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1.
Sci Total Environ ; 675: 31-40, 2019 Jul 20.
Artigo em Inglês | MEDLINE | ID: mdl-31026641

RESUMO

MnO2 is a common material for the fabrication and design of capacitive deionization (CDI) devices but there is little information on the role of MnO2 crystal phase on CDI performance. A series of MnO2 (α, ß, γ, and δ phase) were synthesized and fabricated as cathodes for studying the CDI performance as affected by pH in simple batch mode experiments. Our results revealed that the deionization efficiency decreased with increased negative surface charge as a result of the deprotonated surface. Importantly, this correlation was pH independent and the surface heterogeneity due to different MnO2 phase was likely responsible for the different degree of surface ionization and consequently the CDI efficiency. Results of electrochemical impedance spectroscopy analyses further implicated that a highly ionized surface would result in a diffusion layer with a great resistance that conversely inhibited the access of co-ions in the CDI process. This indicated the applied potential was mainly responsible for driving ions transporting through the double layer resistance instead of accommodating them (electrosorption). Based on our results, the surface heterogeneity as a result of different spatially distributed MnO6 octahedral would be accounted for the varying degree of surface ionization and consequently the discrepancy in CDI efficiency among different MnO2 phases.

2.
Artigo em Inglês | MEDLINE | ID: mdl-30746626

RESUMO

This study evaluated the use of magnetite (Fe3O4), carbon black (CB), and Fe3O4-CB composites activated by persulfate (PS) at circumneutral pH to oxidize polycyclic aromatic hydrocarbons (PAHs) in marine sediments. In addition, the in vitro cytotoxic activity and apoptotic response of the obtained degradation products were investigated. Chemical analyses showed that the total PAH concentration was 26,263 ng/g for sediment samples from an industrial port area. Highly toxic BaP was the main contributor to the TEQ in sediments. Source analyses demonstrated that the PAHs in the sediment were derived from coal combustion. In this study, we found that the PS oxidation processes effectively degrade PAHs at concentration levels of 1.7 × 10-5 M at pH 6.0. The 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay was employed to assess the cytotoxicity of the PAH degradation products before and after Fe3O4/PS, CB/PS, and Fe3O4-CB/PS oxidation treatment using a human hepatoma carcinoma cell line (HepG2) and a zebrafish (Danio rerio) embryonic cell line (ZF4). Each sample extract showed a marked dose-related response, with the cell viability reduced by 82% in the case of HepG2 and 58% in the case of ZF4 at 100 µg/mL after the Fe3O4-CB/PS process. The PAH degradation products had different effects on the cell morphologies of the two cell lines. The results suggested that the ZF4 cell model is more sensitive than HepG2 to the toxicity of the PAH samples.

3.
Langmuir ; 35(3): 628-640, 2019 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-30607960

RESUMO

Associating MnO2 with carbonaceous supports profoundly enhances capacitive deionization (CDI) efficiency. A fundamental question of how the surface chemistry of MnO2 itself influences CDI efficiency is not yet fully understood. In this study, the effect of surface ionization on the CDI efficiencies of Fe-, Co-, and Ni-doped α-MnO2 (<0.1 mol %) as a model cathode material was studied. A pattern that CDI efficiency decreased with increasing negative surface charge density resulting from surface deprotonation was noted. This is likely attributed to the appreciable co-ion expulsion occurring at a highly ionized surface in the mesopores of MnO2. It is thus concluded that the combination of surface charge modification and a microporous environment would be important for CDI efficiency enhancement by minimizing co-ion exclusion effect. In the former case, structural stress adjustment by doping elements would be a practical route to regulate the p Ka1 and p Ka2 values and consequently the degree of surface ionization of MnO2.

