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1.
Sci Total Environ ; 731: 138951, 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32417472

RESUMO

Pyrite, a naturally occurring mineral, can be found extensively in coal. The change in the pyrite structure that occurs during coaling process, the ability of the pyrite-derived α-Fe2O3 to convert NO in the presence of NH3 before catalyst bed and the kinetic study were investigated in this work. The pyrite-derived α-Fe2O3 was obtained by calcining at 500, 600, 700, 800 °C and was characterized by the X-ray diffraction (XRD), N2 physisorption, the X-ray photoelectron spectrometer (XPS), the scanning electron microscope (SEM), UV-visible near-infrared spectroscopy (UV-vis DRS), the temperature-programmed desorption of ammonia (NH3-TPD) and the in situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS). The results indicated that the α-Fe2O3 derived from natural pyrite exhibited an affirmative effect on NO conversion in the presence of NH3 at reaction temperatures of 200-450 °C, particularly at 350 °C, the pyrite-derived α-Fe2O3 displayed the best efficiency for the NO conversion. In addition, the formed sulfate derived from the oxidation of pyrite enhanced the NO conversion at the temperature of 300-450 °C, while hinder the NO conversion at 200-275 °C. The in-situ DRIFTS and kinetic studies demonstrated that both the Eley-Rideal and Langmuir-Hinshelwood mechanism contributed to the selective catalytic reduction (SCR) of NO when the reaction temperature was over 200 °C, while selective catalytic oxidization (CO) happened over 300 °C. This study favored the understanding of the NO behavior in flue gas pipeline after sprawling NH3 and the mechanism of NO conversion before the catalyst bed.

2.
Environ Sci Pollut Res Int ; 27(11): 12376-12385, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31993902

RESUMO

Siderite is a naturally occurring mineral that can be found extensively in coal. The structural evolution of siderite in the process of coaling and its performance in the transformation of NO in the presence of NH3 were investigated in this work. In addition, the effects of the coexisting component, including vapor, SO2, and the alkali metal K, were also discussed. Heat treatment was performed at 450, 500, 550, 600, and 700 °C to obtain siderite-derived α-Fe2O3, which was then evaluated in de-NOx via the selective catalytic reduction (SCR) of NO with NH3 in a fixed bed. The X-ray diffraction (XRD), the X-ray fluorescence spectrometer (XRF), N2 adsorption-desorption (BET), the X-ray photoelectron spectrometer (XPS), the scanning electron microscope (SEM), and the transmission electron microscope (TEM) were used to investigate the variations in the morphology and structure of the thermally treated siderite. The results showed that siderite was gradually oxidized and decomposed into α-Fe2O3 with a nanoporous structure and large surface area of 27.27 m2 g-1 after calcination under an air atmosphere. The α-Fe2O3 derived from siderite at 500 °C (H500) exhibited an excellent SCR performance, where the NO conversion rate was great than 90% between 250 and 300 °C due to the pore structure and high specific surface area, additional adsorbed oxygen states, abundant oligomeric Fe oxide clusters, and large amount of acid sites. Regardless of the vapor content, SO2 concentration, and reaction temperature, the α-Fe2O3 derived from siderite at 500 °C (H500) still favored the conversion of NO. When the reaction temperature was lower than 350 °C, H500 favored the conversion of NO even in the presence of an alkali metal (K). The experimental data demonstrated the positive effect of siderite-derived α-Fe2O3 in SCR technology and provided insight into NO behavior in coaling flue gas after NH3 injection.

3.
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
4.
Huan Jing Ke Xue ; 40(10): 4553-4561, 2019 Oct 08.
Artigo em Chinês | MEDLINE | ID: mdl-31854823

RESUMO

δ-MnO2/zeolite nanocomposites were prepared with natural zeolite, potassium permanganate, and manganese sulfate by oxidation-reduction precipitation, which were used to simultaneously remove Fe2+, Mn2+, and NH4+-N from groundwater. To investigate the performance and mechanism of Fe2+, Mn2+, and NH4+-N removal from groundwater by δ-MnO2/zeolite nanocomposites, static batch experiments were conducted under different environmental conditions in a zero-oxygen atmosphere using SEM, TEM, Zeta potential, FTIR, and XPS techniques. The experimental results showed that the manganese-oxide-coated natural zeolite was δ-MnO2, and Fe2+, Mn2+, and NH4+-N adsorption on the δ-MnO2/zeolite nanocomposites could be best described with the pseudo-second-order kinetic model and the Langmuir model. In addition, the maximum adsorption capacities of Fe2+, Mn2+, and NH4+-N were calculated to be 215.1, 23.6, and 7.64 mg·g-1, respectively. The removal mechanism of NH4+-N from the solutions by zeolite was via the action of ion exchange, and the adsorption and oxidation catalysis of δ-MnO2-coated zeolite were responsible for the removal of Fe2+ and Mn2+. This research indicates that δ-MnO2/zeolite nanocomposites could be used as highly efficient adsorbents to simultaneously remove Fe2+, Mn2+, and NH4+-N from water.

