Local coordination of Zn in hydroxy-interlayered minerals and implications for Zn retention in soils     

Olivier Jacquat  Ruben Kretzschmar 《Geochimica et cosmochimica acta》2009,73(2):348-7172

The objective of this study was to determine the local coordination of Zn in hydroxy-interlayered smectite (HIS) as a function of Zn loading and synthesis conditions and to assess the importance of hydroxy-interlayered minerals (HIM) for Zn retention in contaminated soils. Published and newly collected extended X-ray absorption fine structure (EXAFS) spectra of HIS reacted with Zn at molar Zn/hydroxy-Al ratios from 0.013 to 0.087 (corresponding to final Zn contents of 1615-8600 mg/kg Zn) were evaluated by shell fitting. In Zn-HIS, Zn was octahedrally coordinated to oxygen at 2.06-2.08 Å and surrounded by Al atoms at 3.03-3.06 Å in the second-shell. With increasing molar Zn/hydroxy-Al ratio, the coordination number of second-shell Al decreased from 6.6 to 2.1. These results were interpreted as a progressive shift from Zn incorporation in the vacancies of gibbsitic Al-polymers to Zn adsorption to incomplete Al-polymers and finally uptake by cation exchange in the polymer-free interlayer space of HIS with increasing Zn loadings. In a second part, we determined the speciation of Zn in eight contaminated soils (251-1039 mg/kg Zn) with acidic to neutral pH (pH 4.1-6.9) using EXAFS spectroscopy. All soils contained hydroxy-Al interlayered vermiculite (HIV). The analysis of EXAFS spectra by linear combination fitting (LCF) showed that a substantial fraction of total Zn (29-84%) was contained in HIM with high Zn loading. The remaining Zn was adsorbed to organic and inorganic soil components and incorporated into phyllosilicates. In sequential extractions of Zn-HIS spiked into quartz powder and the Zn contaminated soils, Zn was mainly released in the two most resistant fractions, in qualitative agreement with the findings from LCF. Our results suggest that formation of Zn-HIM may strongly retain Zn in pristine and moderately contaminated acidic to neutral soils. Due to their limited sorption capacity, however, HIM do not allow for the accumulation of high levels of Zn in response to continued Zn input into soils.  相似文献   

Isolation and purification of Cu-free methanobactin from Methylosinus trichosporium OB3b     

Marie-Laure Pesch  Iso Christl  Kurt Barmettler  Stephan M Kraemer  Ruben Kretzschmar 《Geochemical transactions》2011,12(1):2

Background  

The isolation of highly pure copper-free methanobactin is a prerequisite for the investigation of the biogeochemical functions of this chalkophore molecule produced by methane oxidizing bacteria. Here, we report a purification method for methanobactin from Methylosinus trichosporium OB3b cultures based on reversed-phase HPLC fractionation used in combination with a previously reported resin extraction. HPLC eluent fractions of the resin extracted product were collected and characterized with UV-vis, FT-IR, and C-1s NEXAFS spectroscopy, as well as with elemental analysis and ESI-MS.  相似文献   

Origin of high Zn contents in Jurassic limestone of the Jura mountain range and the Burgundy: evidence from Zn speciation and distribution     

Olivier Jacquat  Claire Rambeau  Andreas Voegelin  Natalia Efimenko  André Villard  Karl B. Föllmi  Ruben Kretzschmar 《Swiss Journal of Geoscience》2011,104(3):409-424

In order to better understand the origin and enrichment mechanisms leading to elevated Zn concentrations in Jurassic limestone of the Jura mountain range (JMR) and the Burgundy (B), we investigated four locations of Bajocian age (JMR: Lausen–Schleifenberg, Gurnigel; B: Vergisson–Davayé, Lucy-le-Bois) and two locations of Oxfordian age (JMR: Dornach, Pichoux) for their Zn distribution and speciation. Measurements of the acid-extractable and bulk Zn contents showed that Zn is stratigraphically and spatially heterogeneously distributed, in association with permeable carbonate levels. Up to 3,580 and 207 mg/kg Zn was detected in Bajocian and Oxfordian limestone, respectively, with numerous limestone samples having Zn contents above 50 mg/kg. Using X-ray absorption near edge structure spectroscopy and micro-X-ray fluorescence spectrometry, the speciation and micro-scale distribution of Zn was investigated for selected limestone samples. In Bajocian limestone sphalerite and/or Zn-substituted goethite and a minor fraction of Zn-bearing carbonates were identified. In contrast, Zn-bearing carbonates (Zn-substituted calcite and hydrozincite) were accounting for most of the total Zn in Oxfordian limestone. The micro-scale distribution of Zn for Bajocian and Oxfordian limestone was however similar with localized Zn-rich zones in the limestone cement and at the rim of oolites. The stratigraphic sporadicity and microscale heterogeneity of the Zn distribution together with the Zn speciation results point to a hydrothermal origin of Zn. Occurence of Zn-goethite is probably linked to the oxidative transformation of framboidal pyrite and hydrothermal sphalerite in contact with meteoritic waters. Difference in speciation between Bajocian limestone and Oxfordian limestone may be related to differences in rock permeability and/or to various hydrothermal events. Isotopic dating of the different mineralizations will be needed to decipher differences in Zn speciation and the precise chronology of hydrothermal episodes.  相似文献   