4.
ACS Appl Mater Interfaces ; 10(38): 32736-32746, 2018 Sep 26.
Artigo em Inglês | MEDLINE | ID: mdl-30180542

RESUMO

Energy consumption is always a major issue hindering the universal application of membrane-based filtration system. We herein demonstrated a low-energy-consumption microfiltration system that can be operated under ambient pressure while a great metal ion rejection rate (>95%) accompanied by a high permeate flux (100 L/m2h) was concurrently reached. This achievement was closely correlated to the enhanced metal ion adsorption by grafted carboxyl groups at the cellulose filter paper through esterification. Adsorbed metal ions consequently enhanced Donnan exclusion effect and therefore high rejection rate was achieved. Rejection rate of modified membrane was strongly correlated to the formation constant of associated carboxyl group to metal ions. Our results would be important for developing low-energy-consumption filtration systems for water and wastewater treatment application.

5.
Polymers (Basel) ; 9(7)2017 Jun 23.
Artigo em Inglês | MEDLINE | ID: mdl-30970919

RESUMO

Laser patterning on polymeric materials is considered a green and rapid manufacturing process with low material selection barrier and high adjustability. Unlike microelectromechanical systems (MEMS), it is a highly flexible processing method, especially useful for prototyping. This study focuses on the development of polymer surface modification method using a 193 nm excimer laser system for the design and fabrication of a microfluidic system similar to that of natural vasculatures. Besides from poly(dimethyl siloxane) (PDMS), laser ablation on biodegradable polymeric material, poly(glycerol sebacate) (PGS) and poly(1,3-diamino-2-hydroxypropane-co-polyol sebacate) (APS) are investigated. Parameters of laser ablation and fabrication techniques to create microchannels are discussed. The results show that nano/micro-sized fractures and cracks are generally observed across PDMS surface after laser ablation, but not on PGS and APS surfaces. The widths of channels are more precise on PGS and APS than those on PDMS. Laser beam size and channel depth are high correlation with a linear relationship. Repeated laser ablations on the same position of scaffolds reveal that the ablation efficiencies and edge quality on PGS and APS are higher than on PDMS, suggesting the high applicability of direct laser machining to PGS and APS. To ensure stable ablation efficiency, effects of defocus distance into polymer surfaces toward laser ablation stability are investigated. The depth of channel is related to the ratio of firing frequency and ablation progression speed. The hydrodynamic simulation of channels suggests that natural blood vessel is similar to the laser patterned U-shaped channels, and the resulting micro-patterns are highly applicable in the field of micro-fabrication and biomedical engineering.

6.
Environ Monit Assess ; 188(3): 180, 2016 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-26899028

RESUMO

The elemental content of fish scales is known to be a reliable biogeochemical tag for tracing the origin of fishes. In this study, this correlation is further confirmed to exist on the surface of fish scales using a novel environmental analytical method, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), which bypasses several complicated sample preparation procedures such as acid digestion and pre-concentration. The results suggest that the elemental ratios of Sr/Ca, Ba/Ca, and Mn/Ca on the surface of fish scales are strongly correlated with the geochemical environment of their original habitat. This correlation is further demonstrated to be sensitive to variation of water in the habitat due to the adsorbed inorganic ions. In this sense, the limitation of fish scales as a biogeochemical tag is the sensitivity of LA-ICP-MS toward the studied elements. Graphical abstract Illustration of the connection between element distribution pattern over the surface of fish scales and biogeochemical environment of its habitat.


Assuntos
Ecossistema , Monitoramento Ambiental/métodos , Peixes/metabolismo , Oligoelementos/metabolismo , Poluentes Químicos da Água/metabolismo , Animais , Meio Ambiente , Espectrometria de Massas , Oligoelementos/análise , Poluentes Químicos da Água/análise
7.
J Colloid Interface Sci ; 466: 28-35, 2016 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-26704473

RESUMO

The consideration of water energy nexus inspires the environmental engineering community to pursue a more sustainable strategy in the wastewater treatment. One potential response would be to enhance the performance of the low-pressure driven filtration system. To reach this objective, it is essential to have a better understanding regarding the surface interaction between the target substance and the surface of membrane. In this study, the hollow fiber ceramic membranes were coated with a goethite layer in order to enhance the Co(2+) rejection. Experimental results indicate that higher Co(2+) rejections are always accompanied with the significant reduction in the permeability. Based on the consideration of electroviscous effect, the surface interactions including the induced changes in viscosity, pore radius and Donnan effect in the goethite layer are likely responsible for the pH dependent behaviors in the rejection and permeability. These results could be valuable references to develop the filtration system with high rejection along with acceptable degree of permeability in the future.

