Proteins are a substantial nitrogen source in soils provided that they can be hydrolyzed into bio... more Proteins are a substantial nitrogen source in soils provided that they can be hydrolyzed into bioavailable small peptides or amino acids. However, the strong associations between proteins and soil minerals restrict such proteolytic reactions. This study focused on how an extracellular fungal protease (Rhizopus sp.) hydrolyzed iron oxide-associated bovine serum albumin (BSA) and the factors that affected the proteolysis. We combined batch experiments with sizeexclusion and reversed phase liquid chromatography and in situ infrared spectroscopic measurements to monitor the generation of proteolytic products in solution as well as the real-time changes of the adsorbed BSA during 24 h. Results showed that protease hydrolyzed the iron oxide-associated BSA directly at the surface without an initial desorption of BSA. Concurrently, the protease was adsorbed to vacant surface sites at the iron oxides, which significantly slowed down the rate of proteolysis. This inhibiting effect was counteracted by the presence of preadsorbed phosphate or by increasing the BSA coverage, which prevented protease adsorption. Fast initial rates of iron oxide-associated BSA proteolysis, comparable to proteolysis of BSA in solution, and very slow rates at prolonged proteolysis suggest a large variability in mineral-associated proteins as a nitrogen source in soils and that only a fraction of the protein is bioavailable.
Modern vibrational spectroscopy techniques enable rapid collection of thousands of spectra in a s... more Modern vibrational spectroscopy techniques enable rapid collection of thousands of spectra in a single hyperspectral image, allowing researchers to resolve spatially heterogeneous samples down to a resolution of a few μm. A number of algorithms have been developed to correct for effects such as atmospheric absorption, light scattering by cellular structures and varying baseline levels. Following such preprocessing, spectra are commonly decomposed and clustered to reveal informative patterns and subtle spectral changes. Several of these steps are slow, labor-intensive and require programming skills to make use of published algorithms and code. We here present a free and platform-independent graphical toolbox that allows rapid processing of large sets of spectroscopic images, including atmospheric correction and an algorithm for resonant Mie scattering with improved speed and stability. The software includes modules for decomposition into constituent spectra using the popular MCR-ALS ...
Through geological time, cyanobacterial picoplankton have impacted the global carbon cycle by seq... more Through geological time, cyanobacterial picoplankton have impacted the global carbon cycle by sequestrating CO2 and forming authigenic carbonate minerals. Various studies have emphasized the cyanobacterial cell envelopes as nucleation sites for calcium carbonate formation. Little is known, however, about how environmental conditions (e.g., nutrient content) trigger a cell surface and its properties and, consequently, influence biomineralization. Our study aims to understand how phosphorus (P) concentration impacts the properties of cell surfaces and cell–mineral interactions. Changes to the surface properties of marine Synechococcus strains grown under various P conditions were characterized by potentiometric titrations, X-ray photoelectron spectroscopy (XPS), and tip-enhanced Raman spectroscopy (TERS). Biomineralization experiments were performed using cyanobacterial cells, which were grown under different P concentrations and exposed to solutions slightly oversaturated with respec...
Soil organic matter (SOM) constitutes the largest terrestrial C pool. An emerging, untested, view... more Soil organic matter (SOM) constitutes the largest terrestrial C pool. An emerging, untested, view is that oxidation and depolymerization of SOM by microorganisms promote the formation of SOM-mineral associations that is critical for SOM stabilization. To test this hypothesis we performed laboratory-scale experiments involving one ectomycorrhizal and one saprotrophic fungus that represent the two major functional groups of microbial decomposers in the boreal forest soils. Fungal decomposition enhanced the retention of SOM on goethite, partly because of oxidative modifications of organic matter (OM) by the fungi. Moreover, both fungi secreted substantial amounts (>10% new biomass C) of aromatic metabolites that also contributed to an enhanced mineral retention of OM. Our study demonstrates that soil fungi can form mineral-stabilized SOM not only by oxidative conversion of the SOM but also by synthesizing mineral surface-reactive metabolites. Metabolites produced by fungal decompose...
