Boron Adsorption to Ferrihydrite with Implications for Surface Speciation in Soils : Experiments and Modeling
Eynde, Elise Van; Mendez, Juan C. ; Hiemstra, Tjisse ; Comans, Rob N.J. - \ 2020
ACS Earth and Space Chemistry 4 (2020)8. - ISSN 2472-3452 - p. 1269 - 1280.
boron - CD-MUSIC modeling - ferrihydrite - goethite - humic acid
The adsorption and desorption of boric acid onto reactive materials such as metal (hydr)oxides and natural organic matter are generally considered to be controlling processes for the leaching and bioavailability of boron (B). We studied the interaction of B with ferrihydrite (Fh), a nanosized iron (hydr)oxide omnipresent in soil systems, using batch adsorption experiments at different pH values and in the presence of phosphate as a competing anion. Surface speciation of B was described with a recently developed multisite ion complexation (MUSIC) and charge distribution (CD) approach. To gain insight into the B adsorption behavior in whole-soil systems, and in the relative contribution of Fh in particular, the pH-dependent B speciation was evaluated for soils with representative amounts of ferrihydrite, goethite, and organic matter. The pH-dependent B adsorption envelope of ferrihydrite is bell-shaped with a maximum around pH 8-9. In agreement with spectroscopy, modeling suggests formation of a trigonal bidentate complex and an additional outer-sphere complex at low to neutral pH values. At high pH, a tetrahedral bidentate surface species becomes important. In the presence of phosphate, B adsorption decreases strongly and only formation of the outer-sphere surface complex is relevant. The pH-dependent B adsorption to Fh is rather similar to that of goethite. Multisurface modeling predicts that ferrihydrite may dominate the B binding in soils at low to neutral pH and that the relative contribution of humic material increases significantly at neutral and alkaline pH conditions. This study identifies ferrihydrite and natural organic matter (i.e., humic substances) as the major constituents that control the B adsorption in topsoils.
Carbonate Adsorption to Ferrihydrite : Competitive Interaction with Phosphate for Use in Soil Systems
Mendez, Juan C. ; Hiemstra, Tjisse - \ 2019
ACS Earth and Space Chemistry 3 (2019)1. - ISSN 2472-3452 - p. 129 - 141.
CD model - competition - ferrihydrite - goethite - ion adsorption - nanoparticles - solubility - surface complexation
Carbonate (CO3) interacts with Fe-(hydr)oxide nanoparticles, affecting the availability and geochemical cycle of other important oxyanions in nature. Here, we studied the carbonate-phosphate interaction in closed systems with freshly prepared ferrihydrite (Fh), using batch experiments that cover a wide range of pH values, ionic strength, and CO3 and PO4 concentrations. The surface speciation of CO3 has been assessed by interpreting the ion competition with the Charge Distribution (CD) model, using CD coefficients derived from MO/DTF optimized geometries. Adsorption of CO3 occurs predominately via formation of bidentate inner-sphere complexes, either (=FeO)2CO or (=FeO)2CO··Na+. The latter complex is electrostatically promoted at high pH and in the presence of adsorbed PO4. Additionally, a minor complex is present at high CO3 loadings. The CD model, solely parametrized by measuring the pH-dependent PO4 adsorption as a function of the CO3 concentration, successfully predicts the CO3 adsorption to Fh in single-ion systems. The adsorption affinity of CO3 to Fh is higher than to goethite, particularly at high pH and CO3 loadings due to the enhanced formation (=FeO)2CO··Na+. The PO4 adsorption isotherm in 0.5 M NaHCO3 can be well described, being relevant for assessing the reactive surface area of the natural oxide fraction with soil extractions and CD modeling. Additionally, we have evaluated the enhanced Fh solubility due to Fe(III)-CO3 complex formation and resolved a new species (Fe(CO3)2(OH)2 3(aq)), which is dominant in closed systems at high pH. The measured solubility of our Fh agrees with the size-dependent solubility predicted using the surface Gibbs free energy of Fh.
The critical soil P levels for crop yield, soil fertility and environmental safety in different soil types
Bai, Z.H. ; Li, H.G. ; Yang, X.Y. ; Zhou, B.K. ; Shi, X.J. ; Wang, B.R. ; Li, D.C. ; Shen, J.B. ; Chen, Q. ; Qin, W. ; Oenema, O. ; Zhang, F.S. - \ 2013
Plant and Soil 372 (2013)1-2. - ISSN 0032-079X - p. 27 - 37.