8.
J Hazard Mater ; 270: 92-101, 2014 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-24553353

RESUMO

In this paper, we demonstrate a means of simultaneously solving two serious environmental issues by reutilization of calcinated mixture of pulverized waste oyster shells blending with poly(methyl methacrylate) (PMMA) nanospheres to prepare CaO-based sorbents for CO2 capture. After 10 cycles of isothermal carbonation/calcination at 750°C, the greatest CO2 uptake (0.19 g CO2/g sorbent) was that for the sorbent featuring 70 wt% of PMMA, which was almost three times higher than that (0.07 g CO2/g sorbent) of untreated waste oyster shell. The greater CO2 uptake was likely a result of particle size reduction and afterwards surface basicity enhancement and an increase in the volume of mesopores and macropores. Following simplified life cycle assessment, whose all input values were collected from our experimental results, suggested that a significant CO2 emission reduction along with lesser human health and ecosystems impacts would be achieved immediately once waste is reutilized. Most importantly, the CO2 uptake efficiency must be greater than 20% or sorbents prepared from limestone mining would eventually produce a net positive CO2 emission.


Assuntos
Poluentes Atmosféricos/química , Exoesqueleto , Compostos de Cálcio/química , Dióxido de Carbono/química , Nanosferas/química , Óxidos/química , Polimetil Metacrilato/química , Adsorção , Animais , Sequestro de Carbono , Ostreidae , Tamanho da Partícula , Reciclagem , Propriedades de Superfície , Gerenciamento de Resíduos/métodos , Resíduos
9.
J Radioanal Nucl Chem ; 300(1): 393-407, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-26224970

RESUMO

Diffusion is a dominant mechanism regulating the transport of released nuclides. The through-diffusion method is typically applied to determine the diffusion coefficients (D). Depending on the design of the experiment, the concentrations in the source term [i.e., inlet reservoir (IR)] or the end term [i.e., outlet reservoir (OR)] can be fixed or vary. The combinations involve four distinct models (i.e., the CC-CC model, CC-VC model, VC-CC model, and the VC-VC model). Studies discussing the VC-CC model are scant. An analytical method considering the decay effect is required to accurately interpret the radioactive nuclide diffusion experiment results. Therefore, we developed a CC-CC model and a CC-VC model with a decay effect and the simplified formulas of these two models to determine the diffusion coefficient (i.e., the CC-CC method and CC-VC method). We also proposed two simplified methods using the VC-VC model to determine the diffusion coefficient straightforwardly based upon the concentration variation in IR and OR. More importantly, the best advantage of proposed method over others is that one can derive three diffusion coefficients based on one run of experiment. In addition, applying our CC-VC method to those data reported from Radiochemica Acta 96:111-117, 2008; and J Contam Hydrol 35:55-65, 1998, derived comparable diffusion coefficient lying in the identical order of magnitude. Furthermore, we proposed a formula to determine the conceptual critical time (Tc), which is particularly beneficial for the selection of using CC-VC or VC-VC method. Based on our proposed method, it becomes possible to calculate diffusion coefficient from a through-diffusion experiment in a shorter period of time.

