Search

The very large surface associated with aerogels made them attractive in the field of sorption. Herein, silica aerogels were characterized and used for the sorption of U(VI) in solution. The effects of specific surface area (SSA), pH and coexistent electrolyte ions on the surface site density, aggregation and sorption properties have been carefully investigated. The site distributions of silica aerogels were calculated with Visual MINTEQ. The sorption of U(VI) is affected significantly by the solution pH. The sorption increases with increasing SSA due to the increased amount of surface active sites of silica aerogels. Electrolyte ions (Na + , K + , NO 3 − , Cl − ) were added to investigate the competition ability to U(VI) adsorbed on active sites. The influence of humic acid (HA), silicate and phosphate on U(VI) sorption in multiphase systems were also discussed. The kinetics data were used to investigate the sorption process and pseudo-second-order model was used to simulate the kinetic data. Spectroscopic analyses were also utilized to explain the role of OH groups in the U(VI) sorption. [ABSTRACT FROM AUTHOR]

This study explored the sorption behavior and mechanism of U(VI) on sericite. The surface properties of sericite were investigated, and the effects of several environmental factors on U(VI) sorption to sericite were evaluated. The experimental data were simulated by different isotherm models and kinetic models. Humic acids affects U(VI) sorption obviously while silicate promotes the process in the whole pH range. The sorption-desorption hysteresis suggests an irreversible sorption process. Spectroscopic analyses indicate that the −OH groups have an important effect in the U(VI) sorption. [ABSTRACT FROM AUTHOR]

Radioactive waste is usually sealed in steel canisters surrounded by a layer of compacted clay back-fill, and permanent buried in a deep geological repository. Unavoidably, the radionuclide contaminants can be released from repository and then sorbed onto the waste container corrosion products or the Fe-rich minerals. Herein, we characterized the Fe(III)-saturated montmorillonite (Fe(III)-MMT) by using Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET), and found the changes of the surface incorporating Fe(III) and surface micropores. The sorption of U(VI) on Fe(III)-MMT and Na-montmorillonite (Na-MMT) was investigated by batch experiments. The larger surface area and cation exchange capacity, and the existence of Fe(III) (hydr)oxide phases in Fe(III)-MMT contributed greatly to its sorption capacity. In the whole pH range, the sorption of U(VI) on Fe(III)-MMT was higher than on Na-MMT, and the sorption was strongly depended on pH and ionic strength. The sorption isotherms were simulated well by the Langmuir and Freundlich models. The thermodynamic parameters ( ΔH, ΔS and ΔG) calculated from the temperature dependent sorption isotherms indicated that the sorption of U(VI) on Fe(III)-MMT was an endothermic and spontaneous process. The observations suggest that the interactions between U(VI) and Fe(III)-MMT are important in controlling U(VI) retention. The phenomena need to be considered in risk assessment and reactive transport modeling. [ABSTRACT FROM AUTHOR]

ABSTRACT The sorption of solvents from the vapour phase to solid substrates is important in producing heavy oil and bitumen, particularly from the oil sands. We investigated the sorption and desorption equilibrium and kinetics of cyclohexane, toluene, and water on kaolinite, fine solids, and organic-rich fine solids isolated from Athabasca oil sands over a wide range of solvent vapour concentrations using a gravimetric method. The isotherms for both adsorption and desorption of solvent vapour were determined, and the Brunauer-Emmett-Teller equation was used to fit the experimental data. The initial kinetic rate constants for the adsorption and desorption of solvent vapour were determined with the linear driving force model. The results were compared and discussed in terms of the type of solvent, the content of organic materials, and the surface area of the solid substrates. The results suggest that, in addition to the adsorption of solvent on mineral surfaces, the contribution from solvent partitioning in the organic materials and the porosity resulting from high amounts of organic materials are significant factors for solvent uptake and kinetic rate constants. In mixed solvent vapours, the competitive sorption of water and cyclohexane was observed in the solid substrates. However, the degree of competitiveness decreased with an increase in the content of organic materials in the substrates. [ABSTRACT FROM AUTHOR]

