| 1. |
- Berggren Kleja, Dan, et al.
(författare)
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Characterization of iron in floating surface films of some natural waters using EXAFS
- 2012
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Ingår i: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 326, s. 19-26
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Tidskriftsartikel (refereegranskat)abstract
- Floating, iron bearing films have been observed in a wide range of environments, including wetlands, seep waters in ground water discharge areas, small rivers and lakes. To date, knowledge about their formation and composition is scarce. We have investigated the form of iron in floating iron-rich films of different origin, including a pond and a brook, as well as seep water pools of a groundwater discharge area. Sampling sites were located in southern (pond, brook) and central (seep pools) Sweden. Synchrotron-based X-ray absorption spectroscopy (EXAFS and XANES) allowed identification of the iron precipitates present in the films, without any pretreatment. The EXAFS data showed that the iron containing phase formed in the floating films varied in composition between the sites investigated. In the films from two ground water discharge areas, characterized by out-flowing iron(II) rich ground water being high in pH and low in DOC, the iron phase was completely dominated by ferrihydrite. In contrast, surface films sampled from the brook and the pond, the iron speciation showed a mixture of iron(III)-organic complexes and iron (hydr)oxide (most likely ferrihydrite). These waters were oxic and contained higher concentration of DOC than the seep water pools in the ground water discharge areas. The position of the pre-edge peak, which is sensitive to the oxidation state of iron, did not indicate occurrence of iron (II) in any of the films. Elemental composition of one film (seep water), suggested that films contained about one third of organic matter. Ferrihydrite is probably present as small particles with humic material sorbed onto surfaces or included in the particles, making the particles sufficiently hydrophobic to not settle without physical disturbance. The films are fragile and break easily down and become suspended upon disturbance. More studies are warranted in order to understand the mechanism of the formation of these fascinating films and their biogeochemical role.
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| 2. |
- Sjöstedt, Carin, 1981-, et al.
(författare)
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Iron speciation in soft-water lakes and soils as determined by EXAFS spectroscopy and geochemical modelling
- 2013
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533 .- 0046-564X. ; 105, s. 172-186
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Tidskriftsartikel (refereegranskat)abstract
- Complexation of iron by organic matter can potentially compete with toxic metals for binding sites. Iron(III) forms both monomeric and di/trimeric complexes with fulvic and humic acids, but the nature and extent of complexation with natural organic matter samples from soft-water lakes has not been extensively studied. The aim of this study was to determine the coordination of iron in complexes with organic matter in two soft-water lakes and in the surrounding Oe soil horizons. Iron K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy was performed on particles and large colloids (>0.45. μm) collected by in-line pre-filtration, and on smaller colloids isolated both on an AGMP-1 anion-exchange column and by concentration using 1000. Da ultrafiltration. The results showed that iron(III) was mainly present in monomeric complexes with organic matter, both in the lake water smaller colloids and in the soil samples. Evidence for iron(III) (hydr)oxides was found for the lake particles, in the ultrafiltration retentates, and in some of the soils. Overall, the results suggest that complexation of iron(III) to organic matter prevents hydrolysis into polymeric forms. Strong complexation of iron(III) would lead to competition with other metals for organic-matter binding sites.
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| 3. |
- Berggren Kleja, Dan, et al.
(författare)
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Silver(I) Binding Properties of Organic Soil Materials Are Different from Those of Isolated Humic Substances
- 2016
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 50:14, s. 7453-7460
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Tidskriftsartikel (refereegranskat)abstract
- The solubility of silver(I) in many soils is controlled by complexation reactions with organic matter. In this work we have compared the ability of isolated humic and fulvic acids to bind silver(I) with that of mor and peat materials. One new data set for Suwannee River Fulvic Acid was produced, which was consistent with published data sets for isolated fulvic and humic acids. The ability of soil materials to bind silver(I) was studied as a function of pH in the range 2.5-5.0, at a wide range of silver(I)-to-soil ratios (10(-4.2) - 10(-1.9) mol kg(-1)). By calibrating the Stockholm Humic Model on the humic and fulvic acids data sets, we showed that binding of silver(I) to both types of soil materials was much stronger (up to 2 orders of magnitude) than predicted from the silver(I) binding properties of the isolated humic materials. Thus, the approach taken for many other metals, that is, to model solubility in soils by using metal and proton binding parameters derived from isolated humic and fulvic acids, cannot be used for silver(I). One possible explanation for the discrepancy could be that silver(I) predominately interacted with various biomolecules in the soil samples, instead of humic- and fulvic-acid type materials.