10.
ACS Appl Mater Interfaces ; 5(16): 7937-49, 2013 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-23865744

RESUMO

It has been suggested that a high concentration of Fe(3+) in solution, a low pH, and noncomplexing ions of high ionic strength are all essential for developing a high-quality hematite array. Our curiosity was piqued regarding the role of the electrolyte ions in the hydrothermal synthesis of hematite photoanodes. In this study, we prepared hematite photoanodes hydrothermally from precursor solutions of 0.1 M FeCl3 at pH 1.55 with a background electrolyte of 1.0 M sodium halide (NaF, NaCl, NaBr, or NaI). We compared the structures and properties of the as-obtained hematite photoanodes with those of the material prepared in 1.0 M NaNO3, the most widely adopted electrolyte in previous studies. Among our studied systems, we found that the hematite photoanode prepared in NaCl solution was the only one possessing properties similar to those of the sample obtained from the NaNO3 solution-most importantly in terms of photoelectrochemical performance (ca. 0.2 mA/cm(2) with +0.4 V vs SCE). The hematites obtained from the NaF, NaBr, and NaI solutions exhibited much lower (by approximately 2 orders of magnitude) photocurrent densities under the same conditions, possibly because of their relatively less ordered crystallinity and the absence of rodlike morphologies. Because the synthetic protocol was identical in each case, we believe that these two distinct features reflect the environments in which these hematite photoanodes were formed. Consistent with the latest studies reported in the literature of the X-ray photoelectron spectra of fast-frozen hematite colloids in aqueous solutions, it appears that the degree of surface ion loading at the electrolyte-hematite interface (Stern layer) is critical during the development of hematite photoanodes. We suspect that a lower ion surface loading benefits the hematite developing relatively higher-order and a rodlike texture, thereby improving the photoelectrochemical activity.


Assuntos
Eletrodos , Compostos Férricos/química , Brometos/química , Catálise , Compostos Férricos/síntese química , Cloreto de Sódio/química , Compostos de Sódio/química , Fluoreto de Sódio/química , Iodeto de Sódio/química
11.
J Agric Food Chem ; 61(21): 5009-15, 2013 May 29.
Artigo em Inglês | MEDLINE | ID: mdl-23646931

RESUMO

In this study, the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was adopted to determine the distribution of inorganic elements, including Ca, Cu, Fe, Mg, Mn, S, P, Pb, and Zn, in honeybees (Apis melifera L.). Two features are particularly noteworthy. First, it was found there is a significant amount of Fe located at the fringe of the abdomen in worker bees; ultrasonic imaging, scanning electron microscopy, and magnetic resonance imaging revealed that it arose from magnetic Fe-bearing nanoparticles (NPs) having an average diameter of approximately 40 nm. Interestingly, only worker bees contained these magnetic Fe-bearing NPs; no similar features appeared in larvae, pupae, wasps, or drones. Second, a detectable amount of Pb accumulated particularly in the alimentary canals of worker bees. Again, no detectable amounts of Pb in larvae, pupae, drones, or wasps, yet a level of 0.24 ± 0.05 mg/kg of Pb in pollen; therefore, the diet appears to be the primary pathway for environmental pollutants entering the honeybees' food chain.


Assuntos
Abelhas/química , Abelhas/fisiologia , Poluentes Ambientais/análise , Comportamento Alimentar , Metais/análise , Animais , Poluentes Ambientais/metabolismo , Terapia a Laser , Espectrometria de Massas , Metais/metabolismo
12.
Anal Bioanal Chem ; 404(10): 3025-36, 2012 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-23052863

RESUMO

Understanding the cytotoxicity of quantum dots strongly relies upon the development of new analytical techniques to gather information about various aspects of the system. In this study, we demonstrate the in vivo biodistribution and fate of CdSe quantum dots in the murine model by means of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). By comparing the hot zones of each element acquired from LA-ICP-MS with those in fluorescence images, together with hematoxylin and eosin-stained images, we are able to perceive the fate and in vivo interactions between quantum dots and rat tissues. One hour after intravenous injection, we found that all of the quantum dots had been concentrated inside the spleen, liver and kidneys, while no quantum dots were found in other tissues (i.e., muscle, brain, lung, etc.). In the spleen, cadmium-114 signals always appeared in conjunction with iron signals, indicating that the quantum dots had been filtered from main vessels and then accumulated inside splenic red pulp. In the liver, the overlapped hot zones of quantum dots and those of phosphorus, copper, and zinc showed that these quantum dots have been retained inside hepatic cells. Importantly, it was noted that in the kidneys, quantum dots went into the cortical areas of adrenal glands. At the same time, hot zones of copper appeared in proximal tubules of the cortex. This could be a sign that the uptake of quantum dots initiates certain immune responses. Interestingly, the intensity of the selenium signals was not proportional to that of cadmium in all tissues. This could be the result of the decomposition of the quantum dots or matrix interference. In conclusion, the advantage in spatial resolution of LA-ICP-MS is one of the most powerful tools to probe the fate, interactions and biodistribution of quantum dots in vivo.