The close linkage between iron (Fe) and phosphorus (P) suggests that changes in Fe speciation may... more The close linkage between iron (Fe) and phosphorus (P) suggests that changes in Fe speciation may have a strong effect on the bioavailability of P. At the same time Fe speciation in natural oxic environments is known to be affected by the presence of organic matter (OM), pH and total Fe concentrations, thus these parameters should also influence the Fe-P interactions. The main objective of the present work was to study how OM affected the distribution of P(V) in the presence of Fe(III) and to address the questions if and by what mechanism(s) OM influenced the concentration of aqueous phosphate. This was accomplished by investigating the ternary P(V)-Fe(III)-OM system over a wide range of chemical conditions; [Fe] tot =5000-50 000 μg g-1 , Fe/P=0.5-2.0 at pH 2.9-7. Iron speciation was probed via Fe K-edge X-ray absorption spectroscopy, P speciation and concentrations were analyzed via infrared spectroscopy, and chemical equilibrium modeling was conducted to simulate the distribution of chemical species of
Hydroquinones are important mediators of electron transfer reactions in soils with a capability t... more Hydroquinones are important mediators of electron transfer reactions in soils with a capability to reduce Fe(III) minerals and molecular oxygen, and thereby generating Fenton chemistry reagents. This study focused on 2,6-dimethoxy hydroquinone (2,6-DMHQ), an analogue to a common fungal metabolite, and its reaction with ferrihydrite and goethite under variable pH and oxygen concentrations. Combined wet-chemical and spectroscopic analyses showed that both minerals effectively oxidized 2,6-DMHQ in the presence of oxygen. Under anaerobic conditions the first-order oxidation rate constants decreased by one to several orders of magnitude depending on pH and mineral. Comparison between aerobic and anaerobic results showed that ferrihydrite promoted 2,6-DMHQ oxidation both via reductive dissolution and heterogeneous catalysis while goethite mainly caused catalytic oxidation. These results were in agreement with changes in the reduction potential (EH) of the Fe(III) oxide/Fe(II)aq redox coup...
Cu(Il) complexation at the water-goethite (a-FeOOH) interface was studied by XAFS, potentiomefxy,... more Cu(Il) complexation at the water-goethite (a-FeOOH) interface was studied by XAFS, potentiomefxy, and sorption experiments. Thermodynamic data indicate that the initial C u m sorption is not accompanied by release of a H*. As pH is raised, hydrolysis occurs, and a maximum of two H* are released per sorbed ion. Sorption experiments also show that Cu(Q complexation is insensitive to variation in ionic strength, indicating inner-spherc Cu complexes. The Cu Kedge XAFS suggest that the C u m surface complexes are Jahn-Teller distorted with an equatorial plane of oxygens at approximately 1.95 A. At pH 5, no 2nd coordination shell is observed. However, at pH 8 there is a well-defined 2nd shell which is best modeled with two Cu atoms at 2.96 A. The appearance of a 2nd coordination shell at higher pH is attributed to the formation of hydroxo-bridged C u p) surface polymers.
Recent studies have shown that dissolved organic matter (DOM) decomposed by ectomycorrhizal (ECM)... more Recent studies have shown that dissolved organic matter (DOM) decomposed by ectomycorrhizal (ECM) fungi increases adsorptive properties of organic matter towards soil mineral surfaces. Concomitantly, ECM fungi secrete secondary metabolites with iron reducing capacity that are thought to participate in non-enzymatic Fenton-based decomposition of DOM. The aim of this study was to investigate if the iron reduction induced by the ECM fungus Paxillus involutus during organic matter decomposition was conserved in the decomposed DOM. We explored how the modified DOM reductively dissolved ferrihydrite and goethite nanoparticles and how these processes affected the reactions with H2O2 and the Fenton-based oxidation of mineral-associated organic matter. Culture filtrates were obtained from incubation of the ECM fungus on DOM from forest litter of a spruce forest. This modified DOM was separated by extraction into an ethyl acetate and a water fraction. These fractions were reacted with ferrihy...
