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Berlin Brandenburg

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  • 1
    Language: English
    In: Journal of Colloid And Interface Science, Sept 1, 2013, Vol.405, p.44(7)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jcis.2013.05.041 Byline: Matthias Handel, Thilo Rennert, Kai U. Totsche Abstract: Display Omitted Article History: Received 20 February 2013; Accepted 17 May 2013
    Keywords: Oxides ; Manganese Compounds
    ISSN: 0021-9797
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Environmental pollution, 2011, Vol.159(5), pp.1398-1405
    Description: Arsenic mobility may increase in liquid phase due to association with colloidal Fe oxides. We studied the association of As with Fe oxide colloids in the effluent from water-saturated soil columns run under anoxic conditions. Upon exfiltration, the solutions, which contained Fe²⁺, were re-aerated and ferrihydrite colloids precipitated. The entire amount of effluent As was associated with the ferrihydrite colloids, although PO₄ ³⁻, SiO₄ ⁴⁻, CO₃ ²⁻ and dissolved organic matter were present in the effluent during ferrihydrite colloid formation. Furthermore, no subsequent release of As from the ferrihydrite colloids was observed despite the presence of these (in)organic species known to compete with As for adsorption on Fe oxides. Arsenic was bound via inner-sphere complexation on the ferrihydrite surface. FTIR spectroscopy also revealed adsorption of PO₄ ³⁻ and polymerized silica. However, these species could not impede the quantitative association of As with colloidal ferrihydrite in the soil effluents. ; p. 1398-1405.
    Keywords: Iron Oxides ; Dissolved Organic Matter ; Effluents ; Arsenic ; Adsorption ; Polymerization ; Anaerobic Conditions ; Ferrihydrite ; Iron ; Colloids ; Silica ; Fourier Transform Infrared Spectroscopy ; Soil
    ISSN: 0269-7491
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  • 3
    Language: English
    In: Environmental Pollution, August, 2013, Vol.179, p.301(14)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.envpol.2013.04.029 Byline: Markus Wehrer, Juliane Mai, Sabine Attinger, Kai U. Totsche Abstract: Release of contaminants from non-aqueous phase liquids (NAPLs) is often limited by the dynamic exchange with aqueous solutions governed by a priori unknown kinetic laws. Release experiments require a thorough evaluation of the potential and limitations of kinetic models to reveal release processes. In this study, we investigated the characteristic concentration-time profiles of various models for the release of contaminants from an organic phase into an aqueous solution under no flow conditions. Criteria have been tested that allow for distinction of a first order one domain, a first order two domain, a spherical diffusion model, a spherical diffusion model with a time variable diffusion coefficient, a model for diffusion in a sphere with organic film, and a model for diffusion in a sphere with an aqueous film. The results can serve to evaluate the processes potentially governing release of organic contaminants from non-aqueous liquid phases. Author Affiliation: (a) Department of Earth and Environmental Sciences, Rutgers, The State University of New Jersey, 101 Warren Street, Newark 07102, United States (b) Lehrstuhl fur Hydrogeologie, Institut fur Geowissenschaften, Friedrich-Schiller-Universitat Jena, Burgweg 11, 07749 Jena, Germany (c) Department Computational Hydrosystems CHS, Helmholtz Centre for Environmental Research GmbH - UFZ, Permoserstra[sz]e 15, 04318 Leipzig, Germany Article History: Received 31 October 2012; Revised 13 March 2013; Accepted 15 April 2013
    ISSN: 0269-7491
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Geochimica et Cosmochimica Acta, 15 November 2015, Vol.169, pp.167-183
    Description: Iron oxides represent a substantial fraction of secondary minerals and particularly affect the reactive properties of natural systems in which they formed, e.g. in soils and sediments. Yet, it is still obscure how transient conditions in the solution will affect the properties of in situ precipitated Fe oxides. Transient compositions, i.e. compositions that change with time, arise due to predominant non-equilibrium states in natural systems, e.g. between liquid and solid phases in soils. In this study, we characterize Fe–OM co-precipitates that formed in pH-neutral exfiltrates from anoxic topsoils under transient conditions. We applied soil column outflow experiments, in which Fe was discharged with the effluent from anoxic soil and subsequently oxidized in the effluent due to contact with air. Our study features three novel aspects being unconsidered so far: (i) the transient composition of soil-derived solutions, (ii) that pedogenic Fe oxides instead of Fe salts serve as major source for Fe in soil solution and (iii) the presence of exclusively soil-derived organic and inorganic compounds during precipitation. The experiments were carried out with two topsoil materials that differed in composition, texture and land use. Derived from Mössbauer spectroscopy, broad distributions in quadrupole splittings (0–2 mm s ) and magnetic hyperfine fields (35–53 T) indicated the presence of low-crystalline ferrihydrite and even lower crystalline Fe phases in all Fe–OM co-precipitates. There was