Assuntos
Compostos de Cádmio/farmacocinética , Terapia a Laser , Espectrometria de Massas , Pontos Quânticos , Compostos de Selênio/farmacocinética , Animais , Rim/ultraestrutura , Terapia a Laser/métodos , Fígado/ultraestrutura , Espectrometria de Massas/métodos , Camundongos , Microscopia de Fluorescência , Baço/ultraestrutura , Distribuição Tecidual
13.
J Contam Hydrol ; 138-139: 1-14, 2012 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-22771814

RESUMO

A valid performance assessment of radioactive waste repositories strongly depends on the reliability of nuclide transport parameters, including distribution and diffusion coefficients. To reduce the waste produced and time spent conducting diffusion experiments, a robust model is required to accurately interpret the experiment results. Therefore, we developed a through-diffusion model with parent-daughter nuclide decay chain. We validated our model through comparisons with the Moridis model (Moridis, 1999) and Bharat model (Bharat et al., 2009), assessing our model and these two models using the distribution of parent nuclide concentrations. This strongly supports the rationality and functionality of extending our proposed model to daughter nuclides. In this study, we derived analytical solutions for the parent nuclides of the through-diffusion experiment using the multicompartment (MC) model. We also propose a simplified formula for estimating the apparent diffusion coefficient of parent nuclides based on the analytical solutions. Through numerical experiments, we verified the feasibility of the formula. Our models are useful for determining the apparent diffusion coefficient of daughter nuclides when conducting through-diffusion experiments with parent-daughter nuclide decay chains. Additionally, the proposed models offer the advantages of saving time and reducing experimental waste.


Assuntos
Modelos Químicos , Resíduos Radioativos/análise , Radioatividade , Difusão
14.
Chem Commun (Camb) ; 48(5): 729-31, 2012 Jan 18.
Artigo em Inglês | MEDLINE | ID: mdl-22117192

RESUMO

Films of crystalline WO(3) nanosheets oriented perpendicular to tungsten substrates were grown by a surfactant-free hydrothermal method, followed by sintering. The films exhibit photoelectrochemical oxygen evolution at low overpotential.

15.
J Hazard Mater ; 192(3): 1079-87, 2011 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-21763071

RESUMO

A reliable performance assessment of radioactive waste repository depends on better knowledge of interactions between nuclides and geological substances. Numerical fitting of acquired experimental results by the surface complexation model enables us to interpret sorption behavior at molecular scale and thus to build a solid basis for simulation study. A lack of consensus on a standard set of assessment criteria (such as determination of sorption site concentration, reaction formula) during numerical fitting, on the other hand, makes lower case comparison between various studies difficult. In this study we explored the sorption of cesium to argillite by conducting experiments under different pH and solid/liquid ratio (s/l) with two specific initial Cs concentrations (100mg/L, 7.5 × 10(-4)mol/L and 0.01 mg/L, 7.5 × 10(-8)mol/L). After this, numerical fitting was performed, focusing on assessment criteria and their consequences. It was found that both ion exchange and electrostatic interactions governed Cs sorption on argillite. At higher initial Cs concentration the Cs sorption showed an increasing dependence on pH as the solid/liquid ratio was lowered. In contrast at trace Cs levels, the Cs sorption was neither s/l dependent nor pH sensitive. It is therefore proposed that ion exchange mechanism dominates Cs sorption when the concentration of surface sorption site exceeds that of Cs, whereas surface complexation is attributed to Cs uptake under alkaline environments. Numerical fitting was conducted using two different strategies to determine concentration of surface sorption sites: the clay model (based on the cation exchange capacity plus surface titration results) and the iron oxide model (where the concentration of sorption sites is proportional to the surface area of argillite). It was found that the clay model led to better fitting than the iron oxide model, which is attributed to more amenable sorption sites (two specific sorption sites along with larger site density) when using clay model. Moreover, increasing s/l ratio would produce more sorption sites, which helps to suppress the impact of heterogeneous surface on Cs sorption behavior under high pH environments.