6.
Sci Total Environ ; 651(Pt 1): 1020-1028, 2019 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-30266047

RESUMO

Magnetic biochar composites were successfully fabricated by pyrolysis of siderite and rice husk under N2 condition. The results of a variety of characterization implied magnetic biochar displayed porous structures with larger specific surface area. The batch adsorption experiments showed high adsorption properties of magnetic biochar composites toward U(VI) (52.63 mg/g at pH 4.0), whereas U(VI) adsorption was significantly influenced by Na2CO3 and HA. U(VI) adsorbed onto magnetic biochar was reduced to U(IV) by Fe3O4 according to XPS and XANES analyses. In addition, no significant effect of ionic strength of NaCl and EXAFS results, illustrated the inner-sphere surface complexation of U(VI) on magnetic biochar. Owing to the simple synthesis procedure, low cost, high adsorption efficiency, easy separation and environmental friendly, magnetic biochar can be considered as a potential adsorbent for the purification of U(VI)-bearing wastewater in environmental remediation.

7.
Environ Sci Pollut Res Int ; 25(31): 31091-31100, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30187409

RESUMO

The photochemical oxidation of di-n-butyl phthalate (DBP) by •OH radicals from nitrous acid (HONO) in atmospheric hydrometeors was explored by two techniques, steady-state irradiation, and laser flash photolysis (LFP). The effects of atmospheric liquid parameters on DBP transformation were systematically evaluated, showing that DBP does not react with HONO directly and •OH-initiated reactions are crucial steps for consumption and transformation of DBP. Two reaction channels are operative: •OH addition and hydrogen atom abstraction. The overall rate constant for the reaction of DBP with •OH is 5.7 × 109 M-1 s-1, and its specific rate constant for addition is 3.7 × 109 M-1 s-1 determined by using laser flash photolysis technique. Comparing the individual reaction rate constant for aromatic ring addition with the total rate constant, the majority of the •OH radicals (about 65%) attack the aromatic ring. The major transformation products were identified by GC-MS, and the trends of their yields derived from both ring addition and H-abstraction with time are discussed. These results provide important insights into the photochemical transformation of DBP in atmospheric hydrometeors and contribute to atmospheric aerosol chemistry.


Assuntos
Dibutilftalato/química , Radical Hidroxila/química , Ácido Nitroso/química , Aerossóis , Cromatografia Gasosa-Espectrometria de Massas , Cinética , Oxirredução
8.
Huan Jing Ke Xue ; 39(9): 4215-4221, 2018 Sep 08.
Artigo em Chinês | MEDLINE | ID: mdl-30188063

RESUMO

Nitrogen elements play an important role in the biogeochemical cycle of artificial wetlands. In this study, we investigated the anaerobic transformation of ammonia nitrogen and its main pathways in sediment in an artificial wetland. Results showed that the anaerobic ammonia oxidation (ANAMMOX) process and iron reduction occurred in wetland sediment, coupled with anaerobic ammonia oxidation (Feammox). Feammox used Fe(Ⅲ) to oxidize ammonia nitrogen to produce nitrogen; intermediate products were nitrate, nitrite, and N2O. Addition of ferrihydrite promoted the Feammox process and ammonia nitrogen loss caused by Feammox was enhanced from 1.69 to 2.72 mg·(kg·d)-1. When ferrihydrite was added, a loss of 28% of total nitrogen (TN) in the wetland occurred, associated with Feammox, increasing to 42%. Anaerobic ammonia oxidation was significantly inhibited with addition of ferrihydrite and TN loss in the system decreased by about 25%. Results showed that the formation of goethite by mineralization of ferrihydrite inhibited the ANAMMOX process, promoting Feammox to lead to competing electronic donors for the S-ANAMMOX process, causing inhibition of the S-ANAMMOX process. This achieves the purpose of reducing TN loss in the wetland system. In addition, this may have some significance for further understanding the interaction between iron reduction and the nitrogen cycle in the wetland.