The removal of Pb(II) from wastewater by Ca-rectorite was investigated as various environmental factors containing contact time, pH, ionic strength, solid content, coexisting ions, humic acid (HA), and temperature. The kinetic sorption of Pb(II) on Ca-rectorite was well described by the pseudo second-order model. The sorption process was strongly dependent on pH and ionic strength. The results indicated that the presence of HA and coexisting ions influenced the sorption of Pb(II) on Ca-rectorite obviously. Besides, the Langmuir and Freundlich models were employed to simulate the sorption isotherms. The thermodynamic parameters indicated that the sorption process was spontaneous and endothermic. It is possible to conclude that Ca-rectorite has a good potential for disposal of lead-contaminated wastewater. [ABSTRACT FROM PUBLISHER]

The effect of soluble silicate on the sorption of U(VI) to γ -Al 2 O 3 was investigated by batch experiments and extended X-ray absorption fine structure (EXAFS) method. The presence of silicate enhanced the sorption of U(VI) on γ -Al 2 O 3 surface and the sorption was attributed to inner-sphere surface complexation. The structure of the adsorbed U(VI) and silicate on γ -Al 2 O 3 was investigated in the analysis of EXAFS spectra. The fitting of the experimental EXAFS data was obtained by including two uranium coordination shells with 2 axial (O ax ) and 5 equatorial (O eq ) oxygen atoms at 1 . 79 ± 0 . 02 and 2 . 43 ± 0 . 02 Å, respectively, and the third coordination shells with Al atom at ∼3.35 Å. Silicate contributed to the formation of ternary inner-sphere surface complexes, acting as “bridge” between U(VI) and γ -Al 2 O 3 and enhanced the sorption of U(VI). The observations suggested that the interactions between U(VI) and silicate were important in controlling U(VI) retention. [ABSTRACT FROM AUTHOR]

We review the analysis of lanthanide speciation at solid-water interfaces. We summarize the various mechanisms of lanthanide interaction with sorbent surfaces, such as surface complexation, precipitation and surface-induced redox reactions. There are a wide variety of available analytical techniques for understanding the speciation of lanthanides on surfaces and the reaction mechanisms of sorption. We also review recent advances in the utilization of quantum chemistry that widen the scope of lanthanide speciation studies. We review, summarize and discuss in detail the speciation of lanthanides, mainly Eu(III), at natural or synthetic mineral surfaces, and the available analytical techniques. We aim to collate valuable information about recent results for surface speciation analysis of lanthanides at solid-water interfaces. [ABSTRACT FROM AUTHOR]

Abstract: Oxidized multiwalled carbon nanotubes (MWCNTs) were employed as sorbent to study the sorption characteristic of Pb(II) from aqueous solution as a function of contact time, pH, ionic strength, foreign ions, and oxidized MWCNTs’ contents under ambient conditions using batch technique. The results indicate that sorption of Pb(II) on oxidized MWCNTs is strongly dependent on pH values, and independent of ionic strength and the type of foreign ions. The removal of Pb(II) to oxidized MWCNTs is rather quickly and the kinetic sorption can be described by a pseudo-second-order model very well. Sorption of Pb(II) is mainly dominated by surface complexation rather than ion exchange. The efficient removal of Pb(II) from aqueous solution is limited at pH 7–10. X-ray photoelectron spectroscopy (XPS) is performed to study the sorption mechanism at a molecular level and thereby to identify the species of the sorption processes. The 3-D relationship of pH, C eq and q indicates that all the data of C eq − q lie in a straight line with slope −V/m and intercept C 0 V/m for the same initial concentration of Pb(II) and same content of oxidized MWCNTs of each experimental data. [Copyright &y& Elsevier]

