Distinguishing between interlayer and external sorption sites of clay minerals using X-ray absorption spectroscopy

Papelis, Charalambos; Hayes, Kim F.

doi:10.1016/0927-7757(95)03370-x

Cited by 103 publications

(70 citation statements)

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“…Models of the EDL that approximate liquid water as a uniform dielectric continuum (such as the Poisson-Boltzmann equation [17,18], hypernetted chain theory [19,20], or the primitive model [18,21]) inherently cannot describe surface complexes [17,18]. Spectroscopic methods that probe the local molecular environment of "reporter atoms" (for example, nuclear magnetic resonance (NMR) [22,23] or x-ray absorption spectroscopy (XAS) [24,25]) have shown that adsorbed inorganic ions can adopt several different configurations that include both fully-and partly-solvated species. Resonant anomalous x-ray reflectivity (RAXR) studies, which probe solute concentration as a function of distance from a planar surface, have confirmed that EDL ions can adsorb simultaneously in both ISSCs and OSSCs [26][27][28][29][30].…”

Section: Introductionmentioning

confidence: 99%

“…Following Tournassat et al [52], we focus on smectites because these ubiquitous clay mineral nanoparticles play important roles in soil chemistry [55,56], soil mechanics [57], fault friction [58,59], materials chemistry [60], landfill and contaminated site isolation [61,62], high-level radioactive waste storage [63,64], CO 2 sequestration [65,66], and gas hydrate stability in marine sediments [67,68]. Their adsorption properties for small inorganic ions have been extensively studied using macroscopic [55,56,69], spectroscopic [24,25], and MD simulation techniques [18,35,37,45,49,52].…”

Section: Introductionmentioning

confidence: 99%

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Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl–CaCl2) solutions

Bourg

Sposito

2011

Journal of Colloid and Interface Science

254

224

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We report new molecular dynamics results elucidating the structure of the electrical double layer (EDL) on smectite surfaces contacting mixed NaCl-CaCl 2 electrolyte solutions in the range of concentrations relevant to pore waters in geologic repositories for CO 2 or high-level radioactive waste (0.34 to 1.83 mol c dm -3 ). Our results confirm the existence of three distinct ion adsorption planes (0-, β-, and d-planes), often assumed in EDL models, but with two important qualifications: (1) the location of the β-and dplanes are independent of ionic strength or ion type and (2) "indifferent electrolyte" ions can occupy all three planes. Charge inversion occurred in the diffuse ion swarm because of the affinity of the clay surface for CaCl + ion pairs. Therefore, at concentrations ≥ 0.34 mol c dm -3 , properties arising from long-range electrostatics at interfaces (electrophoresis, electro-osmosis, co-ion exclusion, colloidal aggregation) will not be correctly predicted by most EDL models. Co-ion exclusion, typically neglected by surface speciation models, balanced a large part of the clay mineral structural charge in the more concentrated solutions. Water molecules and ions diffused relatively rapidly even in the first statistical water monolayer, contradicting reports of rigid "ice-like" structures for water on clay mineral surfaces.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl–CaCl2) solutions

Bourg

Sposito

2011

Journal of Colloid and Interface Science

254

224

View full text Add to dashboard Cite

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“…Recent studies using EXAFS (extend X-ray absorption fine structure) have shown that heavy metals are sorbed on clay and oxide surfaces accompanied by the formation of multinuclear or polynuclear surface complexes (i.e., surface precipitate) much more frequently than previously expected based on the thermodynamical models. [5][6][7][8][9] These microscopic studies have promoted our understanding of the real sorption mechanism. EXAFS analyses of Cd species on the montmorillonite, however, have never been reported in spite of its importance for soil pollution mainly because the K-edge EXAFS requires X-rays with higher energy than 23 keV.…”

