| 1. |
- Braun, Sabina, et al.
(author)
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Modelling heterogeneous phosphate sorption kinetics on iron oxyhydroxides and soil with a continuous distribution approach
- 2018
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In: European Journal of Soil Science. - : Wiley. - 1351-0754 .- 1365-2389. ; 69, s. 475-487
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Journal article (peer-reviewed)abstract
- The kinetics of orthophosphate (PO4) sorption in soil has far reaching consequences on its long-term fate. Traditionally, a distinction is made between fast, reversible adsorption and slow fixation. The kinetics are commonly described by compartmental models (CMs) assuming kinetically distinct homogeneous pools (e.g. a rapid- and slow-sorbing pool), with phenomenological equations or with complex diffusion-based models. Alternatively, this process can be described by assuming frequency distributions of both adsorption and desorption rate constants and, thereby, enabling better description of experimental data with fewer adjustable parameters. Here, we developed such a rate constant distribution (RCD) model and compared it with CMs and other commonly used rate equations. Batch (PO4)-P-33 sorption was measured in agitated suspensions between 2minutes and 20days after spiking in 13 contrasting types of soil and two iron oxyhydroxides. Overall, the RCD model, with three adjustable parameters, describes the data better than the other models tested. The so-called slow reactions, denoted as the factor change in soluble (PO4)-P-33 between 1 and 20days after spiking, were described better by the RCD model and ranged from 1.0 (i.e. no change) to 6.9. The extent of slow reactions increased with the increase in the fraction of poorly crystalline iron in the soil (r=0.69; P=0.0088). Equilibrium was elusive up to 20days for PO4 sorption on ferrihydrite and on soil samples with a large fraction of poorly crystalline iron oxyhydroxides. The RCD model code is available as freeware from the first author.
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| 2. |
- Campos Pereira, H., et al.
(author)
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Sorption of perfluoroalkyl substances (PFASs) to an organic soil horizon – Effect of cation composition and pH
- 2018
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In: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 207, s. 183-191
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Journal article (peer-reviewed)abstract
- Accurate prediction of the sorption of perfluoroalkyl substances (PFASs) in soils is essential for environmental risk assessment. We investigated the effect of solution pH and calculated soil organic matter (SOM) net charge on the sorption of 14 PFASs onto an organic soil as a function of pH and added concentrations of Al3+, Ca2+ and Na+. Often, the organic C-normalized partitioning coefficients (KOC) showed a negative relationship to both pH (Δlog KOC/ΔpH = −0.32 ± 0.11 log units) and the SOM bulk net negative charge (Δlog KOC = −1.41 ± 0.40 per log unit molc g−1). Moreover, perfluorosulfonic acids (PFSAs) sorbed more strongly than perfluorocarboxylic acids (PFCAs) and the PFAS sorption increased with increasing perfluorocarbon chain length with 0.60 and 0.83 log KOC units per CF2 moiety for C3–C10 PFCAs and C4, C6, and C8 PFSAs, respectively. The effects of cation treatment and SOM bulk net charge were evident for many PFASs with low to moderate sorption (C5–C8 PFCAs and C6 PFSA). However for the most strongly sorbing and most long-chained PFASs (C9–C11 and C13 PFCAs, C8 PFSA and perfluorooctane sulfonamide (FOSA)), smaller effects of cations were seen, and instead sorption was more strongly related to the pH value. This suggests that the most long-chained PFASs, similar to other hydrophobic organic compounds, are preferentially sorbed to the highly condensed domains of the humin fraction, while shorter-chained PFASs are bound to a larger extent to humic and fulvic acid, where cation effects are significant.
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| 3. |
- Gustafsson, Jon Petter, 1964-, et al.
(author)
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Aluminium and base cation chemistry in dynamic acidification models - need for a reappraisal?
