Distribution of barium and fulvic acid at the mica–solution interface using in-situ X-ray reflectivity

Lee, Sang Soo; Nagy, Kathryn L.; Fenter, Paul

doi:10.1016/j.gca.2007.05.031

Cited by 43 publications

(144 citation statements)

References 77 publications

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“…No significant interfacial roughness was observed by X-ray reflectivity, which is typical for muscovite in aqueous conditions (Cheng et al, 2001;Schlegel et al, 2006;Lee et al, 2007;Fenter et al, 2010). Dissolution of the muscovite substrate is expected to be negligible for the experiments (Lee et al, 2009.…”

Section: Muscovite Substratesmentioning

confidence: 90%

Effects of the background electrolyte on Th(IV) sorption to muscovite mica

Schmidt

Hellebrandt

Knope

et al. 2015

Geochimica et Cosmochimica Acta

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The adsorption of tetravalent thorium on the muscovite mica (0 0 1) basal plane was studied by X-ray crystal truncation rod (CTR) and resonant anomalous X-ray reflectivity (RAXR) measurements and alpha spectrometry in the presence of perchlorate background electrolytes LiClO 4 , NaClO 4 , and KClO 4 ([Th(IV)] = 0.1 mM, I = 0.1 M or 0.01 M, pH = 3.3 ± 0.3). RAXR data directly reveal a strong influence of the background electrolyte on the actinide sorption. No significant Th adsorption was observed in 0.1 M NaClO 4 , i.e., the Th coverage h(Th), the number of Th per unit cell area of the muscovite surface (A UC = 46.72 Å 2 ), was 60.01 Th/A UC , whereas limited uptake (h(Th) $ 0.04 Th/A UC ) was detected at a lower ionic strength (I = 0.01 M). These results are in stark contrast to the behavior of Th in 0.1 M NaCl which showed a coverage of 0.4 Th/A UC (Schmidt et al., 2012a). Th uptake was also influenced by the electrolyte cation. Weak adsorption was observed in 0.1 M KClO 4 (h(Th) $ 0.07 Th/A UC ) similar to the results in NaClO 4 at lower ionic strength. In contrast, strong adsorption was found in 0.1 M LiClO 4 , with h(Th) = 4.9 Th/A UC , a $10-fold increase compared with that previously reported in NaCl. These differences are confirmed independently by ex situ alpha spectrometry, which shows no measurable Th coverage in 0.1 M NaClO 4 background in contrast to a large coverage of 1.6 Th/A UC in 0.1 M LiClO 4 . Alpha spectrometry cannot be obtained in situ, but sample preparation requires several washing steps that may affect Th(IV) sorption, RAXR, however, is considered to reflect the in situ sorption structure. The CTR/RAXR analyses of Th-LiClO 4 show the sorption structure consisting of Th species that are broadly distributed, centered at heights of 4.1 Å and 29 Å distance from the interface. Neither the very large distribution height of the second species nor the high coverage can be explained with (hydrated) ionic adsorption, suggesting that the enhanced uptake is presumably due to the formation and sorption of Th nanoparticles.

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Section: Muscovite Substratesmentioning

confidence: 90%

Effects of the background electrolyte on Th(IV) sorption to muscovite mica

Schmidt

Hellebrandt

Knope

et al. 2015

Geochimica et Cosmochimica Acta

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“…No significant interfacial roughness was observed by Xray reflectivity, which is typical for muscovite in aqueous conditions (Cheng et al, 2001;Schlegel et al, 2006;Lee et al, 2007;Fenter et al, 2010). Dissolution of the muscovite substrate is expected to be negligible for the experiments (Lee et al, 2009(Lee et al, , 2010a.…”