silty clay loam - phosphate adsorption - calcareous soils - winter-wheat - food-chain - atr-ftir - olsen p - phosphorus - china - goethite
Sufficient soil phosphorus (P) is important for achieving optimal crop production, but excessive soil P levels may create a risk of P losses and associated eutrophication of surface waters. The aim of this study was to determine critical soil P levels for achieving optimal crop yields and minimal P losses in common soil types and dominant cropping systems in China. Four long-term experiment sites were selected in China. The critical level of soil Olsen-P for crop yield was determined using the linear-plateau model. The relationships between the soil total P, Olsen-P and CaCl2-P were evaluated using two-segment linear model to determine the soil P fertility rate and leaching change-point. The critical levels of soil Olsen-P for optimal crop yield ranged from 10.9 mg kg(-1) to 21.4 mg kg(-1), above which crop yield response less to the increasing of soil Olsen-P. The P leaching change-points of Olsen-P ranged from 39.9 mg kg(-1) to 90.2 mg kg(-1), above which soil CaCl2-P greatly increasing with increasing soil Olsen-P. Similar change-point was found between soil total P and Olsen-P. Overall, the change-point ranged from 4.6 mg kg(-1) to 71.8 mg kg(-1) among all the four sites. These change-points were highly affected by crop specie, soil type, pH and soil organic matter content. The three response curves could be used to access the soil Olsen-P status for crop yield, soil P fertility rate and soil P leaching risk for a sustainable soil P management in field.
Simultaneous analysis of small organic acids and humic acids using high performance size exclusion chromatography
Qin, X.P. ; Liu, F. ; Wang, G.C. ; Weng, L.P. - \ 2012
Journal of Separation Science 35 (2012)24. - ISSN 1615-9306 - p. 3455 - 3460.
spectroscopic properties - molecular-weight - iron-oxide - adsorption - substances - goethite - matter - water - polydispersity - complexation
An accurate and fast method for simultaneous determination of small organic acids and much larger humic acids was developed using high performance size exclusion chromatography. Two small organic acids, i.e. salicylic acid and 2,3-dihydroxybenzoic acid, and one purified humic acid material were used in this study. Under the experimental conditions, the UV peaks of salicylic acid and 2,3-dihydroxybenzoic acid were well separated from the peaks of humic acid in the chromatogram. Concentrations of the two small organic acids could be accurately determined from their peak areas. The concentration of humic acid in the mixture could then be derived from mass balance calculations. The measured results agreed well with the nominal concentrations. The detection limits are 0.05 mg/L and 0.01 mg/L for salicylic acid and 2,3-dihydroxybenzoic acid, respectively. Applicability of the method to natural samples was tested using groundwater, glacier, and river water samples (both original and spiked with salicylic acid and 2,3-dihydroxybenzoic acid) with a total organic carbon concentration ranging from 2.1 to 179.5 mg C/L. The results obtained are promising, especially for groundwater samples and river water samples with a total organic carbon concentration below 9 mg C/L.
Adsorption of Phosphonate Antiscalant from Reverse Osmosis Membrane Concentrate onto Granular Ferric Hydroxide
Boels, L. ; Keesman, K.J. ; Witkamp, G.J. - \ 2012
Environmental Science and Technology 46 (2012)17. - ISSN 0013-936X - p. 9638 - 9645.
water-treatment systems - seawater desalination - phosphate adsorption - scale inhibitors - goethite - removal - ro - sorption - desupersaturation - precipitation
Adsorptive removal of antiscalants offers a promising way to improve current reverse osmosis (RO) concentrate treatment processes and enables the reuse of the antiscalant in the RO desalination process. This work investigates the adsorption and desorption of the phosphonate antiscalant nitrilotris(methylenephosphonic acid) (NTMP) from RO membrane concentrate onto granular ferric hydroxide (GFH), a material that consists predominantly of akaganéite. The kinetics of the adsorption of NTMP onto GFH was predicted fairly well with two models that consider either combined film–pore or combined film–surface diffusion as the main mechanism for mass transport. It is also demonstrated that NTMP is preferentially adsorbed over sulfate by GFH at pH 7.85. The presence of calcium causes a transformation in the equilibrium adsorption isotherm from a Langmuir type to a Freundlich type with much higher adsorption capacities. Furthermore, calcium also increases the rate of adsorption substantially. GFH is reusable after regeneration with sodium hydroxide solution, indicating that NTMP can be potentially recovered from the RO concentrate. This work shows that GFH is a promising adsorbent for the removal and recovery of NTMP antiscalant from RO membrane concentrates.
