Parameterization of adsorption onto minerals by Extended Triple Layer Model

Fukushi, Keisuke; Okuyama, Akihiro; Takeda, Natsumi; Kosugi, Shigeyori

doi:10.1016/j.apgeochem.2021.105087

Cited by 6 publications

(7 citation statements)

References 61 publications

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“…This atypical sorption phenomenon cannot be explained by empirical sorption models, where the sorption processes are expressed by fixed K d values. 4,11,13 This is the manifestation of a change in the affinity constant of the surface due to the correlated incorporation of the metal ions. This change in the sorbent surface energetics may also be driven by the increasing entropy of interfacial systems, which can potentially lead to other subsequent reactions including mineral replacement reactions.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…However, this simplified approach fails to convey the intrinsic complexity of sorption processes at the molecular scale, such as adsorption (adhesion of ions to a mineral surface), incorporation (absorption of ions into the mineral), and heterogeneous precipitation (surface-induced nucleation and growth of a secondary mineral phase) . Explaining these processes requires the development of mechanistic models that consider specific interactions between sorbates and sorbents, such as the 1 pK/2 pK basic Stern, , the charge-distribution multi-site complexation, , and extended triple layer models. , Some models consider the impact of site heterogeneity on the ion adsorption expressed based on the bond valence theory and charge variation of the surface functional groups with solution pH. , Other models consider the impact of the complex hydration structure on ion adsorption by considering different levels of molecular layers based on the distribution of ions and water molecules adsorbed at the interface. , These surface complexation theories have been widely applied to study the reactivity of various geochemical interfaces, especially those of common oxides and silicates, with respect to changes in surface charge due to (de)protonation (i.e., pH-dependent charge), site-specific interactions, and adsorption geometries of ions (e.g., inner-sphere vs outer-sphere surface complexes). − …”

Section: Introductionmentioning

confidence: 99%

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Synergistic Enhancement of Lead and Selenate Uptake at the Barite (001)–Water Interface

Yang

Rampal

Weber

et al. 2022

Environ. Sci. Technol.

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The interactions of heavy metals with minerals influence the mobility and bioavailability of toxic elements in natural aqueous environments. The sorption of heavy metals on covalently bonded minerals is generally well described by surface complexation models (SCMs). However, understanding sorption on sparingly soluble minerals is challenging because of the dynamically evolving chemistry of sorbent surfaces. The interpretation can be even more complicated when multiple metal ions compete for sorption. In the present study, we observed synergistically enhanced uptake of lead and selenate on the barite (001) surface through two sorption mechanisms: lattice incorporation that dominates at lower coverages and two-dimensional monolayer growth that dominates at higher coverages. We also observed a systematic increase in the sorption affinity with increasing co-sorbed ion coverages, different from the assumption of invariant binding constants for individual adsorption processes in classical SCMs. Computational simulations showed thermodynamically favorable co-incorporation of lead and selenate by simultaneously substituting for barium and sulfate in neighboring sites, resulting in the formation of molecular clusters that locally match the net dimension of the substrate lattice. These results emphasize the importance of ion−ion interactions at mineral−water interfaces that control the fate and transport of contaminants in the environment.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Synergistic Enhancement of Lead and Selenate Uptake at the Barite (001)–Water Interface

Yang

Rampal

Weber

et al. 2022

Environ. Sci. Technol.

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“…Over the years, a number of models have been used for describing ion adsorption onto ferrihydrite. Examples include the generalized two-layer model and versions thereof, , the extended triple-layer model (ETLM), and the Charge Distribution MUltisite Ion Complexation (CD-MUSIC) model. , As shown in many papers, these SCMs can describe the data of single-ion systems well. The challenge is to describe also competitive systems, with two or more interacting ions in the same system, in a consistent manner, which is commonly the case in the environment.…”

Section: Introductionmentioning

confidence: 99%

“…Over the years, a number of models have been used for describing ion adsorption onto ferrihydrite. Examples include the generalized two-layer model and versions thereof, 3,28 the extended triple-layer model (ETLM), 29 and the Charge Distribution MUltisite Ion Complexation (CD-MUSIC) model. 30,31 As shown in many papers, these SCMs can describe the data of single-ion systems well.…”

Section: ■ Introductionmentioning

confidence: 99%

Competitive Arsenate and Phosphate Adsorption on Ferrihydrite as Described by the CD-MUSIC Model

Gustafsson

Antelo

2022

ACS Earth Space Chem.

