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  • 1
    In: Soil Science Society of America Journal, March-April, 2002, Vol.66(2), p.437(8)
    Description: The Fe-cyanide complexes ferricyanide, [[Fe[(CN).sub.6]].sup.3-], and ferrocyanide, [[Fe[(CN).sub.6]].sup.4-], are of an anthropogenic source in soils. As the complexes are largely charged, sorption on the soil matrix is a possible retention mechanism for these anions. To evaluate soil properties controlling Fe-cyanide complex sorption, experiments were performed with 17 uncontaminated soil horizons by a batch technique. Soil organic matter (SOM) was destroyed in six horizons. The experiments were conducted at soil pH, reaction time of 24 h, and an ionic strength of 0.01 (NaN[O.sub.3]). The affinity of the Fe-cyanide complexes for the soil matrix differed, because 14 samples sorbed higher amounts of ferrocyanide than of ferricyanide. Calculated sorption maxima were quantitatively explained by physical and chemical soil properties using multiple regressions. The regression equations were checked by variance analysis. The regression equations for all samples showed that the sorption of both complexes depended on organic C ([C.sub.org]), clay, and oxalate-extractable Fe ([Fe.sub.o]). The sorption of the complexes on soils containing 〈10 g [C.sub.org] [kg.sup.-1] was governed by pH and clay contents. Clay and oxalate-extractable Al ([Al.sub.o]) were the most important properties influencing ferricyanide sorption on samples containing high amounts of [C.sub.org]. On the same samples, ferrocyanide sorption was governed by [Al.sub.o]. Organic matter promotes the sorption of both complexes, especially on Fluvisol samples. Destruction of SOM of these samples minimized the sorption by up to 99%. Therefore organic matter in these soils may have a special affinity for Fe-cyanide complexes possibly because of the reaction between Fe-cyanide N and reactive groups of SOM.
    Keywords: Soil Science -- Research ; Cyanides -- Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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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: Water, Air, and Soil Pollution, 2010, Vol.205(1), pp.93-105
    Description: As floodplain soils are often contaminated, we studied the release of trace metals from three topsoil horizons in column experiments with variable flow interruptions and flow velocities, compared it with that in batch leaching tests and evaluated the column data by inverse simulations. Only small proportions (〈1%) of trace metals present in the neutral and humic soils were mobilised by the batch leaching tests and the column experiments. Release of Cr, Cu, Ni and Zn in the column experiments was rate-limited, as detected by increased concentrations after flow interruptions. A combination of linear equilibrium and non-equilibrium isotherms reflected the Ni and Zn elution data, with Zn release being slower. Simulated values for initially bound metals available for release are in the same order of magnitude as those determined by the batch leaching tests. However, the consistency of both experimental approaches decreases with increasing rate limitation, as detected here for Zn.
    Keywords: Soil contamination ; Trace metals ; Column experiment ; Kinetics ; Wetland soils
    ISSN: 0049-6979
    E-ISSN: 1573-2932
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  • 4
    Language: English
    In: Environmental Pollution, August 2013, Vol.179, pp.315-325
    Description: Mass transfer processes of pollutants from non-aqueous phase liquids (NAPL) may control groundwater pollution at abandoned industrial sites. We studied release kinetics of polycyclic aromatic hydrocarbons (PAHs) from fresh and aged tar phases using a dialysis tubing technique. Time for equilibration ranged from several days to more than three years. For fresh tar materials the release seems to be limited by retarded pore diffusion, while for two of three aged tars diffusion limited release influenced by dissolved organic matter (DOM) was assumed. The equilibration process was driven by solubilization thermodynamics expressed by Raoult's law. Yet, solubility enhancement was observed potentially due to the presence of organic mobile sorbents. The results show that the release of PAHs from tar phases is generally rate limited and partitioning according to Raoult's law is the driving mechanism of the exchanges process. Release of PAHs from tar phases is severely restricted by retarded pore diffusion.
    Keywords: Aging ; Coal Tar ; Manufactured Gas Plant Sites ; Tar Processing Facilities ; Reactive Transport ; Dissolved Organic Matter ; Polycyclic Aromatic Hydrocarbons ; Engineering ; Environmental Sciences ; Anatomy & Physiology
    ISSN: 0269-7491
    E-ISSN: 1873-6424
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  • 5
    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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  • 6
    Language: English
    In: Environmental Geochemistry and Health, 2017, Vol.39(2), pp.331-344
    Description: Central European floodplain soils are often contaminated with potentially toxic metals. The prediction of their aqueous concentrations is a prerequisite for an assessment of environmental concerns. We tested the aqueous concentrations of cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) derived from multi-surface adsorption modelling (on hydrous iron, aluminum and manganese oxides, clay and soil organic matter) against those analyzed in situ in the soil solution of four horizons of floodplain soils at the Elbe River, Germany. The input data for the reactive metals were derived from a seven-step sequential extraction scheme or from extraction with 0.43 M nitric acid (HNO 3 ) and evaluated in four modelling scenarios. In all scenarios, measured and modelled concentrations were positively related, except partially for Pb. Close reproduction of the measured data was obtained using measured data of accompanying cations and anions together with amounts of reactive metals from both the sequential extraction or from 0.43 M HNO 3 extraction, except for Cu, which was often strongly overestimated, and partially Cd. We recommend extraction with 0.43 M HNO 3 to quantify reactive metals in soil because the modelling results were metal-specific with better or equal results using the single extractant, the application of which is also less laborious. Approximations of ion concentrations and water contents yielded similar results. Modelled solid-phase speciation of metals varied with pH and differed from that from sequential extraction. Multi-surface modelling may be an effective tool to predict both aqueous concentrations and solid-phase speciation of metals in soil.