Formation and Transformation of Iron Oxide-Kaolinite Associations in the Presence of Iron(II)
Wei, S.Y. ; Liu, F. ; Feng, X.H. ; Tan, W.F. ; Koopal, L.K. - \ 2011
Soil Science Society of America Journal 75 (2011)1. - ISSN 0361-5995 - p. 45 - 55.
clay-minerals - organic-matter - soil clays - ferrihydrite - hematite - goethite - fe(ii) - acid - lepidocrocite - reactivity
Iron oxide-kaolinite associations are important components of tropical and subtropical soils and have significant influence on the physical and chemical properties of soils. In this study, the formation and transformation of Fe oxide-kaolinite associations as a function of pH, temperature, and time were investigated at different Fe(II)/ Fe(III) molar ratios (R). Results show that the formation of crystalline Fe oxides was significantly inhibited due to the presence of kaolinite, while accelerated by Fe(II). The formation of lepidocrocite- and goethite-kaolinite associations were accelerated by Fe(II) at R = 0.04 to 0.06, an initial pH (pHi) of 5 to 8, and a temperature (T) of 50 to 70°C; the formation of hematite-kaolinite association was accelerated by Fe(II) at R = 0.06, pHi 7 to 8, and T= 60 to 80°C; magnetite-kaolinite association was obtained at R = 0.06, pHi 9, and T = 60°C or at R = 0.1 to 0.5, pHi 7, and T = 60°C. The pH as a function of time (pHt) decreased sharply when crystalline Fe oxides were formed in the presence of Fe(II), Fe(III), and kaolinite. The decrease in pHt was slow, however, in the system with Fe(III) and kaolinite but without Fe(II) and in the system with Fe(II) and kaolinite but without Fe(III). The morphologies of lepidocrocite, goethite, hematite, and magnetite in associations are strip shaped, nanorod like, pseudo-cubic shaped, and nanosphere like, respectively. In a system with Fe(II), Fe(III), and kaolin
Competitive and synergistic effects in pH dependent phosphate adsorption in soils: LCD modeling
Weng, L.P. ; Vega, F.A. ; Riemsdijk, W.H. van - \ 2011
Environmental Science and Technology 45 (2011)19. - ISSN 0013-936X - p. 8420 - 8428.
induced chemical-changes - humic substances - charge-distribution - solution interface - ion adsorption - goethite - surface - phosphorus - binding - parameters
The pH dependency of soluble phosphate in soil was measured for six agricultural soils over a pH range of 3–10. A mechanistic model, the LCD (ligand charge distribution) model, was used to simulate this change, which considers phosphate adsorption to metal (hydr)oxides in soils under the influence of natural organic matter (NOM) and polyvalent cations (Ca2+, Al3+, and Fe3+). For all soils except one, the description in the normal pH range 5–8 is good. For some soils at more extreme pH values (for low P-loading soils at low pH and for high P-loading soils at high pH), the model over predicts soluble P. The calculation shows that adsorption is the major mechanism controlling phosphate solubility in soils, except at high pH in high P-loading soils where precipitation of calcium phosphate may take place. NOM and polyvalent cations have a very strong effect on the concentration level of P. The pattern of pH dependency of soluble P in soils differs greatly from the pH effects on phosphate adsorption to synthetic metal (hydr)oxides in a monocomponent system. According to the LCD model, the pH dependency in soil is mainly caused by the synergistic effects of Ca2+ adsorption to oxides. Adsorption of Al3+ to NOM adsorbed plays an important role only at a pH <4.5. Presence of NOM coating strongly competes with phosphate for the adsorption and is an important factor to consider in modeling phosphate adsorption in natural samples
Nanoparticles in natural systems II: The natural oxide fraction at interaction with natural organic matter and phosphate
Hiemstra, T. ; Antelo, J. ; Los, A.M.D. ; Riemsdijk, W.H. van - \ 2010
Geochimica et Cosmochimica Acta 74 (2010)1. - ISSN 0016-7037 - p. 59 - 69.