mulation of Al and Fe in organic soils increases the capac- ity of phosphate sorption (Cuttle, 19... more mulation of Al and Fe in organic soils increases the capac- ity of phosphate sorption (Cuttle, 1983; Richardson, 1985; Groundwater discharge areas in boreal forest ecosystems can po- Nieminen and Jarva, 1996). Furthermore, model experi- tentially be areas where Fe and Al accumulate in the forest floor and affect the solubility of P. This study was conducted to determine ments
This has been a long journey and so many people have contributed in so many different ways that I... more This has been a long journey and so many people have contributed in so many different ways that I feel I cannot express all the gratitude they deserve in words. Thus, I will restrict myself to acknowledge some of the key individuals and institutions.
The predominant forms of arsenic (As) in anoxic and oxic environments are As(III) and As(V), resp... more The predominant forms of arsenic (As) in anoxic and oxic environments are As(III) and As(V), respectively, and the fate of these forms is influenced by interactions with mineral surfaces and organic matter (OM). Interactions between As(V) and OM are believed to occur mainly via iron(Fe)-bridges in ternary Fe-arsenate complexes, but direct evidence for these interactions are scarce. Furthermore, since the speciation of Fe in the presence of organic matter varies as a function of pH and Fe concentration, a central question is how different chemical conditions will affect the As-Fe-OM interactions. In order to answer this, the As(V)-Fe(III)-OM system have been studied under a large range of experimental conditions (6485-67 243 ppm Fe(III) and Fe(III):As(V) ratios of 0.5-20 at pH 3-7), with Suwannee River Natural organic matter and Suwannee River Fulvic acids as sources of OM, using Fe and As K-edge X-ray absorption spectroscopy (XAS), infrared (IR) spectroscopy and chemical equilibrium modeling. Our collective results showed that interactions in the ternary As(V)-Fe(III)-OM system were strongly influenced by pH, total concentrations and ratios among the reactive species. In particular, the high stability of the Fe(III)-OM complexes exerted a strong control on the speciation. The predominant species identified were mononuclear Fe(III)-OM complexes, Fe(III) (hydr)oxides and FeAsO 4 solids. The experimental results also showed that at low concentrations the Fe(III)-SRFA/SRN complexes were sufficiently stable to prevent reaction with arsenate. The chemical equilibrium models developed corroborated the spectroscopic results and indicated that As(V) was distributed over two solid phases, namely FeAsO 4 (s) and Fe(OH) 1.5 (AsO 4) 0.5 (s). Thus, neither ternary As(V)-Fe(III)-OM complexes nor As(V) surface complexes on Fe(III) (hydr)oxides were necessary to explain the collective results presented in this study.
forest facts 4 • 2013 • Results from the Swedish University of Agricultural Sciences • The boreal... more forest facts 4 • 2013 • Results from the Swedish University of Agricultural Sciences • The boreal forest is important for carbon storage, biodiversity, and the Swedish economy. Therefore it is important to understand what mechanisms determine forest growth. • Although nitrogen (N) is considered the most crucial nutrient for growth in the boreal forest, phosphorus (P) may be locally limiting.
The nature of the interaction between mellitic acid (benzene hexacarboxylic acid) and the common ... more The nature of the interaction between mellitic acid (benzene hexacarboxylic acid) and the common soil mineral goethite (alpha-FeOOH) has been investigated as a function of pH and ionic strength by use of attenuated total reflection Fourier transform infrared spectroscopy. Molecular orbital calculations of the theoretical vibrational frequencies of the mellitate ion (L6-) and dihydrogen mellitate (H2L4-) have allowed the measured absorption frequencies to be accurately assigned. At pH values above 6, adsorption involves outer-sphere complexation of the deprotonated L6- ion. At lower pH values, there is evidence of a second outer-sphere surface complex involving a partially protonated species, although the extent of protonation of the surface species is significantly less than that found for the solution species at the same pH. While there is no evidence of inner-sphere complexation, increasing the ionic strength to 2.0 M does not displace the adsorbed species but does increase the fraction present on the surface as the fully deprotonated L6-. The small effect of ionic strength suggests that the adsorptive interaction, although outer-sphere in character, is still relatively strong, which indicates that hydrogen bonds may play a significant role. Hydrogen bonding may also help to account for the observed outer-sphere complexation at pH values above the pHiep of goethite.
