-coagulating rubber latex with clay suspension and after that, compounded with SMR 20 using melt mixing method. The aim is to investigate the efficiency of surface modification via cation exchange treatment on treated NR/PAL nanocomposite properties as compared to untreated NR/PAL nanocomposite. The organo-modified palygorskite was characterized by fourier transform infrared spectroscopy (FTIR) and X-Ray diffraction (XRD). The NR/PAL composites were subjected to cure characteristic, tensile, tear, hardness and scanning electron microscopy (SEM) with energy dispersive x-ray (EDX) testing. The treated NR/PAL nanocomposite showed higher mechanical properties compared to untreated samples. FTIR revealed the functional group from 1-dodecylammonium chloride react with PAL. The dispersion of PAL in the rubber matrix, can be seen clearly using XRD and SEM/EDX. [ABSTRACT FROM AUTHOR]

This paper first time reports the geochemical processes that are controlling fluoride enrichment in the groundwater of western Kumamoto area, Japan. Fifty (50) groundwater samples were collected and analyzed for the study where fluoride (F) concentration ranges from 0.1 to 1.57 mg/L. About 58 % of the shallow groundwater and 26 % of the deep groundwater samples contain fluoride concentration beyond the Japanese drinking water permissible limit (0.8 mg/L). High F is largely accumulated in the stagnant zone of the Kumamoto Plain area and associated with Na-HCO-type groundwater. High pH, high HCO, low Ca, and high Na are the major characteristics of high-F groundwater. Hydrolysis of F-bearing minerals and desorption of F from hydrous metal oxides are considered to be the primary sources of fluoride in groundwater. A positive correlation between F and Na/Ca ratio ( r = 0.53) indicates that major ion chemistry plays a significant role in fluoride mobilization. Weakly alkaline nature of groundwater with high pH (7.05-9.45) expedites the leaching process of exchangeable F from F-bearing minerals as well as favors desorption of F from metal oxide surfaces. High HCO and high PO in the groundwater facilitate desorption process as competing anions, while high Na/Ca ratio largely control this process by decreasing positive-charge density of the metal-oxide surfaces. High Na/Ca ratio is attributed due to the cation-exchange process, while high pH and HCO are the result of both silicate hydrolysis and microbial reduction processes. In addition, calcite and fluorite seem to have a control on groundwater fluoride geochemistry. [ABSTRACT FROM AUTHOR]

Two primary mechanisms of titanium dioxide (TiO2) efficiency inhibition in ultraviolet (UV)‐driven photocatalytic reactions are the high recombination rate and sintering. To address these challenges, TiO2 nanocrystals were grown in‐situ onto sepiolite modified with MnII and EuIII ions. The resulting nanocomposites were characterized and evaluated for photocatalytic activity for Orange G (OG) degradation under UV irradiation. Resultant reduction in activity over Mn‐sepiolite‐TiO2 is attributed to charge‐carrier scavenging by unstable Mn and adsorption‐mediated chromophore protection by Mn‐oxyhydroxide. Dye removal over Eu‐sepiolite‐TiO2 was only slightly more efficient than over the control despite relevant Eu concentrations; potentially related to inhibited TiO2‐Eu interfacial synergy and superoxide radical scavenging. The results of this investigation corroborate prior observations that substrate cation‐exchange results in unpredictable behavior of the cations introduced during subsequent fabrication steps which may be of benefit or detriment to the final material. [ABSTRACT FROM AUTHOR]