Assuntos
Césio/análise , Resíduos Perigosos , Resíduos Radioativos/análise , Eliminação de Resíduos/métodos , Adsorção , Silicatos de Alumínio , Cromatografia por Troca Iônica/métodos , Argila , Compostos Férricos/análise , Substâncias Perigosas , Concentração de Íons de Hidrogênio , Modelos Teóricos , Propriedades de Superfície , Taiwan
16.
Appl Radiat Isot ; 68(12): 2140-6, 2010 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-20656497

RESUMO

In this work the desorption of cesium ions from crushed granite in synthetic groundwater (GW) and seawater (SW) was investigated. Results were compared with those obtained in deionized water (DW) and in two kinds of extraction solutions, namely: MgCl(2) and NaOAc (sodium acetate). In general, the desorption rate of Cs from crushed granite increased proportionally with initial Cs loadings. Also, amounts of desorbed Cs ions followed the tendency in the order SW>GW>NaOAc approximately equal MgCl(2)>DW solutions. This indicated that the utilization of extraction reagents for ion exchange will underestimate the Cs desorption behavior. Fitting these experimental data by Langmuir model showed that these extraction reagents have reduced Cs uptake by more than 90%, while only less than 1% of adsorbed Cs ions are still observed in GW and SW solutions in comparison to those in DW. Further SEM/EDS mapping studies clearly demonstrate that these remaining adsorbed Cs ions are at the fracture areas of biotite.


Assuntos
Césio/química , Dióxido de Silício , Adsorção , Microscopia Eletrônica de Varredura , Modelos Teóricos , Água
17.
Environ Sci Technol ; 44(13): 5142-7, 2010 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-20536145

RESUMO

Cationic surfactants modified clays exhibit high sorptive capability toward anionic radionuclides but retention of cationic radionuclides was concurrently reduced. In this study, organoclays were synthesized by intercalating a variety of primary/quaternary alkylammonium species (NH(2)R/(CH(3))(3)N(+)RBr(-), where R = benzyl, dodecyl, and octadecyl) into bentonite MX-80. The effect of surfactant's properties on enhancing or limiting cationic sorption capability was investigated by performing Cs sorption experiments. Experimental results were analyzed using the MINEQL+ software by considering Cs uptake by structural and edge sorption sites. Bentonites that were intercalated with primary alkylammonium surfactants had a higher sorptive capacity than those intercalated with quaternary alkylammonium surfactants. Samples intercalated with octadecyl-bearing surfactants had the lowest sorption rate. XRD and FTIR analyses revealed that each organoclay had a characteristic arrangement of alkyl chains. The cation retention of organoclays was dominated by the extent of hydrophobic interactions affected by the local distribution and arrangement of surfactants. The intercalated primary alkylammoniun surfactants tended to transform into local clusters with a high packing density, leaving more structural sites available for Cs uptake. In contrast, the NH(3)R(+)-surfactants tended to form a denser monolayer over clay surface, inhibiting the retention of Cs at structural sites.


Assuntos
Césio/química , Compostos Orgânicos/química , Tensoativos/química , Adsorção , Algoritmos , Silicatos de Alumínio , Cátions , Argila , Concentração de Íons de Hidrogênio , Interações Hidrofóbicas e Hidrofílicas , Modelos Teóricos , Software , Espectroscopia de Infravermelho com Transformada de Fourier , Difração de Raios X
18.
J Hazard Mater ; 173(1-3): 335-42, 2010 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-19747773

RESUMO

In this study, the performance of phosphoric acid activated montmorillonite (PAmmt) was evaluated by cesium ions adsorption experiments. The PAmmt samples were obtained by activating with 1, 3 and 5 mol L(-1) of phosphoric acid, respectively under reflux for 3, 12, and 24h. Experimental results demonstrated that the treatment of raw K-10 montmorillonite with phosphoric acid increased the materials' affinity for Cs uptake and no significant amount of suspension solids were produced. A relatively insignificant variation in the CEC value was observed. Furthermore, PAmmt also showed high adsorption selectivity toward Cs ions. The improved sorptive properties were mainly related to the increased surface area and the relatively higher surface charge density. Increased specific surface area was the resulted from partial decomposition of lamellar structure of mmt; while the higher surface charge density was caused by the protonation of octahedral Al-OH sites during the acid activation. Generally speaking, stronger acid concentration and longer activation times would produce relatively more decomposed PAmmt particles. However, as the activation exceeds 3h, the precipitation of Si(4+) would passivate PAmmt against further acid attacks. Based upon our results, acid activation by phosphoric acid could produce PAmmt samples with high sorption capacity and selectivity, and good structural integrity, which are beneficial to be used at radioactive waste repository.