Assuntos
Amônia/química , Mineração , Águas Residuárias/química , Purificação da Água , Áreas Alagadas , Anaerobiose , Compostos Férricos/química , Nitrogênio/química , Oxirredução
9.
J Environ Radioact ; 192: 219-226, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-29982006

RESUMO

Pantoea sp. TW18 isolated from radionuclide-contaminated soils was used for the bioremediation of radionuclides pollution. Accumulation mechanism of U(VI) on Pantoea sp. TW18 was investigated by batch experiments and characterization techniques. The batch experiments revealed that Pantoea sp. TW18 rapidly reached accumulation equilibrium at approximately 4 h with a high accumulation capacity (79.87 mg g-1 at pH 4.1 and T = 310 K) for U(VI). The accumulation data of U(VI) onto Pantoea sp. TW18 can be satisfactorily fitted by pseudo-second-order model. The accumulation of U(VI) on Pantoea sp. TW18 was affected by pH levels, not independent of ionic strength. Analysis of the FT-IR and XPS spectra demonstrated that accumulated U(VI) ions were primarily bound to nitrogen- and oxygen-containing functional groups (i.e., carboxyl, amide and phosphoryl groups) on the Pantoea sp. TW18 surface. This study showed that Pantoea sp. TW18 can be considered as a promising sorbent for remediation of radionuclides in environmental cleanup.


Assuntos
Biodegradação Ambiental , Pantoea/metabolismo , Microbiologia do Solo , Poluentes Radioativos do Solo/metabolismo , Urânio/metabolismo , Recuperação e Remediação Ambiental , Concentração Osmolar , Radioisótopos , Solo/química , Espectroscopia de Infravermelho com Transformada de Fourier
10.
Chemosphere ; 199: 130-137, 2018 May.
Artigo em Inglês | MEDLINE | ID: mdl-29433026

RESUMO

The potential of simultaneous removal of nitrate and phosphate from wastewater by a single anaerobic Fe(II) oxidizing denitrifiers (the strain PXL1) was assessed using siderite biofilters under different influent TOC concentrations and hydraulic retention times (HRTs) over a 160-day trial. Higher TOC concentrations promoted NO3- removal, while there was no significant influence on PO43- removal. Lowering down HRT from 10 h to 5 h did not significantly influence NO3- and PO43- removal. The NO3- removal performance and microbial community structure in the biofilters indicated that NO3- was reduced to N2 by both strain PXL1 and heterotrophic Acidovorax delafieldii. Iron content analysis of the used siderite along the biofilters showed that PO43- removal was improved by the bio-oxidation of Fe(II) in siderite to Fe(III) via the strain PXL1. The coexistence of the strain PXL1 and natural siderite in nitrate-contaminated aquifers provides a practical technology for in situ remediation of nutrient contaminated waterbodies.


Assuntos
Desnitrificação , Nitratos/isolamento & purificação , Fosfatos/isolamento & purificação , Águas Residuárias/química , Purificação da Água/métodos , Processos Autotróficos , Reatores Biológicos , Compostos Férricos , Filtração/métodos , Água Subterrânea , Nitratos/química
11.
Environ Technol ; 39(3): 317-326, 2018 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-28278084

RESUMO

Natural manganese ore catalysts for selective catalytic reduction (SCR) of NO with NH3 at low temperature in the presence and absence of SO2 and H2O were systematically investigated. The physical and chemical properties of catalysts were characterized by X-ray diffraction, Brunauer-Emmett-Teller (BET) specific surface area, NH3 temperature-programmed desorption (NH3-TPD) and NO-TPD methods. The results showed that natural manganese ore from Qingyang of Anhui Province had a good low-temperature activity and N2 selectivity, and it could be a novel catalyst in terms of stability, good efficiency, good reusability and lower cost. The NO conversion exceeded 85% between 150°C and 300°C when the initial NO concentration was 1000 ppm. The activity was suppressed by adding H2O (10%) or SO2 (100 or 200 ppm), respectively, and its activity could recover while the SO2 supply is cut off. The simultaneous addition of H2O and SO2 led to the increase of about 100% in SCR activity than bare addition of SO2. The formation of the amorphous MnOx, high concentration of lattice oxygen and surface-adsorbed oxygen groups and a lot of reducible species as well as adsorption of the reactants brought about excellent SCR performance and exhibited good SO2 and H2O resistance.


