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1.
Chemosphere ; 260: 127548, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-32688312

RESUMO

A novel Ag-doped SnS2@InVO4 composite was successfully synthesized for efficient uranium removal from wastewater through a facile hydrothermal method. The structure, morphology and optical property of materials were characterized using various instruments. The results proved that Ag-doped SnS2@InVO4 composite presented as hexangular nanosheets with about 4.87 nm pore size and 101.58 m2/g specific surface area. Further characterization demonstrated that photo-adsorption ability of visible light was enhanced and band gap was narrowed. The adsorption kinetics and isotherm of U(VI) on Ag-doped SnS2@InVO4 composite could be depicted via the Langmuir model and pseudo-second-order mode, and the maximum adsorption capacity of U(VI) reached 167.79 mg/g. The elimination of U(VI) of as-synthesized composites was studied by a synergy of adsorption and visible-light photocatalysis, and the optimal content of InVO4 was found to be 2 wt% with the highest removal efficiency of 97.6%. In addition, compared with pure SnS2 and Ag-doped SnS2, the Ag-doped SnS2@InVO4 composites exhibited superior photocatalytic performance for the conversion of soluble U(VI) to insoluble U(IV) under visible light. The excellent photocatalytic performance was mainly attributed to numerous surface-active sites, strong optical adsorption ability and narrow band gap. Simultaneously, the heterojunction between Ag-doped SnS2 and InVO4 promoted the separation and transfer of photoexcited charges. The cyclic experiments indicated the Ag-doped SnS2@InVO4 composite remained good structural stability and reusability. Finally, the possible mechanism was discussed based on the experimental analysis.


Assuntos
Urânio/química , Adsorção , Catálise , Luz , Prata , Águas Residuárias
2.
Chemosphere ; 258: 127152, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32544809

RESUMO

Graphene oxide (GO) has been proved with favorable affinity to U(VI), while some drawbacks such as poor dispersity and low adsorption performance limit its application. Herein, cetyltrimethylammonium bromide (CTAB) modified graphene oxide (MGO) composites were successfully fabricated, characterized and compared with graphene oxide (GO) in the sequestration of U(VI) in aqueous solutions. The results showed that maximum adsorption rate of MGO (99.21%) was obviously higher than that of GO (66.51%) under the same initial condition. Simultaneous introduction of C-H and NO coupled with the enhanced dispersity of GO after modification were mainly responsible for the updated performance verified with multiple characterization techniques. Based on the results of kinetics and isotherms investigations, the experimental data were best described by Pseudo-first-order kinetic model and Redlich-Peterson isotherm model. The results of ΔH, ΔS and ΔG show that adsorptive behaviors of uranyl ion on MGO are endothermic and spontaneous. The study provides a feasible alternative to the chemical modification of GO and enhancing the performance towards uranyl ion removal from solution.


Assuntos
Grafite/química , Urânio/química , Poluentes Químicos da Água/química , Adsorção , Cetrimônio/química , Concentração de Íons de Hidrogênio , Íons , Cinética , Microscopia Eletrônica de Varredura , Modelos Químicos , Espectroscopia de Infravermelho com Transformada de Fourier , Fatores de Tempo , Urânio/isolamento & purificação , Água , Poluentes Químicos da Água/isolamento & purificação , Poluentes Radioativos da Água/química , Poluentes Radioativos da Água/isolamento & purificação , Difração de Raios X
3.
Chemosphere ; 258: 127246, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32535442

RESUMO

Uranium may pose a hazard to ecosystems and human health due to its chemotoxic and radiotoxic properties. The long half-life of many U isotopes and their ability to migrate raise concerns over disposal of radioactive wastes. This work examines the long-term U bioavailability in aerobic soils following direct deposition or transport to the surface and addresses two questions: (i) to what extent do soil properties control the kinetics of U speciation changes in soils and (ii) over what experimental timescales must U reaction kinetics be measured to reliably predict long-term of impact in the terrestrial environment? Soil microcosms spiked with soluble uranyl were incubated for 1.7 years. Changes in UVI fractionation were periodically monitored by soil extractions and isotopic dilution techniques, shedding light on the binding strength of uranyl onto the solid phase. Uranyl sorption was rapid and strongly buffered by soil Fe oxides, but UVI remained reversibly held and geochemically reactive. The pool of uranyl species able to replenish the soil solution through several equilibrium reactions is substantially larger than might be anticipated from typical chemical extractions and remarkably similar across different soils despite contrasting soil properties. Modelled kinetic parameters indicate that labile UVI declines very slowly, suggesting that the processes and transformations transferring uranyl to an intractable sink progress at a slow rate regardless of soil characteristics. This is of relevance in the context of radioecological assessments, given that soil solution is the key reservoir for plant uptake.