- 2018
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In: SOIL. - : COPERNICUS GESELLSCHAFT MBH. - 2199-3971 .- 2199-398X. ; 4:4, s. 237-250
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Journal article (peer-reviewed)abstract
- Long-term simulations of the water composition in acid forest soils require that accurate descriptions of aluminium and base cation chemistry are used. Both weathering rates and soil nutrient availability depend on the concentrations of Al3+, of H+, and of base cations (Ca2+, Mg2+, Na+, and K+). Assessments of the acidification status and base cation availability will depend on the model being used. Here we review in what ways different dynamic soil chemistry models describe the processes governing aluminium and base cation concentrations in the soil water. Furthermore, scenario simulations with the HD-MINTEQ model are used to illustrate the difference between model approaches. The results show that all investigated models provide the same type of response to changes in input water chemistry. Still, for base cations we show that the differences in the magnitude of the response may be considerable depending on whether a cation-exchange equation (Gaines-Thomas, Gapon) or an organic complexation model is used. The former approach, which is used in many currently used models (e.g. MAGIC, ForSAFE), causes stronger pH buffering over a relatively narrow pH range, as compared to state-of-the-art models relying on more advanced descriptions in which organic complexation is important (CHUM, HD-MIN PLQ). As for aluminium, a "fixed" gibbsite constant, as used in MAGIC, SMART/VSD, and ForSAFE, leads to slightly more pH buffering than in the more advanced models that consider both organic complexation and Al(OH)(3) (s) precipitation, but in this case the effect is small. We conclude that the descriptions of acid-base chemistry and base cation binding in models such as MAGIC, SMART/VSD, and ForSAFE are only likely to work satisfactorily in a narrow pH range. If the pH varies greatly over time, the use of modern organic complexation models is preferred over cation-exchange equations.
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| 4. |
- Gustafsson, Jon-Petter
(author)
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Copper Mobilization and Immobilization along an Organic Matter and Redox Gradient-Insights from a Mofette Site
- 2018
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 52, s. 13698-13707
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Journal article (peer-reviewed)abstract
- Mofettes (natural geogenic CO2 exhalations) represent excellent sites to study the behavior of Cu in soils and the co-occurrence of different mobilization and immobilization processes since they exhibit both a gradient in redox conditions (oxic to permanently anoxic) and in soil organic matter (SOM; low to high contents). Soil and pore water samples from an 18 m-transect over a mofette showed a complex behavior of Cu, with highest mobility in the transition between oxic and anoxic conditions. Cu(II) sorption experiments on SOM-rich topsoil revealed that Cu mobility under oxic conditions was confined by adsorption to SOM while in the oxygen-free mofette center reduction and precipitation of sulfides was the dominating Cu-sequestering process. In transition areas with low amounts of oxygen (<10%), there was no mineral precipitation, instead high dissolved-to-soil organic carbon ratios strongly increased Cu mobility. Our results show that low stability of SOM formed under oxygen-limited conditions leads to increased Cu mobility unless sulfur-reducing conditions cause Cu sequestration by sulfide precipitation. The interplay of these (im)mobilization processes and especially the unexpectedly high mobility under suboxic conditions have to be considered when assessing Cu mobility along spatial or temporal redox gradients, e.g., at contamination sites or periodically flooded soils.
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| 5. |
- Gustafsson, Jon-Petter
(author)
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Monothioarsenate Transformation Kinetics Determining Arsenic Sequestration by Sulfhydryl Groups of Peat
- 2018
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 52, s. 7317-7326
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Journal article (peer-reviewed)abstract
- In peatlands, arsenite was reported to be effectively sequestered by sulfhydryl groups of natural organic matter. To which extent porewater arsenite can react with reduced sulfur to form thioarsenates and how this affects arsenic sequestration in peatlands is unknown. Here, we show that, in the naturally arsenic enriched peatland Gola di Lago, Switzerland, up to 93% of all arsenic species in surface and porewaters were thioarsenates. The dominant species, monothioarsenate, likely formed from arsenite and zerovalent sulfur-containing species. Laboratory incubations with sulfide-reacted, purified model peat showed increasing total arsenic sorption with decreasing pH from 8.5 to 4.5 for both, monothioarsenate and arsenite. However, Xray absorption spectroscopy revealed no binding of monothioarsenate via sulfhydryl groups. The sorption observed at pH 4.5 was acid-catalyzed dissociation of monothioarsenate, forming arsenite. The lower the pH and the more sulfhydryl sites, the more arsenite sorbed which in turn shifted equilibrium toward further dissociation of monothioarsenate. At pH 8.5, monothioarsenate was stable over 41 days. In conclusion, arsenic can be effectively sequestered by sulfhydryl groups in anoxic, slightly acidic environments where arsenite is the only arsenic species. At neutral to slightly alkaline pH, monothioarsenate can form and its slow transformation into arsenite and low affinity to sulfhydryl groups suggest that this species is mobile in such environments.
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| 6. |
- Kianmeher, Peiman, et al.
