The use of assemblage models to describe trace element partitioning, speciation, and fate: a review
Groenenberg, J.E. ; Lofts, S. - \ 2014
Environmental Toxicology and Chemistry 33 (2014)10. - ISSN 0730-7268 - p. 2181 - 2196.
dissolved organic-matter - metal-ion binding - oxide-water interface - nica-donnan model - electrical double-layer - upland uk catchment - long-term chemistry - savanna river site - humic substances - cation-binding
The fate of trace elements in soils, sediments, and surface waters is largely determined by their binding to reactive components, of which organic matter, metal oxides, and clays are considered most important. Assemblage models, combining separate mechanistic complexation models for each of the reactive components, can be used to predict the solid-solution partitioning and speciation of trace elements in natural environments. In the present review, the authors provide a short overview of advanced ion-binding models for organic matter and oxides and of their application to artificial and natural assemblages. Modeling of artificial assemblages of mineral components and organic matter indicates that the interactions between organic and mineral components are important for trace element binding, particularly for oxyanions. The modeling of solid-solution partitioning in natural systems is generally adequate for metal cations but less so for oxyanions, probably because of the neglect of organic matter-oxide interactions in most assemblage models. The characterization of natural assemblages in terms of their components (active organic matter, reactive oxide surface) is key to successful model applications. Improved methods for characterization of reactive components in situ will enhance the applicability of assemblage models. Collection of compositional data for soil and water archetypes, or the development of relationships to estimate compositions from geospatially available data, will further facilitate assemblage model use for predictive purposes. Environ Toxicol Chem 2014;33:2181-2196. (c) 2014 SETAC
Lead binding to soil fulvic and humic acids: NICA-Donnan modeling and XAFS spectroscopy
Xiong, J. ; Koopal, L.K. ; Tan, W. ; Fang, L. ; Wang, W. ; Zhao, W. ; Liu, T. ; Zhang, J. ; Weng, L. - \ 2013
Environmental Science and Technology 47 (2013)20. - ISSN 0013-936X - p. 11634 - 11642.
natural organic-matter - metal-ion binding - conditional affinity spectra - ombrotrophic peat bog - proton binding - chemical-composition - contaminated soils - cation-binding - molecular-size - substances
Binding of lead (Pb) to soil fulvic acid (JGFA), soil humic acids (JGHA, JLHA), and lignite-based humic acid (PAHA) was investigated through binding isotherms and XAFS. Pb binding to humic substances (HS) increased with increasing pH and decreasing ionic strength. The NICA-Donnan model described Pb binding to the HS satisfactorily. The comparison of the model parameters showed substantial differences in median Pb affinity constants among JGFA, PAHA, and the soil HAs. Milne’s “generic” parameters did not provide an adequate prediction for the soil samples. The Pb binding prediction with generic parameters for the soil HAs was improved significantly by using the value nPb1 = 0.92 instead of the generic value nPb1 = 0.60. The nPb1/nH1 ratios obtained were relatively high, indicating monodentate Pb binding to the carboxylic-type groups. The nPb2/nH2 ratios depended somewhat on the method of optimization, but the values were distinctly lower than the nPb1/nH1 ratios, especially when the optimization was based on Pb bound vs log [Pb2+]. These low values indicate bidentate binding to the phenolic-type groups at high Pb concentration. The NICA-Donnan model does not consider bidentate binding of Pb to a carboxylic- and a phenolic-type group. The EXAFS results at high Pb loading testified that Pb was bound in bidentate complexes of one carboxylic and one phenolic group (salicylate-type) or two phenolic groups (catechol-type) in ortho position.
Proton binding to soil humic and fulvic acids: Experiments and NICA-Donnan modelling
Tan, W. ; Xiong, J. ; Li, Y. ; Wang, M. ; Weng, L. ; Koopal, L.K. - \ 2013
Colloids and Surfaces. A: Physicochemical and Engineering Aspects 436 (2013). - ISSN 0927-7757 - p. 1152 - 1158.