Assuntos
Monitoramento Ambiental/métodos , Poluentes Radioativos do Solo/análise , Solo/química , Urânio/análise , Adsorção , Disponibilidade Biológica , Ecossistema , Cinética , Poluentes Radioativos do Solo/química , Solubilidade , Reino Unido , Urânio/química
4.
PLoS One ; 15(5): e0229452, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32357150

RESUMO

Most of South Africa's energy is derived from the combustion of coal in pulverized coal-fired power plants (CFPP). However, when compared with the rest of the world, limited information regarding the main radioactive elements (U and Th) and specific radionuclides of interest (K40, Ra226 and Th232) from South African CFPP is available in the public domain. This paper aims to quantify the U, Th and specific radionuclides found in the coal used in selected South African CFPP in comparison to world averages found in literature. The U and Th concentrations were obtained by ICP-MS. The main radionuclides, K40, Ra226 and Th238, were quantified using gamma spectrometry. The U concentration and Th concentrations for the coal used in all the power plants was above the world average of 1.9 mg/kg and 3.2 mg/kg respectively. The coals with the highest Th content originated from the Mpumalanga power plant, while the U content in the Freestate power plant samples was the highest of the three. The concentrations of the K40 were between 88.43±10.75-110.76±8.92 Bq/kg, which are in-line with world averages of 4-785 Bq/kg. Similarly, the Ra226 and Th232 values were between 21.69±2.83-52.63±4.04 Bq/kg and 19.91±1.24-22.97±1.75 Bq/kg respectively, which are also in line with the world averages of 1-206 Bq/kg and 1-170 Bq/kg respectively. Radiological hazard indices such as radium equivalent (Raeq); external hazard index (Hex) and internal hazard index (Hin), that were estimated from these average radionuclide concentrations were less than the prescribed values found in literature. This indicated that no significant health risk was posed by the coal being used from these coal fields.


Assuntos
Carvão Mineral/análise , Centrais Elétricas , Poluentes Radioativos do Solo/isolamento & purificação , Cinza de Carvão/análise , Humanos , Doses de Radiação , Monitoramento de Radiação , Radioisótopos/química , Radioisótopos/isolamento & purificação , Rádio (Elemento)/química , Rádio (Elemento)/isolamento & purificação , Poluentes Radioativos do Solo/química , África do Sul , Espectrometria gama , Tório/química , Tório/isolamento & purificação , Urânio/química , Urânio/isolamento & purificação
5.
Chemosphere ; 255: 126942, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32387732

RESUMO

Knowledge of the geochemical behavior of uranium is critical for the safe disposal of radioactive wastes. Biotite, a Fe(II)-rich phyllosilicate, is a common rock-forming mineral and a major component of granite or granodiorite. This work comprehensively studied the sorption of U(VI) on biotite surface with batch experiments and analyzed the uranium speciation with various spectroscopic techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and time-resolved fluorescence spectra (TRFS). Our results indicated that uranyl ions could penetrate into the interlayer of biotite, this ion-exchange process was pH-dependent and only favorable under acidic condition. Instead of precipitation or reduction to uraninite, the TRFS results strongly suggests U(VI) forms surface complexes under the neutral and alkaline condition, though the number and structure of surface species could not be identified accurately. Besides, the oxidation of biotite with peroxide hydrogen showed that structural Fe(II) would have a very low redox reactivity. With leaching experiments, zeta potential analysis and thermodynamics calculation, we discussed the possible reasons for inhibition of U(VI) reduction at the biotite-water interface. Our results may provide insight on interaction mechanism of uranium at mineral-water interface and help us understand the migration behavior of uranium in natural environments.