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The solubility and bioavailability of arsenic in the environment are to a large extent governed by adsorption reactions with iron (hydr)oxides, the extent of which is affected by competitive interactions with other ions, for example, phosphate. Here, batch experiments were performed with ferrihydrite suspensions to determine the adsorption of arsenate [As(V)] and phosphate (PO4) at different As(V)–PO4 ratios. A surface complexation model based on the Charge Distribution MUltisite Ion Complexation (CD-MUSIC) concept (the “Ferrihydrite CD-MUSIC model”) was developed to describe these interactions in a way consistent with results from spectroscopic studies. For this purpose, several previously published data sets on As(V) and PO4 adsorption in ferrihydrite suspensions were reviewed, including a number of systems containing other major ions (CO3 2– and Ca2+), and new surface complexation constants were derived. During model development, it was found that the inclusion of ternary complexes was not needed to describe the observed Ca2+–PO4 interactions. For both As(V) and PO4, the resulting model predicts the presence of corner-sharing bidentate complexes as well as monodentate complexes, with the latter being important particularly at low pH. The experimental results showed that As(V) and PO4 displayed similar adsorption patterns in the single-ion systems studied, which were conducted using a constant anion-to-Fe ratio of 0.2. Even so, As(V) was preferentially adsorbed over PO4 in competitive systems, particularly at low As(V)-to-PO4 ratios when the K d values for As(V) were up to 2.1 times as high as those for PO4. The model, which described these patterns very well, suggests that adsorbed As(V) consists of a larger fraction of bidentate complexes than in the case of PO4. This causes a flatter adsorption isotherm for As(V), which leads to a stronger As(V) adsorption as the As(V)-to-Fe ratio decreases, compared to that for PO4.

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“…While the effect of phosphate competition on arsenate adsorption can be assessed by the differences in the curvature and plateau of their adsorption isotherm data, such empirical descriptions lack the ability to extrapolate to water compositions outside the experimental conditions as the parameters of simple isotherm models (e.g., Langmuir) are not intrinsic. To address this ambiguity, surface complexation models (SCMs) can provide a unified framework with a set of mole balance and mass action equations that can reproduce the data of both arsenate and phosphate adsorption, individually or coexisting. ,− In addition, SCM can account for the surface electrostatic effects through which the surface complexation of oxyanions could introduce negative surface charge rendering further oxyanion binding less favorable. − Karamalidis and Dzombak compiled the double-layer SCM parameters for gibbsite, which include phosphate and arsenate. However, these thermodynamic equilibrium constants in the model were calculated based on the experimental data of single ion adsorption.…”

Section: Introductionmentioning

confidence: 99%

Effects of Phosphate Competition on Arsenate Binding to Aluminum Hydroxide Surfaces

Wang

et al. 2021

ACS Earth Space Chem.

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Aluminum hydroxide plays a substantial role in regulating the environmental fate and transport of arsenate and phosphate. These minerals display multiple types of surface reactive sites with distinct adsorption affinities. As arsenate and phosphate coexist in many natural systems, a detailed understanding of their interactive adsorption behaviors on aluminum hydroxides and the underlying binding mechanisms is thus required to develop predictive models of their fate and mobility. In this study, we explore how phosphate affects arsenate adsorption onto the aluminum hydroxide polymorphs gibbsite and bayerite and develop a unified surface complexation model (SCM) to predict arsenate adsorption under diverse conditions parameterized only from noncompetitive uptake data. Macroscopic studies show that both oxyanions behave similarly in individual adsorption experiments. The addition of phosphate reduces arsenate adsorption on both minerals with a greater effect observed on gibbsite. Extended X-ray absorption fine structure spectroscopy reveals that similar arsenate species occur on both minerals and are unchanged in the presence of phosphate. This indicates that competitive adsorption does not affect arsenate surface speciation. These results demonstrate that arsenate and phosphate primarily interact on aluminum hydroxide surfaces via site competition. Notably, their similar pK a values and adsorption affinities minimize modification of adsorption behavior from surface electrostatic effects. The SCMs demonstrate that multiple arsenate surface species are needed to reproduce the observed competitive uptake data, in apparent conflict with the spectroscopic results that reveal no change in coordination at different surface coverages. This indicates that the molecular-scale drivers of differences in surface complex stability are not only from distinct local coordination, instead other factors, such as hydrogen bonding among the adsorbates, surface oxygens, and interfacial water or different surface complexes coordinating to functional groups with distinct connections to the underlying mineral structure, may also play an important role.

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Parameterization of adsorption onto minerals by Extended Triple Layer Model

Cited by 6 publications

References 61 publications

Synergistic Enhancement of Lead and Selenate Uptake at the Barite (001)–Water Interface

Synergistic Enhancement of Lead and Selenate Uptake at the Barite (001)–Water Interface

Competitive Arsenate and Phosphate Adsorption on Ferrihydrite as Described by the CD-MUSIC Model

Effects of Phosphate Competition on Arsenate Binding to Aluminum Hydroxide Surfaces

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