Abstract: Thorium is considered as a chemical analog of other tetravalent actinides. Herein, the sorption of Th(IV) on TiO2 in the presence or absence of soil fulvic acid (FA)/humic acid (HA) as a function of pH, ionic strength and FA/HA concentration has been studied by a batch method. The morphology was characterized by scanning electron microscopy (SEM). The results indicate that sorption of Th(IV) on TiO2 increases from 0% to ∼94% at pH 1∼4, and then maintains level with increasing pH values. Both FA and HA have a positive effect on Th(IV) sorption at low pH values and the contribution of FA on Th(IV) sorption is rather higher than that of HA at pH<4. The sorption is weakly dependent on the concentration of KNO3 in solution, but the cations K+, Na+ and Li+ influence Th(IV) sorption more obviously. The batch results indicate that the inner sphere complex formation is formed at bare surfaces or FA/HA-bound TiO2 particle surfaces. Results of SEM analysis show that the particle sizes of TiO2, Th–TiO2 and Th–HA–TiO2 colloids are quite different. Surface complexation may be considered as the main sorption mechanism. [Copyright &y& Elsevier]

Abstract: The removal of Th(IV) from aqueous solution by using nanoparticles of anatase is studied under ambient conditions. The sorption of Th(IV) on TiO2 increases markedly at pH 1.5–4 and then maintains level with increasing pH values. The presence of HA/FA enhances the sorption of Th(IV) on TiO2 at low pH values. The Langmuir, Freundlich, Redlich-Peterson and Dubini-Radushkevich models are used to simulate the sorption isotherms, respectively. The results suggest that the sorption of Th(IV) on TiO2 occurs mainly by surface complexation. The adsorbed Th(IV) is very difficult to be desorbed from the solid surface. The results of XRD and Raman analysis indicate that the matrix of TiO2 does not undergo any structural change after the sorption of Th(IV) ions. The Ti-O-H stretching occurred in the IR spectral region of 1000–1300cm−1 for the hydrated TiO2 samples is responsible for sorption of metal binding, and provides indirect evidence for the surface complexation mechanism. [Copyright &y& Elsevier]

Abstract: The distribution coefficients of radionuclides derived from batch experiments are used to evaluate the migration behavior of radionuclides 99Tc and 243Am in compacted bentonite after different times. The effects of times, dispersion coefficient, distribution coefficient and pore water velocity on the concentration distribution of 99Tc and 243Am in the environment are also calculated from the theoretical migration equation. 99Tc is poorly sorbed to bentonite and moves quickly into the environment. Migration of radionuclide increases with increasing dispersion coefficient and decreasing distribution coefficient. The effects of water velocity on the migration of Tc and Am are obvious. Most 243Am is retained in the first several meters, and 20m of the backfill-compacted bentonites are sufficient to prevent the migration of radionuclide Am from the repository to the environment. [Copyright &y& Elsevier]

Humic acid (HA) can markedly change the surface charge of clay minerals and influences the sorption of uranium(U) on clay minerals in aquatic environments. Furthermore, HA can potentially affect the mobility of U(VI) in the natural environment. The effect of HA on the surface charge, aggregation, sorption and bonding properties of attapulgite [(Mg,Al) 4 (Si) 8 (O,OH,H 2 O) 26 ·nH 2 O] was investigated using fluorescence spectroscopy technique in combination with other analytical tools. The UV–vis absorbance spectra and fluorescence peaks obtained in the experiments are attributed to a large number of electron donating substitutes, such as carboxylic acid-like and phenolic acid-like fluorophores, in HA. Electrostatic attraction and ligand exchanges are the primary interaction mechanisms between attapulgite and HA. A significant modification of excitation-emission matrix (EEM) spectra and emission intensity of HA are observed after the interaction, indicating a different binding complex of HA on attapulgite at the molecular level. The sorption kinetics indicate that strong chemical interactions and/or surface complexation primarily contributed to U(VI) sorption. An analysis of U(VI) sorption isotherms and model fitting reveals that the sorption of U(VI) onto attapulgite is a spontaneous and endothermic process. The presence of HA is an important factor that greatly influences the immobilization and removal of U(VI) ions from aqueous solutions. [ABSTRACT FROM AUTHOR]

