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This work found that rectorite (REC) has a good adsorption effect on cationic pollutants such as ciprofloxacin (CIP), with a maximum adsorption capacity of 79.73 mg/g for CIP. The zeta potential analysis showed that the electronegativity of the REC surface would be weakened after CIP adsorption under acidic conditions. Through adsorption kinetics, isotherm study, XRD, FTIR, and other characterizations, the phenomenon of reduced negative charge on the surface of REC adsorbed with CIP under acidic conditions was explained. Based on the Langmuir and Temkin models, the adsorption process of CIP on REC is a spontaneous endothermic adsorption process. The adsorption kinetics can be better described using a pseudo-second-order model, indicating that the adsorption rate is mainly controlled by chemical adsorption. The characterization further proved that REC adsorbed ciprofloxacin mainly through hydrogen bonding, cation exchange, and electrostatic gravitational interaction. CIP, as an emerging contaminant discharged into the water environment, will be harmful to the ecological environment and human health. Therefore, the utilization of REC for the removal of CIP from an aqueous solution has potential prospects. [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]

Clinoptilolite (CLN) from Bigadiç and that of calcined forms after NH4NO3 modification were investigated to demonstrate their possible usability in industrial applications. -modified forms were prepared using 0.2, 1.0, and 2.0 M NH4NO3 solutions at 90°C for 3 and 6 h, and then all samples were calcined at 400°C for 13 h. All samples were characterized using XRD, XRF, SEM and nitrogen adsorption methods. BET specific surface areas (17.8–272.9 m2 g–1) and total pore volumes (0.055–0.197 cm3 g–1) of the clinoptilolites were calculated from nitrogen adsorption isotherms obtained at 77 K by 3Flex (Micromeritics) equipment volumetrically. After increasing the molarity and processing time of the ammonium nitrate solutions, the calcination of the samples significantly affected both morphological and textural features. Compared to starting material, XRD peaks of the samples calcined at 400°C broadened and agglomeration of clinoptilolite crystals decreased. In addition, calcined clinoptilolite samples showed different ammonia adsorption capacities (4.853–5.388 mmol g–1). [ABSTRACT FROM AUTHOR]

This work reports the use of smectite clays (raw and modified samples) as adsorbents in the adsorption process for removing benzene, toluene, and metal ions present in wastewater generated in the petrochemical industries. Smectite clay was used in the adsorption of organic compounds and in the cation exchange process for the removal of heavy metal ions Cu(II) and Pb(II) as a post-treatment process for refinery effluents. From the chemical treatment of raw smectite clay with sodium carbonate (Na-modified smectite clay, Na-MSC) it has been achieved a good exchange of Ca(II) and Mg(II) ions for Na(I). Moreover, characterization analysis evidenced that the raw smectite and Na-MSC had mesoporous structure. The number of exchangeable ions increased from 81.34 to 89.39 meq 100 g−1 after Na-addition. The adsorption and cation exchange experiments were conducted in batch mode using the sodium clays as adsorbents in the kinetic and equilibrium study. The isotherm of Langmuir–Freundlich was the most representative, and the adsorption capacity monolayer for benzene and toluene were 7.28 and 7.39 mg g−1. The ionic exchange model was applied to represent the removal of Cu(II) and Pb(II), which indicated a capacity of 0.99 mg g−1 and 1.10 mg g−1 respectively. Kinetic constants obtained for benzene and toluene were 0.0016 L mg−1 min−1 and 0.019 L mg−1 min−1. Finally, Na-MSC obtained kinetic constants 0.049 L mg−1 min−1 and 0.063 L mg−1 min−1 for Cu(II) and Pb(II) respectively. The results acquired in batch experiments evidence the high efficiency of Na-MSC to remove BTEX and heavy metals from wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ranitidine (RT) removal from water by natural Ca-montmorillonite (SAz-1) was studied. • Maximum RT adsorption value was 369.2 mg/g. • Cation exchange was the main mechanism for RT removal. • Molecular morphology of RT was crucial for its interaction with SAz-1. Adsorption behavior of ranitidine hydrochloride (RT) on a Ca-montmorillonite (SAz-1) was studied in aqueous system through batch experiments. The adsorption kinetics revealed that the equilibrium reached within 0.25 h and the data fitted well to the pseudo-second order kinetic equation (R2 = 0.98). The maximum RT adsorption capacity of SAz-1 was 369.2 mg/g and the adsorption isotherm data followed the Langmuir model (R2 = 0.99). The adsorption of RT and desorption of exchangeable cations from the clay mineral were linearly correlated, suggesting that cation exchange was the dominant mechanism of RT adsorption. The XRD examination of RT-adsorbed SAz-1 samples (unsaturated/saturated) after heating enabled the calculation of RT occupied area in the interlayer of the clay mineral. The results suggested that adsorbed-RT at low loading rate could lay on the internal surfaces in a free style to reduce the basal spacing (d 001 value) of SAz-1. When the RT loading rate was increased, a limited surface space enforced more RT molecules to lay in a tilted style and caused interlayer swelling of SAz-1 increasing the d 001 value. The trend of rising decomposition temperature of RT with increasing RT loading rates confirmed intercalation of RT molecules in SAz-1. Infrared spectral analysis revealed the participation of amide and furan groups of RT in binding between RT and SAz-1. Thus, this study indicated that SAz-1 is an efficient adsorbent to remove RT from contaminated water, and the chain-like molecular structure of RT could cause an irregular change in the basal spacing of swelling type clay minerals. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) is a toxic heavy metal with very low permissible exposure limits and is, thus, a very dangerous pollutant for the environment and public health and is considered by the World Health Organisation as one of the ten chemicals of major public concern. Adsorption onto solid phases and (co)precipitation processes are the most powerful mechanisms to retain pollutants and limit their migration; thus, the understanding of these processes is fundamental for assessing the risks of their presence in the environment. In this study, the immobilisation of Cd by smectite clay has been investigated by batch sorption tests, and the experimental data were interpreted with a thermodynamic model, including cation exchange and surface complexation processes. The model can describe the adsorption of Cd in smectite under a wide range of experimental conditions (pH, ionic strength, and Cd concentration). Under the conditions analysed in this study, the precipitation of otavite (CdCO3) is shown to have a limited contribution to Cd immobilisation. [ABSTRACT FROM AUTHOR]