fulvic-acid - humic substances - water interface - competitive adsorption - surface complexation - charge-distribution - mineral surfaces - ion adsorption - iron-oxides - goethite
Information on the particle size and reactive surface area of natural samples and its interaction with natural organic matter (NOM) is essential for the understanding bioavailability, toxicity, and transport of elements in the natural environment. In part I of this series (Hiemstra et al., 2010), a method is presented that allows the determination of the effective reactive surface area (A, m2/g soil) of the oxide particles of natural samples which uses a native probe ion (phosphate) and a model oxide (goethite) as proxy. In soils, the natural oxide particles are generally embedded in a matrix of natural organic matter (NOM) and this will affect the ion binding properties of the oxide fraction. A remarkably high variation in the natural phosphate loading of the oxide surfaces (G, µmol/m2) is observed in our soils and the present paper shows that it is due to surface complexation of NOM, acting as a competitor via site competition and electrostatic interaction. The competitive interaction of NOM can be described with the charge distribution (CD) model by defining a =NOM surface species. The interfacial charge distribution of this =NOM surface species can be rationalized based on calculations done with an evolved surface complexation model, known as the ligand and charge distribution (LCD) model. An adequate choice is the presence of a charge of -1 v.u. at the 1-plane and -0.5 v.u. at the 2-plane of the electrical double layer used (Extended Stern layer model). The effective interfacial NOM adsorption can be quantified by comparing the experimental phosphate concentration, measured under standardized field conditions (e.g. 0.01 M CaCl2), with a prediction that uses the experimentally derived surface area (A) and the reversibly bound phosphate loading (G, µmol/m2) of the sample (part I) as input in the CD model. Ignoring the competitive action of adsorbed NOM leads to a severe under-prediction of the phosphate concentration by a factor 10 to 1000. The calculated effective loading of NOM is low at a high phosphate loading (G) and vice versa, showing the mutual competition of both constituents. Both constituents in combination usually dominate the surface loading of natural oxide fraction of samples and form the backbone in modeling the fate of other (minor) ions in the natural environment. Empirically, the effective NOM adsorption is found to correlate well to the organic carbon content (OC) of the samples. The effective NOM adsorption can also be linked to DOC. For this, a Non-Ideal Competitive adsorption (NICA) model is used. DOC is found to be a major explaining factor for the interfacial loading of NOM as well as phosphate. The empirical NOM–OC relation or the parameterized NICA model can be used as an alternative for estimating the effective NOM adsorption to be implemented in the CD model for calculation of the surface complexation of field samples. The biogeochemical impact of the NOM–PO4 interaction is discussed
Identification of Uranyl Surface Complexes an Ferrihydrite: Advanced EXAFS Data Analysis and CD-MUSIC Modeling
Rossberg, A. ; Ulrich, K.U. ; Weiss, S. ; Tsushima, S. ; Hiemstra, T. ; Scheinost, A.C. - \ 2009
Environmental Science and Technology 43 (2009)5. - ISSN 0013-936X - p. 1400 - 1406.
transformation factor-analysis - uranium(vi) sorption - adsorption - acid - hematite - spectroscopy - goethite - u(vi)
Previous spectroscopic research suggested that uranium(VI) adsorption to iron oxides is dominated by ternary uranyl-carbonato surface complexes across an unexpectedly wide pH range. Formation of such complexes would have a significant impact on the sorption behavior and mobility of uranium in aqueous environments. We therefore reinvestigated the identity and structural coordination of uranyl sorption complexes using a combination of U LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and iterative transformation factor analysis, which enhances the resolution in comparison to conventional EXAFS analysis. A range of conditions (pH, CO2 partial pressure, ionic strength) made it possible to quantify the variations in surface speciation. In the resulting set of spectral data (N = 11) the variance is explained by only two components, which represent two structurally different types of surface complexes: (1) a binary uranyl surface complex with a bidentate coordination to edges of Fe(O,OH)6 octahedra and (2) a uranyl triscarbonato surface complex where one carbonate ion bridges uranyl to the surface. This ternary type B complex differs from a type A complex where uranyl is directly attached to surface atoms and carbonate is bridged by uranyl to the surface. Both surface complexes agree qualitatively and quantitatively with predictions by a charge distribution (CD) model. According to this model the edge-sharing uranyl complex has equatorial ligands (-OH2, -OH, or one -CO3 group) that point away from the surface. The monodentate uranyl triscarbonato surface complex (type B) is relevant only at high pH and elevated pCO2. At these conditions, however, it is responsible for significant uranyl sorption, whereas standard models would predict only weak sorption. This paper presents the first spectroscopic evidence of this ternary surface complex, which has significant implications for immobilization of uranyl in carbonate-rich aqueous environments
Phosphorus removal from soil using Fe oxide-impregnated paper: Processes and applications
Los, A.M.D. ; Temminghoff, E.J.M. ; Schenkeveld, W.D.L. ; Hiemstra, T. ; Riemsdijk, W.H. van - \ 2009
Geoderma 151 (2009)3-4. - ISSN 0016-7061 - p. 282 - 289.
