Surface speciation of yttrium and neodymium sorbed on rutile: Interpretations using the charge distribution model

Ridley, Moira K.; Hiemstra, Tjisse; Machesky, Michael L.; Wesolowski, David J.; Riemsdijk, W.H. van

doi:10.1016/j.gca.2012.07.033

Cited by 11 publications

(19 citation statements)

References 56 publications

(96 reference statements)

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“…Consistent with previous studies that examine the influence of temperature on metal-ion adsorption at the mineral–water interface, ,,,− the adsorption of U VI onto hematite is endothermic, with an adsorption enthalpy, Δ H ads , of +71 ± 1 kJ mol –1 . This value was calculated from a van’t Hoff analysis (Figure ), for which the linear relationship between the (FeO) 2 UO 2 formation constants (log K SC ) and inverse absolute temperature confirms that Δ H ads is constant over the studied temperature range (i.e., Δ C p ≈ 0).…”

Section: Resultssupporting

confidence: 86%

“…Although confinement of U VI at the hematite surface will decrease entropy, the displacement of water molecules from the surface and from the uranyl coordination sphere upon adsorption increases entropy. Considering that many previous studies also indicate that heavy metal-ion adsorption at the solid–water interface is endothermic and entropically driven, ,,,− we suspect that changes in interfacial water structure dominate the entropic gains driving these adsorption reactions. Comparison of the hydration entropies of U VI (−422 J K –1 mol –1 ) and Eu III (−488 J K –1 mol –1 ) does not immediately provide insight into the differences between the adsorption entropies.…”

Section: Discussionmentioning

confidence: 84%

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Enthalpy of Uranium Adsorption onto Hematite

Estes

Powell

2020

Environ. Sci. Technol.

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The influence of temperature on the adsorption of metal ions at the solid–water interface is often overlooked, despite the important role that adsorption plays in metal-ion fate and transport in the natural environment where temperatures vary widely. Herein, we examine the temperature-dependent adsorption of uranium, a widespread radioactive contaminant, onto the ubiquitous iron oxide, hematite. The multitemperature batch adsorption data and surface complexation models indicate that the adsorption of uranium, as the hexavalent uranyl (UO2 2+) ion, increases significantly with increasing temperature, with an adsorption enthalpy (ΔH ads) of +71 kJ mol–1. We suggest that this endothermic, entropically driven adsorption behavior is linked to reorganization of the uranyl-ion hydration and interfacial water structures upon UVI adsorption at the hematite surface. Overall, this work provides fundamental insight into the thermodynamics driving metal-ion adsorption reactions and provides the specific enthalpy value necessary for improved predictive geochemical modeling of UVI adsorption in the environment.

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Section: Resultssupporting

confidence: 86%

Section: Discussionmentioning

confidence: 84%

Enthalpy of Uranium Adsorption onto Hematite

Estes

Powell

2020

Environ. Sci. Technol.

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“…46 The fitting approach was used to successfully model the primary charging behavior of the nanoanatase samples in NaCl media 14 and has been used effectively to model the specific adsorption of multivalent ions on rutile. 24…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

Experimental Study of Strontium Adsorption on Anatase Nanoparticles as a Function of Size with a Density Functional Theory and CD Model Interpretation

2015

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The effect of particle size on the adsorption of Sr2+ onto monodisperse nanometer diameter (4, 20, and 40 nm) anatase samples has been evaluated quantitatively with macroscopic experimental studies. The adsorption of Sr2+ onto the anatase particles was evaluated by potentiometric titrations in NaCl media, at two ionic strengths (0.03 and 0.3 m), and over a wide range of pH (3–11) and surface loadings, at a temperature of 25 °C. Adsorption of Sr2+ to the surface of the 20 and 40 nm diameter samples was similar, whereas the Sr2+ adsorption titration curves were shallower for the 4 nm diameter samples. At high pH, the smallest particles adsorbed slightly less Sr2+ than was adsorbed by the larger particles. At the molecular scale, density functional theory (DFT) calculations were used to evaluate the most stable Sr2+ surface species on the (101) anatase surface (the predominant crystal face). An inner-sphere Sr-tridentate surface species was found to be the most stable. The experimental data were described with a charge distribution (CD) and multisite complexation (MUSIC) model, with a Basic Stern layer description of the electric double layer. The resulting surface complexation model explicitly incorporated the molecular-scale information from the DFT simulation results. For 20 and 40 nm diameter anatase, the CD value for the Sr-tridentate species was calculated using a bond valence interpretation of the DFT-optimized geometry. The CD value for the 4 nm sample was smaller than that for the 20 and 40 nm samples, reflecting the shallower Sr2+ adsorption titration curves. The adsorption differences between the smallest and larger anatase particles can be rationalized by water being more highly structured near the 4 nm anatase sample and/or the Sr-tridentate surface species may require more well-developed surface terraces than are present on the 4 nm particles.

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“…Here, we investigate oxalate adsorption by rutile to 150 °C via a combined batch adsorption and molecular modeling approach and interpret these combined results with constrained surface complexation models (SCMs), following our approach for interpreting cation adsorption data. , We are aware of no other systematic study of anion adsorption that extends into the hydrothermal realm. Moreover, our molecular modeling results indicate that oxalate adsorbs on the perfect (110) surface of rutile as hydrogen-bonded outer-sphere complexes, which is at odds with IR spectroscopic data (summarized above), indicating that inner-sphere adsorption predominates.…”

Section: Introductionmentioning

confidence: 99%

Oxalic Acid Adsorption on Rutile: Experiments and Surface Complexation Modeling to 150 °C

et al. 2019

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Here, we characterize oxalate adsorption by rutile in NaCl media (0.03 and 0.30 m) and between pH 3 and 10 over a wide temperature range which includes the near hydrothermal regime (10–150 °C). Oxalate adsorption increases with decreasing pH (as is typical for anion binding by metal oxides), but systematic trends with respect to ionic strength or temperature are absent. Surface complexation modeling (SCM) following the CD-MUSIC formalism, and as constrained by molecular modeling simulations and IR spectroscopic results from the literature, is used to interpret the adsorption data. The molecular modeling simulations, which include molecular dynamics simulations supported by free-energy and ab initio calculations, reveal that oxalate binding is outer-sphere, albeit via strong hydrogen bonds. Conversely, previous IR spectroscopic results conclude that various types of inner-sphere complexes often predominate. SCMs constrained by both the molecular modeling results and the IR spectroscopic data were developed, and both fit the adsorption data equally well. We conjecture that the discrepancy between the molecular simulation and IR spectroscopic results is due to the nature of the rutile surfaces investigated, that is, the perfect (110) crystal faces for the molecular simulations and various rutile powders for the IR spectroscopy studies. Although the (110) surface plane is most often dominant for rutile powders, a variety of steps, kinks, and other types of surface defects are also invariably present. Hence, we speculate that surface defect sites may be primarily responsible for inner-sphere oxalate adsorption, although further study is necessary to prove or disprove this hypothesis.

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Surface speciation of yttrium and neodymium sorbed on rutile: Interpretations using the charge distribution model

Cited by 11 publications

References 56 publications

Enthalpy of Uranium Adsorption onto Hematite

Enthalpy of Uranium Adsorption onto Hematite

Experimental Study of Strontium Adsorption on Anatase Nanoparticles as a Function of Size with a Density Functional Theory and CD Model Interpretation

Oxalic Acid Adsorption on Rutile: Experiments and Surface Complexation Modeling to 150 °C

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