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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]

Lithium (Li) isotopes have shown large potential in tracing weathering in various water bodies, but there is limited study on Li isotopes in subsurface conditions where CO 2 has been largely consumed. In this study, we use a thick sandstone aquifer in the Ordos Basin, NW China, as a natural setting to investigate the behaviors of Li isotopes in hydrogeochemical conditions with different concentrations of dissolved CO 2. For young groundwater in the recharge area (group R) where CO 2 is abundant (mean P CO2 = 10-2.5 atm), clay formation accompanying with weathering leads to the enrichment of 7Li in groundwater. The four deep samples in the recharge area have uniform Li/Na ratios (with a mean of 2.52 μmol/mmol) and δ7Li (with a mean of 25.0‰), corresponding to a mean Li removal rate of 81.2% compared with the sandstone leachate. For groundwater in the shallow part of the discharge area (group D1), Li was firstly removed by clay formation during weathering in the recharge area and was later removed by physisorption when CO 2 becomes much lower (mean P CO2 = 10-3.1 atm). Different degrees of weathering lead to a wide range of δ7Li varying from 19.7‰ in the deepest well to 33.0‰ in the shallowest well. The proportion of Li removal caused by physisorption is found to increase with groundwater age. After the stage of Li removal by adsorption, Li was released in the deeper part of the discharge area (group D2), and the positive correlation of δ7Li versus Li/Na is explained by a ternary mixing model. The endmember of water brought by cation exchange is inferred to have a heavier δ7Li than sandstone leachate, demonstrating that cation exchange could cause an enrichment of 7Li in water. This study enhances our understanding of the controlling factors of Li isotopes in deep groundwater with low dissolved CO 2 , which have implications for the application of Li isotopes in subsurface water. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) is a toxic heavy metal with very low permissible exposure limits and is, thus, a very dangerous pollutant for the environment and public health and is considered by the World Health Organisation as one of the ten chemicals of major public concern. Adsorption onto solid phases and (co)precipitation processes are the most powerful mechanisms to retain pollutants and limit their migration; thus, the understanding of these processes is fundamental for assessing the risks of their presence in the environment. In this study, the immobilisation of Cd by smectite clay has been investigated by batch sorption tests, and the experimental data were interpreted with a thermodynamic model, including cation exchange and surface complexation processes. The model can describe the adsorption of Cd in smectite under a wide range of experimental conditions (pH, ionic strength, and Cd concentration). Under the conditions analysed in this study, the precipitation of otavite (CdCO3) is shown to have a limited contribution to Cd immobilisation.

[Display omitted] • Natural Na-montmorillonite (SWy-2) adsorbed 0.88 meq/g amitriptyline (AMI) from water. • AMI adsorption was fast (<4h) and exceeded the clay mineral's CEC. • AMI removal was mainly via a cation exchange mechanism. • AMI removal was unaffected by pH in the range 2–11. • Amine groups and benzene rings in AMI controlled molecular orientation in the clay interlayer. Amitriptyline (AMI) is one of the most common tricyclic antidepressant personal care medications. Due to its environmental persistence and bioaccumulation, release of AMI into the environment via wastewater streams in elevated levels could lead to significant ecological and human health impacts. In this study, the adsorption of AMI by montmorillonite (SWy-2), a naturally abundant smectite clay with sodium ions as the main interlayer cations, was investigated. Maximum AMI adsorption (276 mg/g) occurred at pH 7–8. After adsorption, examination of the adsorbent's X-ray diffraction pattern indicated that interlayer expansion had occurred, where chemical stoichiometry confirmed cation exchange as the principal adsorption mechanism. AMI adsorption reached equilibrium within 4 h, with kinetic data best fitting the pseudo-second order kinetic model (R2 = 0.98). AMI adsorption was unaffected by solution pH in the range 2–11, where adsorption was endothermic, and molecular simulations substantiated by Fourier transform infrared spectroscopy and thermogravimetric investigations indicated that the orientation of AMI molecules in the interlayer was via an amine group and a benzene ring. Overall this research shows that SWy-2 has significant potential as a low cost, effective, and geologically derived natural material for AMI removal in wastewater systems. [ABSTRACT FROM AUTHOR]