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| 4. |
- Bergqvist, Claes, et al.
(författare)
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Plants influence on arsenic availability and speciation in the rhizosphere, roots and shoots of three different vegetables
- 2014
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Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491 .- 1873-6424. ; 184, s. 540-546
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Tidskriftsartikel (refereegranskat)abstract
- The toxicity of arsenic (As) in the environment is controlled by its concentration, availability and speciation. The aims of the study were to evaluate the accumulation and speciation of As in carrot, lettuce and spinach cultivated in soils with various As concentrations and to estimate the concomitant health risks associated with the consumption of the vegetables. Arsenic concentration and speciation in plant tissues and soils was analysed by HPLC, AAS and XANES spectroscopy. To estimate the plants influence in the rhizosphere, organic acids in lettuce root exudates were analysed by ion chromatography. The results showed that the As accumulation was higher in plants cultivated in soil with higher As extractability. Arsenate predominated in the soils, rhizosphere and root exudates of lettuce. Succinic acid was the major organic acid in lettuce root exudates. Ingestion of the tested vegetables may result in an intake of elevated levels of inorganic As.
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| 5. |
- Gustafsson, Jon Petter, et al.
(författare)
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Chromium(III) complexation to natural organic matter : Mechanisms and modeling
- 2014
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 48:3, s. 1753-1761
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Tidskriftsartikel (refereegranskat)abstract
- Chromium is a common soil contaminant, and it often exists as chromium(III). However, limited information exists on the coordination chemistry and stability of chromium(III) complexes with natural organic matter (NOM). Here, the complexation of chromium(III) to mor layer material and to Suwannee River Fulvic Acid (SRFA) was investigated using EXAFS spectroscopy and batch experiments. The EXAFS results showed a predominance of monomeric chromium(III)-NOM complexes at low pH (<5), in which only Cr··C and Cr-O-C interactions were observed in the second coordination shell. At pH > 5 there were polynuclear chromium(III)-NOM complexes with Cr···Cr interactions at 2.98 Å and for SRFA also at 3.57 Å, indicating the presence of dimers (soil) and tetramers (SRFA). The complexation of chromium(III) to NOM was intermediate between that of iron(III) and aluminum(III). Chromium(III) complexation was slow at pH < 4: three months or longer were required to reach equilibrium. The results were used to constrain chromium-NOM complexation in the Stockholm Humic Model (SHM): a monomeric complex dominated at pH < 5, whereas a dimeric complex dominated at higher pH. The optimized constant for the monomeric chromium(III) complex was in between those of the iron(III) and aluminum(III) NOM complexes. Our study suggests that chromium(III)-NOM complexes are important for chromium speciation in many environments.
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| 6. |
- Larsson, Maja, et al.
(författare)
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Vanadate complexation to ferrihydrite : X-ray absorption spectroscopy and CD-MUSIC modelling
- 2017
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Ingår i: Environmental Chemistry. - : CSIRO Publishing. - 1448-2517 .- 1449-8979. ; 14:3, s. 141-150
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Tidskriftsartikel (refereegranskat)abstract
- The mobility of vanadium in the environment is influenced by sorption to metal (hydr)oxides, especially those containing iron. The aim of this study is to understand the adsorption behaviour of vanadium on poorly ordered (two-line) ferrihydrite (Fh). A further objective was to determine the binding mechanism of vanadate(V) to ferrihydrite surfaces in aqueous suspension to constrain the CD-MUSIC surface complexation model. Vanadium adsorption to ferrihydrite was evaluated by batch experiments which included series with different Fh-to-V ratios and pH values. Vanadate(V) adsorption was also evaluated in the presence of phosphate to compete with vanadate(V) for the available surface sites on ferrihydrite. In agreement with earlier studies, vanadate(V) was strongly adsorbed to ferrihydrite and the adsorption increased with decreasing pH. In the presence of phosphate, less vanadate(V) was adsorbed. Analysis by X-ray absorption near-edge structure spectroscopy revealed that the adsorbed vanadium was tetrahedral vanadate(V), VO4, regardless of whether vanadate(V) or vanadyl(IV) was added to the system. Spectra collected by extended X-ray absorption fine structure spectroscopy showed that vanadate(V) is bound primarily as an edge-sharing bidentate complex with VFe distances around 2.8 angstrom. Based on this information, a surface complexation model was set up in which three bidentate vanadate(V) complexes with different degrees of protonation were included. The model provided a satisfactory description of vanadate(V) adsorption over most of the pH and concentration ranges studied, also in the presence of competing phosphate ions.