Complexation of o-phthalate (1,2-benzenedicarboxylate) and competitive complexation of phosphate ... more Complexation of o-phthalate (1,2-benzenedicarboxylate) and competitive complexation of phosphate and phthalate at the goethite-water interface have been studied in 0.1 M Na (NO3) media at 298.2 K within the range 3.0 < -log [H+] < 8.5. Equilibrium measurements were performed as potentiometric titrations supplemented with spectrophotometric phosphate and phthalate analyses.The binary and ternary chemical subsystems H+-goethite and H+-goethite-H2PO4− have been
A surface complexation model describing the adsorption of three benzenecarboxylates (phthalate, t... more A surface complexation model describing the adsorption of three benzenecarboxylates (phthalate, trimellitate, and pyromellitate) on goethite (α-FeOOH) was calibrated on data using goethite particles of 37 and 43 m 2 /g surface area. The models predict potentiometric titration and batch adsorption data with the multisite complexation model coupled with the three-plane model to account for surface electrostatics. The modeling parameters were found to be similar to those calibrated on benzenecarboxylate adsorption data on goethite particles of 90 m 2 /g (Boily et al. Geochim. Cosmochim. Acta, in press). The significance of the benzenecarboxylate-dependent values of the modeling parameters is also discussed. The values of the capacitances of the inner-and outer-Helmholtz planes were shown to be important modeling parameters to model the benzenecarboxylate-dependent slopes of the adsorption edges. It was shown that the larger the charge of the ligand, the larger the capacitance of the outer-Helmholtz plane.
The complexation of sulfate ions at the goethite-water interface has been studied by equilibrium ... more The complexation of sulfate ions at the goethite-water interface has been studied by equilibrium measurements at 298.2 ± 0.5 K and by infrared spectroscopy. A unified set of data from potentiometric titrations and batch adsorption experiments were evaluated according to an extended Constant Capacitance Model. The obtained equilibrium model consists of two outer-sphere complexes: ≡FeOH2+, SO42− (log β1,1,1(intr)out = 8.3 ± 0.03) and ≡FeOH2+, HSO4− (log β2,1,1(intr)out = 13.5 ± 0.07) and an inner capacitance, C1, of 4.5 and an outer capacitance, C2, of 1.8. The outer-sphere model was confirmed by the infrared data and adsorption experiments at different ionic strengths. Furthermore, the infrared measurements provided direct evidence for protonation of the sulfate ions at the interface.
The complexation of Cd(II) and Cd(II)-phthalate at the goethite/water interface were investigated... more The complexation of Cd(II) and Cd(II)-phthalate at the goethite/water interface were investigated by EXAFS and IR spectroscopy, by batch adsorption experiments and by potentiometric titrations at 298.15 K. The EXAFS spectra showed Cd(II) to form only inner-sphere corner-sharing complexes with the goethite surface sites in the presence and absence of phthalate. EXAFS spectra also showed the presence of Cd(II)-chloride complexes in 0.1 mol/L NaCl. IR spectra also showed phthalate to form (1) an inner-sphere complex with adsorbed corner-sharing Cd(II) surface complexes in the pH 3.5 to 9.5 and (2) an outer-sphere complex with the same type of corner-sharing Cd(II) complex however at pH Ͼ 6, in addition to the innerand outer-sphere complexes of phthalate reported in a previous study. The potentiometric titration and the batch adsorption data were used to constrain the formation constants of the different Cd(II)-phthalate surface complexes on the dominant {110} and the {001} planes of the goethite. The models were carried out with the Charge Distribution Multisite Complexation model coupled to the Three Plane Model and can predict the molecularscale speciation of cadmium and phthalate in the presence of goethite. Cd(II) adsorption models calibrated on a 90 m 2 /g goethite also could accurately predict experimental data for a 37 m 2 /g goethite of slightly different basic charging properties.