Assuntos
Silicatos de Alumínio/química , Compostos Ferrosos/química , Urânio/química , Concentração de Íons de Hidrogênio , Troca Iônica , Minerais , Oxirredução , Espectroscopia Fotoeletrônica , Resíduos Radioativos , Dióxido de Silício , Termodinâmica
6.
Chemosphere ; 255: 126948, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32387733

RESUMO

Uranium phosphites have recently emerged as promising materials to remediate radioactive contamination. In this study, the redox mechanisms of uranyl phosphites at mineral surfaces have been addressed by periodic DFT calculations with dispersion corrections. Different from other ligands, the phosphite anions (H2PO3-, HPO32-) are efficient reducing agents for uranyl reduction, and the redox reactions are divided into three steps, as isomerization between two phosphite anion isomers (Step 1), conformational transition (Step 2) and dissociation of the water molecule (Step 3). A second water molecule is critical to lower the activation barriers of Step 1, and all activation barriers are moderate so that the redox reactions occur favorably under normal conditions, which are further dramatically accelerated by the highly exergonic Step 3. Accordingly, formation of uranyl phosphites becomes an effective approach to manage uranium pollution. Moreover, the lower activation barriers for H2PO3- rather than HPO32- rationalize the superior reduction activities of uranyl phosphites and the enhanced stability of U(IV) products at lower pH conditions. Owing to the cooperative proton/electron transfer, the U(VI) reduction to U(IV) and P(III) oxidation to P(V) are completed within one step, with transition states being featured by the U(V) and P(IV) species.


Assuntos
Minerais/química , Fosfitos/química , Urânio/química , Transporte de Elétrons , Elétrons , Oxirredução , Prótons
7.
Chemosphere ; 255: 126951, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32417512

RESUMO

The processing of sediment to accurately characterize the spatially-resolved depth profiles of geophysical and geochemical properties along with signatures of microbial density and activity remains a challenge especially in complex contaminated areas. This study processed cores from two sediment boreholes from background and contaminated core sediments and surrounding groundwater. Fresh core sediments were compared by depth to capture the changes in sediment structure, sediment minerals, biomass, and pore water geochemistry in terms of major and trace elements including pollutants, cations, anions, and organic acids. Soil porewater samples were matched to groundwater level, flow rate, and preferential flows and compared to homogenized groundwater-only samples from neighboring monitoring wells. Groundwater analysis of nearby wells only revealed high sulfate and nitrate concentrations while the same analysis using sediment pore water samples with depth was able to suggest areas high in sulfate- and nitrate-reducing bacteria based on their decreased concentration and production of reduced by-products that could not be seen in the groundwater samples. Positive correlations among porewater content, total organic carbon, trace metals and clay minerals revealed a more complicated relationship among contaminant, sediment texture, groundwater table, and biomass. The fluctuating capillary interface had high concentrations of Fe and Mn-oxides combined with trace elements including U, Th, Sr, Ba, Cu, and Co. This suggests the mobility of potentially hazardous elements, sediment structure, and biogeochemical factors are all linked together to impact microbial communities, emphasizing that solid interfaces play an important role in determining the abundance of bacteria in the sediments.


Assuntos
Sedimentos Geológicos/química , Urânio/química , Poluentes Radioativos da Água/química , Bactérias , Água Subterrânea/química , Nitratos/análise , Compostos Orgânicos , Sulfatos/análise , Urânio/análise , Poluentes Radioativos da Água/análise
8.
Chemosphere ; 254: 126855, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32361538

RESUMO

Under suboxic and anoxic environments, magnetite is one corrosion product of iron being used in nuclear waste canisters. Previous studies have reported a complete reduction of U(VI) on the surfaces of biogenic and natural magnetite crystals, while incomplete reductions to U(V)/U(IV)-containing species have been observed on chemosynthetic magnetite. To date, the reasons behind such disparities remain poorly studied. This study shows that uranyl nitrate or uranyl acetate is mainly reduced to UO2+x oxides (e.g., U4O9, U3O8, etc.) by chemosynthetic magnetite under acidic conditions. When extra zero valent-iron was added, the reaction rate was significantly increased, and an improved but still incomplete U(VI) reduction was observed. Nitrate and ferric ions are ubiquitous in natural environment. Results demonstrate that the nitrate ion associated with uranyl and the ferric ion contained in magnetite or generated from U(VI) reduction have a non-negligible oxidative effect on the final products, which could mainly account for the incomplete reduction of U(VI) by chemosynthetic magnetite in the absence or presence of extra zero valent-iron observed in this study. Furthermore, the surface loading of uranium in U-Fe systems can, in part, unravel the discrepancies in various observations. An enhanced understanding of the U-Fe reaction mechanism can facilitate predictions of the extent of uranium mobility with respect to nuclear waste disposal and radioactive decontamination.