One of the major issues in surveying the sorption and mobility of elements is awareness of the behavior and reactions of elements in soils and their distribution coefficient (Kd) values. This study was conducted to investigate the adsorption of potassium (K), sodium (Na), calcium (Ca), and magnesium (Mg) in six calcareous soils saturated with mentioned cations. The initial equivalent fraction of K, Na, Ca, and Mg in solutions increased from 0.1 to 1 at a total electrolyte of 30 meq L−1. The shape of isotherm curves and the amount of cations adsorbed varied in different binary exchange systems. The adsorption of cations increased gradually with increasing initial concentrations. The average values of Kd (L kg−1) in different binary systems were arranged in the following order: Ca-Mg (23.4) > Mg-Na (21.5) > Mg-K (20.7) > Mg-Ca (20.1) > Ca-Na (16.0) > Ca-K (15.4) > K-Mg (5.6) > K-Na (5.0) > K-Ca (4.6) > Na-Ca (2.7) > Na-Mg (1.9) > Na-K (1.7). The average values of Gaines-Thomas selectivity coefficients of cations in different binary exchange systems followed this order: K-Ca (16.5) > K-Mg (7.8) > Ca-Mg (4.1) > Mg-Ca (3.1) > Mg-Na (2.1) > K-Na (1.7) > Mg-K (1.0) > Ca-Na (0.8) > Ca-Na (0.6) > Na-Ca (0.5) > Na-Mg (0.1) = Na-K (0.1). So, the affinity of cations for adsorption by soils followed this order: K > Ca > Mg > Na which differed from the classical lyotropic series. The high affinity of K for adsorption by soils was attributed to the presence of illite. The free cations were the most abundant species (above 90%) in all soil solutions after reaching equilibrium with initial concentrations of 3 and 30 meq L−1. The saturation index (SI) values of minerals in all exchange systems were negative. [ABSTRACT FROM AUTHOR]

Illite, smectite and illite/smectite mixed layers are major phases in various argillaceous rock formations foreseen as potential host rocks for the deep geological disposal of high-level radioactive waste and are important sorbents for cationic radionuclides potentially released in the repository. 226Ra is a critical radionuclide in the safety analysis and an important source of radioactivity in technically enhanced naturally occurring radioactive materials. A comprehensive study was carried out on the adsorption of Ba and Ra on purified homoionic Na-illite (Illite du Puy) over a wide range of experimental conditions (pH, concentration, ionic strength) allowing for the development of a quasi-mechanistic Ba/Ra adsorption model for illite. Ba adsorption isotherms obtained at fixed ionic strength and pH exhibit a non-linear behaviour in the Ba equilibrium concentration range between ∼10−7 and ∼10−2 M. The pH dependent adsorption of trace 226Ra and Ba was investigated at different ionic strengths and evidenced a more pronounced adsorption of 226Ra than Ba on illite. Finally, a competition experiment of trace 226Ra in the presence of increasing Ba concentrations showed an unexpected 226Ra adsorption behaviour which was not observed for montmorillonite in earlier studies. This large set of experimental data could be successfully modelled by Ba/226Ra exchange reactions against Na, together with selectivity coefficients, on two different site types, namely planar sites and high affinity sites. The modelling of the pH dependent adsorption of Ba and 226Ra at high ionic strength and high pH required an additional surface complexation reaction. Two additional exchange sites had to be introduced to quantitatively describe the 226Ra uptake on illite in the 226Ra/Ba competition experiment. The nature of these sites, however, remains unclear. The implementation of the 226Ra adsorption model into predictive transport modelling codes is of key importance for the safety analysis of deep geological disposal of radioactive waste. • 226Ra has stronger affinity for illite than Ba. • Adsorption of Ba and 226Ra on illite is mainly governed by cation exchange. • Surface complexation reaction is necessary to describe adsorption at high pH and high ionic strength. • Four cation exchange sites are necessary to quantitatively describe Ra uptake on illite. [ABSTRACT FROM AUTHOR]

In this study, magnetic composite microspheres (SCFP) were prepared by cross-linking chitosan (CS), sodium alginate (SA), poly(vinyl alcohol) (PVA), and ferric tetraoxide (Fe 3 O 4) in a CaCl 2 solution. CS and Fe 3 O 4 were encapsulated in gel spheres formed by cross-linking SA with Ca(II), while PVA facilitated the dispersion of CS in SA. SCFP was utilized as an adsorbent to remove Cu(II) from water. The effects of the initial pH of the solution, SCFP dosage, and initial Cu(II) concentration on the adsorption efficiency were investigated through batch experiments. The results demonstrated that the adsorption capacity reached 58.260 mg/g (removal rate = 97.1%) after 100 min of adsorption at a pH of 5. The removal rate remained above 90% even after 6 cycles of the cycling experiment. The incorporation of CS with other functional materials allowed SCFP to compensate for its inherent drawbacks such as low mechanical strength, poor acid resistance, and short service life. The pseudo-first-order kinetic model and Freundlich adsorption isotherm provided better descriptions of the adsorption process. A comprehensive analysis was conducted on the structure and adsorption mechanism of SCFP using characterization techniques such as SEM-EDS, FTIR, BET, XRD, etc. In summary, SCFP has the potential to be an excellent environmentally friendly material for the removal of Cu(II). [Display omitted] • SCFP was prepared by a simple method. • At pH 5 for 100 min, the adsorption capacity and removal rate for Cu(Ⅱ) reached 58.260 mg/g and 97.1%. • SCFP can be reused successfully in repeated adsorption-desorption cycles. • Adsorption mechanisms involved physical adsorption and chemical adsorption. [ABSTRACT FROM AUTHOR]