Proteins are a substantial nitrogen source in soils provided that they can be hydrolyzed into bio... more Proteins are a substantial nitrogen source in soils provided that they can be hydrolyzed into bioavailable small peptides or amino acids. However, the strong associations between proteins and soil minerals restrict such proteolytic reactions. This study focused on how an extracellular fungal protease (Rhizopus sp.) hydrolyzed iron oxide-associated bovine serum albumin (BSA) and the factors that affected the proteolysis. We combined batch experiments with sizeexclusion and reversed phase liquid chromatography and in situ infrared spectroscopic measurements to monitor the generation of proteolytic products in solution as well as the real-time changes of the adsorbed BSA during 24 h. Results showed that protease hydrolyzed the iron oxide-associated BSA directly at the surface without an initial desorption of BSA. Concurrently, the protease was adsorbed to vacant surface sites at the iron oxides, which significantly slowed down the rate of proteolysis. This inhibiting effect was counteracted by the presence of preadsorbed phosphate or by increasing the BSA coverage, which prevented protease adsorption. Fast initial rates of iron oxide-associated BSA proteolysis, comparable to proteolysis of BSA in solution, and very slow rates at prolonged proteolysis suggest a large variability in mineral-associated proteins as a nitrogen source in soils and that only a fraction of the protein is bioavailable.
Modern vibrational spectroscopy techniques enable rapid collection of thousands of spectra in a s... more Modern vibrational spectroscopy techniques enable rapid collection of thousands of spectra in a single hyperspectral image, allowing researchers to resolve spatially heterogeneous samples down to a resolution of a few μm. A number of algorithms have been developed to correct for effects such as atmospheric absorption, light scattering by cellular structures and varying baseline levels. Following such preprocessing, spectra are commonly decomposed and clustered to reveal informative patterns and subtle spectral changes. Several of these steps are slow, labor-intensive and require programming skills to make use of published algorithms and code. We here present a free and platform-independent graphical toolbox that allows rapid processing of large sets of spectroscopic images, including atmospheric correction and an algorithm for resonant Mie scattering with improved speed and stability. The software includes modules for decomposition into constituent spectra using the popular MCR-ALS ...
Through geological time, cyanobacterial picoplankton have impacted the global carbon cycle by seq... more Through geological time, cyanobacterial picoplankton have impacted the global carbon cycle by sequestrating CO2 and forming authigenic carbonate minerals. Various studies have emphasized the cyanobacterial cell envelopes as nucleation sites for calcium carbonate formation. Little is known, however, about how environmental conditions (e.g., nutrient content) trigger a cell surface and its properties and, consequently, influence biomineralization. Our study aims to understand how phosphorus (P) concentration impacts the properties of cell surfaces and cell–mineral interactions. Changes to the surface properties of marine Synechococcus strains grown under various P conditions were characterized by potentiometric titrations, X-ray photoelectron spectroscopy (XPS), and tip-enhanced Raman spectroscopy (TERS). Biomineralization experiments were performed using cyanobacterial cells, which were grown under different P concentrations and exposed to solutions slightly oversaturated with respec...
Soil organic matter (SOM) constitutes the largest terrestrial C pool. An emerging, untested, view... more Soil organic matter (SOM) constitutes the largest terrestrial C pool. An emerging, untested, view is that oxidation and depolymerization of SOM by microorganisms promote the formation of SOM-mineral associations that is critical for SOM stabilization. To test this hypothesis we performed laboratory-scale experiments involving one ectomycorrhizal and one saprotrophic fungus that represent the two major functional groups of microbial decomposers in the boreal forest soils. Fungal decomposition enhanced the retention of SOM on goethite, partly because of oxidative modifications of organic matter (OM) by the fungi. Moreover, both fungi secreted substantial amounts (>10% new biomass C) of aromatic metabolites that also contributed to an enhanced mineral retention of OM. Our study demonstrates that soil fungi can form mineral-stabilized SOM not only by oxidative conversion of the SOM but also by synthesizing mineral surface-reactive metabolites. Metabolites produced by fungal decompose...