Assuntos
Óxido Ferroso-Férrico/química , Urânio/química , Poluentes Radioativos da Água/química , Ferro/química , Nitratos , Compostos Organometálicos , Oxirredução , Resíduos Radioativos , Nitrato de Uranil , Poluentes Radioativos da Água/análise
9.
Chemosphere ; 254: 126671, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32334243

RESUMO

Efficient elimination of U(VI) from uranium wastewater is an urgent task for sustainable nuclear energy and environmental protection. In this study, magnetic graphene oxide decorated graphitic carbon nitride (mGO/g-C3N4) nanocomposite was prepared and used for photocatalytic reduction of U(VI) in wastewater under visible LED light irradiation for the first time. The batch experiments indicated that the mGO/g-C3N4 (mGCN) nanocomposite could efficiently reduce U(VI) under visible LED light, and a high U(VI) extraction capacity of 2880.6 mg/g was obtained with an extraction efficiency of 96.02%. The transmission electron microscopy (TEM) elemental mapping, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analyses demonstrated that the soluble U(VI) was immobilized by transforming it to metastudtite ((UO2)O2·2H2O) by mGCN nanocomposite under visible LED light irradiation. This work indicated that the mGCN is a promising visible light catalyst for treatment of uranium wastewater.


Assuntos
Processos Fotoquímicos , Urânio/química , Poluentes Radioativos da Água/química , Catálise , Grafite , Luz , Óxido de Magnésio , Nanocompostos/química , Compostos de Nitrogênio , Águas Residuárias/química
10.
Chemosphere ; 250: 126315, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32234624

RESUMO

Uranium (U) is both chemically toxic and radioactive. Uranium mill tailings (UMTs) are one of the most important sources of U contamination in the environment, wherein the mechanisms that control U release from UMTs with different granularities have not yet been well understood. Herein, the release behaviours and underlying release mechanisms of U from UMTs with five different particle size fractions (<0.45, 0.45-0.9, 0.9-2, 2-6 and 6-10 mm) were studied with a well-defined leaching test (ANS 16.1) combined with geochemical and mineralogical characterizations. The results showed that the most remarkable U release unexpectedly emerged from UMT2-6 mm; in contrast, the smallest particle size UMT<0.45 mm contributed to the least U release. The predominant mechanism of U release from UMT2-6 mm was the oxidative dissolution of U-bearing sulfides, while abundant gypsum present in UMT<0.45 mm inhibited U release. The study highlights the importance of combined geochemical and mineralogical investigation when performing leaching tests of mineral-containing hazardous materials such as UMTs with consideration of particle size effects. The findings also indicate that elevating the content of gypsum and avoiding the oxidation of sulfides can effectively help immobilize and minimize the residual U release from the UMTs.


Assuntos
Urânio/química , Poluentes Radioativos da Água/química , Sulfato de Cálcio , Minerais , Tamanho da Partícula , Radioatividade , Poluentes Radioativos do Solo/análise , Poluentes Radioativos do Solo/química , Urânio/análise , Poluentes Radioativos da Água/análise
11.
Dalton Trans ; 49(10): 3209-3221, 2020 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-32091513

RESUMO

A new chitosan/aluminum sludge composite aerogel (CS/ASca) exhibiting good selectivity, easy separation potential, and high adsorption capacity was synthesized by combining chitosan (CS) and aluminum sludge from waterworks (AS). The adsorption of U(vi) by the CS/ASca was assessed as a function of solution pH, adsorption time, temperature, initial concentrations of uranium, and coexisting ions. The systematic batch experiments reveal that the adsorption kinetics is described by a pseudo-second-order model, and the sorption thermodynamics involves spontaneous endothermic processes. At a pH of 4, 308 K, and initial uranium concentrations of 10-700 mg L-1, the maximum adsorption capacity of the CS/ASca for U(vi) (simulated by the Langmuir model) was 434.64 mg g-1. Data from scanning electron microscopy/energy dispersive spectrometry, Fourier-transform infrared, and X-ray photoelectron spectroscopy indicated that uranyl ion adsorption was predominantly associated with the complexation of U(vi) with the amino and hydroxyl groups on the surface of the CS/ASca. In addition, our results demonstrated that the Mg(ii), Pb(ii), Na(i), and K(i) ions had little or no effect on the sorption of U(vi) on the CS/ASca. This study provides new clues for the treatment of radioactive wastewater.