p-i test - filter-paper - available phosphorus - ionic-strength - phosphate - adsorption - goethite - desorption - extraction - aluminum
Fe oxide-impregnated paper (Pi-paper) is used as an artificial Phosphorus (P) sink to study P availability in soils and runoff. Pi-papers were introduced as they would mimic P uptake by plant roots by decreasing the P concentration in solution to negligibly low levels and thus enhancing P desorption from the soils solid phase. The rate of transfer of P from soil to Pi-paper would thus be limited by the soil P desorption rate. The maximum desorption rate is indeed achieved when the original method is used in which (at least) four Pi-papers per gram soil are placed in a soil suspension (soil–solution ratio of 0.025 kg L- 1). In several studies this method has however been adapted depending on the research question of interest without investigating the effect of this adaptation to the processes involved in the transfer of P from soil to Pi-paper. The aim of this study is to improve our understanding of the processes that occur in the Pi-paper–solution–soil system and so to extend the theoretical basis of this method. Insight is gained in these processes by comparing the experimentally determined P transfer from soil to Pi-paper with P transfer that is modeled based on the measured P concentration in solution and the (kinetic) Langmuir equation of the Pi-paper. P adsorption by a Pi-paper from standard solutions is not instantaneous but can be described with a kinetic Langmuir equation that is a characteristic of the Pi-paper. Over time, the Pi-paper reaches equilibrium with the solution, and the kinetic Langmuir equation can be rewritten to a Langmuir equation. Regardless if there is equilibrium or not, P adsorption to the Pi-paper is a function of the P concentration in solution. By adding Pi-paper to a soil suspension, a re-distribution of P takes place between the reactive surface area of the soil and the new reactive surface area of the Pi-paper that initially contains no adsorbed phosphate. As opposed to the original method where the desorption rate was limiting the overall P transfer, the adsorption rate to the Pi-paper is limiting when one Pi-paper per gram soil is placed in a soil suspension (soil–solution ratio of 0.1 kg L- 1). In this situation, the P concentration in solution is found to be in equilibrium with the soil's solid phase. With increasing contact time (> ~ 24 h) the whole system approaches equilibrium. With each successive Pi-paper newly added, more P is removed from the soil system and the decrease of P in solution will be governed by the soil P desorption isotherm. Varying the number of Pi-papers and the soil to solution ratio thus has a large effect on the transfer rate between soil and Pi-paper and if either the soil desorption rate, the Pi-paper adsorption rate or a combination limits this transfer rate. With increased insight in the P transfer between soil and Pi-paper sink, it becomes possible to tailor the experimental design to help answer the research question one is interested in.
Humic Nanoparticles at the Oxide-Water Interface: Interactions with Phosphate Ion Adsorption
Weng, L.P. ; Riemsdijk, W.H. van; Hiemstra, T. - \ 2008
Environmental Science and Technology 42 (2008)23. - ISSN 0013-936X - p. 8747 - 8752.
surface structural approach - dissolved organic-matter - charge-distribution - fulvic-acid - iron-oxides - molecular-weight - substances - goethite - model - competition
In this work, data for the interactions between humic acid (HA) or fulvic acid (FA) with phosphate ions at the surface of goethite (alpha-FeOOH) are presented. The results show very clear differences between HA and FA in their interactions with phosphate at goethite surface. HA is strongly bound to goethite but surprisingly does not strongly affect the phosphate binding, whereas FA is less strongly bound, but these molecules have a very large effect on the phosphate adsorption, and vice versa. Phosphate adsorption to goethite in the presence of adsorbed HA or FA can be well predicted with the LCD model (ligand and charge distribution). According to the model calculations, the nature of the interactions between HA or FA with phosphate at goethite surface is mainly electrostatic. The stronger effects of FA on phosphate adsorption are caused by its spatial location which is closer to the oxide surface, and as a consequence, the electrostatic interactions between adsorbed FA particles and phosphate ions are much stronger than for HA particles. This is the first time that effects of natural organic matter (NOM) on an anion adsorption are predicted successfully using an integrated ion-binding model for oxides and for humics that accounts for chemical heterogeneity of NOM.
Eigen kinetics in surface complexation of aqueous metal ions
Leeuwen, H.P. van - \ 2008
Langmuir 24 (2008)20. - ISSN 0743-7463 - p. 11718 - 11721.
solution/gamma-alumina interface - debye-huckel theory - adsorption-desorption - gamma-al2o3 surface - cobalt ions - goethite - equilibrium - reactivity - speciation - geometries
The mechanism of chemisorption of aqueous metal ions at surfaces has long been a topical issue in such fields as soil chemistry and bioenvironmental science. Here it is quantitatively demonstrated for the first time that release of water from the inner hydration shell is the rate-limiting step in inner-sphere surface complexation. The reactive intermediate is an outer-sphere complex between metal ion and surface site, with an electrostatically controlled stability defined by Boltzmann statistics. Using tabulated dehydration rate constants for metal ions, the resulting scheme allows for prediction of rates of sorption of aqueous metal ions at any type of complexing surface
Binding of cationic surfactants to humic substances
Ishiguro, M. ; Tan, W. ; Koopal, L.K. - \ 2007
Colloids and Surfaces. A: Physicochemical and Engineering Aspects 306 (2007)1-3. - ISSN 0927-7757 - p. 29 - 39.