Assuntos
Bentonita/química , Ácidos Fosfóricos/química , Resíduos Radioativos/análise , Eliminação de Resíduos/métodos , Ácidos , Adsorção , Tampões (Química) , Césio/química , Fluoretos/química , Porosidade , Espectroscopia de Infravermelho com Transformada de Fourier , Sulfatos/química , Propriedades de Superfície , Termodinâmica , Difração de Raios X
19.
J Hazard Mater ; 161(2-3): 854-61, 2009 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-18515005

RESUMO

The adsorption of cesium onto crushed granite was investigated under different physicochemical conditions including contact time, Cs loading, ionic strength and temperature. In addition, the distribution of adsorbed Cs was examined by X-ray diffraction (XRD) and EDS mapping techniques. The results showed that Cs adsorption to crushed granite behaved as a first-order reaction with nice regression coefficients (R(2) > or = 0.971). Both Freundlich and Langmuir models were applicable to describe the adsorption. The maximum sorption capacity determined by Langmuir model was 80 micromol g(-1) at 25 degrees C and 10 micromol g(-1) at 55 degrees C. The reduced sorption capacity at high temperature was related to the partial enhancement of desorption from granite surface. In general, Cs adsorption was exothermic (DeltaH<0, with median of -12 kJ mol(-1)) and spontaneous (DeltaG<0, with median of -6.1 at 25 degrees C and -5.0 kJ mol(-1) at 55 degrees C). The presence of competing cations such as sodium and potassium ions in synthetic groundwater significantly reduces the Cs adsorption onto granite. The scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM/EDS) mapping method provided substantial evidences that micaceous minerals (biotite in this case) dominate Cs adsorption. These adsorbed Cs ions were notably distributed onto the frayed edges of biotite minerals. More importantly, the locations of these adsorbed Cs were coincided with the potassium depletion area, implying the displacement of K by Cs adsorption. Further XRD patterns displayed a decreased intensity of signal of biotite as the Cs loading increased, revealing that the interlayer space of biotite was affected by Cs adsorption.


Assuntos
Césio/química , Dióxido de Silício/química , Adsorção , Silicatos de Alumínio/química , Físico-Química/métodos , Compostos Ferrosos/química , Concentração de Íons de Hidrogênio , Íons , Cinética , Microscopia Eletrônica de Varredura/métodos , Modelos Químicos , Potássio/química , Temperatura , Termodinâmica , Poluentes Químicos da Água/química , Difração de Raios X
20.
J Hazard Mater ; 162(1): 530-5, 2009 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-18579288

RESUMO

This study investigated breakthrough curves (BTCs) from a series of column experiments, including different column lengths and flow rates, of a conservative tracer, tritium oxide (HTO), and a radionuclide, cesium, in crushed granite using a reactive transport model. Results of the short column, with length of 2cm, showed an underestimation of the retardation factor and the corresponding HTO BTCs cannot be successfully modeled even with overestimated fluid dispersivity. Column supporting elements, including filters and rings, on both ends of packed granite were shown to be able to induce additional dispersive mixing, thus significantly affecting BTCs of short columns while those of the long column, with length of 8cm, were less affected. By increasing flow rates from 1mL/min to 5mL/min, the contribution of structural dispersive mixing to the false tilting of short column BTCs still cannot be detached. To reduce the influence of structural dispersivity on BTCs, the equivalent pore volume of column supporting materials should be much smaller than that of packed porous medium. The total length of column supporting structures should be greatly shorter than that of porous medium column.


Assuntos
Césio/química , Dióxido de Silício/química , Algoritmos , Radioisótopos de Césio/química , Modelos Químicos , Politetrafluoretileno , Água do Mar/análise , Solubilidade , Trítio/química , Água/química , Abastecimento de Água/análise
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