Assuntos
Alumínio/química , Quitosana/química , Urânio/química , Eliminação de Resíduos Líquidos/métodos , Poluentes Radioativos da Água/química , Adsorção , Resíduos Industriais , Cinética , Termodinâmica
12.
Chemosphere ; 249: 126116, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32058132

RESUMO

The present studies interpret the speciation of uranyl (UO22+) with the most ubiquitous class of natural species named pyrazines in terms of stability, speciation and its identification, thermodynamics, spectral properties determined by a range of experimental techniques and further evidenced by theoretical insights. UO22+ forms ML and ML2 kind of species with a qualitative detection of ML3 species, while the ESI-MS identified the formation of all the complexes including ML3. Both the ligands act as bidentate chelators with a difference in ring size and coordinating atoms in the complex formed. The ML3 complexes involve the third ligand participation as monodentate via carboxylate only due to the restricted coordination number and space around the UO22+ ion to accommodate three ligand molecules in its primary coordination sphere. All the complexes are found to be endothermic and purely entropy driven formations. The complex formations showed redshift in the absorption spectra and the shift was further enhanced from ML to ML2 formation. The UO22+ ion redox properties are used to explore the redox potential and heterogeneous electron-transfer kinetic parameters as a function of pH and concentration of UO22+ in presence of pyrazine carboxylates. Interestingly, the cyclic voltammograms identified the ligands also as redox sensitive. The theoretical calculation gave inputs to understand the complex formation at the molecular level with major emphasis on geometry optimization, energetics, bonding parameters, molecular orbital diagrams and bond critical point analyses. The experimental observations in combination with theoretical addendum provided detailed knowledge on the interaction of UO22+ with pyrazine-2-carboxylate and pyrazine-2,3-dicarboxylates.


Assuntos
Pirazinas/química , Urânio/química , Poluentes Químicos da Água/química , Ácidos Carboxílicos , Cinética , Ligantes , Oxirredução , Termodinâmica , Compostos de Urânio/química
13.
Chemosphere ; 244: 125411, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-32050322

RESUMO

Uranium is a long lived radioactive element which is naturally present in minute concentrations in igneous, sedimentary and metamorphic rocks. These rocks when subjected to weathering results in the formation of soil which also has traces of uranium. Distribution coefficient (Kd) is a crucial parameter in environmental assessment which is used to predict the interaction and transport of uranium in groundwater. The objective of the study is to estimate the Kd of uranium in soils and to develop a relation between this and the soil parameters. Seven rock samples and twenty three soil samples were collected during this study. The Kd of rock samples of different grain sizes where determined and the soil samples were analysed for electrical conductivity, pH, grain size, bulk density, particle density, porosity, calcium carbonate, cation exchange capacity and Kd. The Kd of the soil increases with increase in soil pH up to 6, after which it gradually decreases. Multiple regression analysis was performed to quantify the effect of various soil parameters on soil Kd and equations were statistically significant. Thus, soil Kd in a region could be predicted using limited soil properties with such statistically significant equations.


Assuntos
Água Subterrânea/química , Poluentes Radioativos do Solo/química , Solo/química , Urânio/química , Concentração de Íons de Hidrogênio , Análise de Regressão , Poluentes Radioativos do Solo/análise , Urânio/análise , Poluentes Radioativos da Água/análise , Poluentes Radioativos da Água/química
14.
Sci Total Environ ; 703: 135604, 2020 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-31771849