Bicarbonate ions (HCO3−) are abundant in karst water with poor lead (Pb) utilization and biodegradation. This study aimed to investigate the mechanism of HCO3− on the Pb removal efficiency and uptake ability of Pontederia crassipes (a widespread hydrophyte in the karst area) from karst water. The Pb concentration, Pontederia crassipes morphology, and functional group were detected. As the HCO3− molarity in karst water increased (3, 4, and 5 mmol/L), the removal of Pb increased (85.31%, 93.28%, and 95.16%), whereas the bioconcentration amount of Pb decreased (573, 501, and 301 mg/kg), mainly due to the insoluble PbCO3 and Pb (OH)2. The Pb bioconcentration factor was the highest (15,564) at 4 mmol/L HCO3− due to the maximum strength of cation exchange and cell wall protein C=O. High HCO3− molarities changed the variety of positive ions of cation exchange (HCO3− ≤ 4 mmol/L: Na, K, and Mg; HCO3− > 4 mmol/L: Mg and K), and relieved the breaking of roots, stomatal closure, and vascular system shrinking. Moreover, high HCO3− molarities diminished the C≡C oxidation, enlarged the displacement of SO42− and C-O, and stimulated the methyl transfer reaction and the bonding between -CH3 and Pb. [ABSTRACT FROM AUTHOR]

In situ diffusion experiments are performed in underground research laboratories for understanding and quantifying radionuclide diffusion from underground radioactive waste repositories. The in situ diffusion and retention, DR, experiment was performed at the Mont Terri underground research laboratory, Switzerland, to characterize the diffusion and retention parameters of the Opalinus clay. Several tracers were injected instantaneously in the circulating artificial water and were then allowed to diffuse into the clay rock through two porous packed-off sections of a borehole drilled normal to the bedding of the clay formation. This paper presents a single-site multicomponent reactive transport model of Cs, a tracer used in the DR experiment which sorbs onto Opalinus clay via cation exchange. The reactive transport model accounts for the diffusive-reactive transport of 11 primary species and 22 aqueous complexes, and the water-rock interactions for 5 cation exchange and 3 mineral dissolution/precipitation reactions. Most of the solutes except for Cs diffuse from the Opalinus clay formation into the injection interval because the concentrations in the initial Opalinus clay pore water are larger than those of the initial water in the circulation system. Calcite dissolves near the borehole while dolomite precipitates. Dissolved Cs sorbs by exchanging with Ca in the exchange complex. The computed dilution curve of Cs in the circulating fluid is most sensitive to the effective diffusion, D, of the filter, the selectivity coefficient of Na to Cs, K and D of the borehole disturbed zone. The apparent distribution coefficient of Cs, $$K_{\text{d}}^{\text{a}}$$ , in the formation varies in space and time from 100 to 165 L/kg due to the temporal changes in the water chemistry in the formation. The results of a sensitivity run in which the initial chemical composition of the Opalinus pore water is the same as the initial chemical composition of the water in the circulation system show that the changes in $$K_{\text{d}}^{\text{a}}$$ are negligible. The dilution curve of Cs computed with the reactive transport model coincides with that obtained with the K model. The tracer concentrations along the overcoring profiles computed with the K model, however, differ significantly from those computed with the reactive transport model. Therefore, a reactive transport model is needed for the appropriate interpretation of the Cs overcoring data from the DR diffusion experiment. [ABSTRACT FROM AUTHOR]

This paper focuses on the Qareh Sou Basin in Golestan Province, Iran. Golestan Province is the third largest cereal producer in Iran and water scarcity and salinity are major problems in this area. This study attempts to facilitate the comprehension of system behavior with respect to water quality issues and hydro-geochemical coefficients within the Qareh Sou Basin. This study was carried out during the year 2010. Various parameters, such as pH, EC, chloride, sulfate, bicarbonate, sodium, potassium, calcium and magnesium have been determined for evaluation purposes. Then, Ca/Mg, Na/Cl, Mg/(Ca + Mg), Ca/HCO, (Ca + Mg)-(HCO + SO), (Na + K)-Cl, (Ca + Mg + Na + K)-Cl, HCO + SO, Ca + Mg and chloro-alkaline indices (CAI) were calculated. Results show that cation exchange probably is an important factor in the hydrochemistry and silicate mineral weathering. Also, CAI-1 plot against CAI-2 demonstrates that most of samples have positive values which suggest normal ion exchange in the system. The carbonic acid is the main agent of calcite, limestone and dolomite weathering which occurs in some stations. According to Chadha's diagram, the type of water is determined as Ca-Mg-HCO. [ABSTRACT FROM AUTHOR]