To contribute to the comprehension of Eu(III) sorption properties in oxide-organic material systems, the influence of humic acid (HA) on Eu(III) sorption on bare and HA-bounded γ-Al 2 O 3 is studied using batch experiments and time resolved laser fluorescence spectroscopy (TRLFS). The effect of pH and addition sequences of Eu(III)/HA/Al 2 O 3 on Eu(III) sorption is carried out at different experimental conditions, and the results show that the sorption of Eu(III) is strongly dependent on pH and ionic strength. The sorption of Eu(III) is mainly dominated by ion exchange or outer-sphere surface complexation at low pH, and by inner-sphere surface complexation at high pH values. The presence of HA enhances Eu(III) sorption at low pH, but reduces Eu(III) sorption at high pH values. The addition sequences of Eu(III)/HA to alumina suspensions do not affect Eu(III) sorption, which is also evidenced by the TRLFS measurements. The surface complexes are characterized by their emission spectra [the ratio of emission intensities of 5 D 0 → 7 F 1 ( λ = 594 nm) and 5 D 0 → 7 F 2 ( λ = 619 nm) transitions] and their fluorescence lifetime. The TRLFS results show clearly that no effect of addition sequences on the sorption and speciation of Eu(III) in HA–Al 2 O 3 hybrids after equilibration. These findings on the effect of humic substances in the complexation properties of Eu(III) indicate that the clarification of the environmental behavior of humic substances is necessary to understand the physicochemical properties of Eu(III), or its analog trivalent lanthanide and actinide ions in the natural environment. [ABSTRACT FROM AUTHOR]

A novel magnesium silicate/diatomite sorbent (MSD) was fabricated using a facile hydrothermal method. The interaction mechanism of U(VI) on MSD was investigated by batch, spectroscopic and modeling techniques. The maximum adsorption capacity of MSD for U(VI) (31.54 mg/g) is significantly higher than that of diatomite (12.74 mg/g). XPS analysis indicated that the oxygen-containing groups (e.g., Si OH) of MSD were responsible for the high efficient removal of U(VI) from aqueous solutions. The fitted results of surface complexation modeling showed that the adsorption of U(VI) on MSD at pH < 4.0 and pH > 4.5 was attributed to cation exchange and inner-sphere surface complexation, respectively. These findings suggested that MSD could be a favorable sorbent for the efficient removal of U(VI) in the environmental cleanup. [ABSTRACT FROM AUTHOR]

Novel hierarchical core/shell structured polydopamine@MgAl-layered double hydroxides (PDA@MgAl-LDHs) composites involving MgAl-layered double hydroxide shells and PDA cores were fabricated thought one-pot coprecipitation assembly and methodically characterized by X-ray diffraction, Fourier transformed infrared spectroscopy, scanning/transmission electron microscopy, selected area electron diffraction, elemental mapping, thermogravimetric analysis and X-ray photoelectron spectroscopy technologies. U(VI) and Eu(III) sorption experiments showed that the PDA@MgAl-LDHs exhibited higher sorption ability with a maximum sorption capacity of 142.86 and 76.02 mg/g at 298 K and pH 4.5, respectively. More importantly, according to XPS analyses, U(VI) and Eu(III) were sorbed on PDA@MgAl-LDHs via oxygen-containing functional groups, and the chemical affinity of U(VI) by oxygen-containing functional groups is higher than that of Eu(III). These observations show great expectations in the enrichment of radionuclides from aquatic environments by PDA@MgAl-LDHs. [ABSTRACT FROM AUTHOR]