RESUMO

Novel iron/carbon composites were successfully prepared via coupling of cellulose with iron oxides (e.g. α-FeOOH, Fe2O3 and Fe(NO3)3·9H2O) at different temperatures under nitrogen atmosphere. Characterization by various techniques implied that chemical interaction between cellulose and Fe3O4/Fe0 existed in the as-prepared iron/carbon composites. The site of interaction between cellulose and iron precursors was illustrated (mainly combined with COO-). The self-reduction of Fe3+ to Fe2+ or even Fe0 and the interaction between carbon and Fe3O4/Fe0 in the calcination process realized the strong magnetism of the composites. Batch experiments and spectroscopic techniques indicated that the maximum adsorption capacity of MHC-7 for U(VI) (105.3 mg/g) was significantly higher than that of MGC-7 (86.0 mg/g) and MFC-7 (79.0 mg/g), indicating that Fe2O3 can be regarded as the remarkable iron resource for the iron/carbon composites. XPS results revealed that the oxygen-containing groups were responsible for the adsorption process of U(VI) on iron/carbon composites, and the adsorption of carbon and reduction of Fe0/Fe3O4 toward U(VI) were synergistic during the reaction process. In addition, the iron/carbon composites exhibited a good recyclability, recoverability and stability for U(VI) adsorption in the regeneration experiments. These findings demonstrated that the iron/carbon composites can be considered as valuable adsorbents in environmental cleanup and the Fe2O3 was a promising iron resource for the preparation of iron/carbon composites.


Assuntos
Celulose/química , Ferro/química , Urânio/química , Poluentes Radioativos da Água/química , Adsorção , Carbono , Recuperação e Remediação Ambiental , Compostos Férricos/química , Nitrogênio
15.
Environ Geochem Health ; 42(8): 2547-2556, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31858357

RESUMO

Uranium is a contaminant of major concern across the US Department of Energy complex that served a leading role in nuclear weapon fabrication for half a century. In an effort to decrease the concentration of soluble uranium, tripolyphosphate injections were identified as a feasible remediation strategy for sequestering uranium in situ in contaminated groundwater at the Hanford Site. The introduction of sodium tripolyphosphate into uranium-bearing porous media results in the formation of uranyl phosphate minerals (autunite) of general formula {X1-2[(UO2)(PO4)]2-1·nH2O}, where X is a monovalent or divalent cation. The stability of the uranyl phosphate minerals is a critical factor that determines the long-term effectiveness of this remediation strategy that can be affected by biogeochemical factors such as the presence of bicarbonates and bacterial activity. The objective of this research was to investigate the effect of bicarbonate ions present in the aqueous phase on Ca-autunite dissolution under anaerobic conditions, as well as the role of metal-reducing facultative bacterium Shewanella oneidensis MR1. The concentration of total uranium determined in the aqueous phase was in direct correlation to the concentration of bicarbonate present in the solution, and the release of Ca, U and P into the aqueous phase was non-stoichiometric. Experiments revealed the absence of an extensive biofilm on autunite surface, while thermodynamic modeling predicted the presence of secondary minerals, which were identified through microscopy. In conclusion, the dissolution of autunite under the conditions studied is susceptible to bicarbonate concentration, as well as microbial presence.


Assuntos
Bicarbonatos/química , Shewanella/metabolismo , Urânio/química , Anaerobiose , Água Subterrânea , Minerais/química , Minerais/metabolismo , Fosfatos/química , Fosfatos/metabolismo , Polifosfatos , Solubilidade , Termodinâmica , Urânio/metabolismo , Compostos de Urânio/química , Compostos de Urânio/metabolismo , Poluentes Químicos da Água/química , Poluentes Químicos da Água/metabolismo
16.
Inorg Chem ; 58(21): 14626-14634, 2019 Nov 04.
Artigo em Inglês | MEDLINE | ID: mdl-31613591

RESUMO

The special linear dioxo cation structure of the uranyl cation, which relegates ligand coordination to an equatorial plane perpendicular to the O═U═O vector, poses an unusual challenge for the rational design of efficient chelating agents. Therefore, the planar hexadentate ligand rational design employed in this work incorporates two bidentate catecholamine (CAM) chelating moieties and a flexible linker with a ß-dicarbonyl chelating moiety (ß-dicarbonyl(CAM)2 ligands). The solution thermodynamics of ß-dicarbonyl(CAM)2 with a uranyl cation was investigated by potentiometric and spectrophotometric titrations. The results demonstrated that the pUO22+ values are significantly higher than for the previously reported TMA(2Li-1,2-HOPO)2, and efficient chelation of the uranyl cation was realized by the planar hexadentate ß-dicarbonyl(CAM)2. The efficient chelating ability of ß-dicarbonyl(CAM)2 was attributed to the presence of the more flexible ß-dicarbonyl chelating linker and planar hexadentate structure, which favors the geometric arrangement between ligand and uranyl coordinative preference. Meanwhile, ß-dicarbonyl(CAM)2 also exhibits higher antiradical efficiency in comparison to butylated hydroxyanisole. These results indicated that ß-dicarbonyl(CAM)2 has potential application prospects as a chelating agent for efficient chelation of a uranyl cation.