Lead chalcogenide nanoplatelets (NPLs) have emerged as a promising material for devices operating in the near IR and IR spectrum region. Here, we first apply the cation exchange method to PbSe/PbS core/shell NPL synthesis. The shell growth enhances NPL colloidal and environmental stability, and passivates surface trap states, preserving the main core physical properties. To prove the great potential for optoelectrical applications, we fabricate a photoconductor using PbSe/PbS NPLs. The device demonstrates enhanced conductivity and responsivity with fast rise and fall times, resulting in a 13 kHz bandwidth. The carrier transport was investigated with the field effect transistor method, showing p-type conductivity with charge mobility of 1.26 × 10−2 cm2·V−1·s−1. [ABSTRACT FROM AUTHOR]

This paper provides insight into the quality of groundwater used for public water supply on the territory of Kikinda municipality (Vojvodina, Serbia) and main processes which control it. The following parameters were measured: color, turbidity, pH, KMnO consumption, TDS, EC, NH, Cl, NO, NO, Fe, Mn, total hardness, Ca, Mg, SO, HCO, K, Na, As. The correlations and ratios among parameters that define the chemical composition were determined aiming to identify main processes that control the formation of the chemical composition of the analyzed waters. Groundwater from 11 analyzed sources is Na-HCO type. Intense color and elevated organic matter content of these waters originate from humic substances. The importance of organic matter decay is assumed by positive correlation between organic matter content and TDS, HCO content. There is no evidence that groundwater chemistry is determined by the depth of captured aquifer interval. The main processes that control the chemistry of all analyzed water are cation exchange and feldspar weathering. [ABSTRACT FROM AUTHOR]

This paper systematically investigated the interference of calcium and magnesium in protein measurement with a modified Lowry method first proposed by Frølund et al. (Appl Microbiol Biotechnol 43:755-761, ). This interference has in the past been largely ignored resulting in variable and unreliable results when applied to natural water matrices. We discovered significant formation of calcium and magnesium precipitates that lead to a decline in light absorbance at 750 nm during protein determination. Underestimation of protein concentration (sometimes even yielding negative concentrations) and low experiment reproducibility were demonstrated at high concentrations of divalent cations (e.g., [Ca] over 1 mmol L). To eliminate interference from calcium and magnesium, two pretreatment strategies were established based on cation exchange and dialysis. These pretreatments were convenient and were found to be highly effective in removing calcium and magnesium in protein samples. By using the modified Lowry method with these pretreatments, proteins in standard solutions and in wastewater samples were successfully quantified with good reliability and reproducibility. In addition, we demonstrated that simultaneous quantification of humic substances with the modified Lowry method was not affected by the two pretreatments. These approaches are expected to be applicable to protein and humic substance determination in different research fields, in cases where the modified Lowry method is sensitive to divalent cation concentrations. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Hydroxyapatite/biochar nanocomposites (HAP/BC-NCs) were hydrothermally synthesized. • HAP/BC-NCs were used for Cu(II) removal and exhibited high adsorption affinity. • The adsorption rate of Cu(II) was mainly controlled by film diffusion mechanism. • The maximum adsorption capacity was determined to be 99.01 mg/g at 298 K. • Adsorption mechanism involved cation exchange and inner-sphere surface complexation. Abstract In this study, hydroxyapatite/biochar nanocomposites (HAP/BC-NCs) were synthesized through a simple one-pot hydrothermal process and utilized as an adsorbent for the removal of copper(II) from aqueous media. Characterization results revealed that rod-shaped HAP nanoparticles were successfully incorporated on the surfaces of synthesized HAP/BC-NCs. A set of systematically designed batch experiments were carried out to determine the influences of adsorbent dosage, solution pH, ionic strength, and temperature on the adsorption behavior of the HAP/BC-NCs. Overall findings from batch experiments and extended X-ray absorption fine structure analysis demonstrated that the potential mechanisms responsible for the removal of Cu(II) from aqueous media are cation exchange between Cu2+ in solution and Ca2+ in the HAP on the surfaces of the as-synthesized nanocomposites and the formation of inner-sphere surface complexes on the surfaces of the HAP/BC-NCs. Kinetic studies revealed that the adsorption process follows the pseudo-second-order model and that the overall adsorption rate is controlled by film diffusion as the dominant mechanism and intraparticle diffusion as a secondary mechanism. Adsorption isotherms were accurately represented by a Langmuir isotherm model and the maximum adsorption capacity was determined to be 99.01 mg/g at 298 K, which represents a higher efficiency for Cu(II) adsorption compared to previously reported composite materials. Thermodynamic analysis indicated that the process is thermodynamically spontaneous and endothermic process. Overall, the findings presented in this paper suggest that HAP/BC-NCs have promising applicability for the removal of heavy metals from aqueous media as an alternative, low-cost, and eco-friendly adsorbent for environmental remediation. [ABSTRACT FROM AUTHOR]