Nanociliates of the order Prostomatida: Their relevance in the microbial food web of a mesotrophic lake     

Ruben Sommaruga  Roland Psenner 《Aquatic Sciences - Research Across Boundaries》1993,55(3):179-187

Two nanociliates of the order Prostomatida,Pseudobalanion planctonicum (12–18 µm) andUrotricha furcata (12–21 µm), were found to be the most abundant ciliates in the epilimnion of Piburger See, a small mesotrophic lake. Temperature and food availability were the main factors controlling the sudden increase in abundance, which reached a maximum of 101 cell ml^–1 at the beginning of summer. During their exponential development in numbers and biomass, a strong decrease in chlorophylla and in the abundance of phytoplankton, especiallyRhodomonas, was observed. We assume, therefore, thatPseudobalanion planctonicum andUrotricha furcata together with rotifers, mainlyPolyarthra dolichoptera, are able to reduce the phytoplankton biomass in the upper epilimnion to the same level as found during the clearwater phase. Preliminary results of grazing on bacteria suggest that these nanociliates are omnivorous, although their impact on bacterial assemblages was low (3.1% of the standing stock grazed per day). Feeding on the base of the food web combined with their high abudance at certain times makes them an important link for higher trophic levels. This study constitutes the second report onPseudobalanion as an important component of the microbial food web in lakes.  相似文献   

Formation of Zn-rich phyllosilicate, Zn-layered double hydroxide and hydrozincite in contaminated calcareous soils     

Olivier Jacquat  André Villard  Ruben Kretzschmar 《Geochimica et cosmochimica acta》2008,72(20):5037-5054

Recent studies demonstrated that Zn-phyllosilicate- and Zn-layered double hydroxide-type (Zn-LDH) precipitates may form in contaminated soils. However, the influence of soil properties and Zn content on the quantity and type of precipitate forming has not been studied in detail so far. In this work, we determined the speciation of Zn in six carbonate-rich surface soils (pH 6.2-7.5) contaminated by aqueous Zn in the runoff from galvanized power line towers (1322-30,090 mg/kg Zn). Based on 12 bulk and 23 micro-focused extended X-ray absorption fine structure (EXAFS) spectra, the number, type and proportion of Zn species were derived using principal component analysis, target testing, and linear combination fitting. Nearly pure Zn-rich phyllosilicate and Zn-LDH were identified at different locations within a single soil horizon, suggesting that the local availabilities of Al and Si controlled the type of precipitate forming. Hydrozincite was identified on the surfaces of limestone particles that were not in direct contact with the soil clay matrix. With increasing Zn loading of the soils, the percentage of precipitated Zn increased from ∼20% to ∼80%, while the precipitate type shifted from Zn-phyllosilicate and/or Zn-LDH at the lowest studied soil Zn contents over predominantly Zn-LDH at intermediate loadings to hydrozincite in extremely contaminated soils. These trends were in agreement with the solubility of Zn in equilibrium with these phases. Sequential extractions showed that large fractions of soil Zn (∼30-80%) as well as of synthetic Zn-kerolite, Zn-LDH, and hydrozincite spiked into uncontaminated soil were readily extracted by 1 M NH₄NO₃ followed by 1 M NH₄-acetate at pH 6.0. Even though the formation of Zn-precipitates allows for the retention of Zn in excess to the adsorption capacity of calcareous soils, the long-term immobilization potential of these precipitates is limited.  相似文献   