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| 7. |
- Tiberg, Charlotta, et al.
(författare)
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Phosphate effects on copper(II) and lead(II) sorption to ferrihydrite
- 2013
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier. - 0016-7037 .- 1872-9533 .- 0046-564X. ; 120, s. 140-157
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Tidskriftsartikel (refereegranskat)abstract
- Transport of lead(II) and copper(II) ions in soil is affected by the soil phosphorus status. Part of the explanation may be that phosphate increases the adsorption of copper(II) and lead(II) to iron (hydr)oxides in soil, but the details of these interactions are poorly known. Knowledge about such mechanisms is important, for example, in risk assessments of contaminated sites and development of remediation methods. We used a combination of batch experiments, extended X-ray absorption fine structure (EXAFS) spectroscopy and surface complexation modeling with the three-plane CD-MUSIC model to study the effect of phosphate on sorption of copper(II) and lead(II) to ferrihydrite. The aim was to identify the surface complexes formed and to derive constants for the surface complexation reactions. In the batch experiments phosphate greatly enhanced the adsorption of copper(II) and lead(II) to ferrihydrite at pH < 6. The largest effects were seen for lead(II). Based on interpretation of the EXAFS spectra edge-sharing bidentate copper(II) or lead(II) complexes predominated in the single-sorbate systems with ferrihydrite. Lead(II) EXAFS spectra suggested a distinct change of coordination in the presence of phosphate, i.e. the signal from edge-sharing complexes diminished and a longer Pb center dot center dot center dot Fe distance appeared at about 4 angstrom. A similar, but less pronounced, pattern was observed for copper(II). Based on the results from interpretation of EXAFS spectra and surface complexation modeling with the CD-MUSIC model the enhanced sorption in presence of phosphate was most satisfactorily explained by the appearance of ternary metal-phosphate complexes in which the metal interacts directly with the surface. In conclusion, geochemical models used for simulating trace element behavior in acidic environments seem to require ternary metal-phosphate surface complexes to properly describe partitioning of metals between solution and the solid phase.
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| 8. |
- Cornelis, Geert, et al.
(författare)
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Solubility and transport of Cr(III) in a historically contaminated soil – Evidence of a rapidly reacting dimeric Cr(III) organic matter complex
- 2017
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Ingår i: Chemosphere. - : Elsevier BV. - 0045-6535 .- 1879-1298. ; 189, s. 709-716
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Tidskriftsartikel (refereegranskat)abstract
- Chromium is a common soil contaminant and, although it has been studied widely, questions about its speciation and dissolutions kinetics remain unanswered. We combined information from an irrigation experiment performed with intact soil columns with data from batch experiments to evaluate solubility and mobilization mechanisms of Cr(III) in a historically contaminated soil (>65 years). Particulate and colloidal Cr(III) forms dominated transport in this soil, but their concentrations were independent of irrigation intensity (2-20 mm h(-1)). Extended X-ray absorption fine structure (EXAFS) measurements indicated that Cr(III) associated with colloids and particles, and with the solid phase, mainly existed as dimeric hydrolyzed Cr(III) bound to natural organic matter. Dissolution kinetics of this species were fast (<= 1 day) at low pH (<3) and slightly slower (<= 5 days) at neutral pH. Furthermore, it proved possible to describe the solubility of the dimeric Cr(III) organic matter complex with a geochemical equilibrium model using only generic binding parameters, opening the way for use of geochemical models in risk assessments of Cr(III)-contaminated sites. (C) 2017 The Authors. Published by Elsevier Ltd.
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| 9. |
- Gustafsson, Jon Petter, 1964-, et al.