Abstract Constraining sources and site-specific processes of trace elements in speleothem geochemical records is key to an informed interpretation. This paper examines a 10-year data set of drip water solutes from Harrie Wood Cave, south-eastern Australia, and identifies the processes that control their response to El Niño-Southern Oscillation events which varies the site water balance. The contributions of aerosol and bedrock end-members are quantified via hydrochemical mass balance modelling. The parent bedrock is the main source for the drip water solutes: Mg, Sr, K and trace elements (Ba, Al, V, Cr, Mn, Ni, Co, Cu, Pb and U), while atmospheric aerosol inputs also contribute significantly to drip water trace elements and Na, K and Zn. A laboratory investigation evaluating water-soluble fractions of metals in soil samples and soil enrichment factors provided a basis for understanding metal retainment and release to solution and transport from the soil zone. These results identified the role of the soil as a sink for: trace metals, Na and K, and a secondary source for Zn. Further, soil processes including: cation exchange, K-fixation, metal adsorption to colloids and the release of Zn associated with organic matter degradation further modify the chemical composition of the resultant drip waters. This research is significant for the south-eastern Australian region, as well as other sites in a karst setting with clay-rich soil. In particular these results reveal that the response of drip water chemistry to hydroclimatic forcing is non-linear, with the greatest response observed when the long-term gradient in the cumulative water balance reverses. This longer-term drip water monitoring dataset is significant because it provides the pivotal framework required to reliably identify suitable trace element proxies for interpretation in geochemical speleothem records on multi-decadal timescales. Graphical abstract Unlabelled Image Highlights • Atmospheric inputs contribute to drip water: Na, K, Zn and other trace elements. • K-fixation in soils controlled drip water K during the Millennium Drought. • Na and K respond to soil processes and to higher water flux at drought termination. • Zn colloidal mobilisation is linked to a decrease in soil pH. • Na, K and Zn show promise as speleothem palaeo-climate proxies. [ABSTRACT FROM AUTHOR]

This paper presents the preparation and characterization of the smectite clay Laponite modified by intercalation of dimethyldioctadecylammonium chloride and the cationic dye methylene blue. The modified clay (Laponite Blue) has been characterized by FT-IR, X-Ray diffraction, thermogravimetric analysis, SEM and solid state NMR. The exploitation of several characterization techniques and of an extended multinuclear and multi-technique solid state NMR approach allowed us to obtain detailed information on the intercalation of the dye in the clay and the structural and dynamic properties of the organicinorganic interface between the clay surface and the organic modifiers. Laponite Blue appears interesting for the future preparation of polymer nanocomposites with good mechanical and barrier performances as well as exploitable optical properties. [ABSTRACT FROM AUTHOR]