(author)
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Enhancement of Physicochemical Properties of Dubai's Sand to Conserve Irrigation Water
- 2018
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In: PROCEEDINGS OF 3RD INTERNATIONAL SUSTAINABLE BUILDINGS SYMPOSIUM (ISBS 2017), VOL 1. - Cham : SPRINGER INTERNATIONAL PUBLISHING AG. ; , s. 644-654
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Conference paper (peer-reviewed)abstract
- Freshwater scarcity has been a considerable issue in the Gulf Region. The cities in the region including in the UAE depend mainly on seawater desalination. Their demand escalated about 15% annually regardless of seawater desalination direct cost of 1 US$/M-3. Thus, calling all water conservation techniques to reducing indoor and outdoor water demands is inevitable. Using Hydrophobic Sand (HS) to reduce water seepage and increase the contact time between irrigation water and plants' roots was seen as potential conservation technique. The HS is Normal Sand (NS) coated by a thin layer of hydrophobic organic silica compound called trimethylsilanol. However, concerns were raised about the leaching of harmful organic coating chemicals into the soil and groundwater. Assessing the potential risks of leaching additives is one of the objectives of this research. For some plants, requiring a certain range of soil permeability suggests a mixture of NS and HS. The permeability of mixtures of HS with abundant NS was examined to assess its validity and cost effectiveness when a certain permeability is required. Several elements leaching tests were conducted. The soil was classified and constant head permeability test was conducted for different configurations and mixtures of NS and HS. The leached elements, nutrients and organic silica were within the allowable limits set by the typical standards. Further experiments indicates that HS does not constitute an environmental hazard. Mixing different portions of NS and HS revealed unforeseen increase in the permeability. Instead, some layer configurations could reduce soil permeability.
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| 7. |
- Löv, Åsa, et al.
(author)
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Particle- and colloid-facilitated Pb transport in four historically contaminated soils - Speciation and effect of irrigation intensity
- 2018
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In: Applied Geochemistry. - : Elsevier BV. - 0883-2927. ; 96, s. 327-338
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Journal article (peer-reviewed)abstract
- Due to the low solubility of lead (Pb) in many soils, colloidal and particulate transport may have large effects on Pb leaching. However, the role of colloidal and particulate transport varies considerably between soils and the mechanisms controlling mobilisation are complex and poorly known. Furthermore, increased frequency of high-intensity rainfall events is expected in some parts of Europe and North America in response to climate change, which might increase the mobilisation of particles and colloids. In this work, we investigated transport of particulate ( > 0.45 mu m), colloidal (10 kDa-0.45 mu m) and truly dissolved ( < 10 kDa) Pb in an irrigation experiment on intact soil columns from four historically contaminated soils. We also investigated the effect of irrigation intensity (2-20 mmh(-1)) on Pb leaching in these fractions. The mechanism binding Pb on particles and colloids was evaluated by extended X-ray absorption fine structure (EXAFS) spectroscopy and geochemical modelling. A 10-fold increase in irrigation intensity brought about at most a three-fold change in leached particulate and colloidal Pb concentrations. In contrast, the fraction of leached Pb associated with particles and colloids varied by one order of magnitude between soils. Hence, the results suggest that it is more important to consider soil type than potential future increases in rainfall. For one soil with high concentrations of both arsenic (As) and Pb, geochemical modelling indicated that mimetite, Pb-5(AsO4)(3)Cl(s), was the major Pb species in the colloidal and particulate fractions. For the other three soils, EXAFS of Pb on isolated particles and colloids indicated that ferrihydrite was a major phase-sorbing Pb and this was supported by geochemical equilibrium modelling. Thus geochemical modelling can be used to indicate the speciation of Pb in particles and colloids leached in intact soils.
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| 8. |
- Renman, Gunno, et al.