Section: Muscovite Substratesmentioning

confidence: 91%

Sorption of tetravalent thorium on muscovite

Schmidt

Lee

Wilson

et al. 2012

Geochimica et Cosmochimica Acta

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Adsorption of tetravalent thorium to the (0 0 1) basal surface of the phyllosilicate muscovite from an aqueous solution (1 Â 10 À4 mol/L Th(IV) in 1 Â 10 À1 mol/L NaCl, pH = 3.2) was studied by crystal truncation rod (CTR) and resonant anomalous X-ray reflectivity (RAXR) measurements. Th uptake to the muscovite surface from solutions with total Th concentrations [Th] tot = 1 Â 10 À6 -4.88 Â 10 À3 mol/L and 1 Â 10 À1 mol/L NaCl, pH = 3.2 was quantified by alpha-spectrometry. The uptake measurements showed that Th adsorption to the muscovite surface follows a Langmuir isotherm with an apparent adsorption constant K app = 2 Â 10 4 L/mol up to [Th] tot = 1.02 Â 10 À3 mol/L. The CTR and RAXR results identified one dominant Th species with a very broad distribution centered $10 Å above the surface, in agreement with strongly hydrated extended outer sphere sorption. The findings indicate that the large energy of hydration (DG hyd = À5815 kJ/mol (Marcus, 1991)) for the small and highly-charged Th 4+ cation is a controlling parameter in its surface speciation. The surface occupancy (0.4 Th per unit cell area, A UC ) measured by RAXR exceeds the expected level for surface charge compensation by tetravalent Th (0.25 Th/A UC ). However, the radiometric uptake measurements show smaller occupancies (0.21 Th/A UC ) after rinsing by deionized water, indicating a partial removability of sorbed thorium. Thorium oligomerization was observed at total Th concentrations [Th] tot P 2.0 Â 10 À3 mol/L in presence of the surface, although solubility studies suggest that Th is soluble under these solution conditions.

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“…Furthermore, competition and displacement of Ba 2+ on clay mineral surface adsorption sites by K + can be rather strong due to their similar ionic radii (Kabata-Pendias, 2010). Therefore, the KCl rinsing process may have (i) reduced Ba 2+ densities locally as well as the X-ray photon attenuation on clay mineral surfaces and (ii) underestimated CEC 2+ Ba of clay-rich samples in contrast to organic-matter-rich samples where Ba 2+ can be bound in OM complexes (Bodek et al, 1988;Bradl, 2004;Lee et al, 2007;Pichtel et al, 2000). The low CEC…”

Section: Comparison With Ammonium Acetate Methodsmentioning

confidence: 99%

Quantitative imaging of the 3-D distribution of cation adsorption sites in undisturbed soil

Keck

Strobel

Gustafsson

et al. 2017

SOIL

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Abstract. Several studies have shown that the distribution of cation adsorption sites (CASs) is patchy at a millimetre to centimetre scale. Often, larger concentrations of CASs in biopores or aggregate coatings have been reported in the literature. This heterogeneity has implications on the accessibility of CASs and may influence the performance of soil system models that assume a spatially homogeneous distribution of CASs. In this study, we present a new method to quantify the abundance and 3-D distribution of CASs in undisturbed soil that allows for investigating CAS densities with distance to the soil macropores. We used X-ray imaging with Ba 2+ as a contrast agent. Ba 2+ has a high adsorption affinity to CASs and is widely used as an index cation to measure the cation exchange capacity (CEC). Eight soil cores (approx. 10 cm 3 ) were sampled from three locations with contrasting texture and organic matter contents. The CASs of our samples were saturated with Ba 2+ in the laboratory using BaCl 2 (0.3 mol L −1 ). Afterwards, KCl (0.1 mol L −1 ) was used to rinse out Ba 2+ ions that were not bound to CASs. Before and after this process the samples were scanned using an industrial X-ray scanner. Ba 2+ bound to CASs was then visualized in 3-D by the difference image technique. The resulting difference images were interpreted as depicting the Ba 2+ bound to CASs only. The X-ray image-derived CEC correlated significantly with results of the commonly used ammonium acetate method to determine CEC in well-mixed samples. The CEC of organic-matter-rich samples seemed to be systematically overestimated and in the case of the clay-rich samples with less organic matter the CEC seemed to be systematically underestimated. The results showed that the distribution of the CASs varied spatially within most of our samples down to a millimetre scale. There was no systematic relation between the location of CASs and the soil macropore structure. We are convinced that the approach proposed here will strongly aid the development of more realistic soil system models.

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Distribution of barium and fulvic acid at the mica–solution interface using in-situ X-ray reflectivity

Cited by 43 publications

References 77 publications

Effects of the background electrolyte on Th(IV) sorption to muscovite mica

Effects of the background electrolyte on Th(IV) sorption to muscovite mica

Sorption of tetravalent thorium on muscovite

Quantitative imaging of the 3-D distribution of cation adsorption sites in undisturbed soil

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