Geosynthetic clay liners (GCLs) are used in landfill liner applications and there is a need for a better control of the properties of the bentonite in the GCL received on site, particularly in the European context where a wide variety of bentonites can be encountered. This paper presents the results of a project aimed at a rapid identification of the nature of the bentonite in a given GCL. The interaction between the bentonite and the fluid was increased by producing dispersions then testing its structure within a few hours with filter press tests and flow curves. The results of those tests were compared with swell index tests, electrical conductivity values and oedopermeametric tests. Eight GCLs were studied. Two of these GCLs contained natural calcium bentonites; they presented poor swelling properties and high permittivities. The dispersions had a low viscosity and their filtration under pressure led to large amounts of filtrate. A further two GCLs contained natural sodium bentonites and the remaining four contained sodium-activated calcium bentonites. Their permittivities, swell indices and filtrate masses were similar; however, their rheometrical behaviours were different due to a difference in the values of electrical conductivity. Thus it seems that electrical conductivity measurements and rheological tests can provide a good and fast way of identifying the nature of the bentonite contained in GCLs. [ABSTRACT FROM AUTHOR]

Statistical analysis can be an important tool to identify and classify different sources of groundwater salinisation. This paper refers to the application of Stepwise Discriminant Analysis (SDA) as an effective technique for the identification of major constituent ratios which can be used for efficiently identifying various salinity sources. The effectiveness of the SDA method was tested on five groups of groundwater samples known for their salinisation. Three were taken from the brackish groundwater of the Nestos River delta, from the geothermal field of Nea Kessani and the brackish groundwater of the western coastal area of Rhodope, in Greece. The remaining two groups were taken from bibliographic sources and they refer to the degraded groundwater of the Wittmund area in coastal NW Germany as well as from the underground brines of Sichuan Basin in China. The method of SDA has demonstrated its effectiveness of classifying different groundwater groups, and its usefull contribution to the groundwater contamination. In this way, possible expensive field investigations and analyses of chemical parameters can be eliminate. [ABSTRACT FROM AUTHOR]

Owing to their favorable properties, ionic liquids have recently gained recognition as possibly environmentally benign solvents. Now among the most promising industrial chemicals, they have already been labeled “green”, but this appellation seems due entirely to their very low vapor pressure. This growing interest in the various applications of ionic liquids will soon result in their presence in the environment. Therefore, reliable analytical tools for the environmental analysis of ionic liquids need to be developed urgently. This paper presents a newly developed analytical procedure for the enrichment of 1-alkyl- and 1-aryl-3-methylimidazolium ionic liquids from water samples. The method is based on cation exchange solid-phase extraction followed by selective elution. Pre-concentrated samples are subjected to high-performance liquid chromatography (HPLC) with an advanced methodology for qualitative and quantitative analysis. The overall procedure was verified by using standard spiked samples of tap water, seawater, and freshwater. [ABSTRACT FROM AUTHOR]

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In this paper, titanate nanotubes/cobalt ferrite/tetraethylenepentamine (TNTs/CoFe 2 O 4 /TEPA) adsorbents were prepared for the adsorption of uranium (VI) from the solution. Its morphology was observed by transmission electron microscopy (TEM) and exhibited the uniform well tubular structure. TNTs/CoFe 2 O 4 /TEPA composites were easily separated from solution by an external magnetic field. The removal of uranium (VI) from aqueous solution (ppm level) and simulated seawater (ppb level) were investigated by the TNTs/CoFe 2 O 4 /TEPA composites. Batch adsorption experiments were conducted to determine the effect of varying pH, contact time, and reaction temperature. The best fit for uranium (VI) adsorption was obtained with the Langmuir model, and the highest adsorption of TNTs/CoFe 2 O 4 /TEPA composites reached 509.89 mg-U/g-adsorbent at pH 6. From an investigation of the adsorption by XRD, FTIR and XPS, it is suggested that the surface complexation and cation exchange were the main adsorption mechanism. In addition, TNTs/CoFe 2 O 4 /TEPA composites maintained good adsorption properties after five sorption-desorption cycles. Therefore, we conclude that the adsorbents are promising materials for the removal of uranium (VI) from aqueous solutions. [ABSTRACT FROM AUTHOR]