Assuntos
Amônia/química , Modelos Químicos , Óxido Nítrico/química , Temperatura , Catálise , Manganês/química , Oxirredução , Dióxido de Enxofre/química , Difração de Raios X
12.
J Hazard Mater ; 343: 176-180, 2018 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-28950205

RESUMO

Iron oxide may interact with other pollutants in the aquatic environments and further influence their toxicity, transport and fate. The current study was conducted to investigate the biodegradation of 2,4-dinitrophenol (2,4-DNP) in the presence of iron oxide of goethite under anoxic condition using nitrate as the electron acceptor. Experiment results showed that the degradation rate of 2,4-DNP was improved by goethite. High performance liquid chromatography-mass spectra analysis results showed that goethite promoted degradation and transformation of 2,4-diaminophenol and 2-amino-4-nitrophenol (2-nitro-4-aminophenol). Microbial community analysis results showed that the abundance of Actinobacteria, which have the potential ability to degrade PAHs, was increased when goethite was available. This might partially explain the higher degradation of 2,4-DNP. Furthermore, another bacterium of Desulfotomaculum reducens which could reduce soluble Fe(III) and nitrate was also increased. Results further confirmed that nanomaterials in the aquatic environment will influence the microbial community and further change the transformation process of toxic pollutants.


Assuntos
2,4-Dinitrofenol/metabolismo , Compostos de Ferro/química , Minerais/química , Nitratos/metabolismo , Poluentes Químicos da Água/metabolismo , 2,4-Dinitrofenol/química , Bactérias/genética , Bactérias/metabolismo , Biodegradação Ambiental , Reatores Biológicos , Genes Bacterianos/genética , Nitrogênio/metabolismo , Oxirredução , RNA Ribossômico 16S/genética , Poluentes Químicos da Água/química
13.
Chemosphere ; 188: 667-676, 2017 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-28923730

RESUMO

The photochemical behavior of goethite has been one of the most important topics in the field of environmental science due to it plays a significant role in the removal and transformation process of numerous pollutants. However, the interfacial electron transfer process of goethite is not clear. Using a nanosecond laser flash photolysis spectrometer, we report the transient spectroscopic observations of interfacial electron-transfer reactions in goethite dispersion under UV irradiation. Excitation of goethite generated conduction-band electron (ecb-) and hole (h+). The conduction band electron (ecb-) reacted with an electron acceptor, methylviologen dichloride hydrate (MV2+), forming reduced methylviologen (MV+) with a second-order rate constant of (2.6 ± 0.3) × 109 L mol-1 s-1. The concentration of MV+ was strongly influenced by MV2+ initial concentration and pH values. The flat band potential of goethite was calculated to be Efb (goethite, pH = 7) = 0.24 V (vs NHE). Oxygen did not react with conduction band electron of goethite. The present study provides a reliable method to investigate the photo-induced interfacial charge transfer of goethite.


Assuntos
Elétrons , Compostos de Ferro/química , Minerais/química , Processos Fotoquímicos/efeitos da radiação , Raios Ultravioleta , Cinética , Suspensões
14.
Artigo em Inglês | MEDLINE | ID: mdl-28956849

RESUMO

Manganese (Mn) oxide is a ubiquitous metal oxide in sub-environments. The adsorption of Cd(II) on Mn oxide as function of adsorption time, pH, ionic strength, temperature, and initial Cd(II) concentration was investigated by batch techniques. The adsorption kinetics showed that the adsorption of Cd(II) on Mn oxide can be satisfactorily simulated by pseudo-second-order kinetic model with high correlation coefficients (R² > 0.999). The adsorption of Cd(II) on Mn oxide significantly decreased with increasing ionic strength at pH < 5.0, whereas Cd(II) adsorption was independent of ionic strength at pH > 6.0, which indicated that outer-sphere and inner-sphere surface complexation dominated the adsorption of Cd(II) on Mn oxide at pH < 5.0 and pH > 6.0, respectively. The maximum adsorption capacity of Mn oxide for Cd(II) calculated from Langmuir model was 104.17 mg/g at pH 6.0 and 298 K. The thermodynamic parameters showed that the adsorption of Cd(II) on Mn oxide was an endothermic and spontaneous process. According to the results of surface complexation modeling, the adsorption of Cd(II) on Mn oxide can be satisfactorily simulated by ion exchange sites (X2Cd) at low pH and inner-sphere surface complexation sites (SOCd⁺ and (SO)2CdOH- species) at high pH conditions. The finding presented herein plays an important role in understanding the fate and transport of heavy metals at the water-mineral interface.