Perfluorooctanesulfonate (PFOS) is a hazardous chemical, and its presence in surface and groundwater poses a risk to environmental quality and human health. Containment is often applied to immobilize PFOS to stop or minimize the exposure. Mineral-based materials became promising adsorbents. However, there is scope to develop adsorbents using locally available minerals and understand their adsorption mechanisms. Here, we developed oleylamine-modified composites using naturally occurring Iranian zeolite and diatomaceous earth (DE). The mineralogy and surface properties of materials were fully characterized, and the adsorption of PFOS from simulated wastewater was linked to it. Clinoptilolite in zeolite sample, calcite and kaolinite in DE were main mineral assemblages. The raw samples also contained silica as a main constituent of them. Thermogravimetric analysis suggested that the materials were successfully modified with the oleylamine molecules in the material's structure and surfaces. These were further supported by scanning electronic microscopy (SEM), Fourier transmission infrared spectroscopy (FTIR), and surface and pore size analysis. After adsorption at various pHs, the isotherm of adsorption was also performed at ambient temperature. Modified DE and zeolite tend to adsorb PFOS (14.1 and 25.5 mg/g, respectively) more than their raw counterparts (4.72 and 0.39 mg/g, respectively). Adsorption models suggest monolayer and, in rare cases multilayer binding capacities and affinities toward PFOS. We analyzed the post-adsorption materials and discovered that electrostatic and hydrophobic interaction was likely the main cause of PFOS adsorbed to the material. This research helps to improve our knowledge of how PFOS adheres to untreated and surfactant-altered zeolite and DE in aquatic environments. [Display omitted] • Locally sourced Iranian zeolite and diatomite characterized mineralogically. • Materials modified with primary amine (oleylamine) without prior processing • Perfluorooctane sulfonate (PFOS) was removed from water by the modified minerals. • Amine-modified zeolite appears to be low cost and efficient adsorbent for PFOS. • Mechanistic study suggests adsorbent removed PFOS electrostatically and hydrophobically. [ABSTRACT FROM AUTHOR]

Abstract In this study, we report on the effects of Ag+ cations exchange within clinoptilolite zeolite in relation to both the physicochemical and the gas adsorption characteristics. Clinoptilolites cation-exchanged with AgNO 3 to varying degrees were investigated and the influence of naturally occurring cations (Mg2+, Ca2+, K+) distributed within the material is discussed. The morphology and elemental composition of the untreated clinoptilolite and the Ag+ cation exchanged variants were characterized by XRD, EDS, FTIR, and N 2 sorption experiments performed at 77 K. From the pore property analysis, we show that a slight reduction in the micropore distribution occurs for the highly exchanged Ag+ clinoptilolite compared to the untreated clinoptilolite, indicating a likely decrease in the average effective micropore size. Equilibrium adsorption isotherms of CH 4 and N 2 were measured at 303 K. The adsorption uptake rate of both gases was also studied and it slowed by the addition of Ag+ cations. The modified samples showed decreasing adsorption capacity for the larger CH 4 gas molecule, whereas adsorption of the smaller N 2 gas was less affected. This effect was most pronounced for the highly exchanged Ag+ clinoptilolite samples (AgNO 3 exchange solution above 0.2M) whereby more N 2 was adsorbed than CH 4. At 1 atm and 303 K, the N 2 /CH 4 equilibrium selectivity values of highly exchanged Ag+ clinoptilolite ranged from 2.8 to 7.6, which are higher than many clinoptilolite types. Graphical abstract Image 1 Highlights • Natural clinoptilolite displays increased N 2 /CH 4 equilibrium selectivity following exchange with Ag+ cations. • Reduced CH 4 equilibrium adsorption capacity resulting from pore blocking in the Ag+ exchanged clinoptilolite is observed. • Higher microporous diffusion resistance for Ag+ clinoptilolite compared to natural clinoptilolite. [ABSTRACT FROM AUTHOR]

The article discusses the sorption of purification of water bodies from impurities using natural inorganic sorbents. The availability and low cost of minerals are an important economic advantage of their use for the purification of all types of water. The article describes a method of using an effective sorbent with high ion-exchange and sorption properties for purification of light oil products, for the purification of drinking or industrial water with a high content of heave technogenic metal ions and organic substances. Based on the data obtained, conclusions are drawn about the possibility of using the studied natural mineral sorbents for the extraction of impurities from waste and natural waters.