The close linkage between iron (Fe) and phosphorus (P) suggests that changes in Fe speciation may... more The close linkage between iron (Fe) and phosphorus (P) suggests that changes in Fe speciation may have a strong effect on the bioavailability of P. At the same time Fe speciation in natural oxic environments is known to be affected by the presence of organic matter (OM), pH and total Fe concentrations, thus these parameters should also influence the Fe-P interactions. The main objective of the present work was to study how OM affected the distribution of P(V) in the presence of Fe(III) and to address the questions if and by what mechanism(s) OM influenced the concentration of aqueous phosphate. This was accomplished by investigating the ternary P(V)-Fe(III)-OM system over a wide range of chemical conditions; [Fe] tot =5000-50 000 μg g-1 , Fe/P=0.5-2.0 at pH 2.9-7. Iron speciation was probed via Fe K-edge X-ray absorption spectroscopy, P speciation and concentrations were analyzed via infrared spectroscopy, and chemical equilibrium modeling was conducted to simulate the distribution of chemical species of
Hydroquinones are important mediators of electron transfer reactions in soils with a capability t... more Hydroquinones are important mediators of electron transfer reactions in soils with a capability to reduce Fe(III) minerals and molecular oxygen, and thereby generating Fenton chemistry reagents. This study focused on 2,6-dimethoxy hydroquinone (2,6-DMHQ), an analogue to a common fungal metabolite, and its reaction with ferrihydrite and goethite under variable pH and oxygen concentrations. Combined wet-chemical and spectroscopic analyses showed that both minerals effectively oxidized 2,6-DMHQ in the presence of oxygen. Under anaerobic conditions the first-order oxidation rate constants decreased by one to several orders of magnitude depending on pH and mineral. Comparison between aerobic and anaerobic results showed that ferrihydrite promoted 2,6-DMHQ oxidation both via reductive dissolution and heterogeneous catalysis while goethite mainly caused catalytic oxidation. These results were in agreement with changes in the reduction potential (EH) of the Fe(III) oxide/Fe(II)aq redox coup...
Cu(Il) complexation at the water-goethite (a-FeOOH) interface was studied by XAFS, potentiomefxy,... more Cu(Il) complexation at the water-goethite (a-FeOOH) interface was studied by XAFS, potentiomefxy, and sorption experiments. Thermodynamic data indicate that the initial C u m sorption is not accompanied by release of a H*. As pH is raised, hydrolysis occurs, and a maximum of two H* are released per sorbed ion. Sorption experiments also show that Cu(Q complexation is insensitive to variation in ionic strength, indicating inner-spherc Cu complexes. The Cu Kedge XAFS suggest that the C u m surface complexes are Jahn-Teller distorted with an equatorial plane of oxygens at approximately 1.95 A. At pH 5, no 2nd coordination shell is observed. However, at pH 8 there is a well-defined 2nd shell which is best modeled with two Cu atoms at 2.96 A. The appearance of a 2nd coordination shell at higher pH is attributed to the formation of hydroxo-bridged C u p) surface polymers.
Recent studies have shown that dissolved organic matter (DOM) decomposed by ectomycorrhizal (ECM)... more Recent studies have shown that dissolved organic matter (DOM) decomposed by ectomycorrhizal (ECM) fungi increases adsorptive properties of organic matter towards soil mineral surfaces. Concomitantly, ECM fungi secrete secondary metabolites with iron reducing capacity that are thought to participate in non-enzymatic Fenton-based decomposition of DOM. The aim of this study was to investigate if the iron reduction induced by the ECM fungus Paxillus involutus during organic matter decomposition was conserved in the decomposed DOM. We explored how the modified DOM reductively dissolved ferrihydrite and goethite nanoparticles and how these processes affected the reactions with H2O2 and the Fenton-based oxidation of mineral-associated organic matter. Culture filtrates were obtained from incubation of the ECM fungus on DOM from forest litter of a spruce forest. This modified DOM was separated by extraction into an ethyl acetate and a water fraction. These fractions were reacted with ferrihy...