Assuntos
Antioxidantes/química , Catecolaminas/química , Quelantes/química , Termodinâmica , Urânio/química , Antioxidantes/síntese química , Antioxidantes/farmacologia , Compostos de Bifenilo/antagonistas & inibidores , Catecolaminas/síntese química , Catecolaminas/farmacologia , Cátions/química , Quelantes/síntese química , Quelantes/farmacologia , Ligantes , Estrutura Molecular , Picratos/antagonistas & inibidores
17.
Environ Sci Pollut Res Int ; 26(33): 34487-34498, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31642018

RESUMO

A novel assembly method was used to prepare the sulfhydryl functionalized magnetic SBA-15 (SH-M-SBA-15). The physicochemical properties of SH-M-SBA-15 were characterized by TEM, XRD, EDS, FT-IR, BET, and VSM. Batch adsorption experiments were conducted to investigate the influence of initial uranium concentration, dosage of adsorbent, pH values, contact time, and temperature on the adsorption efficiency and behaviors. The adsorption types were analyzed from the aspects of kinetic, isotherms, and thermodynamic. The results show that the specific surface area of SH-M-SBA-15 is 316.67 m2/g, which is smaller than that of SBA-15 (692.18 m2/g). However, compared with SBA-15, SH-M-SBA-15 has more surface sulfhydryl functional groups. The addition of this group can improve the adsorption of uranyl ions by SH-M-SBA-15. The optimal adsorption conditions were adsorption dosage 40 mg/L, pH 6, temperature 35 °C, contact time 180 min, and initial uranium concentration 35 mg/L. Under this condition, the maximum adsorption amount of uranyl ion by SH-M-SBA-15 can reach 804.79 mg/g, which is much higher than the highest adsorption capacity of uranyl ion by SBA-15 (146.23 mg/g). The adsorption process was better depicted by the Langmuir isotherm model. The process was consistent with the quasi-second-order model. ΔG was negative and ΔH was positive, indicating spontaneous and endothermic adsorption.


Assuntos
Modelos Químicos , Dióxido de Silício/química , Compostos de Sulfidrila/química , Adsorção , Concentração de Íons de Hidrogênio , Íons , Cinética , Fenômenos Magnéticos , Magnetismo , Espectroscopia de Infravermelho com Transformada de Fourier , Temperatura , Termodinâmica , Urânio/química , Purificação da Água
18.
Ecotoxicol Environ Saf ; 186: 109746, 2019 Dec 30.
Artigo em Inglês | MEDLINE | ID: mdl-31606641

RESUMO

In this paper, polypropylene (PP) nanofibers were prepared using the melt forcespinning technology by a handmade device. Then, the surface of PP nanofibers was grafted through the high energy electron beams (EB) pre-irradiation method by acrylonitrile and methacrylic acid monomers with grafting percentage of 145.55%. The 92% of grafted cyano functional groups on nanofibers were converted to amidoxime groups, then modified by an alkaline solution. Characterization and surface morphology of nanofibers were investigated by Fourier Transform Infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The produced adsorbent was used to adsorb U(VI) ions from simulated seawater. The maximum adsorption was 83.24 mg/g in the optimal time of 60 min and optimal pH of 4. The optimum desorption efficiency was 80% in HCl 0.5 M. The kinetic data in optimum conditions showed that the adsorption followed an S-shaped kinetic model. The Adsorption equilibrium studies presented S-shape isotherm model that confirmed the adsorption occurs both on the adsorbent surface and in its pores The thermodynamic studies indicated spontaneous adsorption of uranyl ions and the higher efficiency adsorption at higher temperatures. The selectivity of adsorbent for metal ions followed the order V(V)>U(VI)>CO(II)>Ni(II)>Fe(II). These results shows that the prepared and modified nanofibers in this work can be considered as an effective and promising adsorbents for removal of uranium ions from seawater with high efficiency.