natural organic-matter - metal-ion binding - potentiometric titrations - affinity distributions - base properties - substances - heterogeneity - parameters - adsorption
Proton binding to one soil fulvic acid (JGFA), two soil humic acids (JGHA, JLHA) and a lignite-based humic acid (PAHA) was investigated. The results were fitted to NICA-Donnan model and compared directly with the predictions using the generic parameters. NICA-Donnan model can describe proton binding satisfactorily when parameter fitting is allowed for humic substance (HS). However, predictions based on the generic parameter sets deviate for soil samples in a non-systematic way from the measured results. Replacing Qmax,H1 in generic parameter sets with material-specific values improves the predictions for soil HA significantly. For JGFA, the agreement between the model prediction and data is still not satisfactory after substitution. This is due to a very different pattern of site distribution of JGFA from that of generic FA. For two other soil FAs (FH-14, FH-22 of Milne's database) the generic predictions can be improved significantly with material-specific Qmax,H1. Adjusting also Qmax,H2 to HS material-specific value improves the prediction only slightly further. In practice, Qmax,H1 and Qmax,H2 of HS can be obtained in a relatively simple way by performing one acid–base titration at a given ionic strength and applying the procedure of Lenoir et al. to fit data to NICA equation. Introduction of thus obtained Qmax,H1 and Qmax,H2 into generic parameter sets improves the generic predictions significantly. The functional group contents as obtained by SG-method are not adequate for this purpose.
Evaluation of the performance and limitations of empirical partition-relations and process based multisurface models to predict trace element solubility in soils
Groenenberg, J.E. ; Dijkstra, J.J. ; Bonten, L.T.C. ; Vries, W. de; Comans, R.N.J. - \ 2012
Environmental Pollution 166 (2012). - ISSN 0269-7491 - p. 98 - 107.
metal-ion binding - natural organic-matter - humic substances - heavy-metals - contaminated soils - complexation models - agricultural soils - assemblage model - cation-binding - zn
Here we evaluate the performance and limitations of two frequently used model-types to predict trace element solubility in soils: regression based “partition-relations” and thermodynamically based “multisurface models”, for a large set of elements. For this purpose partition-relations were derived for As, Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sb, Se, V, Zn. The multi-surface model included aqueous speciation, mineral equilibria, sorption to organic matter, Fe/Al-(hydr)oxides and clay. Both approaches were evaluated by their application to independent data for a wide variety of conditions. We conclude that Freundlich-based partition-relations are robust predictors for most cations and can be used for independent soils, but within the environmental conditions of the data used for their derivation. The multisurface model is shown to be able to successfully predict solution concentrations over a wide range of conditions. Predicted trends for oxy-anions agree well for both approaches but with larger (random) deviations than for cations.
Chemodynamics of soft nanoparticulate complexes: Cu(II) and Ni(II) complexes with fulvic acids and aquatic humic acids
Town, R.M. ; Leeuwen, H.P. van; Buffle, J. - \ 2012
Environmental Science and Technology 46 (2012)19. - ISSN 0013-936X - p. 10487 - 10498.
nuclear-magnetic-resonance - dissolved organic-matter - metal-ion binding - dynamic speciation analysis - deposition potential sscp - aqueous-solutions - copper-binding - water exchange - stripping chronopotentiometry - dissociation kinetics
The dynamics of metal complexation by small humic substances (fulvic acid and aquatic humic acid, collectively denoted as "fulvic-like substance", FS) are explored within the framework of concepts recently developed for soft nanoparticulate complexants. From a comprehensive collection of published equilibrium and dissociation rate constants for CuFS and NiFS complexes, the association rate constant, k(a), is determined as a function of the degree of complexing site occupation, theta. From this large data set, it is shown for the first time that k(a) is independent of theta. This result has important consequences for finding the nature of the rate limiting step in the association process. The influence of electric effects on the rate of the association process is described, namely (i) the accelerating effect of the negatively charged electrostatic field of FS on the diffusion of metal ions toward it, and (ii) the extent to which metal ions electrostatically accumulate in the counterionic atmosphere of FS. These processes are discussed qualitatively in relation to the derived values of k(a). For slowly dehydrating metal ions such as Ni(H2O)(6)(2+) (dehydration rate constant, k(w)), k(a) is expected to derive straight from k(w). In contrast, for rapidly dehydrating metal ions such as Cu(H2O)(6)(2+), transport limitations and electric effects involved in the formation of the precursor outer-sphere associate appear to be important overall rate-limiting factors. This is of great significance for understanding the chemodynamics of humic complexes in the sense that inner-sphere complex formation would not always be the (sole) rate-limiting step.