This study aims to synthesize and characterize organoclays developed from an Argentinian montmorillonite (Bent) using hexadecyltrimethylammonium bromide (HDTMA-Br) as the intercalation agent. Subsequently, an adsorption mechanism is proposed. The obtained organoclays were more hydrophobic than the starting clay. Surfactant molecules were adsorbed initially through cation exchange in sites placed in the interlayer space of the clay. Adsorption in such sites continued until the interlayer space was saturated. Depending on the surfactant loading introduced during the intercalation process, different organizations of surfactant in the interlayer were obtained. Further adsorption of surfactant occurred in the mesopores generated by tactoids in the "house of cards" organization. This process kept surfactant molecules relatively free and out of the interlayer space.

Mesoporous silica gel containing embedded phosphotungstic acid (PTA) was synthesized by sol-gel co-condensation of tetraethoxysilane with PTA in acidic media. The obtained material had high BET surface area and pore volume. A characteristic band of the Keggin structure of PTA was present in its FT-IR spectrum while its XRD patterns were absent. This proved the embedding of PTA on a sub-molecular level. The material demonstrated high adsorption capacity of Cs. Unexpectedly, porosity of the adsorbent increased after substitution of most protons by cesium cations. Cation exchange also favored agglomeration of the material particles. Kinetic studies showed that the adsorption data correlates strongly with the pseudo-second order model. The adsorbent had two types of adsorption sites: heteropolyacid anions and silanol groups. However, adsorption on silanol groups was very sensitive to the temperature. At the increased temperature, the nature of adsorption fit the Langmuir model extremely well. The obtained results can be used in the development of an effective adsorbent for clean-up of water contaminated by radioactive cesium-137. [ABSTRACT FROM AUTHOR]

In this research, the natural bentonite clays collected from different areas in Iran were utilized as adsorbent to study the removal behavior of different Iranian bentonitic clays vs. Ni(II) and Co(II) from their aqueous solutions. The original bentonite clays were characterized with the help of pH, Swell Index, Sediment Index, granulometric (screen) analysis, cation exchange capacity measurement, powder X-ray diffraction, X-ray fluorescence, scanning electron microscopy with energy dispersive atomic X-ray; Brunauer, Emmett, and Teller surface area measurements; and Barrett, Joyner, and Halenda pore size distribution analysis, Fourier transform infrared spectroscopy. While the thermal stability of the samples was studied using thermo gravimetry (TGA-DSC), adsorption experiments were conducted under some constant solution conditions and the removal of Co2+and Ni2+ions from their aqueous solutions was tested on various bentonite types and certain bentonite characteristics including pore size, surface properties, etc. The maximum adsorption of 92% took place on sampleA1 in the removal process of Co2+and Ni2+. The adsorption capacities followed the order of Co2+ > Ni2+in single-component systems for sampleA2 andA3. The results showed the prevailing metal removal process was adsorption and cation exchange with the initiation in precipitation. [ABSTRACT FROM PUBLISHER]

Natural zeolite chabazite was studied for the discoloration of rhodamine 6G solutions in dark and under sunlight irradiation. The discoloration of rhodamine aqueous solutions containing chabazite was monitored by UV–vis absorption and photoluminescence spectroscopies and high-performance liquid chromatography measurements on aliquots of the rhodamine solutions. After the discoloration experiments the chabazite powders were collected, dried and analyzed by Fourier-Transform Infrared spectroscopy to obtain additional information about the discoloration process. The results show that chabazite produces the discoloration of the rhodamine solutions in both conditions, dark and under sunlight, with different discoloration mechanisms and rates. In dark, chabazite removes the rhodamine molecules from the solution by adsorption and cation exchange mechanisms. Under sunlight irradiation, additional photo induced mechanisms produce the degradation of the rhodamine molecules and a faster discoloration of the solution. The discoloration process followed a first order kinetics with rate constants of 4.9 × 10 −3 and 1.2 × 10 −2 min −1 in dark and under sunlight conditions, respectively. It is proposed a mechanism for the photodegradation of rhodamine molecules under sunlight irradiation, where the role of chabazite is fundamental. [ABSTRACT FROM AUTHOR]

Diffuse reflectance (DR) spectra in the visible (VIS) and near-infrared (NIR) region of methylene blue (MB) adsorbed on clay samples of different mineral composition and varying MB/clay ratios were analyzed. This type of investigation is not affected by unadsorbed MB molecules and can be used in clay-mineral determination. When the MB dye/clay loading was increased, enhancement of bands in the DR-VIS and DR-NIR was observed. The distribution of various MB aggregates was interpreted according to mineral composition and MB loading. The NIR spectrum of H2O overtone provides insights about the intercalated MB aggregation, consistent with VIS spectra. Critical MB concentration for formation of dimeric structure was between 0.7 and 1.75 mmol/100 g followed with suppression of monomers. Different orientations of vectors of polarized light allowed calculations of the possible orientation and tilting angle of MB molecules on the surface of the clay particles in accordance with XRD data. [ABSTRACT FROM AUTHOR]

The sorption capacity of synthetic montmorillonites of the composition Na(Al,Mg)SiO(OH) · nHO (where 0 < x < 1) in relation to the methylene blue dye has been investigated. The obtained results from the data for natural samples of montmorillonite (K10) and activated carbon have been compared. The effect of the montmorillonite composition and the medium acidity on the degree of dye adsorption has been studied. The chemical composition of montmorillonite, which is optimal for solving tasks in the field of ecology and medicine, has been determined. The character of the interaction of montmorillonites with the adsorbed substance from the point of view of the physical-chemical sorption models has also been studied. [ABSTRACT FROM AUTHOR]