streaming current detector - natural organic-matter - sodium dodecyl-sulfate - nica-donnan model - fulvic-acid - mineral particles - ion-binding - adsorption - goethite - water
Commercial surfactants are introduced into the environment either through waste products or site-specific contamination. The amphiphilic nature of both surfactants and humic substances (HS) leads to their mutual attraction especially when surfactant and HS are oppositely charged. Binding of the cationic surfactants dodecyl-pyridinium chloride (DPC) and cetyl- or hexadecyl-pyridinium chloride (CPC) to purified Aldrich humic acid (PAHA), Dando humic acid (DHA), Inogashira humic acid (IHA), Laurentian fulvic acid (LFA) and Strichen Bs fulvic acid (SFA) is studied at pH 4.5¿5 at 0.005 M NaCl. For PAHA CPC binding is also studied at pH 5 and 0.1 M NaCl. Measurements with the Mütek Particle Charge Detector (PCD) and poly-DADMAC, a strong cationic polyelectrolyte, are used to determine the charge of the HS samples. PCD measurements with the surfactants reveal that the surfactant¿HS complexes reach their iso-electric-point (IEP) before the critical micelle concentration (CMC) is reached. At the IEP the adsorption values (mol/g) of CP+ and DP+ to PAHA are the same, i.e. at the IEP the charge associated with the HS is neutralized by bound surfactant ions. For the other humic acids (HAs) CPC binding at the CMC corresponds with the charge obtained with poly-DADMAC, but for the fulvic acid (FA) samples CP(C) adsorption at the IEP is larger than the FA charge. The surfactant¿HS complexes flocculate around the IEP. Binding isotherms are obtained using surfactant electrodes. The results for CPC and DPC to the HA samples show a pseudo-plateau near the IEP, which is missing in the isotherms to the FA samples. The CP+¿PAHA isotherms at 0.005 M and 0.1 M intersect at the IEP. The affinity of CP+ binding to PAHA is larger than that of DP+ due to the longer aliphatic tail of CPC. The bound amount of DP(C) decreases in the order PAHA IHA ¿ DHA LFA ¿ SFA. The results demonstrate that cationic surfactant binding to HS is due both to electrostatic and hydrophobic attraction and that the fate of HS in aqueous environmental systems can be strongly affected by cationic surfactants.
Surface charge regulation upon polyelectrolyte adsorption, hematite, polystyrene sulfonate, surface charge regulation - Theoretical calculations and hematite-poly(styrene sulfonate) system
Riemsdijk, W.H. van; Koopal, L.K. ; Stuart, M.A.C. ; Klein Wolterink, J. - \ 2006
Colloids and Surfaces. A: Physicochemical and Engineering Aspects 291 (2006)1-3. - ISSN 0927-7757 - p. 13 - 23.
metal-oxide surfaces - variable-charge - ion adsorption - humic-acid - interfacial electrochemistry - weak polyelectrolytes - cationic surfactants - anionic surfactants - silver-iodide - goethite
The charge regulation of a mineral surface upon adsorption of a strong polyelectrolyte is studied theoretically and experimentally. Self-consistent-field calculations were done to evaluate the charge characteristics of a model oxide surface in the absence and presence of a linear strong polyelectrolyte. The calculations show high affinity adsorption isotherms for the polyelectrolyte at different pH. At the adsorption plateau the surface charge is overcompensated by the charge of the adsorbed polyelectrolyte. The increase in surface charge upon polyelectrolyte adsorption is substantial. For a bare surface a similar adjustment would require a pH change by about three units. At a given pH and salt concentration the proton co-adsorption ratio increases with the adsorbed polyelectrolyte charge till the charge compensation point is reached and then it decreases again. The measured adsorption isotherms of linear poly(styrene sulfonate) (PSS) on hematite do not show a high affinity character. This might be due to fast flocculation and a non-equilibrium polymer conformation at the surface. At pH 7 the adsorption plateau is reached and the surface charge is overcompensated by the adsorbed polyelectrolyte charge. The adsorption of PSS increases the surface charge, similarly as in the calculations. The increase of the surface charge with increasing PSS adsorption is about linear up to the charge compensation point and decreases beyond the charge compensation point
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
Ion adsorption modeling as a tool to characterize metal (hydr)oxide behavior in soil
Rahnemaie, R. - \ 2005
Wageningen University. Promotor(en): Willem van Riemsdijk. - Wageningen : WUR - ISBN 9789085041887 - 141
ionen - goethiet - fosfaten - carbonaten - adsorptie - bodem - metaalionen - modellen - ions - goethite - phosphates - carbonates - adsorption - soil - metal ions - models