(författare)
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Chromium (III) and bismuth (III) complexation to organic matter : EXAFS Spectroscopy and equilibrium modeling
- 2013
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Ingår i: Mineralogical magazine. - 0026-461X .- 1471-8022. ; 77:5, s. 1235-
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Tidskriftsartikel (refereegranskat)abstract
- The complexation of chromium(III) and bismuth(III) to organic matter was investigated by batch equilibrations with Suwannee River Fulvic Acid (SRFA) and with mor layer material (Risbergshöjden Oe). In the SRFA systems, 3 mM chromium(III) solutions were equilibrated with 9 g L-1 SRFA and equilibrated at different pH values ranging from 2 to 6. Characterization of the reaction products was made at MAX-Lab, Lund, Sweden, using Cr K-edge EXAFS spectroscopy at 5 989 eV. The spectra were interpreted using both conventional data treatment using EXAFSPAK and with wavelet transform (WT) analysis. The results show that chromium(III) formed monomeric organic complexes with SRFA. There was no evidence of polymerization with the exception of the particulate phase at pH 6, which was attributed to a limited extent of Cr(OH)3 formation.The mor layer material was equilibrated with chromium(III) and bismuth(III) solutions as a function of pH, time and competing ions (iron(III), aluminium(III), copper(II)). Again CrK-edge and Bi L3-edge EXAFS spectroscopy was used, at 5 989 and 13 419 eV. The experiments showed a predominance of monomeric organic complexes for chromium(III). The sorption of chromium(III) was pH-dependent and to some extent found to be influenced by competition from aluminium(III) and copper(II). Chromium(III) complexation was found to be very slow at pH < 4, and equilibration times of three months or longer were required to reach equilibrium under these conditions. Concerning bismuth(III), complexation was quicker and found to be very strong, with more than 94 % bound at pH 1.2 at a high bismuth(III) loading. EXAFS spectroscopy showed that two complexes were involved, one monomeric and one di- or trimeric, with the latter being predominant at higher pH values, although it was present already at pH 1.2. In the organic bismuth(III) complexes, the bismuth(III) octahedron was found to be strongly distorted, which implies strong binding to organic acid functional groups. The complexation of bismuth(III) remained essentially unchanged even in the presence of a potent competitor such as iron(III).The results from the spectroscopic investigation and from the quantitative solution data were used to calibrate new and improved complexation models for the Stockholm Humic (SHM) and the NICA-Donnan models. In the case of the Stockholm Humic Model, both complexes as found by EXAFS spectroscopy were considered explicitly; this ensured the model to predict minimum competition effects in agreement with the laboratory results.
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| 10. |
- Kleja, Dan Berggren, et al.
(författare)
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Binding of Ag(I) by organic soil Materials and isolated humic substances : XANES Spectroscopy and modeling
- 2013
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Konferensbidrag (refereegranskat)abstract
- The binding of silver(I) by organic matter was investigated in batch equilibrations with Suwannee River Fulvic Acid (SRFA), mor (Oe) and peat materials. For the SRFA systems, binding isotherms were determined at pH 4 and 8 using potentiometric titrations, with 0.05 M NaNO3 as background electrolyte. The binding showed a strong pH dependency and was about one order of magnitude stronger at pH 8 compared to pH 4. The data set was consistent with published data sets for isolated fulvic and humic acids. The binding of silver(I) by mor and peat materials was studied as a function of pH in the range 2.5-5.0 in dilute NaNO3 solutions (ca. 0.01 M), at a wide range of silver-to-soil ratios (10-2 – 10-4.5 mol kg-1). The silver(I) binding properties of the two materials were similar, with increasing binding strength with pH. The slope of sorption isotherms determined at pH 2.5 and 4.0 was significantly less than one, indicating heterogeneous binding sites. Ion competition experiments with added 1 mM iron(III) or 1 mM aluminium(III) at pH 2.5 and 4.0 showed no interaction between these ions and the silver(I) ion, indicating highly specific silver(I) binding sites.Silver K-edge XANES in the region 25280-26080 eV was used to characterize the binding mode of silver(I) in the mor and peat materials. A silver-to-soil ratio >10-2.5 mol kg-1 was needed to obtain a significant absorption edge. Comparison of spectra with oxygen, sulfur and nitrogen containing model compounds, indicated that the silver(I) ions, on average, was bound to one oxygen and one nitrogen donor ligand in an approximately linear fashion in both samples. Speciation of sulfur in the mor and peat materials using sulfur K-edge XANES, suggested that thiol groups could contribute to maximum about 20% of the silver binding at the conditions used in the Ag K-edge XANES measurements.The Stockholm Humic Model (SHM) was used as a tool to make a unified interpretation of SRFA and soil data. First, the model was calibrated using SFRA data together with published data on silver binding to isolated fulvic and humic substances, in order to obtain a consistent generic silver binding parameter set. Second, the calibrated SHM was used to predict the experimental silver(I) binding data obtained with the mor and peat materials. Taking this approach the model largely underestimated the silver(I) binding by the mor and peat materials; roughly by a factor of 10-100, dependent on experimental conditions. Thus, our data suggest that silver(I) binding properties of isolated fulvic and humic acids are very different from those of intact soil and peat materials. This will have great implications for how to calibrate and apply geochemical models describing the behavior of silver(I) in soils and natural waters.
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