The Acid/Base Chemistry of Montmorillonite

Wanner, Hans; Albinsson, Yngve; Karnland, Ola; Wieland, Erich; Charlet, Laurent; Wersin, Paul

doi:10.1524/ract.1994.6667.s1.157

Cited by 46 publications

(75 citation statements)

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“…The investigation of the acid/base chemistry of montmorillonite resulted in the identification of variablecharge surface sites, denoted ''SOH sites'', whose protonation and deprotonation constants have been evaluated by using the diffuse double layer model [1,8]. The SOH sites were found to be a factor of about 30 less abundant than the cation exchange sites.…”

Section: Methodsmentioning

confidence: 99%

A thermodynamic surface model for caesium sorption on bentonite

Wanner

Albinsson

Wieland

1996

Analytical and Bioanalytical Chemistry

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Caesium sorption on Wyoming bentonite MX-80 has been studied in solutions of NaCl, KCl, MgCl(2), CaCl(2), NaNO(3) and Ca (NO(3))(2) of concentrations varying between 0.025 and 1 mol/L, as well as in a weakly saline (I=0.004 ml/L) and a strongly saline (I=0.46 mol/L) natural groundwater. These experiments have been used to derive a thermodynamic model for the interaction of caesium with the bentonite surface in accordance with a surface chemical model, including acid/base reactions developed recently for montmorillonite. The sorption behaviour of caesium on bentonite can be described, within the experimental and model uncertainties, in terms of a one-site ion exchange model. The ion exchange constant obtained for the reaction NaX+Cs(+) left arrow over right arrow CsX+Na(+) (where X represents the ion exchange sites on montmorillonite) is log(10) K(0)(ex)=1.6. Impurities in the bentonite, influencing the concentrations of competing cations, such as Na(+), K(+), Mg(2+) and Ca(2+), have a crucial impact on the sorption of caesium. This impact can be adequately quantified with the present model. The model predictions compare well with sorption data published in the open literature on both Wyoming bentonite MX-80 and other types of bentonite. Distribution coefficients from the literature obtained from both batch and diffusion experiments and varying over four orders of magnitude are reproduced and explained successfully by the model.

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Section: Methodsmentioning

confidence: 99%

A thermodynamic surface model for caesium sorption on bentonite

Wanner

Albinsson

Wieland

1996

Analytical and Bioanalytical Chemistry

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“…Prior studies established that sorption on a clay such as montmorillonite consists of ion-exchange at interlayer sites and pH-dependent sorption at crystallite edge sites (Zachara and McKinley, 1993;Chisholm-Brause et al, 1994;Morris et al, 1994;Zachara and Smith, 1994;Wanner et al, 1994;Degueldre et al, 1994, McKinley et al, 1995. As discussed previously, experiments in this study were conducted at relatively high ionic strength (0.1 M NaNO3) which suppressed ionexchange of UO22+ with interlayer cations.…”

Section: Modeling Of U(6+) Sorption Of Montmorillonitementioning

confidence: 99%

Section: Modeling Of U(6+) Sorption Of Montmorillonitementioning

confidence: 99%

“…Wanner et al (1994) estimated that crystallite edges accounted for about 10% of the N2-BET specific surface area measured for their Na-montmorillonite specimen. Assuming the same relative value of 10% observed by Wanner et al (1994), an effective crystallite edge surface area of 9.7 m2/g (10% of the measured N2-BET specific surface area of 97 m2/g) was calculated for the Na-montmorillonite used in this study. The effective surface area, together with a "standard" site density of 2.3 sites/nm 2 recommended for all minerals by Davis and Kent (1990) based on the ferrihydrite work of Dzombak and Morel (1990), was then used to calculate the total number of available edge sites.…”

Section: Modeling Of U(6+) Sorption Of Montmorillonitementioning

confidence: 99%

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Uranium(6+) sorption on montmorillonite: Experimental and surface complexation modeling study