Predictive model of cationic surfactant binding to humic substances
Ishiguro, M. ; Koopal, L.K. - \ 2011
Colloids and Surfaces. A: Physicochemical and Engineering Aspects 379 (2011)1-3. - ISSN 0927-7757 - p. 70 - 78.
natural organic-matter - metal-ion binding - nica-donnan model - proton binding - adsorption - acids - water - polyelectrolytes - complexation - competition
The humic substances (HS) have a high reactivity with other components in the natural environment. An important factor for the reactivity of HS is their negative charge. Cationic surfactants bind strongly to HS by electrostatic and specific interaction. Therefore, a surfactant binding model is developed that takes both the specific and electrostatic interactions explicitly into account. The model is analogous to that of ion binding to HS with the NICA-Donnan model, but competition for the binding sites is not taken into account and the NICA-Donnan model reduces to the Langmuir–Freundlich–Hill–Donnan (LFH-D) model. The parameters of the LFH equation are the maximum binding, the affinity constant and the non-ideality constant. The non-ideality parameter accounts for both the site heterogeneity and the cooperativity due to hydrophobic interaction between surfactant molecules. The affinity constant incorporates the specific (e.g., hydrophobic) interactions between surfactant and HS. The Donnan part of the model accounts in a simple way for the electrostatic interactions by assuming that for a given set of conditions there is only one electrostatic potential that governs the behavior in the Donnan phase. The separation between the specific interactions (LHF) and the electrostatic interactions (D) is based on the so-called master curve (MC) procedure in which the binding is replotted as a function of the “free” surfactant concentration in the Donnan phase. The MC depends only on the specific interactions. Once the MC is obtained it can be fitted to the LFH equation to obtain the model parameters. Subsequently, the surfactant isotherms can be calculated with the LFH-D model. The model is tested using previously obtained data on dodecyl pyridinium chloride (DPC) and cetyl pyridinium chloride (CPC) binding to some purified humic and fulvic acids at pH about 5. The LFH-D model is well suited to describe the surfactant binding to HAs from very low concentrations up to the iso-electric point (IEP). The affinity of DPC for the different HAs allows ranking of the HAs according to their hydrophobicity. Prediction of DPC binding at other pH values also leads to good results for HA. For FAs the model can only describe the surfactant binding up to an adsorbed amount of 0.5 mol/kg. For higher binding values the LFH-D model underestimates the binding.
Proton binding properties of humic substances originating from natural and contaminated materials
Zomeren, A. van; Costa, A. ; Pinheiro, J.P. ; Comans, R.N.J. - \ 2009
Environmental Science and Technology 43 (2009)5. - ISSN 0013-936X - p. 1393 - 1399.
nica-donnan model - acid-base properties - metal-ion binding - organic-matter - fulvic-acids - bottom ash - soil - parameters - copper
Humic substances (HS) are ubiquitous organic constituents in soil and water and can strongly adsorb metal contaminants in natural and waste environments. Therefore, understanding and modeling contaminant-HS interactions is a key issue in environmental risk assessment. Current binding models for HS, such as the nonideal competitive adsorption (NICA)-Donnan model, are developed and calibrated against natural organic matter from soils and surface waters. The aim of this study is to analyze the proton binding properties of humic and fulvic acid samples originating from secondary materials, waste materials and natural samples in order to assess whether the charge development of these HS can be described with generic NICA-Donnan parameters. New proton binding parameters are presented for HS isolated from several natural and contaminated (waste) materials. These parameters are shown to be similar to those of HS originating from natural environments, suggesting that the NICA-Donnan model and generic binding parameters are adequate to describe proton binding to HS in both natural and contaminated materials. These findings widen the range of environments to which the NICA-Donnan model can be applied and justify its use in geochemical speciation modeling of metal mobility in contaminated (waste) materials
Competition from Cu(II), Zn(II) and Cd(II) in Pb(II) binding to Suwannee River Fulvic Acid
Chakraborty, P. ; Chakrabarti, C.L. - \ 2008
Water Air and Soil Pollution 195 (2008)1-4. - ISSN 0049-6979 - p. 63 - 71.
natural organic-matter - metal-ion binding - humic substances - physicochemical heterogeneity - site occupation - complexation - parameters - ligands - voltammetry - lead(ii)
This is a study of trace metal competition in the complexation of Pb(II) by well-characterized humic substances, namely Suwannee River Fulvic Acid (SRFA) in model solutions. It was found that Cu(II) seems to compete with Pb(II) for strong binding sites of SRFA when present at the same concentration as Pb(II). However, Cd(II) and Zn(II) did not seem to compete with Pb(II) for strong binding sites of SRFA. These two metals did compete with Pb(II) for the weaker binding sites of SRFA. Heterogeneity of SRFA was found to play a crucial role in metal-SRFA interactions. The environmental significance of this research for freshwater is that even at relatively low Pb(II) loadings, the metals associated with lead in minerals, e.g. Cu(II), may successfully compete with Pb(II) for the same binding sites of the naturally occurring organic complexants, with the result that some of the Pb(II) may exist as free Pb2+ ions, which has been reported to be one of the toxic forms of Pb in aquatic environment.