The adsorption of ciprofloxacin (CIP) as well as probe compounds, phenylpiperazine (PP) ( NH) and fluorochloroquinolone carboxylic acid (FCQCA) ( COOH), on palygorskite (PFl-1) obeyed the Langmuir isotherm at pH 2, 7, and 11 except the FCQCA adsorption at pH 2. The CIP and PP adsorption onto PFl-1 was 98–160 mmol/kg. In neutral solution the total amount of exchangeable cations desorbed correlated with the adsorbed amount of CIP and PP well with a slope of 0.9–1, indicating a cation-exchange mechanism. A low amount of FCQCA adsorption of 27–57 mmol/kg was observed and the amount of exchangeable cations desorbed negatively correlate with the amount of FCQCA adsorbed as influenced by surface complexation or cation bridging. FTIR band shifting due to the ring-stretch vibration of PP and the keto-carbonyl group stretching of FCQCA suggested strong interactions as PP and FCQCA absorbed on PFl-1 in neutral solution. In the interaction of CIP with PFl-1, the piperazine–amine group played an important role in cation-exchange interaction in acidic to neutral solution, while the deprotonated keto carbonyl group actively partook in cation bridging or surface complexation with metal cations adsorbed on PFl-1 when the CIP was in anionic form in alkaline solution. [ABSTRACT FROM AUTHOR]

The removal of medium-low N-NH4 on activated sludge modified by ferric hydroxide suspension (FHMAS) in batch studies was conducted as a function of pH, concentration of modifier, contact time, and initial concentration. The kinetics study showed that the sorption behavior fit well the pseudo second-order equation. An adsorption isotherms study indicated that FHMAS had a higher adsorption capacity for N-NH4 than other adsorbents. The mechanism of removal of N-NH4 by FHMAS was coexistence of adsorption and cation exchange. Initial N-NH4 concentration being 116 mg/l in metallurgical wastewater was reduced to 11 mg/l after adsorption treatment. [ABSTRACT FROM AUTHOR]

The adsorption of aflatoxin B1 (AFB1) by cation-exchanged clinoptilolite zeolitic tuff and montmorillonite was investigated at 37°C and pH 3.8 from an aqueous electrolyte having a composition similar to that of gastric juices of animals. Both minerals were exchanged from the natural form to the sodium form and then to the Cu2+, Zn2+ and Co2+-rich forms. The cation exchange was different for the different cations, but in all cases the exchanges were larger on montmorillonite than on clinoptilolite. The degree of exchange on montmorillonite was 76 % for copper (from a total of CEC 0.95 meq/g, Cu2+ 0.73 meq/g) and 85 % for zinc and cobalt. Under the same conditions (concentration, temperature, pH, contact time), the degree of exchange on zeolitic tuff was 12 % for Cu2+ (from a total CEC of 1.46 meq/g, Cu2+ 0.17 meq/g), 8 % for Zn2+ and 10 % for Co2+. Both groups of mineral adsorbents showed high AFB1 chemisorption indexes (ca). For the montmorillonite forms, ca ranged from 0.75 for the Cu-exchanged montmorillonite to 0.89 for the natural Ca-form, 0.90 for the Zn-exchanged form and 0.93 for the Co-exchanged montmorillonite. The adsorption of AFB1 on the different exchanged forms of clinoptilolite gave similar values of ca for the Cu and Ca forms (0.90) and values of 0.94 and 0.95 for the Zn- and Co-exchanged form. The impact of the mineral adsorbents on the reduction of essential nutrients present in animal feed (Cu, Zn, Mn and Co) showed that the Ca-rich montmorillonite had a higher capability for the reduction of the microelements than the Ca-rich clinoptilolite.

The adsorption of aflatoxin B1 (AFB1) by cation-exchanged clinoptilolite zeolitic tuff and montmorillonite was investigated at 37ºC and pH 3.8 from an aqueous electrolyte having a composition similar to that of gastric juices of animals. Bothminerals were exchanged from the natural form to the sodium form and then to the Cu2+, Zn2+ and Co2+-rich forms. The cation exchange was different for the different cations, but in all cases the exchanges were larger on montmorillonite than on clinoptilolite. The degree of exchange on montmorillonite was 76 % for copper (from a total of CEC 0.95 meq/g, Cu2+ -0.73 meq/g) and 85 % for zinc and cobalt. Under the same conditions (concentration, temperature, pH, contact time), the degree of exchange on zeolitic tuff was 12 % for Cu2+ (from a total CEC of 1.46 meq/g, Cu2+ -0.17 meq/g), 8 % for Zn2+ and 10 % for Co2+. Both groups of mineral adsorbents showed high AFB1 chemisorption indexes (cα). For the montmorillonite forms, cα ranged from 0.75 for the Cu-exchanged montmorillonite to 0.89 for the natural Ca-form, 0.90 for the Zn-exchanged form and 0.93 for the Co-exchanged montmorillonite. The adsorption of AFB1 on the different exchanged forms of clinoptilolite gave similar values of cα for the Cu and Ca forms (0.90) and values of 0.94 and 0.95 for the Zn- and Co-exchanged form. The impact of the mineral adsorbents on the reduction of essential nutrients present in animal feed (Cu, Zn, Mn and Co) showed that the Ca-rich montmorillonite had a higher capability for the reduction of the microelements than the Ca-rich clinoptilolite.