Understanding the rate and extent of 63 Ni(II) sorption and desorption on/from mineral surfaces are important to predict its mobility performance in the natural environment. We herein systematically investigated the effects of pH, electrolyte cations, humic acid (HA) and temperature on 63 Ni(II) sorption/desorption on/from Na-montmorillonite. The results indicated that the sorption/desorption of 63 Ni(II) on/from Na-montmorillonite were strongly dependent on pH and electrolyte cations. Desorption abilities of 63 Ni(II) were Na + ≈ K + > Ca 2+ ≈ Mg 2+ at the cationic concentration of 0.2 mol/L, which was associated with the clay tactoid size. The kinetic results suggested that 63 Ni(II) sorption/desorption initially increased rapidly and remained constant as time increasing. The presence of HA influenced 63 Ni(II) sorption clearly and promoted 63 Ni(II) desorption as a result of the dissolution of ternary surface complexes. Increasing temperature was favorable for the sorption reaction owing to the formation of strong inner-sphere complexes, however, hampered the desorption reaction because of the increased stability of inner-sphere complexes or the aggregation of montmorillonite. The results are crucial to understand the physicochemical behavior of radionickel in the natural environment. [ABSTRACT FROM AUTHOR]

Review: 212 refs. [ABSTRACT FROM AUTHOR]

Clay minerals have been studied extensively due to their strong sorption and complexation ability toward various environmental pollutants. In this study, the sorption of 90 Sr(II) on Na-montmorillonite was studied as a function of various environmental conditions such as pH, ionic strength, humic acid (HA) and temperature. The results indicated that the sorption of 90 Sr(II) on Na-montmorillonite was strongly dependent on pH and ionic strength. The experimental data of 90 Sr(II) sorption was simulated by the diffuse-layer model (DLM) well with the aid of Visual Minteq 3.0. At low pH, the sorption of 90 Sr(II) was dominated by outer-sphere surface complexation and ion exchange with Na + /H + on Na-montmorillonite surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence of HA enhanced 90 Sr(II) sorption at pH < 7.0 but decreased 90 Sr(II) sorption at pH > 7.0. Langmuir and Freundlich models were used to simulate the sorption isotherms of 90 Sr(II) at three different temperatures of 303, 318 and 333 K. The thermodynamic parameters (Δ H , Δ S and Δ G ) calculated from the temperature-dependent sorption isotherms indicated that the sorption of 90 Sr(II) on Na-montmorillonite was an endothermic and spontaneous process. The thermodynamic parameters calculated from temperature-dependent sorption data were crucial to understand the interaction behavior of 90 Sr(II) with Na-montmorillonite. [ABSTRACT FROM AUTHOR]

Highlights: [•] Water-soluble polyacrylamide coated-Fe3O4 magnetic composites were synthesized successfully. [•] PAM@Fe3O4 showed high efficient enrichment of U(VI) from wastewater. [•] The Q max of U(VI) on PAM@Fe3O4 reached 220.9mg/g. [•] Amide groups on the surface of PAM@Fe3O4 facilitated U(VI) sorption. [•] The used PAM@Fe3O4 could be effectually regenerated. [ABSTRACT FROM AUTHOR]

Abstract: The effect of pH, ionic strength, solid/liquid ratio, contact time and temperature on sorption of Pb(II) to NKF-6 zeolite is investigated using batch technique under ambient conditions. The NKF-6 zeolite is characterized using XRD and FTIR. The sorption results indicate that the sorption of Pb(II) on NKF-6 zeolite is strongly dependent on pH. The sorption of Pb(II) is affected by ionic strength at pH<6, while it is independent of ionic strength at pH>6. The sorption of Pb(II) is dominated by ion exchange or outer-sphere surface complexation at low pH values, and by inner-sphere surface complexation at high pH values. The thermodynamic parameters (ΔH 0, ΔS 0 and ΔG 0) calculated from the temperature dependent sorption isotherms suggest that the sorption of Pb(II) on NKF-6 zeolite is endothermic and spontaneous process. The results are quite important to understand the interaction of Pb(II) with zeolite in aqueous solutions. This investigation shows that the NKF-6 zeolite can be used as a suitable adsorbent for the preconcentration and solidification of Pb(II) from large volumes of aqueous solutions. [Copyright &y& Elsevier]