Cu2+ and Ca2+ adsorption to goethite in the presence of fulvic acids
Weng, L.P. ; Riemsdijk, W.H. van; Hiemstra, T. - \ 2008
Geochimica et Cosmochimica Acta 72 (2008)24. - ISSN 0016-7037 - p. 5857 - 5870.
nica-donnan model - surface structural approach - dissolved organic-matter - solid-solution interface - oxide-water interface - metal-ion binding - humic substances - charge-distribution - proton binding - mineral surfaces
The interaction between copper ions (Cu2+), Strichen fulvic acid (FA), and goethite has been studied with batch experiments in the pH range of 3¿11. Similar systems with Ca2+ have been studied previously and are used here for comparison. Depending on the pH and Cu2+ loading, the binding of Cu ions to the solid phase is enhanced or reduced by the presence of FA. Cu2+ complexation in the ternary systems can be mostly described reasonably well with the assumption of linear additivity neglecting the interaction of FA and Cu2+ at the goethite surface, except for low Cu loading and high FA loading. A surface complexation model, the Ligand and Charge Distribution (LCD) model, is used to describe Cu binding to the mixture of goethite and FA. By considering both type A (goethite¿Cu¿FA) and type B (goethite¿FA¿Cu) ternary complexes, the LCD model descriptions of Cu adsorption are in general in good agreement with the data. Results show that the ternary complex with cation bridging (type A) is the dominating Cu species at low pH, low Cu loading and high FA loading, whereas Cu bound to goethite only is more important at high pH, high Cu loading and low FA loading. Complexation by only ligands of adsorbed FA (type B ternary complexes) is not important for Cu. In the interface, Ca2+ ions attribute more charge than Cu2+ to the 1-plane, where a large fraction of the negative charge of the FA resides, which explains the stronger enhancement of FA adsorption in the presence of Ca2+ compared to Cu2+.
The leaching of major and trace elements from MSWI bottom ash as a function of pH and time
Dijkstra, J.J. ; Sloot, H.A. van der; Comans, R.N.J. - \ 2006
Applied Geochemistry 21 (2006)2. - ISSN 0883-2927 - p. 335 - 351.
nica-donnan model - metal-ion binding - natural organic-matter - humic substances - heavy-metals - aqueous-solutions - fly-ash - waste - speciation - dissolution
In this paper, the leaching behaviour of major components (Al, Ca, SO4, Mg, Si, Fe, Na and DOC) and trace elements (Ni, Zn, Cd, Cu, Pb, Mo and Sb) from MSWI bottom ash is studied as a function of time over a wide range of pH, under pH-controlled conditions. Equilibrium geochemical modelling using the modelling framework ORCHESTRA is used to enable a process-based interpretation of the results and to investigate whether 'equilibrium' is attained during the time scale of the experiments. Depending on the element and setpoint-pH value, net concentration increases or decreases of up to one order of magnitude were observed. Different concentration-time trends (increase or decrease) are observed in different pH ranges. The direction of the concentration-time trends depends on: (1) the shape of the 'equilibrium' solubility curve, and (2) the position of the setpoint-pH in the leaching test relative to the natural pH of the sample. Although the majority of the elements do not reach steady state, leached concentrations over a wide pH range have been shown to closely approach 'equilibrium' model curves within an equilibration time of 168 h. The different effects that leaching kinetics may have on the pH dependent leaching patterns have been identified for a wide range of elements, and can generally be explained in a mechanistic way. The results are in support of the currently prescribed equilibration time of 48 h in the European standard for the pH-static leaching test (TS14997). Finally, this study demonstrates that pH-static leaching experiments such as described in the European standards (TS14497 and TS14429), in combination with selective chemical extractions and a mechanistically based modelling approach, constitute a powerful set of tools for the characterization of leaching processes in waste materials over a wide range of conditions.