1997

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Sorption interactions with montmorillonite and other clay minerals in soils, sediments, and rocks are potentially important mechanisms for attenuating the mobility of U(6+) and other radionuclides through the subsurface environment. Batch experiments were conducted (in equilibrium with atmospheric Pco2) to determine the effects of varying pH (2 to 9), solid-mass to solution-volume ratio (M/V = 0.028 to 3.2 g/L), and solution concentration (2 x 10 -7 and 2 x 10 -6 M 233U) on U(6+) sorption on SAz-1 montmorillonite. The study focused on U(6+) surface complexation on hydroxylated edge sites as the sorption mechanism of interest because it is expected to be the predominant sorption mechanism at pHs typical of natural waters (pH ~6 to ~9). Thus, the experiments were conducted with a 0.1 M NaNO3 matrix to suppress ion-exchange between U(6+) in solution and interlayer cations. The results show that U(6+) sorption on montmorillonite is a strong function ofpH, reaching a maximum at near-neutral pH (,~6 to ~6.5) and decreasing sharply towards more acidic or more alkaline conditions. A comparison of the pH-dependence of U(6+) sorption with that of U(6+) aqueous speciation indicates a close correspondence between U(6+) sorption and the predominance field of U(6+)-hydroxy complexes. At high pH, sorption is inhibited due to formation of aqueous U(6+)-carbonate complexes. At low pH, the low sorption values indicate that the 0.1 M NaNO3 matrix was effective in suppressing ion-exchange between the uranyl (UO] +) species and interlayer cations in montmorillonite. At pH and carbonate concentrations typical of natural waters, sorption of U(6+) on montmorillonite can vary by four orders of magnitude and can become negligible at high pH.The experimental results were used to develop a thermodynamic model based on a surface complexation approach to permit predictions of U(6+) sorption at differing physicochemical conditions. A Diffuse-Layer model (DLM) assuming aluminol (>A1OH °) and silanol (>SiOH °) edge sites and two U(6+) surface complexation reactions per site effectively simulates the complex sorption behavior observed in the U(6+)--H20----4202-montmorillonite system at an ionic strength of 0.1 M and pH > 3.5. A comparison of model predictions with data from this study and from published literature shows good agreement and suggests that surface complexation models based on parameters derived from a limited set of data could be useful in extrapolating radionuclide sorption over a range of geochemical conditions. Such an approach could be used to support transport modeling by providing a better alternative to the use of constant K~ s in transport calculations.

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“…Their sorption on bentonite has been investigated considering sorption isotherms and a cation-exchange reaction mechanism [3][4][5][6]. Also model parameters of bentonite and smectite for both cationexchange and the surface complexation reactions have been carried out and used in modelling studies of radionuclide migration behaviour [7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Sorption and diffusion behaviours of strontium in sodium-type bentonite bed

2006

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Sorption and diffusion of Sr were examined using a typical Japanese bentonite. The experimental results showed that Sr sorption on the bentonite had linear relationship between the equilibrium Sr concentration and Sr sorption amount, i.e., Henry's type of sorption, in wide initial Sr concentration from 1.1 × 10 -9 to 1.1 × 10 -4 mol L -1 at pH 10. The Sr sorption also indicated pH dependence in pH range between 2 and 12. Sorption modelling calculation indicated that cationexchange reactions contributed to Sr sorption in the pH range studied and a surface complexation reaction was predominant above pH 8. Diffusion of Sr in loosely compacted bentonite bed was described by pore and surface diffusion and surface complexation of Sr. Chemical-transport calculations reproduce the diffusion data at pH 5 using the cation-exchange parameters obtained in the analysis of the batch sorption experiment.

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The Acid/Base Chemistry of Montmorillonite

Cited by 46 publications

References 0 publications

A thermodynamic surface model for caesium sorption on bentonite

A thermodynamic surface model for caesium sorption on bentonite

Uranium(6+) sorption on montmorillonite: Experimental and surface complexation modeling study

Sorption and diffusion behaviours of strontium in sodium-type bentonite bed

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