(author)
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Phosphorus removal by slag depends on its mineralogical composition: A comparative study of AOD and EAF slags
- 2018
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In: Journal of Water Process Engineering. - : Elsevier. - 2214-7144. ; 25, s. 105-112
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Journal article (peer-reviewed)abstract
- Electric arc furnace slag (EAF) and argon oxygen decarburization slag (AOD) were investigated in column experiments to determine the effect of mineralogical composition on their P removal performance and lifespan. Polyethylene glycol (PEG) and NaOH solutions were used for pretreatment of the slags to adjust their dissolution properties. The modified slags exhibited better P removal performance at the beginning of the experiment, but had shorter lifespan than the unmodified slags. AOD and EAF modified with PEG and NaOH achieved 100% P removal during the first 84 and 60 pore volumes, respectively, which were ≥20 pore volumes longer than virgin AOD and EAF. However, virgin EAF and AOD both had a P removal efficiency above 90% during the first 280 pore volumes. Possibly, soluble minerals such as free lime are lost during the modification step, causing a decreased long-term P removal capacity. The XRD results showed that the high P removal ability of AOD and EAF was attributed to the dissolution of beta dicalcium silicate (β-C2) and gamma dicalcium silicate (γ-C2S), which were dominant mineral phases in the slags. Results from SEM-EDS analysis revealed significant P accumulation on the slag surface. Cracks on the EAF slag surface contributed to its longer lifespan. Analysis with P K-edge XANES spectroscopy showed that the P retained on the slag surface was dominated by amorphous calcium phosphate, with a substantial amount of carbonate apatite (around 30%). Amorphous calcium phosphate was transformed to crystalline apatite as the slag aged with column operating time.
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| 9. |
- Schmieder, Frank, et al.
(author)
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Phosphorus speciation in a long-term manure-amended soil profile - Evidence from wet chemical extraction, P-31-NMR and P K-edge XANES spectroscopy
- 2018
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In: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 322, s. 19-27
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Journal article (peer-reviewed)abstract
- Long-term application of manure can lead to an enrichment of phosphorus (P) in agricultural soils. To which extent this P leaches into drainage systems and thereby potentially contributing to eutrophication of surface waters, depends on the distribution and speciation of P present in the soil. In this study the P speciation and related soil characteristics were investigated for a sandy loam soil that had been receiving manure for > 40 years. A combination of solution-state P-31-NMR, P K-edge XANES and wet chemical extractions was applied.Topsoil P contents were with 42 mmol kg(-1) more than twice as high as in the sub soil (14-18 mmol kg(-1)). Linear combination fitting (LCF) of P K-edge XANES spectra indicated that P accumulation in the topsoil occurred predominantly via adsorption of inorganic P to Fe/Al hydroxide surfaces, resulting in substantial P saturation of these mineral phases. Up to 76% of the topsoil P was associated with Al or Fe. The organic P content was low (5-10%), but an additional important topsoil P pool identified with XANES-LCF was amorphous calcium phosphate (30%), which may have been added with manure or formed in situ. Towards the deeper subsoil the relative portion of primary apatite increased progressively and reached 80% of total P at a depth of 70 to 80 cm. These results highlight the importance of Fe and Al mineral phases for P retention in long-term manure-amended soils also under non-acidic conditions.
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| 10. |
- Tiberg, Charlotta, et al.
(author)
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Metal sorption to Spodosol Bs horizons : Organic matter complexes predominate
- 2018
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In: Chemosphere. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0045-6535 .- 1879-1298. ; 196, s. 556-565
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Journal article (peer-reviewed)abstract
- While metal sorption mechanisms have been studied extensively for soil surface horizons, little information exists for subsoils, for example Spodosol Bs horizons. Here the sorption of cadmium(10, copper(II) and lead(II) to seven Bs horizons from five sites was studied. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that cadmium(II) and lead(II) were bound as inner-sphere complexes to organic matter. Addition of o-phosphate (to 1 mu mol l(-1)) did not result in any significant enhancement of metal sorption, nor did it influence EXAFS speciation. An assemblage model using the SHM and CD-MUSIC models overestimated metal sorption for six out of seven soil samples. To agree with experimental results, substantial decreases (up to 8-fold) had to be made for the fraction 'active organic matter', f(Hs), while the point-of-zero charge (PZC) of ferrihydrite had to be increased. The largest decreases of f(HS) were found for the soils with the lowest ratio of pyrophosphate-to oxalate-extractable Al (Al-pyp/Al-ox), suggesting that in these soils, humic and fulvic acids were to a large extent inaccessible for metal sorption. The low reactivity of ferrihydrite towards lead(II) can be explained by potential spillover effects from co-existing allophane, but other factors such as ferrihydrite crystallisation could not be ruled out. In conclusion, organic matter was the predominant sorbent for cadmium(II), copper(II) and lead(II). However, for lead(II) the optimised model suggests additional, but minor, contributions from Fe (hydr) oxide surface complexes. These results will be important to correctly model metal sorption in spodic materials.
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