Biogeochemical speciation of Fe in ocean water
Hiemstra, T. ; Riemsdijk, W.H. van - \ 2006
Marine Chemistry 102 (2006)3-4. - ISSN 0304-4203 - p. 181 - 197.
iron(iii) hydroxide solubility - dissolved organic-matter - equatorial pacific-ocean - metal-ion binding - humic substances - southern-ocean - north pacific - adsorption-isotherms - iron concentrations - atlantic-ocean
The biogeochemical speciation of Fe in seawater has been evaluated using the consistent Non-Ideal Competitive Adsorption model (NICA¿Donnan model). Two types of data sets were used, i.e. Fe-hydroxide solubility data and competitive ligand equilibration/cathodic stripping voltammetry (CLE/CSV) Fe titration data. The difference in solubility of Fe-hydroxide in 0.7 M NaCl and seawater was used to evaluate the speciation of inorganic Fe(III) and was used to parameterize the NICA¿Donnan model for Fe complexation by the marine DOM fraction (b0.025 ¿m), relying for competitive ions on generic parameters derived for fulvic acid. Marine DOM behaves heterogeneously with respect to Fe complexation. This is also observed for Cu(II) complexation. For Cu2+, the complexation in seawater can be predicted with the NICA¿Donnan model using a generic parameter set derived for fulvic acids. The Fe-binding decreases with increasing pHdue to Fe(III) hydrolysis and decreasing Fe-hydroxide solubility.Mg(II) andCa(II) ions are good competitors, reducing the Fe(III) complexation by a factor of about 4 in seawater at pH 8.1. Trace metals like Al(III) and Cu2+ have almost no effect on Fe(III) complexation and vice versa. Interpretation of the non-ideality parameters of Fe(III) as stoichiometry coefficients points to an interaction of Fe3+ with two ligands in the low pH range and with three ligands in high pH range (seawater). The Fe complexation by DOM is almost temperature independent in contrast to the dissolution of Fe-hydroxide (¿Hr=¿78 kJ/mol). The Fe complexation of marine DOM (fraction b0.2/0.4 ¿m) has also been evaluated using Fe titration data of seawater measured with CLE/CSV. In most cases, the same chemical heterogeneity is observed, but variation in Fe binding (mol/kg DOM) exists. The difference is discussed in relation to the variation in the molecular size (HMW/LMW) and composition (refractory/ labile or humic-like/protein-like) of marine DOC. Analysis of the Fe binding during blooming of phytoplankton shows that in such situations the Fe-complexation can be enhanced by a factor 3 compared to non-productive seawater at the same free inorganic Fe concentration. Interestingly, the characteristics remain similar to that of DOM, which might imply that the newly generated organic ligands do not react according to a simple single site Langmuir model. If the increase in Fe complexation is due to newly generated ligands, these ligands have a much higher affinity on a mass basis compared to DOM, suggesting compounds like siderophores or products of cell lysis. The data can be described with the NICA model, only adjusting the average affinity. Analysis of the speciation in the water column of locations in different oceans shows that deepwater in the HNLC areas of the southern hemisphere is generally undersaturated with respect to Fe-hydroxide. In highly productive areas, the dissolved Fe concentration equals about 0.6¿0.7 nM in agreement with the expected Fe-hydroxide solubility at 5 °C and DOC content of about 40 ¿M.
Adsorption free energy of variable-charge nanoparticles to a charged surface in relation to the change of the average chemical state of the particles
Weng, L.P. ; Riemsdijk, W.H. van; Hiemstra, T. - \ 2006
Langmuir 22 (2006)1. - ISSN 0743-7463 - p. 389 - 397.
nica-donnan model - electrical double-layer - natural organic-matter - metal-ion binding - interacting chain molecules - electrostatic free-energy - humic substances - proton binding - affinity distributions - heterogeneous surfaces
Variable-charge nanoparticles such as proteins and humics can adsorb strongly to charged macroscopic surfaces such as silica and iron oxide minerals. To model the adsorption of variable-charge particles to charged surfaces, one has to be able to calculate the adsorption free energy involved. It has been shown that the change in the free energy of variable-charge particles is related to the change in their average chemical state upon adsorption, which is commonly described using surface complexation models. In this work, expressions for the free-energy change in variable-charge particles due to changes in chemical binding are derived for three ion-binding models (i.e., the Langmuir, Langmuir-Freundlich, and NICA models) and for changes due to nonspecific binding for the Donnan model. The expressions for the adsorption free energy of the variable-charge particles to a charged surface are derived on the basis of the equality of the (electro)chemical potential of the particles in the bulk solution and adsorption phase. The expressions derived are general in the sense that they account for the competition between charge-determining ions that bind chemically to the particles, and they also apply in case of the formation of chemical bonds between particle ligands and surface sites. The derived expressions can be applied in the future to model the adsorption of variable-charge nanoparticles to charged surfaces. The results obtained for the NICA-Donnan model make it possible to apply this advanced surface complexation model to describe the adsorption of humics to minerals
Ligand and Charge Distribution (LCD) model for the description of fulvic acid adsorption to goethite
Weng, L.P. ; Riemsdijk, W.H. van; Koopal, L.K. ; Hiemstra, T. - \ 2006
Journal of Colloid and Interface Science 302 (2006)2. - ISSN 0021-9797 - p. 442 - 457.