no unequivocal evidence for other Fe oxides, i.e. lepidocrocite and (nano)goethite. The Fe–OM co-precipitates contained inorganic (P, sulfate, silicate, Al, As) and organic compounds (proteins, polysaccharides), which were concurrently discharged from the soils. Their content in the Fe–OM co-precipitates was controlled by their respective concentration in the soil-derived solution. On a molar basis, OC and Fe were the main components in the Fe–OM co-precipitates (OC/Fe ratio = 0.5–2). The elemental composition of the Fe–OM co-precipitates was in accordance with the sequential precipitation of Fe(III)phosphates/arsenates prior to the formation of ferrihydrite. This explains decreasing Si contents in the Fe–OM co-precipitates with increasing availability of P. With respect to constant mean quadrupole splittings and slightly decreasing mean magnetic hyperfine fields, increasing contents of OC, P and Al in the Fe–OM co-precipitates did not further increase the structural disorder of the Fe polyhedra, while the crystallite interactions slightly decreased. Scanning electron microscopy and dynamic light scattering revealed the coincidental presence of variably sized aggregates and a considerable amount of Fe–OM co-precipitates, which remained dispersed in solution for months. Thus, variably composed Fe–OM co-precipitates with highly diverse aggregate sizes and comparably constant poor crystallinity can be expected after the oxidation of Fe in transient, soil-derived solutions.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 5
    Language: English
    In: Journal of Colloid And Interface Science, 01 September 2013, Vol.405, pp.44-50
    Description: Cryptomelane-type octahedral molecular sieves (K-OMS-2) were successfully synthesized at ambient pressure and temperature by a simple one-step reaction pathway. We designed three synthesis mixes based on redox reactions of either MnSO or MnCl together with KMnO in aqueous solution. The synthesis products were characterized structurally (XRD, FTIR spectroscopy), morphologically (SEM, BET surface area), and chemically (SEM-EDX, ICP-OES). For all mixes, a precursor octahedral layered K-birnessite (K-OL-1) was formed after 1 d that subsequently transformed into K-OMS-2. This transformation process depends on the pH of the reaction solution, the respective Mn(II) salt and time. We obtained K-OMS-2 materials with BET surface areas between 50.4 and 104.5 m g and different crystallinities. The described method is reliable, reproducible, easy to handle and may be the basis to produce well defined Mn oxides that could be used for remediation and catalysis purposes.
    Keywords: Octahedral Molecular Sieve ; K-Oms-2 ; K-Ol-1 ; Nanowires ; Mn Oxide ; Bet Surface ; Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
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  • 6
    Language: English
    In: Journal of colloid and interface science, 2013, Vol.405, pp.44-50
    Description: Cryptomelane-type octahedral molecular sieves (K-OMS-2) were successfully synthesized at ambient pressure and temperature by a simple one-step reaction pathway. We designed three synthesis mixes based on redox reactions of either MnSO₄ or MnCl₂ together with KMnO₄ in aqueous solution. The synthesis products were characterized structurally (XRD, FTIR spectroscopy), morphologically (SEM, BET surface area), and chemically (SEM-EDX, ICP-OES). For all mixes, a precursor octahedral layered K-birnessite (K-OL-1) was formed after 1d that subsequently transformed into K-OMS-2. This transformation process depends on the pH of the reaction solution, the respective Mn(II) salt and time. We obtained K-OMS-2 materials with BET surface areas between 50.4 and 104.5m²g⁻¹ and different crystallinities. The described method is reliable, reproducible, easy to handle and may be the basis to produce well defined Mn oxides that could be used for remediation and catalysis purposes. ; p. 44-50.
    Keywords: Redox Reactions ; Potassium Permanganate ; Aqueous Solutions ; X-Ray Diffraction ; Manganese ; Temperature ; Remediation ; Manganese Oxides ; Catalytic Activity ; Scanning Electron Microscopy ; Ph ; Fourier Transform Infrared Spectroscopy ; Surface Area
    ISSN: 0021-9797
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 7
    Language: English
    In: Environmental pollution, 2013, Vol.179, pp.301-314
    Description: Release of contaminants from non-aqueous phase liquids (NAPLs) is often limited by the dynamic exchange with aqueous solutions governed by a priori unknown kinetic laws. Release experiments require a thorough evaluation of the potential and limitations of kinetic models to reveal release processes. In this study, we investigated the characteristic concentration-time profiles of various models for the release of contaminants from an organic phase into an aqueous solution under no flow conditions. Criteria have been tested that allow for distinction of a first order one domain, a first order two domain, a spherical diffusion model, a spherical diffusion model with a time variable diffusion coefficient, a model for diffusion in a sphere with organic film, and a model for diffusion in a sphere with an aqueous film. The results can serve to evaluate the processes potentially governing release of organic contaminants from non-aqueous liquid phases. ; p. 301-314.