Assuntos
Cádmio/química , Compostos de Manganês/química , Óxidos/química , Adsorção , Concentração de Íons de Hidrogênio , Cinética , Temperatura , Termodinâmica
15.
Environ Sci Technol ; 51(16): 9227-9234, 2017 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-28741938

RESUMO

New nanoscale zerovalent iron/carbon (nZVI/C) composites were successfully prepared via heating natural hematite and pine sawdust at 800 °C under nitrogen conditions. Characterization by SEM, XRD, FTIR, and XPS analyses indicated that the as-prepared nZVI/C composites contained a large number of reactive sites. The lack of influence of the ionic strength revealed inner-sphere complexation dominated U(VI) uptake by the nZVI/C composites. Simultaneous adsorption and reduction were involved in the uptake process of U(VI) according to the results of XPS and XANES analyses. The presence of U-C/U-U shells demonstrated that innersphere complexation and surface coprecipitation dominated the U(VI) uptake at low and high pH conditions, respectively. The uptake behaviors of U(VI) by the nZVI/C composites were fitted well by surface complexation modeling with two weak and two strong sites. The maximum uptake capacity of U(VI) by the nZVI/C composites was 186.92 mg/g at pH 4.0 and 328 K. Additionally, the nZVI/C composites presented good recyclability and recoverability for U(VI) uptake in regeneration experiments. These observations indicated that the nZVI/C composites can be considered as potential adsorbents to remove radionuclides for environmental remediation.


Assuntos
Poluentes Químicos da Água , Adsorção , Carbono , Ferro , Concentração Osmolar
16.
J Biosci Bioeng ; 124(1): 71-75, 2017 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-28279646

RESUMO

Biological treatment played an important role in the treatment of landfill leachate. In the current study, acid mine drainage (AMD) was used as a source of sulfate to strengthen the anaerobic treatment of landfill leachate. Effects of chemical oxygen demand (COD) and SO42- mass concentration ratio on the decomposition of organic matter, methane production and sulfate reduction were investigated and the microbial community was analyzed using the high throughout methods. Results showed that high removal efficiency of COD, methane production and heavy metal removal was achieved when the initial COD/SO42- ratio (based on mass) was set at 3.0. The relative abundance of anaerobic hydrogen-producing bacteria (Candidatus Cloacamonas) in the experimental group with the addition of AMD was significantly increased compared to the control. Abundance of hydrogenotrophic methanogens of Methanosarcina and Methanomassiliicoccus was increased. Results confirmed that AMD could be used as sulfate resource to strengthen the biological treatment of landfill leachate.


Assuntos
Bactérias/metabolismo , Análise da Demanda Biológica de Oxigênio , Metais Pesados/isolamento & purificação , Metais Pesados/metabolismo , Metano/biossíntese , Mineração , Sulfatos/metabolismo , Reatores Biológicos/microbiologia , Precipitação Química , Concentração de Íons de Hidrogênio , Fatores de Tempo , Poluentes Químicos da Água/isolamento & purificação , Poluentes Químicos da Água/metabolismo
17.
Environ Technol ; 38(7): 827-834, 2017 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-27487524

RESUMO

A novel medium containing iron oxide-based porous ceramsite (IPC) and commercial ceramsite (CC) was used in two laboratory-scale upflow biological aerated filters (BAFs) to treat city wastewater to compare their efficacy in wastewater treatment. The IPC BAF and CC BAF were operated in water at 20-26°C, an air/water (A/W) ratio of: 3:1 and hydraulic retention times (HRTs) of 7, 3.5, 1.75, and 0.5 h and the removal of ammonia nitrogen (NH3-N), total nitrogen (TN), total organic carbon (TOC), and phosphorus (P) were studied. Our results indicated that IPC BAF was superior to CC BAF in terms of TOC, TN, NH3-N, and P removal. IPC had higher total porosity and larger total surface area than CC. The interconnected porous structure of IPC was suitable to microbial growth, protozoan, and metazoan organisms were primarily found in the accumulated biofilm layer. Biomass, in the biofilm layer, was detected at three distinct distances (300, 900, and 1500 mm) from the bottom of the inlet filter, again indicating that the IPC was more suitable for biomass growth. The presence of biomass improves the simultaneous removal efficiency of nitrogen and phosphorus in the IPC BAF. Thus, our findings support IPC as a material for use in filter media in wastewater treatment BAFs.