natural organic-matter - nica-donnan model - metal-ion binding - electrical double-layer - interacting chain molecules - surface structural approach - oxide-water interface - humic substances - variable-charge - free-energy
The LCD model (Ligand and Charge Distribution) has recently been proposed to describe the adsorption of humic substances to oxides, in which the CD-MUSIC model and the NICA model for ion binding to respectively oxides and humic substances are integrated. In this paper, the LCD model is improved by applying the ADAPT model (ADsorption and AdaPTation) to calculate the equilibrium distribution of the humic substances based on the change of the average chemical state of the particles. The improved LCD model is applied to calculate the adsorption of fulvic acid (Strichen) to goethite, in which it is assumed that the carboxylic type of groups of fulvic acid can form innersphere complexes with the surface sites. The charge of the carboxylic groups in the innersphere complexes is distributed between the 0- and d-plane, whereas the charge of the other carboxylic and phenolic groups is located in the d-plane. The average distribution of the carboxylic and phenolic groups among their various chemical states (carboxylic groups: innersphere complex, protonated and deprotonated; phenolic groups: protonated and deprotonated) depends on pH, ionic strength and loading, and are the outcome of the model. The calculation shows that the LCD model can describe sufficiently the effects of pH, ionic strength and loading on the adsorption of fulvic acid, using one adjustable parameter (log over(K, ¿)S, 1). The model calculations indicate that the chemical complexation between fulvic acid and goethite is the main driving force of the adsorption, while the electrostatic repulsion between the particles and the surface is the major limiting factor for further adsorption
Analysis of copper binding in the ternary system Cu2+/Humic Acid/Goethite at neutral to acidic pH
Saito, T. ; Koopal, L.K. ; Nagasaki, S. ; Tanaka, S. - \ 2005
Environmental Science and Technology 39 (2005)13. - ISSN 0013-936X - p. 4886 - 4893.
metal-ion binding - adsorbed humic substances - natural organic-matter - competitive adsorption - exchange properties - charge adjustments - exafs spectroscopy - fulvic-acid - goethite - model
Binding of heavy metal and actinide ions to natural colloids, such as humic substances (HSs) and metal (hydr)oxides, plays an important role in the ecotoxicological behavior of these ions. Several thermodynamic models have been constructed to predict the speciation of these ions in metal/HS or metal/oxide binary systems. However, in natural environments the adsorption of HSs on oxides can influence the binding of target metals, leading to deviation from the additivity of calibrated binary models. In this study binding of copper (Cu 2+) to the purified Aldrich humic acid (PAHA)/goethite complex in the neutral to acidic pH region was investigated by measuring Cu2+ binding isotherms. The measured isotherms were compared with the results obtained for the binary systems under similar conditions. The comparison revealed that Cu2+ binding in the ternary system is enhanced with respect to the sum of Cu2+ binding in the corresponding binary systems. From the analysis of the charging behavior of the adsorbed PAHA as well as the smeared-out potential profile near the PAHA/goethite interface, the increase of Cu2+ binding to the complex was mainly attributed to the decrease of proton competition to the functional groups of the adsorbed PAHA and the change of the electrostatic potential in the vicinity of the goethite surface
Measurement of Donnan potentials in gels by in situ microelectrode voltammetry
Davis, T.A. ; Yezek, L.P. ; Pinheiro, J.P. ; Leeuwen, H.P. van - \ 2005
Journal of Electroanalytical Chemistry 584 (2005)2. - ISSN 1572-6657 - p. 100 - 109.
poly(n-isopropylacrylamide-co-acrylic acid) hydrogels - metal-ion binding - glycerol-extracted muscle - positive soil bacterium - isolated cell-walls - humic substances - electrostatic interactions - diffusion-coefficients - model parameters - seaweed biomass
This work describes the electrochemical methodology for the determination of the Donnan potential from diffusion-limited steady-state voltammograms of acrylamide gels. The technique is based upon the measurement of gel-sol systems that have reached Donnan equilibrium and contain Cd2+ as a probe ion. Au-amalgam microelectrodes are used to measure the Cd concentration in the gel phase relative to the solution phase, thus permitting comparison of the Cd voltammograms obtained in both phases. This approach yields two independent measures of the Donnan potential resulting from (i) the potential shift relative to the reference electrode, and (ii) the enhancement of the Cd2+ wave. Two suites of acrylamide gels containing 0.2% and 0.5% Na-acrylate were studied as a function of ionic strength by varying [NaNO3] and maintaining a constant concentration of the electroactive probe ion, [Cd 2+] = 1 × 10-5 mol/L in the equilibrating solutions. Independent model predictions of the Donnan potential as a function of ionic strength that consider the effects of differential swelling on the charge density, the influence of a mixed electrolyte on the potential developed in the gel at the limit of low ionic strength and the effects of incomplete dissociation of the carboxylic functional groups were in agreement with the Donnan potentials independently measured by the twofold steady-state voltammetric approach.
