| 1. |
- Gustafsson, Jon Petter, et al.
(författare)
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Aluminium solubility mechanisms in moderately acid Bs horizons of podzolized soils
- 2001
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Ingår i: European Journal of Soil Science. - : Wiley. - 1351-0754 .- 1365-2389. ; 52:4, s. 655-665
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Tidskriftsartikel (refereegranskat)abstract
- The processes controlling the retention and release of aluminium in acid forest soils are still subject to controversy, and therefore a universal hypothesis as to what mechanisms are operating has not been firmly established. By studying the Bs horizons of Swedish and Swiss podzolized soils, and by analysing data in the literature, we have found that aluminium hydroxide, and in some cases also poorly ordered imogolite, may control Al solubility in moderately acid (pH>4.2-4.3) Bs horizons. The strongest evidence in support of the presence of a quickly reacting Al(OH)(3) pool came from the temperature dependence of Al solubility in a Bs horizon, which was consistent with the reaction enthalpy of an Al(OH)3 phase such as gibbsite, and from the observation that the eon activity product for Al(OH)3 was the same regardless of whether equilibrium was reached from over- or undersaturation. The pool of Al(OH)3 is commonly small and may be completely dissolved after large additions of acid. This may be explained by the continuing redissolution of reactive Al(OH)(3) to form less soluble imogolite-type phases. By using the same methods it was found that soil suspensions did not reach equilibrium with poorly ordered imogolite even after 17 days. Thus, imogolite probably does not control Al solubility in the short term in many soils despite the common occurrence of this mineral. This is due to the relatively slow kinetics of imogolite formation and dissolution, especially at low temperatures and at small solution H4SiO4 concentrations.
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| 2. |
- Gustafsson, Jon Petter, et al.
(författare)
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Cation binding in a mor layer : batch experiments and modelling
- 2003
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Ingår i: European Journal of Soil Science. - : Wiley. - 1351-0754 .- 1365-2389. ; 54:2, s. 295-310
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Tidskriftsartikel (refereegranskat)abstract
- The understanding of cation binding in the mor layer is important to correctly assess the biogeochemical cycling of metals and other cations in forested ecosystems. In a series of batch experiments, the binding of cations was examined in two mor layers from central Sweden. We examined the effect of Ca and Al on the binding of Zn, and also the binding of added Pb, Cu and Cd. Two models, WinHumicV and the Stockholm Humic Model (SHM), were tested for their ability to describe the data obtained. We found that for Zn, the pH at 50% sorption was increased from 2.8 to 4.2 after the addition of 3 mM Al. The proton titration data were well described by both WinHumicV and SHM after optimization of the concentrations of 'active' Al and humic substances. Applying generic parameters for cation binding produced deviations between the model simulations and the observations, particularly for the dissolved Pb and Cu concentrations, which were underestimated. A revised set of cation complexation constants was presented that improved the fit, particularly for SHM. For WinHumicV, there were still poor overall fits. The difference in model performance may be due to the greater number of adjustable parameters in the SHM, but probably also to other model-specific differences. According to the SHM simulations, the binding of Ca, Mg and Mn was mainly non-specific, whereas Pb, Cu and Al were bound as mono- or bidentate complexes. For Zn and Cd, binding occurred through both counter-ion accumulation and monodentate complexation.
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| 3. |
- Gustafsson, Jon Petter, et al.
(författare)
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Modeling metal binding to soils : The role of natural organic matter
- 2003
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 37:12, s. 2767-2774
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Tidskriftsartikel (refereegranskat)abstract
- The use of mechanistically based models to simulate the solution concentrations of heavy metals in soils is complicated by the presence of different sorbents that may bind metals. In this study, the binding of Zn, Pb, Cu, and Cd by 14 different Swedish soil samples was investigated. For 10 of the soils, it was found that the Stockholm Humic Model (SHM) was able to describe the acid-base characteristics, when using the concentrations of active humic substances and Al as fitting parameters. Two additional soils could be modeled when ion exchange to clay was also considered, using a component additivity approach. For dissolved Zn, Cd, Ca, and Mg reasonable model fits were produced when the metal-humic complexation parameters were identical for the 12 soils modeled. However, poor fits were obtained for Pb and Cu in Aquept B horizons. In two of the soil suspensions, the Lund A and Romfartuna Bhs, the calculated speciation agreed well with results obtained by using cation-exchange membranes. The results suggest that organic matter is an important sorbent for metals in many surface horizons of soils in temperate and boreal climates, and the necessity of properly accounting for the competition from Al in simulations of dissolved metal concentrations is stressed.