mulation of Al and Fe in organic soils increases the capac- ity of phosphate sorption (Cuttle, 19... more mulation of Al and Fe in organic soils increases the capac- ity of phosphate sorption (Cuttle, 1983; Richardson, 1985; Groundwater discharge areas in boreal forest ecosystems can po- Nieminen and Jarva, 1996). Furthermore, model experi- tentially be areas where Fe and Al accumulate in the forest floor and affect the solubility of P. This study was conducted to determine ments
This has been a long journey and so many people have contributed in so many different ways that I... more This has been a long journey and so many people have contributed in so many different ways that I feel I cannot express all the gratitude they deserve in words. Thus, I will restrict myself to acknowledge some of the key individuals and institutions.
The predominant forms of arsenic (As) in anoxic and oxic environments are As(III) and As(V), resp... more The predominant forms of arsenic (As) in anoxic and oxic environments are As(III) and As(V), respectively, and the fate of these forms is influenced by interactions with mineral surfaces and organic matter (OM). Interactions between As(V) and OM are believed to occur mainly via iron(Fe)-bridges in ternary Fe-arsenate complexes, but direct evidence for these interactions are scarce. Furthermore, since the speciation of Fe in the presence of organic matter varies as a function of pH and Fe concentration, a central question is how different chemical conditions will affect the As-Fe-OM interactions. In order to answer this, the As(V)-Fe(III)-OM system have been studied under a large range of experimental conditions (6485-67 243 ppm Fe(III) and Fe(III):As(V) ratios of 0.5-20 at pH 3-7), with Suwannee River Natural organic matter and Suwannee River Fulvic acids as sources of OM, using Fe and As K-edge X-ray absorption spectroscopy (XAS), infrared (IR) spectroscopy and chemical equilibrium modeling. Our collective results showed that interactions in the ternary As(V)-Fe(III)-OM system were strongly influenced by pH, total concentrations and ratios among the reactive species. In particular, the high stability of the Fe(III)-OM complexes exerted a strong control on the speciation. The predominant species identified were mononuclear Fe(III)-OM complexes, Fe(III) (hydr)oxides and FeAsO 4 solids. The experimental results also showed that at low concentrations the Fe(III)-SRFA/SRN complexes were sufficiently stable to prevent reaction with arsenate. The chemical equilibrium models developed corroborated the spectroscopic results and indicated that As(V) was distributed over two solid phases, namely FeAsO 4 (s) and Fe(OH) 1.5 (AsO 4) 0.5 (s). Thus, neither ternary As(V)-Fe(III)-OM complexes nor As(V) surface complexes on Fe(III) (hydr)oxides were necessary to explain the collective results presented in this study.
forest facts 4 • 2013 • Results from the Swedish University of Agricultural Sciences • The boreal... more forest facts 4 • 2013 • Results from the Swedish University of Agricultural Sciences • The boreal forest is important for carbon storage, biodiversity, and the Swedish economy. Therefore it is important to understand what mechanisms determine forest growth. • Although nitrogen (N) is considered the most crucial nutrient for growth in the boreal forest, phosphorus (P) may be locally limiting.
The nature of the interaction between mellitic acid (benzene hexacarboxylic acid) and the common ... more The nature of the interaction between mellitic acid (benzene hexacarboxylic acid) and the common soil mineral goethite (alpha-FeOOH) has been investigated as a function of pH and ionic strength by use of attenuated total reflection Fourier transform infrared spectroscopy. Molecular orbital calculations of the theoretical vibrational frequencies of the mellitate ion (L6-) and dihydrogen mellitate (H2L4-) have allowed the measured absorption frequencies to be accurately assigned. At pH values above 6, adsorption involves outer-sphere complexation of the deprotonated L6- ion. At lower pH values, there is evidence of a second outer-sphere surface complex involving a partially protonated species, although the extent of protonation of the surface species is significantly less than that found for the solution species at the same pH. While there is no evidence of inner-sphere complexation, increasing the ionic strength to 2.0 M does not displace the adsorbed species but does increase the fraction present on the surface as the fully deprotonated L6-. The small effect of ionic strength suggests that the adsorptive interaction, although outer-sphere in character, is still relatively strong, which indicates that hydrogen bonds may play a significant role. Hydrogen bonding may also help to account for the observed outer-sphere complexation at pH values above the pHiep of goethite.
