Surface Complexation Modeling

Karamalidis, Athanasios K.; Dzombak, David A.

doi:10.1002/9780470642665

Cited by 76 publications

(114 citation statements)

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“…The IEP of gibbsite shifts to the 4.6 to 4.9 range when reacted with PO 4 . This is macroscopic evidence of the inner-sphere complexation of PO 4 by gibbsite (or surface precipitation), as is often reported in the literature (Karamalidis and Dzombak, 2010). This finding is also consistent with the strong PO 4 adsorption behavior and with the lack of an ionic strength effect on PO 4 retention described below.…”

Section: Resultssupporting

confidence: 79%

“…This is also the common intersection point for the zeta potential measurements in 10 and 100 mmol L −1 KNO 3 . The measured gibbsite IEP is slightly higher than the 7.8 to 10.4 pH pzc range compiled by Karamalidis and Dzombak (2010) but is within the 8.7 to 11 range reported by Adekola et al (2011). An increase in the swamping electrolyte concentration results in a decreasing zeta potential as the pH is decreased below the IEP.…”

Section: Resultsmentioning

confidence: 75%

“…Phosphate is retained by inner-sphere surface complexation mechanisms throughout a broad pH range (Karamalidis and Dzombak, 2010). Phosphate is strongly retained by gibbsite (Fig.…”

Section: Resultsmentioning

confidence: 99%

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Adsorption of Antimonate by Gibbsite: Reversibility and the Competitive Effects of Phosphate and Sulfate

Essington

Stewart

2016

Soil Science Soc of Amer J

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Antimony (sb) is a potential environmental contaminant of emerging concern that occurs in soils in the sb(V) oxidation state as the antimonate species sb(OH) 6 -. In soils, metal oxyhydroxides play an important role in the immobilization of contaminants and in restricting bioaccessibility. One such mineral is gibbsite, which bears the reactive aluminol surface functional group. Both inner-and outer-sphere surface complexation mechanisms have been inferred from conflicting sb(V) adsorption findings involving aluminol-bearing minerals. The objectives of this research are to characterize sb(V) adsorption by gibbsite and to use the macroscopic findings to develop mechanistic adsorption models. Antimonate adsorption envelopes were developed using two equilibrium techniques: continuous pH titration and batch. The adsorption of sb(V) decreases with increasing pH and increasing ionic strength, suggesting that outer-sphere surface complexation is an important adsorption mechanism. However, sb(V) retention is irreversible at pH <6 but is reversible in pH >7 systems, suggesting that inner-sphere species may be significant in acidic environments. Adsorbed sb(V) also generates a downward shift in the gibbsite isoelectric point, further supporting the formation of inner-sphere sb(V) surface complexes. Both PO 4 and sO 4 decrease adsorbed sb(V) concentrations: PO 4 throughout the pH 3 to 10 range and sO 4 in pH <7 systems. The triple-layer surface complexation model successfully predicts sb(V) adsorption by using both outer-sphere and inner-sphere surface species. The triple-layer model also predicts ligand adsorption in the competitive systems without the need for reoptimization.Abbreviations: BET, Brunauer-Emmett-Teller; ICP-AES, inductively coupled argon plasma-atomic emission spectroscopy; IEP, isoelectric point; SCM, surface complexation model; TLM, triple layer model; XRD, x-ray diffraction.A ntimony is one of the least abundant elements in soils, having a median concentration in uncontaminated soils from around the world of 1 mg kg −1 (range, <0.2-10 mg kg −1 ) (Bowen, 1979;Filella et al., 2002;Helmke, 2000). However, anthropogenic activities can result in elevated soil Sb levels (Crecelius et al., 1975;Filella et al., 2002;Li and Thornton, 1993;Nriagu, 1989;Nriagu and Pacyna, 1988;Scheinost et al., 2006). Soils that are particularly affected by Sb are those at military and civilian shooting ranges. Antimony is a hardening agent in lead bullets, which contain ~5% Sb (Carlin, 2000;Johnson et al., 2005;Kilgour et al., 2008). As bullets and bullet fragments corrode, Pb and Sb are released to the soil environment (Clausen and Korte, 2009;Kilgour et al., 2008). The resulting Sb concentrations can far exceed native soil levels. Antimony concentrations in military and civilian shooting range soils have been reported to range from <517 to <17,500 mg kg −1 (Basunia and Landsberger, 2001;Johnson et al., 2005;Kilgour et al., 2008;Knechtenhofer et al., 2003;Mitsunobu et al., 2006;Okkenhaug et al., 2013;Spuller et al., 2007), alth...