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| 4. |
- Gustafsson, Jon Petter
(författare)
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Modeling the acid-base properties and metal complexation of humic substances with the Stockholm Humic Model
- 2001
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 244:1, s. 102-112
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Tidskriftsartikel (refereegranskat)abstract
- To describe the binding of protons and metals to humic substances, the Stockholm Humic Model (SHM) has been developed. The model employs a discrete-site approach similar to that of Model V/VI, although it has another electrostatic submodel, based on the Basic Stern concept. An empirical set of equations has been introduced to account for the extra screening of charge inside the gel-like structures of the humic substances. Six adjustable parameters are needed to describe proton binding to humic or fulvic acids. To simulate metal binding, equilibrium constants are defined for mono- and bidentate coordination and an extra parameter, Delta LK2, accounts for binding-site heterogeneity. It is shown that the SHM appears to be able to describe proton binding well; the quality of the fits is similar to those obtained by Model V/VI and the NICA-Donnan model. The SHM was capable of correctly describing metal binding and competitive interactions over a wide range of conditions, although the model performance was not very convincing concerning the ionic strength dependence of metal binding and stepwise proton-metal exchange stoichiometries.
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| 5. |
- Gustafsson, Jon Petter
(författare)
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Modelling competitive anion adsorption on oxide minerals and an allophane-containing soil
- 2001
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Ingår i: European Journal of Soil Science. - : Wiley. - 1351-0754 .- 1365-2389. ; 52:4, s. 639-653
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Tidskriftsartikel (refereegranskat)abstract
- Can surface complexation constants for anions, drawn from the literature for reference oxides, be combined to describe competitive adsorption in a spodic B horizon sample containing the important adsorbent minerals proto-imogolite allophane and ferrihydrite? To answer this and to derive complexation constants for the corresponding reference oxides, a CD-MUSIC model was used, with arsenate as the sorbing ion. To minimize the interference from competing organic substances, a sample containing little organic matter was used. To describe the adsorption of added arsenate correctly, it was found that competitive interactions from sulphate, silicic acid and phosphate had to be considered. In the model, the specific surface area of singly coordinated AlOH groups of allophane, the sulphate surface complexation constant on allophane, and the total concentration of reactive silicic acid were fitted. All other parameters were fixed using reference oxide values. The results indicated that arsenate, phosphate and silicic acid formed stronger surface complexes on ferrihydrite than on gibbsite or allophane, whereas the reverse was true for sulphate. I conclude that the approach used should provide significant qualitative information on the competitive adsorptive interactions in soils. However, the approach may be impractical for routine simulations and predictions. This is partly due to the uncertainty of the assumption that the properties of allophane and ferrihydrite in real soils can be approximated by those of gibbsite and ferrihydrite synthesized in the laboratory. Another difficulty is that the adsorption of arsenate and phosphate might not reach equilibrium within the limited time of most experiments.
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| 6. |
- Gustafsson, Jon Petter
(författare)
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Modelling molybdate and tungstate adsorption to ferrihydrite
- 2003
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Ingår i: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 200:02-jan, s. 105-115
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Tidskriftsartikel (refereegranskat)abstract
- The environmental geochemistry of molybdenum and tungsten is not well known. To enable predictions of Mo and W concentrations in the presence of ferrihydrite (hydrous ferric oxide), batch equilibrations were made with MoO42-, WO42-, o-phosphate (PO43-) and freshly prepared ferrihydrite suspensions in 0.01 M NaNO3 in the pH range from 3 to 10 at 25°C. The results showed that WO42- is adsorbed more strongly than MoO42- , and that both ions are able to displace PO43- from adsorption sites at low pH. Two models, the Diffuse Layer Model (DLM) and the CD-MUSIC Model (CDM), were tested in an effort to describe the data. In both models, the adsorption of MoO42- and WO42- could be described with the use of two monodentate complexes. One of these was a fully protonated complex, equivalent to adsorbed molybdic or tungstic acid, which was required to fit the data at low pH. This was found to be the case also for a data set with goethite. In competitive systems with PO43- , the models did not always provide satisfactory predictions. It was suggested this may be partly due to the uncertainty in the PO43- complexation constants.
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| 7. |
- Gustafsson, Jon Petter, et al.