    Keywords: Multi-surface modelling ; Metals ; Soil contamination ; Sequential extraction ; Fluvisol
    ISSN: 0269-4042
    E-ISSN: 1573-2983
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  • 7
    Language: English
    In: Water, Air, & Soil Pollution, 2010, Vol.209(1), pp.489-500
    Description: The applicability of laboratory tests for the prediction of soil solution composition and concentrations of inorganic contaminants is still under debate. Therefore, we carried out two batch-leaching tests differing in their liquid/solid ratios and column experiments (saturated flow, two flow velocities, four flow interruptions ranging from 4 h to 21 days) with a contaminated humic horizon (total contents: As, 196 mg kg −1 ; Cd, 4 mg kg −1 ; Cr, 202 mg kg −1 ; Cu, 227 mg kg −1 ; Ni, 64 mg kg −1 ; Pb, 308 mg kg −1 ; Zn, 1,176 mg kg −1 ) from a Mollic Fluvisol near the rivers Elbe and Saale (Germany) and compared the aqueous contaminant concentrations with those of soil solutions obtained in situ with ceramic suction cups on a monthly basis between 2002 and 2006. Contaminant release in the field slightly depended on the water regime, pH, and redox potential and was characterized by partially high concentrations (e.g., As, 47 µg l −1 ; Cd, 136 µg l −1 ; Ni, 328 µg l −1 ; Zn, 8.68 mg l −1 ), which exceeded the German inspection values. Metal concentrations obtained in batch-leaching tests partially fitted to those determined in the soil solution and to those from the column experiments even irrespective of the varying liquid/solid ratios. The column experiments yielded realistic concentrations of Cr, Cu, Ni, and Pb and their ranges. Furthermore, they provided an insight into release kinetics and release processes as well as into potential contaminant release due to enforced reducing conditions. As column experiments allow a larger temporal sampling resolution and enable quickly to manipulate experimental conditions, they are a useful complement of soil solution monitoring.
    Keywords: Wetland soil ; Soil solution ; Metals ; Batch-leaching test ; Column experiments ; Soil contamination
    ISSN: 0049-6979
    E-ISSN: 1573-2932
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  • 8
    Language: English
    In: Geochimica et Cosmochimica Acta, 15 January 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 . Independent of the initial colloid size, the soil effluent ferrihydrite colloids were quickly and completely reduced. The rates of Fe formation ranged between 1.9 and 3.3 fmol h cell , and are in the range of or slightly exceeding previously reported rates of synthetic ferrihydrite colloids (1.3 fmol h cell ), but greatly exceeding previously known rates of macroaggregate-ferrihydrite reduction (0.07 fmol h cell ). 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.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
    Source: ScienceDirect Journals (Elsevier)
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  • 9
    Language: English
    In: Environmental Geochemistry and Health, 2017, Vol.39(6), pp.1291-1304
    Description: European floodplain soils are frequently contaminated with potentially toxic inorganic substances. We used a multi-surface model to estimate the aqueous concentrations of Cd, Cu, Ni, Pb and Zn in three Mollic Fluvisols from the Central Elbe River (Germany). The model considered complexation in solution and interactions with soil organic matter (SOM), a clay mineral and hydrous Al, Fe and Mn oxides. The amounts of reactive metals were derived from extraction with 0.43 M HNO 3 . Modelling was carried out as a function of pH (soil pH ± 1.4) because it varies in floodplain soils owing to redox processes that consume or release protons. The fraction of reactive metals, which were dissolved according to the modelling, was predominantly 〈1%. Depending on soil properties, especially pH and contents of SOM and minerals of the clay fraction, the modelled concentrations partially exceeded the trigger values for the soil–groundwater pathway of the German soil legislation. This differentiation by soil properties was given for Ni, Pb and Zn. On the other hand, Cd was more mobile, i.e., the trigger values were mostly exceeded. Copper represented the opposite, as the modelling did not predict exceeding the trigger values in any horizon. Except for Pb and partially Zn (where oxides were more important), SOM was the most important adsorbent for metals. However, given the special composition and dynamics of SOM in mollic horizons, we suggest further quantitative and qualitative investigations on SOM and on its interaction with metals to improve the prediction of contaminant dynamics.
    Keywords: Floodplain soil ; Metals ; Soil contamination ; Adsorption ; Multi-surface modelling
    ISSN: 0269-4042
    E-ISSN: 1573-2983
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  • 10
    Language: English
    In: Geoderma, February 2013, Vol.193-194, pp.117-121
    Description: The synthesis of pure birnessite (δ-MnO ) by a simple, fast and reliable method is introduced. Birnessite was synthesized by a sol–gel reaction involving the reduction of KMnO by lactate at ambient pressure and temperature. Our method does not include the use of strong acids and bases and does not produce toxic residues. The results from both X-ray diffraction and Fourier-transform infrared spectroscopy, compared with a synthesized reference material, verified our synthesized mineral as birnessite. Secondary electron images showed a micro-porous structure of aggregated birnessite colloids, and consistently, we measured a very large specific BET surface area of 249.15 ± 0.05 m g . Birnessite is known to have a variable mineral formula, and the elemental composition of our mineral is within the range of other birnessites. Birnessite obtained by this procedure could serve as a model mineral for laboratory experiments on the biogeochemistry of Mn, and furthermore it may also have a potential as electron acceptor for remediation purposes. ► Pure birnessite was synthesized by a simple, fast, reliable and inexpensive method. ► This birnessite can serve as a model mineral in studies on the biogeochemistry of Mn. ► It may have potential for the remediation of contaminated soils.
    Keywords: Ftir ; Xrd ; Specific Surface Area ; Manganese Oxide ; Remediation ; Sol–Gel Synthesis ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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