The hydrothermally synthesized layered chalcogenide, K 2 x Mn x Sn 3− x S 6 ( x = 0.5–0.95) (KMS-1), was applied to remove ciprofloxacin from aqueous solution. Kinetic data showed the removal reaction followed a pseudo-second-order kinetic model and the rate controlling step was both through external film and intraparticle diffusion. The adsorption of CIP by KMS-1 is endothermic and the maximum adsorption capacity of KMS-1 was 199.6, 230.9 and 269.5 mg/g at temperature of 10, 25 and 40 °C, respectively. The heavy metal ions had great effect on the removal efficiency of CIP and the degree of inhibition followed the order: Pb 2+ > Zn 2+ > Cd 2+ > Ni 2+ . The shift of Bragg peaks from XRD at various pH accompanying CIP removal and FE-SEM images confirmed that cation exchange is the major mechanism for the adsorption of CIP by KMS-1. In the pH range of 4.0–7.0, the intercalation of cationic CIP adopted a titled orientation of di-molecular CIP in KMS-1 with the titling angle of 68° and 42°, respectively. A vertical arrangement of the zwitterionic CIP adsorbed on the surface of KMS-1 was also confirmed. These results suggested that KMS-1 is an effective adsorbent to remove CIP from water. [ABSTRACT FROM AUTHOR]

Raw montmorillonite (Mt) was cation-exchanged with Ca 2 + , Mg 2 + , and Fe 3 + , and Pb 2 + was tested for its adsorption on the exchanged Mt. The d-value and the cation exchange capacity (CEC) of Ca-exchanged montmorillonite (Ca 2 + + Mt) were larger than those of Mg-exchanged montmorillonite (Mg 2 + + Mt) and Fe-exchanged montmorillonite (Fe 3 + + Mt). The Pb 2 + adsorption on the homoionic Mt was fast and the amount of Pb 2 + adsorption followed the order of Ca 2 + + Mt > Mg 2 + + Mt > Fe 3 + + Mt. Simulation of Pb 2 + adsorption on the Mt revealed a much larger energy drop when Pb 2 + is substituting for Ca 2 + in comparison to Pb 2 + exchanging for Fe 3 + . [ABSTRACT FROM AUTHOR]

Engelhard titanosilicate-2 (ETS-2) has shown to be a promising substrate to load active sites for deep H 2 S removal (to sub-ppm levels) for gas purification applications at room temperature. Because of the high external surface area and the cation exchange capacity of ETS-2, active sites can be highly dispersed and very accessible to H 2 S molecules making it a novel support material for metal-oxide H 2 S adsorbents. In this paper, we report the room temperature H 2 S breakthrough performances of ETS-2 metal exchanged with Ag, Ca, Cu and Zn in comparison to a fully developed commercial H 2 S adsorbent (R3-11G, 36 wt% CuO, BASF). The results indicate the following trend for H 2 S uptake capacities at room temperature: Cu-ETS-2>Ag-ETS-2>Zn-ETS-2≈R3-11G>Ca-ETS-2≈Na-ETS-2. Cu exchanged ETS-2 displays the highest H 2 S capacity of 29.7 mg H 2 S/g adsorbent compared to the other investigated materials, making it the most promising metal-exchanged ETS-2 for room temperature desulfurization. [ABSTRACT FROM AUTHOR]

Highlights: [•] Different sorption sites were available for enrofloxacin (EN) uptake on different types of clays. [•] EN uptake was limited to the external sites for non-swelling clays. [•] Interlayer spaces were the major host sites for EN uptake on swelling clays. [•] Cation exchange was the dominant mechanism for cationic and neutral EN. [Copyright &y& Elsevier]

Ranitidine (RT)-containing wastewater can be hazardous to biotic and abiotic environment, when released into the soil and water bodies without treatment. This work investigated the removal of RT from aqueous solutions by illite (IMt-2), a naturally occurring clay mineral, via systematic batch adsorption experiments under different physicochemical conditions. RT existed in an undissociated form at pH 7–9, and was adsorbed on IMt-2 obeying the Langmuir isotherm model. The maximum RT adsorption capacity was 0.122 mmol/g corresponding to 32 mg/g and the adsorption amount combined with the surface area of IMt-2 suggested that the adsorption occurred on the surface of IMt-2. The best fitted kinetic model for RT adsorption was the pseudo-second order model. The amount of exchangeable cations desorbed from IMt-2 during RT adsorption was linearly correlated to the amounts of RT adsorbed, with a slope of 0.82, implying that a cation exchange-based adsorption mechanism was dominating. The pH and ionic strength effects supported the cation exchange as the main mechanism again. Additionally, the random orientation of RT as horizontal morphology was via FTIR results after adsorption. Detailed x-ray diffraction and Fourier transform infrared analyses confirmed that RT adsorption occurred dominantly on the surface of IMt-2. This study suggested that IMt-2 could be a moderate natural material for removing RT from pharmaceutical and laboratory wastewater. [Display omitted] • Illite (IMt-2) adsorbed 0.122 mmol/g ranitidine (RT) from aqueous solution. • Main mechanism of RT removal was cation exchange in a moderate adsorption (< 4 h). • RT removal was affected by the pKa and PZC factors in the pH range of 2–11. • Amine and dimethylamino groups of RT oriented horizontally on clay surfaces. [ABSTRACT FROM AUTHOR]