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Section: Resultssupporting

confidence: 79%

Section: Resultsmentioning

confidence: 75%

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Adsorption of Antimonate by Gibbsite: Reversibility and the Competitive Effects of Phosphate and Sulfate

Essington

Stewart

2016

Soil Science Soc of Amer J

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“…Calculations using appropriate equilibrium constants, have been used to quantitatively model this surface complexation [35]. Table 3 gives the binding and equilibrium constants used in this case.…”

Section: Ligand Exchange Mechanismmentioning

confidence: 99%

Adsorption of sodium hexanoate on α-alumina

Lee¹,

Welbourn²,

Clarke³

et al. 2013

Journal of Colloid and Interface Science

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a b s t r a c tNeutron reflection and adsorption isotherm measurements have been used to study the adsorption behaviour of hexanoic acid onto a-alumina surfaces. Importantly, the pH dependence of the behaviour has been characterised with a pronounced maximum in adsorption identified at a pH of approximately 5, close to the pK a of the acid. The adsorbed layer is identified as a bilayer, which is reasonable given the hydrophilic nature of both side of the layer, and has a thickness of 13 Å, suggesting significant extent of interdigitation. At pH 5, the layer has much lower extent of hydration relative to the higher pH of 7, consistent with the increased total adsorption at pH 5. A number of different mechanisms for the binding of the hexanoic acid to the surface are considered. The experimental data, combined with calculations using equilibrium/binding constants of the surface and ligands, indicates that a ligand exchange reaction may be the most significant mechanism.

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“…Ferrihydrite and gibbsite were chosen as possible solids for sorption reactions, due to their high measured particulate concentrations and sorption capacities. Sorption was estimated using the diffuse layer model (DLM) using the default database in Visual MINTEQ based on Dzombak and Morel (1990) and Karamalidis and Dzombak (2010) for ferrihydrite and gibbsite, respectively. The only exception was vanadate adsorption to ferrihydrite, for which the adsorption constants were changed based on Wällstedt et al (2010).…”

Section: Modelling Approachmentioning

confidence: 99%

Speciation and hydrological transport of metals in non-acidic river systems of the Lake Baikal basin: Field data and model predictions

et al. 2016

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The speciation of metals in aqueous systems is central to understanding their mobility, bioavailability, toxicity and fate. Although several geochemical speciation models exist for metals, the equilibrium conditions assumed by many of them may not prevail in field-scale hydrological systems with flowing water. Furthermore, the dominant processes and/or process rates in non-acidic systems might differ from well-studied acidic systems. We here aim to increase knowledge on geochemical processes controlling speciation and transport of metals under nonacidic river conditions. Specifically, we evaluate the predictive capacity of a speciation model to novel measurements of multiple metals and their partitioning, under highpH conditions in mining zones within the Lake Baikal basin. The mining zones are potential hotspots for increasing metal loads to downstream river systems. Metals released from such upstream regions may be transported all the way to Lake Baikal, where increasing metal contamination of sediments and biota has been reported. Our results show clear agreement between speciation predictions and field measurements of Fe, V, Pb and Zn, suggesting that the partitioning of these metals mainly was governed by equilibrium geochemistry under the studied conditions. Systematic over-predictions of dissolved Cr, Cu and Mo by the model were observed, which might be corrected by improving the adsorption database for hydroxyapatite because that mineral likely controls the solubility of these metals. Additionally, metal complexation by dissolved organic matter is a key parameter that needs continued monitoring in the Lake Baikal basin because dependable predictions could not be made without considering its variability. Finally, our investigation indicates that further model development is needed for accurate As speciation predictions under non-acidic conditions, which is crucial for improved health risk assessments on this contaminant.

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Surface Complexation Modeling

Cited by 76 publications

References 0 publications

Adsorption of Antimonate by Gibbsite: Reversibility and the Competitive Effects of Phosphate and Sulfate

Adsorption of Antimonate by Gibbsite: Reversibility and the Competitive Effects of Phosphate and Sulfate

Adsorption of sodium hexanoate on α-alumina

Speciation and hydrological transport of metals in non-acidic river systems of the Lake Baikal basin: Field data and model predictions

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