Assuntos
Recuperação e Remediação Ambiental/métodos , Nanofibras/química , Polipropilenos/química , Água do Mar/química , Urânio/química , Poluentes Químicos da Água/química , Adsorção , Concentração de Íons de Hidrogênio , Íons/química , Cinética , Espectroscopia de Infravermelho com Transformada de Fourier , Termodinâmica
19.
J Environ Sci (China) ; 85: 156-167, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31471022

RESUMO

This study evaluated uranium sequestration performance in iron-rich (30 g/kg) sediment via bioreduction followed by reoxidation. Field tests (1383 days) at Oak Ridge, Tennessee demonstrated that uranium contents in sediments increased after bioreduced sediments were re-exposed to nitrate and oxygen in contaminated groundwater. Bioreduction of contaminated sediments (1200 mg/kg U) with ethanol in microcosm reduced aqueous U from 0.37 to 0.023 mg/L. Aliquots of the bioreduced sediment were reoxidized with O2, H2O2, and NaNO3, respectively, over 285 days, resulting in aqueous U of 0.024, 1.58 and 14.4 mg/L at pH 6.30, 6.63 and 7.62, respectively. The source- and the three reoxidized sediments showed different desorption and adsorption behaviors of U, but all fit a Freundlich model. The adsorption capacities increased sharply at pH 4.5 to 5.5, plateaued at pH 5.5 to 7.0, then decreased sharply as pH increased from 7.0 to 8.0. The O2-reoxidized sediment retained a lower desorption efficiency at pH over 6.0. The NO3--reoxidized sediment exhibited higher adsorption capacity at pH 5.5 to 6.0. The pH-dependent adsorption onto Fe(III) oxides and formation of U coated particles and precipitates resulted in U sequestration, and bioreduction followed by reoxidation can enhance the U sequestration in sediment.


Assuntos
Biodegradação Ambiental , Poluentes Radioativos do Solo/metabolismo , Urânio/metabolismo , Sedimentos Geológicos/química , Poluentes Radioativos do Solo/química , Tennessee , Urânio/química
20.
Nucl Med Rev Cent East Eur ; 22(2): 56-59, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31482557

RESUMO

BACKGROUND: 44Sc is becoming attractive as a PET radionuclide due to its decay characteristics. It can be produced from 44Ca present in natural calcium with 2.08% abundance. MATERIALS AND METHODS: The targets were mostly prepared from natural CaCO3 or metallic calcium in the form of pellets. After irradiation they were dissolved in 3 M hydrochloric acid and 44Sc was separated from excess of calcium by precipitation of scandium hydroxide using ammonia. Alternatively, targets were dissolved in 11 M hydrochloric acid and 44Sc was separated by extraction chromatography on UTEVA resin. As the next step, in both processes 44Sc was further purified on a cation exchange resin. Initially, the separation procedures were developed with 46Sc as a tracer. Gamma spectrometry with a high purity germanium detector was used to determine the separation efficiency. Finally, the CaCO3 pellet with 99.2% enrichment in 44Ca was activated with protons via 44Ca(p,n)44Sc nuclear reaction. RESULTS: Altogether twenty two irradiations and separations were performed. The working procedures were developed and the quality of separated 44Sc solution was confirmed by radiolabeling of DOTATATE. The chemical purity of the product was sufficient for preclinical experiments. At the end of around 1 hour proton beam irradiation of CaCO3 pellet with 99.2% enrichment in 44Ca the obtained radioactivity of 44Sc was more than 4.8 GBq. CONCLUSION: 44Sc can be produced inexpensively with adequate yields and radionuclidic purity via 44Ca(p,n)44Sc nuclear reaction in small cyclotrons. The recovery yield in both investigated separation methods was comparable and amounted above 90%. The obtained 44Sc was pure in terms of radionuclide and chemical purity, as shown by the results of peptide radiolabeling.


Assuntos
Elementos da Série Actinoide/química , Precipitação Química , Hidróxidos/química , Radioquímica/métodos , Radioisótopos/química , Radioisótopos/isolamento & purificação , Escândio/química , Escândio/isolamento & purificação , Urânio/química , Carbonato de Cálcio/química , Ciclotrons , Marcação por Isótopo , Radioquímica/instrumentação
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