Tectonic evolution of an intraplate basin: the Lower Tagus Cenozoic Basin,Portugal          下载免费PDF全文

João Carvalho  Carlos Pinto  Ruben Dias  Taha Rabeh  Luis Torres  José Borges  Ricardo Torres  Henrique Duarte 《Basin Research》2017,29(5):636-657

This article focuses on the reinterpretation of well, seismic reflection, magnetic, gravimetric, surface wave and geological surface data, together with the acquisition of seismic noise data to study the Lower Tagus Cenozoic Basin tectono‐sedimentary evolution. For the first time, the structure of the base of the basin in its distal and intermediate sectors is unravelled, which was previously only known in the areas covered by seismic reflection data (distal and small part of intermediate sectors). A complex geometry was found, with three subbasins delimited by NNE‐SSW faults and separated by WNW‐ESE to NW‐SE oriented horsts. In the area covered by seismic reflection data, four horizons were studied: top of the Upper Miocene, Lower to Middle Miocene top, the top of the Palaeogene and the base of Cenozoic. Seismic data show that the major filling of the basin occurred during Upper Miocene. The fault pattern affecting Neogene and Palaeogene units derived here points to that of a polyphasic basin. In the Palaeogene, the Vila Franca de Xira (VFX) and a NNE‐SSW trending previously unknown structure (ABC fault zone) probably acted as the major strike‐slip fault zones of the releasing bend of a pull‐apart basin, which produced a WNW‐ESE to NW‐SE fault system with transtensional kinematic. During the Neogene, as the stress regime rotated anticlockwise to the present NW‐SE to WNW‐ESE orientation, the VFX and Azambuja fault zones acted as the major transpressive fault zones and Mesozoic rocks overthrusted Miocene sediments. The reactivation of WNW‐ESE to NW‐SE fault systems with a dextral strike‐slip component generated a series of horsts and grabens and the partitioning of the basin into several subbasins. Therefore, we propose a polyphasic model for the area, with the formation of an early pull‐apart basin during the Palaeogene caused by an Iberia–Eurasia plates collision that later evolved into an incipient foreland basin along the Neogene due to a NW‐SE to WNE‐ESE oriented Iberia–Nubia convergence. This convergence is producing uplift in the area since the Quaternary except for the Tagus estuary subbasin around the VFX fault, where subsidence is observed. This may be due to the locking or the development of a larger component of strike‐slip movement of the NNE‐SSW to N‐S thrust fault system with the exception of the VFX fault, which is more favourably oriented to the maximum compressive stress.  相似文献   

The imprint of the cosmic dark ages on the near-infrared background     

Ruben Salvaterra  Andrea Ferrara 《Monthly notices of the Royal Astronomical Society》2003,339(4):973-982

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Unresolved X-ray background: clues on galactic nuclear activity at z > 6     

Ruben Salvaterra  Francesco Haardt  Marta Volonteri 《Monthly notices of the Royal Astronomical Society》2007,374(2):761-768

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2- and 3-D Simulations of Magnetocentrifugal Disk-Winds: Acceleration and Stability     

Ruben Krasnopolsky  Zhi-Yun Li  Roger D. Blandford 《Astrophysics and Space Science》2003,287(1-4):75-78

Protostellar jets and winds are probably driven magnetocentrifugally from the surface of accretion disks close to the central stellar objects. The exact launching conditions on the disk, such as the distributions of magnetic flux and mass ejection rate, are poorly known. They could be constrained from observations at large distances, provided that a robust model is available to link the observable properties of the jets and winds at the large distances to the conditions at the base of the flow. We describe a set of 2D axisymmetric simulations that are able to follow the acceleration and propagation of the wind from the disk surface to arbitrarily large distances. After a typical 2D flow reaches the steady state, we impose on it nonaxisymmetric perturbations and follow numerically its 3D evolution. We find that the wind reverts quickly to its initial axisymmetric state, with no indication of rapid growth of instabilities leading to flow disruption. Our calculations strengthen the case for the magnetocentrifugal jet and wind launching.  相似文献   

What caused the spring intensification and winter demise of the 2011 drought over Texas?     

D. Nelun Fernando  Kingtse C. Mo  Rong Fu  Bing Pu  Adam Bowerman  Bridget R. Scanlon  Ruben S. Solis  Lei Yin  Robert E. Mace  John R. Mioduszewski  Tong Ren  Kai Zhang 《Climate Dynamics》2016,47(9-10):3077-3090

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