    Keywords: Nonaqueous Phase Liquids ; Models ; Aqueous Solutions ; Diffusivity
    ISSN: 0269-7491
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 8
    Language: English
    In: Environmental Pollution, 2011, Vol.159(5), pp.1398-1405
    Description: Arsenic mobility may increase in liquid phase due to association with colloidal Fe oxides. We studied the association of As with Fe oxide colloids in the effluent from water-saturated soil columns run under anoxic conditions. Upon exfiltration, the solutions, which contained Fe , were re-aerated and ferrihydrite colloids precipitated. The entire amount of effluent As was associated with the ferrihydrite colloids, although PO , SiO , CO and dissolved organic matter were present in the effluent during ferrihydrite colloid formation. Furthermore, no subsequent release of As from the ferrihydrite colloids was observed despite the presence of these (in)organic species known to compete with As for adsorption on Fe oxides. Arsenic was bound via inner-sphere complexation on the ferrihydrite surface. FTIR spectroscopy also revealed adsorption of PO and polymerized silica. However, these species could not impede the quantitative association of As with colloidal ferrihydrite in the soil effluents. ► Ferrihydrite (Fh) colloids precipitated from a solution derived from soil. ► Arsenic that was discharged from soil entirely associated with these colloids. ► Arsenic was strongly bound to the Fh surface via inner-sphere complexation. ► A complexation of As by organic species discharged from soil was not detected. ► (In)organic solutes in the solution from soil could not impede the As–Fh association. Natural concentrations of competing (in)organic species in soil-derived solutions do not impede the strong and quantitative association between As and colloidal ferrihydrite.
    Keywords: Iron Hydroxide ; Phosphate ; Silicate ; Carbonate ; Dissolved Organic Matter ; Engineering ; Environmental Sciences ; Anatomy & Physiology
    ISSN: 0269-7491
    E-ISSN: 1873-6424
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  • 9
    Language: English
    In: Environmental Pollution, August 2013, Vol.179, pp.301-314
    Description: Release of contaminants from non-aqueous phase liquids (NAPLs) is often limited by the dynamic exchange with aqueous solutions governed by unknown kinetic laws. Release experiments require a thorough evaluation of the potential and limitations of kinetic models to reveal release processes. In this study, we investigated the characteristic concentration-time profiles of various models for the release of contaminants from an organic phase into an aqueous solution under no flow conditions. Criteria have been tested that allow for distinction of a first order one domain, a first order two domain, a spherical diffusion model, a spherical diffusion model with a time variable diffusion coefficient, a model for diffusion in a sphere with organic film, and a model for diffusion in a sphere with an aqueous film. The results can serve to evaluate the processes potentially governing release of organic contaminants from non-aqueous liquid phases. Identification of rate limiting release processes from NAPL requires thorough model evaluation and long experimental duration.
    Keywords: Spherical Film Diffusion ; Contaminant Release ; Napl ; First Order Kinetics ; Dual Domain ; Engineering ; Environmental Sciences ; Anatomy & Physiology
    ISSN: 0269-7491
    E-ISSN: 1873-6424
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  • 10
    Language: English
    In: Geochimica et cosmochimica acta, 2012, Vol.77, pp.444-456
    Description: Recent studies on the microbial reduction of synthetic iron oxide colloids showed their superior electron accepting property in comparison to bulk iron oxides. However, natural colloidal iron oxides differ in composition from their synthetic counterparts. Besides a potential effect of colloid size, microbial iron reduction may be accelerated by electron-shuttling dissolved organic matter (DOM) as well as slowed down by inhibitors such as arsenic. We examined the microbial reduction of OM- and arsenic-containing ferrihydrite colloids. Four effluent fractions were collected from a soil column experiment run under water-saturated conditions. Ferrihydrite colloids precipitated from the soil effluent and exhibited stable hydrodynamic diameters ranging from 281 (±146)nm in the effluent fraction that was collected first and 100 (±43)nm in a subsequently obtained effluent fraction. Aliquots of these oxic effluent fractions were added to anoxic low salt medium containing diluted suspensions of Geobacter sulfurreducens. Independent of the initial colloid size, the soil effluent ferrihydrite colloids were quickly and completely reduced. The rates of Fe²⁺ formation ranged between 1.9 and 3.3fmolh⁻¹cell⁻¹, and are in the range of or slightly exceeding previously reported rates of synthetic ferrihydrite colloids (1.3fmolh⁻¹cell⁻¹), but greatly exceeding previously known rates of macroaggregate-ferrihydrite reduction (0.07fmolh⁻¹cell⁻¹). The inhibition of microbial Fe(III) reduction by arsenic is unlikely or overridden by the concurrent enhancement induced by soil effluent DOM. These organic species may have increased the already high intrinsic reducibility of colloidal ferrihydrite owing to quinone-mediated electron shuttling. Additionally, OM, which is structurally associated with the soil effluent ferrihydrite colloids, may also contribute to the higher reactivity due to increasing solubility and specific surface area of ferrihydrite. In conclusion, ferrihydrite colloids from soil effluents can be considered as highly reactive electron acceptors in anoxic environments. ; p. 444-456.
    Keywords: Colloids ; Iron Oxides ; Dissolved Organic Matter ; Effluents ; Arsenic ; Hydrodynamics ; Solubility ; Ferrihydrite ; Geobacter Sulfurreducens ; Iron ; Surface Area ; Soil
    ISSN: 0016-7037
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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