Abstract: With more pharmaceuticals and personal care products detected in the surface and waste waters, studies on interactions between these contaminants and soils or sediments have attracted great attention. In this study, the removal of ciprofloxacin (CIP), a fluoroquinolone antibiotic, by birnessite, a layered manganese oxide, in aqueous solution was investigated by batch studies supplemented by X-ray diffraction (XRD) and Fourier transform infrared analyses. Stoichiometric release of exchangeable cations accompanying CIP removal from water confirmed cation exchange as the major mechanism for CIP uptake by birnessite. Interlayer expansion after CIP adsorption on birnessite as revealed by XRD analyses indicated that intercalation contributed significantly to CIP uptake in addition to external surface adsorption. Correlation of CIP adsorption to specific surface area and cation exchange capacity suggested that the former was the limiting factor for CIP uptake. At the adsorption maximum, CIP molecules formed a monolayer on the birnessite surfaces. The adsorbed CIP could be partially removed using a cationic surfactant at a low initial concentration and mostly removed by AlCl3 at a higher initial concentration, which further supported the cation exchange mechanism for CIP removal by birnessite. The results indicated that the presence of layered Mn-oxide in the soil and waste water treatment systems may provide host for CIP accumulation. [Copyright &y& Elsevier]

Abstract: The removal of tetracycline (TC) from aqueous environment by illite (IMt-2) was studied in a batch system at different pH and ionic strength conditions. Adsorbent characterizations were determined by XRD and FTIR. The TC adsorption capacity on IMt-2 was 32mg/g at pH 5–6 and the adsorption equilibrium data obeyed the Freundlich isotherm. The kinetics of TC adsorption was moderately fast and almost reached equilibrium in 8h and the results followed pseudo-second-order kinetic model and Elovich model. The X-ray diffraction patterns before and after TC adsorption revealed no changes in basal spacing and intensity under two kinetic adsorption and a few initial TC concentration conditions, indicating that the adsorbed TC molecules were on the external surface of the mineral in contrast to intercalation of TC into swelling clay minerals, such as montmorillonite and rectorite. In spite of its low TC adsorption capacity, the results suggested that IMt-2 could be a good candidate to remove TC from wastewater containing higher amounts of TC and illite would be an important environmental sink for the fate and transport of TC in soils. [Copyright &y& Elsevier]

Abstract: Swelling clays have been extensively studied to remove contaminants from aqueous solution. This research aimed at elucidating the mechanism of adsorption of acridine orange (AO), a cationic dye, on low charge montmorillonite in order to better understand the principles behind AO removal using swelling clays. Proportional desorption of exchangeable cations from the clays accompanying AO adsorption confirmed cation exchange as the most dominant mechanism for AO removal. FTIR analyses further confirmed the presence of cationic dye AOH+ on the surface and in the interlayer of the swelling clays. XRD and TG-DTG analyses revealed interlayer adsorption, thus, intercalation of AO molecules with different conformations at low and higher AO adsorption levels. Molecular simulation showed dimer and horizontal bilayer formation of intercalated AO at the low and high adsorption levels. At the intermediate AO adsorption levels, the dimer intercalated and bilayer intercalated swelling clays formed mixtures at the single crystal scale, resulting in a significant broadening of (001) peak. The results showed that the uptake of AO could far exceed the cation exchange capacity, an advantage of using swelling clays to treat wastewater containing cationic dyes. [Copyright &y& Elsevier]

Abstract: As one of the most important soil components, kaolinite plays a vital role in transport and retention of ionizable contaminants in soils of warm and wet climate. Ciprofloxacin (Cip) is a second generation fluoroquinolone (FQ) antibiotic of high use. It has high aqueous solubility under high and low pH conditions and higher stability in soil system. In this study, the interactions between Cip and kaolinite in aqueous solution were investigated by batch experiments, XRD and FTIR analyses. Quantitative correlation between the exchangeable cations desorbed and Cip adsorbed confirmed experimentally that cation exchange was the dominant mechanism of Cip adsorption on kaolinite. Fitting of experimental data to the cation exchange model resulted in a selectivity coefficient of 27, suggesting a strong affinity of Cip on negatively charged kaolinite surfaces. At the adsorption maximum 190–200Å2 was available per Cip molecule, much larger than the Cip molecule area, confirming charge-limited instead of surface-limited Cip adsorption. The invariable d-spacing after uptake of different amounts of Cip suggested that the adsorption of Cip was on the external surfaces of kaolinite. As solution pH increased beyond 8, the amount of Cip adsorption decreased significantly and reached close to zero at pH 11. The high adsorption rate constant due to surface adsorption instead of intercalation and the wide distribution of kaolinite in different soils suggest that the fate and transport of Cip may be governed by the transport of colloidal sized clays. [Copyright &y& Elsevier]