Assuntos
Compostos Férricos/química , Reatores Biológicos/microbiologia , Filtração , Fósforo/química , Eliminação de Resíduos Líquidos/métodos , Purificação da Água/métodos
18.
J Hazard Mater ; 322(Pt B): 488-498, 2017 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-27776872

RESUMO

The interaction mechanism of U(VI) on pyrrhotite was demonstrated by batch, spectroscopic and modeling techniques. Pyrite was selected as control group in this study. The removal of U(VI) on pyrite and pyrrhotite significantly decreased with increasing ionic strength from 0.001 to 0.1mol/L at pH 2.0-6.0, whereas the no effect of ionic strength was observed at pH >6.0. The maximum removal capacity of U(VI) on pyrite and pyrrhotite calculated from Langmuir model was 10.20 and 21.34mgg-1 at pH 4.0 and 333K, respectively. The XPS analysis indicated the U(VI) was primarily adsorbed on pyrrhotite and pyrite and then approximately 15.5 and 9.8% of U(VI) were reduced to U(IV) by pyrrhotite and pyrite after 20 days, respectively. Based on the XANES analysis, the adsorption edge of uranium-containing pyrrhotite located between UIVO2(s) and UVIO22+ spectra. The EXAFS analysis demonstrated the inner-sphere surface complexation of U(VI) on pyrrhotite due to the occurrence of U-S shell, whereas the U-U shell revealed the reductive co-precipitates of U(VI) on pyrrhotite/pyrite with increasing reaction times. The surface complexation modeling showed that outer- and inner-surface complexation dominated the U(VI) removal at pH<4 and pH>5.0, respectively. The findings presented herein play a crucial role in the removal of radionuclides on iron sulfide in environmental cleanup applications.

19.
Chemosphere ; 167: 462-468, 2017 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-27750170

RESUMO

The photochemical reaction between biphenyl (Bp) and N(III) under irradiation at 365 nm UV light was investigated. The results showed that Bp conversion efficiency was strongly influenced by N (III) concentration, Bp initial concentration and pH. Species-specific rate constants determined by reaction of Bp with H2ONO+ (k1), HONO (k2) and NO2- (k3) were k1 = (0.058 ± 0.005 L mol-1 s-1), k2 = (0.12 ± 0.06 L mol-1 s-1) and k3 = (0.0019 ± 0.0003 L mol-1 s-1), respectively. Laser flash photolysis studies confirmed that OH radical deriving from the photolysis of N(III) attacked aromatic ring to form Bp-OH adduct with a rate constant of 9.4 × 109 L mol-1 s-1. The products analysis suggested that Bp-OH adduct could be nitrated by N (III) and NO2 to generate nitro-compounds.


Assuntos
Poluentes Atmosféricos/química , Compostos de Bifenilo/química , Ácido Nitroso/química , Raios Ultravioleta , Água/química , Aerossóis , Poluentes Atmosféricos/efeitos da radiação , Compostos de Bifenilo/efeitos da radiação , Radical Hidroxila/química , Lasers , Ácido Nitroso/efeitos da radiação , Oxirredução , Processos Fotoquímicos , Fotólise
20.
Huan Jing Ke Xue ; 38(7): 2875-2882, 2017 Jul 08.
Artigo em Chinês | MEDLINE | ID: mdl-29964628

RESUMO

2,4-dichlorophenol(2,4-DCP), a highly toxic and refractory organic compound, was commonly used in pesticide production and thus widely distributed in water and soil. Goethite, magnetite and gypsum were added into the anaerobic system which simulated the natural anaerobic process to evaluate their effects on the anaerobic degradation of 2,4-DCP. It indicated that goethite, magnetite and gypsum had no appreciable adsorption ability toward 2,4-DCP under anaerobic condition. Mass balance analysis showed that only the transformation of 2,4-DCP to 4-chlorophenol(4-CP) occurred in all experimental groups. The addition of sodium acetate doubled the reductive dechlorination rate of 2,4-DCP in comparison with the groups without exogenous carbon source. The reductive dechlorination rate of 2,4-DCP was enhanced by the addition of goethite and magnetite, which was caused by the improved metabolic activity of dechlorination bacteria that played an important role in the anaerobic degradation of 2,4-DCP. Gypsum greatly inhibited or even stopped the degradation process of 2,4-DCP through restraining the growth and activity of dechlorination bacteria. This study will shed light on the migration and degradation of refractory chlorinated organic contaminants in anaerobic sedimentary environment, and the treatment of such matters in environmental technology.


Assuntos
Bactérias/metabolismo , Sulfato de Cálcio/química , Clorofenóis/metabolismo , Óxido Ferroso-Férrico/química , Compostos de Ferro/química , Minerais/química , Anaerobiose
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