This study aims to provide a better basis for application of adsorption models for metal (hydr)oxides to natural multicomponent systems. Adsorption of any ion in the environment will be potentially influenced by the effect of other ions present like calcium, phosphate, carbonate etc. The study starts with a detailed study of the binding of ions as outersphere complexes. The CD model has been extended to use the charge distribution for ions that bind as outersphere surface complex. This indicates that neither innersphere nor outersphere surface complexes are treated as point charges anymore. The new approach was applied to describe the adsorption of various electrolyte ions, phosphate, and carbonate. Batch experiments were performed using goethite as an adsorbent to determine the adsorption behavior of electrolyte ions (Li +1 , Na +1 , K +1 , Cs +1 , Ca +2 , Mg +2 , Cl -1 , NO 3-1 ), phosphate, and carbonate. The adsorption of phosphate and carbonate ions was studied in a 'single ion' system and their interaction in a competition system. The charge distribution value of innersphere surface complexes of phosphate and carbonate was calculated using the new approach. New is also the use of quantum chemical calculations to derive the CD value based on a calculated geometry of the surface complexes. The calculated geometries were interpreted with the Brown bond-valence model, resulting in a calculated CD of the surface complex. The calculated CD values were used as a constraint in the surface complexation modeling. The CD model for inner- and outersphere surface complexation successfully described the adsorption data of electrolyte ions, phosphate, and carbonate. For accommodation of adsorbed ions within the Stern layer, a Three Plane (TP) model was used as a framework. For outersphere surface complexes, it was shown that the minimum distance of approach of adsorbed ions depends on the finite size of ions and their degree of hydration, which determine their relative distances to the surface of minerals. It has been shown that the capacitance of the inner Stern layer is determined by the minimum distance of approach of the ion closest to the surface, while the capacitance of the outer layer is determined by the minimum distance of approach of the ion furthest away from the surface. Modeling of phosphate adsorption data revealed that phosphate adsorbed mainly as a bidentate surface complex. At low pH, protonated species of phosphate are a combination of monodentate and bidentate surface complexes. The new CD approach shows that phosphate interacts with sodium at the mineral surface, which could not be detected using previous approaches. Carbonate adsorption data were successfully described using a bidentate surface complex. This complex interacts with sodium at high pH and high salt level. The new approach not only predicts the shift in the isoelectric point as a function of phosphate loading, but also the measured zeta potential is in quite good agreement with predictions based on the assumption that the zeta potential coincides with the potential of the head end of the DDL. Furthermore, it has been shown that the parameterized CD model can be used to determine the effective reactive surface area of metal (hydr)oxides and the total reversibly adsorbed phosphate fraction in soils.
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
Colloid formation in groundwater by subsurface aeration: characterisation of the geo-colloids and their counterparts
Wolthoorn, A. ; Temminghoff, E.J.M. ; Riemsdijk, W.H. van - \ 2004
Applied Geochemistry 19 (2004)9. - ISSN 0883-2927 - p. 1391 - 1402.
lepidocrocite surface - fe(ii) oxidation - eutrophic lake - scanning force - iron removal - phosphate - goethite - adsorption - transport - media
Subsurface aeration is used to oxidise Fe in situ in groundwater to make the water potable. In a groundwater system with pH > 7, subsurface aeration results in a non-mobile Fe precipitate and mobile Fe colloids. Since originally the goal of subsurface aeration is to remove Fe in situ, the formation of non-mobile Fe precipitate is the desired result. In addition to this intended effect, subsurface aeration may also strongly enhance the microbiological removal of NH4 in the purification station. A hypothesis is that mobile Fe colloids may be the link between subsurface aeration and the positive effect on the microbiological removal of NH4. The objective of this study is to characterise the mobile Fe colloids and to derive a synthetic substitute for the naturally formed Fe colloids in order to be able to apply the Fe colloids as a management tool to enhance the removal of NH4 in the process of producing drinking water from groundwater. At a purification station in The Netherlands natural Fe colloids from an aerated well were sampled. Furthermore, eight synthetic Fe colloids were prepared by oxidising synthetic solutions differing in elemental composition. The colloids were analysed using chemical analysis and electron microscopy (SEM and SEM-EDAX). The Fe colloids sampled in the field contained Fe, Ca, Na, PO4 and Mn. Also in the synthetic Fe colloids PO4, Ca, Na and Mn were the most important elements next to Fe. Phosphate and dissolved organic C strongly influenced the morphology of the synthetic Fe colloids. When both the elemental composition and the morphology of the Fe colloids are taken into account, the synthetic Fe colloids formed in the synthetic solution containing Fe, Mn, PO4, SiO4 and dissolved organic matter best match the Fe colloids from the field. (C) 2004 Elsevier Ltd. All rights reserved.
The relationship between the molecular structure and ion adsorption on goethite
Rietra, R.P.J.J. - \ 2001
Wageningen University. Promotor(en): W.H. van Riemsdijk. - S.l. : S.n. - ISBN 9789058085030 - 117
goethiet - adsorptie - ionen - moleculaire structuur - goethite - adsorption - ions - molecular conformation
Ion adsorption modeling, goethite, iron oxide, CD-MUSIC, phosphate, arsenate, vanadate, molybdate, tungstate, sulfate, selenate.