Interactions of calcium and fulvic acid at the goethite-water interface
Weng, L.P. ; Koopal, L.K. ; Hiemstra, T. ; Meeussen, J.C.L. ; Riemsdijk, W.H. van - \ 2005
Geochimica et Cosmochimica Acta 69 (2005)2. - ISSN 0016-7037 - p. 325 - 339.
metal-ion binding - nica-donnan model - solid-solution interface - natural organic-matter - humic substances - chemical heterogeneity - mineral particles - variable charge - proton binding - heavy-metals
Interactions of calcium and fulvic acid (Strichen) with the surface of goethite were studied with batch and titration experiments. The mutual influence of the interactions on the adsorption of fulvic acid, calcium ions and protons were examined. Adsorption of the fulvic acid to goethite decreased with increase in pH (pH range 3¿11). Addition of Ca (1.0 mM) at intermediate and high pH significantly enhanced the adsorption of fulvic acid. Compared to the adsorption to pure goethite, the presence of fulvic acid enhanced the adsorption of Ca significantly. In comparison to the simple linear sum of Ca bound to fulvic acid and goethite, the interactions between goethite and fulvic acid led to a reduced adsorption of Ca at low pH and an enhanced adsorption at high pH. With the adsorption of fulvic acid, protons were released at low pH and coadsorbed at high pH. When Ca was added, fewer protons were released at low pH and fewer coadsorbed at high pH. The experimental results can be adequately described using a surface complexation model, the Ligand and Charge Distribution (LCD) model, in which the CD-MUSIC model for ion adsorption to mineral oxides and the NICA model for ion binding to humics are integrated. In the model calculations, adequate descriptions of the ternary system data (Ca-fulvic acid-goethite) were obtained with parameters derived from three binary systems (fulvic acid-goethite, Ca-goethite and Ca-fulvic acid) without further adjustment. The model calculations suggest that the interactions between Ca and fulvic acid at the surface of goethite are mainly due to the electrostatic effects.
Application of the NICADonnan model for proton, copper and uranyl binding to humic acid
Saito, T. ; Nagasaki, S. ; Tanaka, S. ; Koopal, L.K. - \ 2004
Radiochimica Acta 92 (2004)9-11. - ISSN 0033-8230 - p. 567 - 574.
metal-ion binding - fulvic-acids - humate interactions - substances - complexation - adsorption - parameters - heterogeneity - uranium(vi) - goethite
Humic acids are natural organic materials that play an important role in the migration of heavy metal and actinide ions in aquatic and soil systems. In the present study, the binding of protons, copper ions and uranyl ions to the purified Aldrich humic acid (PAHA) is investigated and the results are modeled with the Non-Ideal Competitive Adsorption (NICA) model extended with electrostatic interactions according to the Donnan model (NICA-Donnan model). The NICA part of the model enables one to describe the competitive ion binding to a heterogeneous substrate taking into account a different stoichiometry per ion. The NICA-Donnan model can describe the binding of the ions to PAHA in large concentration ranges (3
Adsorption of humic acid on goethite: Isotherms, charge adjustments and potential profiles
Saito, T. ; Koopal, L.K. ; Riemsdijk, W.H. van; Nagasaki, S. ; Tanaka, S. - \ 2004
Langmuir 20 (2004)3. - ISSN 0743-7463 - p. 689 - 700.