mentioning

confidence: 99%

EXAFS Studies about the Sorption of Cadmium Ions on Montmorillonite

Takamatsu¹,

Asakura²,

Chun³

et al. 2006

Chemistry Letters

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We investigated local structures around cadmium (Cd) sorbed on montmorillonite at various pH values by EXAFS (extend X-ray absorption fine structure). We found two sorption types, an outer-sphere complex and a surface precipitate. The outer-sphere complex was mainly formed at a lower pH which had an identical structure to aqueous Cd 2þ , while the surface precipitate was found at high pH which had a one-layerCadmium (Cd) is a toxic heavy metal that results in significant pollution of many soil and groundwater systems. Furtherworse, Cd is known to bioaccumulate. Since the mobility and bioavailability of Cd in polluted systems are strongly related to its sorption structures, it is important to understand the sorption structures on clay minerals which are main soil components. Montmorillonite is a dioctahedral smectite mineral that is prevalent in soil environments and has a high surface area and cationexchange capacity (CEC). Over past several decades, macroscopic investigation on the sorption mechanisms of metals on montmorillonite presented many thermodynamic models such as ''surface complexation models'' to describe metal sorption reactions at the solid-water interface.1 The models explained the pH-dependent sorption properties on the montmorillonite. 2-4Outer-sphere complex is mainly formed on permanent charge sites on the interlayer of montmorillonite at low pH values while inner-sphere complex formation occurs at high pH values, where the metals are fixed to deprotonated surface hydroxides on the edge of montmorillonite. However, we have to determine the molecular structures of the sorbed species directly in order to reveal the real sorption mechanism. Recent studies using EXAFS (extend X-ray absorption fine structure) have shown that heavy metals are sorbed on clay and oxide surfaces accompanied by the formation of multinuclear or polynuclear surface complexes (i.e., surface precipitate) much more frequently than previously expected based on the thermodynamical models. 5-9 These microscopic studies have promoted our understanding of the real sorption mechanism. EXAFS analyses of Cd species on the montmorillonite, however, have never been reported in spite of its importance for soil pollution mainly because the K-edge EXAFS requires X-rays with higher energy than 23 keV. We carried out K-edge Cd EXAFS measurements for Cd sorbed on montmorillonite in a vertical Wiggler beam line in SPring-8 and Photon Factory beam line, which provide a high energy X-ray. EXAFS provides only averaged local structure information for all coexisting metal species having the same absorption edge. We varied the pH values in order to change the sorption species continuously and applied a regression analysis to quantitatively evaluate the composition of each sorption structure.Cd was sorbed on Na-montmorillonite (Kunipia-F, Kunimine Industries Co.) using a batch technique at several different pH values. Cd(NO 3 ) 2 (0.002 mol L À1 ) and NaNO 3 (0.004 mol L À1 ) solutions were applied and the reaction time was 24 h (295 AE 1 K). The p...

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“…Multinuclear metal hydroxides of Pb (II), Co (II), Cu (II), Ni (II) and Cr(III) on clay mineral oxides and aluminosilicates have been discerned with EXAFS (Papelis and Hayes, 1996;, Scheidegger, et al, 1996, Cheah, et al 1998, Elzinga and Sparks, 1999 and electron spin resonance (ESR) spectroscopy McBride et al,1984). The EPR studies of Cu(II) adsorption on titanium dioxide by Bleam and McBride (1986) suggests that Cu(II) forms hydrous clusters when the adsorption of Cu(II) exceeded a critical surface concentration (4% of monolayer coverage).…”

Section: (A) Kinetics and Structure Of Heavy Metals Adsorbed To Minermentioning

confidence: 99%

Kinetics and Mechanism of Metal Retention/Release in Geochemical Processes in Soil - Final Report

Taylor¹

2000

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Distinguishing between interlayer and external sorption sites of clay minerals using X-ray absorption spectroscopy

Cited by 103 publications

References 15 publications

Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl–CaCl2) solutions

Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl–CaCl2) solutions

EXAFS Studies about the Sorption of Cadmium Ions on Montmorillonite

Kinetics and Mechanism of Metal Retention/Release in Geochemical Processes in Soil - Final Report

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