(författare)
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Partitioning of base cations and sulphate between solid and dissolved phases in three podzolised forest soils
- 2000
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Ingår i: Geoderma. - 0016-7061 .- 1872-6259. ; 94:04-feb, s. 311-333
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Tidskriftsartikel (refereegranskat)abstract
- The cation and SO, adsorption properties of O and B horizons of three podzolised soils in Sweden and Finland were studied through analysing the soil solution at six different sampling occasions and through a set of batch experiments. High concentrations of dissolved organic carbon and cations were found in centrifuged soil solutions from the O horizon, especially during autumn. An analysis using the WHAM-S model suggested that most of the dissolved Ca, Mg, K and Mn were counter-ions, residing in the diffuse layers of dissolved fulvic acids. Hence, the solubility of these cations depended on the solubility of organic matter. Model exercises suggested that the solubility of humics in turn was influenced by seasonal differences in hydrophobicity and by the water content. Furthermore, the model results showed that only a low proportion of the B horizon organic matter was involved in calcium binding. This is probably due to the interaction between organic matter and oxide surfaces in this horizon. In the case of sulphate adsorption in the B horizons, a surface complexation model was tested for its ability to describe batch experiment data and temporal differences in soil water chemistry. This model was based on the diffuse-layer model and it was optimised by adjusting the surface site concentration and the point of zero charge. However. the interaction between Ca2+ and SO42- could not be modelled. Comparisons between the model and the field observations proved to be difficult due to a considerable soil heterogeneity.
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| 8. |
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| 9. |
- Gustafsson, Jon Petter
(författare)
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The surface chemistry of imogolite
- 2001
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Ingår i: Clays and clay minerals. - 0009-8604 .- 1552-8367. ; 49:1, s. 73-80
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Tidskriftsartikel (refereegranskat)abstract
- Imogolite is a tubular aluminosilicate which is common in Andosols and Spodosols. The high pH at point-of-zero charge at the outer parts of the tube and the anomalously high chloride adsorption of imogolite suggested that there may be structural charge associated with this mineral. The structural charge may arise because of changes in bond valence imposed by the incorporation of orthosilicate anions in a gibbsite-type sheet. By using a Basic Stem Model approach, it is shown that the surface charge properties of imogolite are explained if the mean Al-O bond valence of the outer -Al2OH groups is higher than the inner -Al2OHSiO3 groups. Hence, a weak positive charge is developed on the outer tube walls whereas a negative charge develops in the tubular pores. The best model fits were obtained where either one or two units of structural charge per unit cell of tube were assumed. The model may also explain why imogolite tubes are normally aggregated in large bundles in close hexagonal packing, because bound counterions may hold the tubes together. However, to arrive at good model descriptions, the deprotonation of -Al2OH groups must occur at a higher pH than that expected when assuming that all surface oxygens form two hydrogen bridges with H2O. A more precise structure of imogolite is required to test fully this hypothesis.
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| 10. |
- Johansson, Lena, 1967-, et al.
(författare)
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Phosphate removal using blast furnace slags and opoka-mechanisms
- 2000
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Ingår i: Water Research. - 0043-1354 .- 1879-2448. ; 34:1, s. 259-265
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Tidskriftsartikel (refereegranskat)abstract
- The abiotic sorption efficiency of on-site wastewater treatment systems can be improved by using a strongly sorbing filter material that, if it retains phosphorus (P) in a plant available way, can be used as fertiliser when P saturation is achieved. Two materials, blast furnace slag and the siliceous sedimentary rock opoka, have shown a high P sorption capacity and were included in a set of experiments to investigate the P retention mechanisms from model P-solution. Experiments focusing on the P sorption, capacity and calcium (Ca) and PO4 determination were carried out. The pH was also measured. The P sorption experiment showed that some slags were efficient P retainers, while the opoka was the least efficient P retainer. The pH decreased in all samples as a function of P addition. In the slag samples, the Ca concentration also decreased as a function of P addition, suggesting Ca-P precipitation as the major P removal mechanism for the slag. The Ca and PO4 speciation data ruled out the formation of amorphous calcium phosphates and/or octacalcium phosphate as the major P removal mechanism. However, the calculated ion activity products displayed clear evidence that hydroxyapatite had precipitated above a certain critical supersaturation limit. This would explain the poor P retention efficiency of the opoka samples in this study as the ion activity products were too low. The finding that direct hydroxyapatite formation is the predominant P removal mechanism might have important implications for their possible use as fertiliser due to the poor solubility of hydroxyapatite.
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