natural organic-matter - oxide-water interface - metal-ion binding - donnan model parameters - fulvic-acid - iron-oxide - polyelectrolyte adsorption - weak polyelectrolytes - humate interactions - surface ionization
The adsorption of natural organic matter (NOM) on mineral (hydr)oxide plays an important role in the evaluation of the speciation of toxic metal ions in the environment. Because both NOM and mineral oxide have variable charges that adjust upon adsorption, a good understanding of proton binding is required before the binding of metal ions can be understood. In this study, the adsorption of purified Aldrich humic acid (PAHA) on goethite was examined as a function of the environmental conditions (pH, salt concentration, and free concentration of PAHA) together with the proton adsorption to PAHA, goethite, and their mixtures. The induced charges on both components were separated on the basis of the difference between the charge/pH curves of the mixture and those of the single components. The electrostatic potential profile across the adsorbed layer was obtained as a numerical solution of the Poisson-Boltzmann equation using the charge density of the adsorbed PAHA and the goethite surface. From the quantitative evaluation of the induced charge on both components, it is revealed that the degree of the charge adjustment is related to the electrostatic affinity between the PAHA segments and the goethite surface, the electrostatic repulsion between the PAHA segments, and the electrostatic shielding by salt ions. Considering the charge distribution of the adsorbed PAHA at the goethite surface, it is concluded that the change of the charge adjustment is sensitive to that of the conformation of the adsorbed PAHA. From the detailed inspection of the assumptions made and the comparison with the reported theoretical calculations, the obtained potential profiles are considered to broadly reflect the true potential profiles. Because a charge adjustment is not frequently considered in detail in relation to the NOM adsorption on metal (hydr)oxides, the obtained results can form the basis for the further development of modeling of the adsorption of NOM on (hydr)oxide surfaces.
Measuring and modeling zinc and cadmium binding by humic acid
Osté, L.A. ; Temminghoff, E.J.M. ; Riemsdijk, W.H. van - \ 2002
Analytical Chemistry 74 (2002)4. - ISSN 0003-2700 - p. 856 - 862.
metal-ion binding - diffusive gradients - organic-matter - fulvic-acids - trace-metals - thin-films - soil - speciation - complexation - substances
Free metal ions in aqueous and terrestrial systems strongly influence bioavailability and toxicity. Most analytical techniques determine the total metal concentration, including the metal ions bound by dissolved organic matter. Ion activity can be measured with ion-specific electrodes (ISEs) for some metals, but an electrode for Zn is not commercially available. As a result, very few data are available on Zn binding by natural dissolved organic matter. The aim of this study is to determine free Zn concentrations in purified humic acid solutions using the recently developed Donnan membrane technique. However, several analytical aspects of the Donnan membrane technique had to be clarified before reliable data could be composed. Cd was chosen for validation. This study shows that free Cd concentrations as measured by the Donnan membrane technique agreed well with Cd ISE measurements. It is also shown that the Donnan membrane technique could be used at high pH. The Donnan membrane technique provided consistent results in a range of p[Cd2+] = 3-9 and p[Zn2+] = 3-8 at pH 4, 6, and 8. Metal speciation in humic acid solutions was also calculated with the consistent NICA-Donnan model using generic parameters. The model could excellently describe the experimental data without adjusting any of the parameters (R2Cd = 0.971, R2Zn = 0.988)
Aluminium speciation in natural waters: measurement using Donnan membrane technique and modeling using NICA-Donnan
Weng, L.P. ; Temminghoff, E.J.M. ; Riemsdijk, W.H. van - \ 2002
Water Research 36 (2002)17. - ISSN 0043-1354 - p. 4215 - 4226.
metaalionen - aluminium - modellen - bodemoplossing - membranen - chemische speciatie - adsorptie - grondanalyse - bodemwater - metal ions - aluminium - models - soil solution - membranes - chemical speciation - adsorption - soil analysis - soil water - dissolved organic-matter - contaminated sandy soil - metal-ion binding - humic substances - ph - complexation - copper - solubility - protons - field
The study of Al speciation is of interest for the assessment of soil and water quality. For the measurement of "free" aluminum (Al3+), a recently developed Donnan membrane technique was tested by measuring Al3+ in aluminum-fluoride solutions and gibbsite suspensions. It shows that the Donnan membrane technique can measure free Al3+ reliably up to 10¿9 M and the equilibration takes 3¿4 days. Next, Al binding to humic acid (HA) purified from a forest soil was measured using either the Donnan membrane technique or gibbsite suspension. Results were compared with those predicted with the non-ideal consistent competitive adsorption (NICA)-Donnan model. The predictions using the generic parameters without fitting were in reasonable agreement with the measured data. Finally, the Donnan membrane technique was used to determine Al binding to dissolved organic matter (DOM) in the solutions of 24 soil samples at pH interval of 3¿7. Measurements agree well with the predictions using the NICA-Donnan model assuming 30% of DOM is HA and 30% is fulvic acid. With this model, the effects of pH and DOM changes on the concentration of Al in 81 soil solutions were predicted reasonably without adjustment of model parameters. The comparison between the results of analysis and the modeling provides a mutual validation for the two methods