A study is presented on the adsorption of inorganic ions on goethite with emphasis on the adsorption of oxyanions. Experimental results for a range of oxyanions (PO4, AsO4, VO4, WO4, MoO4, CrO4, SeO3, SeO4, SO4, Cl, NO3, ClO4) and Ca are presented and interpreted using the CD-MUSIC model. For some of these ions the coordination and structure of the adsorbed ions on goethite are known from spectroscopy (SO4, SeO4, PO4, AsO4, SeO3). Ideally, surface complexes derived from spectroscopy correspond with those resulting from the modeling of macroscopic adsorption data. This would assure that the mechanistic description of ion binding scales from the microscopic molecular structure to the macroscopic adsorption behavior. In the CD-MUSIC model it is assumed that the charge of the adsorbed ions is distributed at the interface as a function of the coordination and structure of the adsorbed ions and that this distribution of charge can be estimated using the bond valence concept of Pauling. In this study it is found that the macroscopic proton-ion adsorption stoichiometry is almost solely determined by the interfacial charge distribution of adsorbed complexes. It is shown that the experimentally determined proton-ion adsorption stoichiometry can be predicted on the basis of the spectroscopically identified structures of sulfate, selenite, phosphate and arsenate on goethite. By doing so a direct relationship is demonstrated between the molecular structure of adsorbed ions and macroscopic adsorption phenomena. By using this knowledge it is in principle possible to identify the structure and coordination of adsorbed complexes from the macroscopic adsorption data and vice versa. It is found that the spectroscopically suggested differentiation between inner- and outersphere complexes of sulfate and selenate, and the differentiation between bidenate and monodentate phosphate can be modeled satisfactory with the CD-MUSIC approach although the differentiation cannot be established solely from the available adsorption data. It is also found that the proton adsorption on goethite decreases in electrolyte solutions of NaCl, NaNO3 and NaClO4 (below the PZC) in the order Cl>NO3>ClO4 while sulfate and phosphate adsorption is lower in the order Cl<NO3<ClO4. These results can be explained well by assuming outersphere complexes of the electrolyte anions on the goethite surface with different intrinsic affinities.
Modeling the adsorption of weak organic acids on goethite : the ligand and charge distribution model
Filius, J.D. - \ 2001
Wageningen University. Promotor(en): W.H. Van Riemsdijk; J.C.L. Meeussen. - S.l. : S.n. - ISBN 9789058084545 - 183
organische zuren - goethiet - adsorptie - biologische beschikbaarheid - transportprocessen - organic acids - goethite - adsorption - bioavailability - transport processes
A detailed study is presented in which the CD-MUSIC modeling approach is used in a new modeling approach that can describe the binding of large organic molecules by metal (hydr)oxides taking the full speciation of the adsorbed molecule into account. Batch equilibration experiments were performed using the iron (hydr)oxide goethite to determine the adsorption of a series of weak organic acids (e.g. lactic acid, oxalic acid, malonic acid, phthalic acid, citric acid, and fulvic acid). In order to develop the new modeling approach, the binding of weak organic acids with a well-defined structure and charging behavior is first described using the classical CD-MUSIC model approach. The adsorption can be described accurately with a limited number of surface species, which differ in the degree of protonation and in the number of inner sphere and outer sphere complexes formed between the reactive groups of the organic molecule and the oxide surface. For the formation of inner and outer sphere complexes, a constant distribution of charge over the solid/water interface is assumed. With the same charge distribution for inner and outer sphere complexes, the adsorption of FA is described with the CD-MUSIC model using a small set of discrete surface species. This approach is not fully satisfactory since it does not take the full speciation of the adsorbed weak organic acids into account as can be inferred from spectroscopic data. In order to take the full possible speciation of the adsorbed organic molecule into account, a new model concept was developed. In the ligand and charge distribution (LCD) model concept, the number of inner sphere, outer sphere and proton complexes of the reactive groups of one adsorbed organic molecule is calculated using the NICCA equation. From the resulting speciation of the adsorbed molecule, the main input parameters of the CD-MUSIC model are obtained. The new model concept is successfully tested on the adsorption and infrared data of benzenecarboxylic acid adsorption on goethite by Boily et al. (2000a,b). The LCD model was extended for the surface complexation of the phenolic groups in order to describe the previously determined data of FA adsorption by goethite. Simultaneously, the concentration, pH, and salt dependency of the FA adsorption are described well. Furthermore, the co-adsorption of protons upon the adsorption of FA by goethite is predicted accurately. The developed model approach offers new insights in the fundamental understanding of ion adsorption under natural conditions.