Complexation of o-phthalate (1,2-benzenedicarboxylate) and competitive complexation of phosphate ... more Complexation of o-phthalate (1,2-benzenedicarboxylate) and competitive complexation of phosphate and phthalate at the goethite-water interface have been studied in 0.1 M Na (NO3) media at 298.2 K within the range 3.0 < -log [H+] < 8.5. Equilibrium measurements were performed as potentiometric titrations supplemented with spectrophotometric phosphate and phthalate analyses.The binary and ternary chemical subsystems H+-goethite and H+-goethite-H2PO4− have been
A surface complexation model describing the adsorption of three benzenecarboxylates (phthalate, t... more A surface complexation model describing the adsorption of three benzenecarboxylates (phthalate, trimellitate, and pyromellitate) on goethite (α-FeOOH) was calibrated on data using goethite particles of 37 and 43 m 2 /g surface area. The models predict potentiometric titration and batch adsorption data with the multisite complexation model coupled with the three-plane model to account for surface electrostatics. The modeling parameters were found to be similar to those calibrated on benzenecarboxylate adsorption data on goethite particles of 90 m 2 /g (Boily et al. Geochim. Cosmochim. Acta, in press). The significance of the benzenecarboxylate-dependent values of the modeling parameters is also discussed. The values of the capacitances of the inner-and outer-Helmholtz planes were shown to be important modeling parameters to model the benzenecarboxylate-dependent slopes of the adsorption edges. It was shown that the larger the charge of the ligand, the larger the capacitance of the outer-Helmholtz plane.
The complexation of sulfate ions at the goethite-water interface has been studied by equilibrium ... more The complexation of sulfate ions at the goethite-water interface has been studied by equilibrium measurements at 298.2 ± 0.5 K and by infrared spectroscopy. A unified set of data from potentiometric titrations and batch adsorption experiments were evaluated according to an extended Constant Capacitance Model. The obtained equilibrium model consists of two outer-sphere complexes: ≡FeOH2+, SO42− (log β1,1,1(intr)out = 8.3 ± 0.03) and ≡FeOH2+, HSO4− (log β2,1,1(intr)out = 13.5 ± 0.07) and an inner capacitance, C1, of 4.5 and an outer capacitance, C2, of 1.8. The outer-sphere model was confirmed by the infrared data and adsorption experiments at different ionic strengths. Furthermore, the infrared measurements provided direct evidence for protonation of the sulfate ions at the interface.
The complexation of Cd(II) and Cd(II)-phthalate at the goethite/water interface were investigated... more The complexation of Cd(II) and Cd(II)-phthalate at the goethite/water interface were investigated by EXAFS and IR spectroscopy, by batch adsorption experiments and by potentiometric titrations at 298.15 K. The EXAFS spectra showed Cd(II) to form only inner-sphere corner-sharing complexes with the goethite surface sites in the presence and absence of phthalate. EXAFS spectra also showed the presence of Cd(II)-chloride complexes in 0.1 mol/L NaCl. IR spectra also showed phthalate to form (1) an inner-sphere complex with adsorbed corner-sharing Cd(II) surface complexes in the pH 3.5 to 9.5 and (2) an outer-sphere complex with the same type of corner-sharing Cd(II) complex however at pH Ͼ 6, in addition to the innerand outer-sphere complexes of phthalate reported in a previous study. The potentiometric titration and the batch adsorption data were used to constrain the formation constants of the different Cd(II)-phthalate surface complexes on the dominant {110} and the {001} planes of the goethite. The models were carried out with the Charge Distribution Multisite Complexation model coupled to the Three Plane Model and can predict the molecularscale speciation of cadmium and phthalate in the presence of goethite. Cd(II) adsorption models calibrated on a 90 m 2 /g goethite also could accurately predict experimental data for a 37 m 2 /g goethite of slightly different basic charging properties.
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