Adsorption of uranium and thorium from aqueous solutions by the clay minerals montmorillonite and vermiculite

Sikalidis, C.; Alexiades, C. A.; Μisaelides, P.

doi:10.1080/02772248909357374

Cited by 33 publications

(16 citation statements)

References 9 publications

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“…A number of experimental studies have been published on U(6+) sorption on montmorillonite (e.g., Borovec, 1981;Tsunashima et al, 1981;Ames et al, 1983;Sikalidis et al, 1989;Zachara and McKinley, 1993;McKinley et al, 1995). These experiments were conducted using different solution chemistry (pH, ionic strength, U concentration, carbonate concentration), montmorillonite specimen, M/V, and/or sorbent preparation methods, all of which could affect U(6+) sorption.…”

Section: Comparison With Other Datamentioning

confidence: 99%

“…Below a pH of 7, their KdS in 0.01 M NaC104 solutions are higher than their Kas at 0.1 M NaC104 solutions due to an ion-exchange sorption mechanism. Data from Sikalidis et al (1989) are also plotted in Figure 8 for comparison. The experiments by Sikalidis et al (1989), which were conducted using a different montmorillonite material (Upton, Wyoming bentonite) and higher ~ U~ (8.4 x 10 -4 to 8.4 × 10 -3 M), resulted in Kas much higher than would be predicted by our DLM model.…”

Section: Comparison With Other Datamentioning

confidence: 99%

“…Data from Sikalidis et al (1989) are also plotted in Figure 8 for comparison. The experiments by Sikalidis et al (1989), which were conducted using a different montmorillonite material (Upton, Wyoming bentonite) and higher ~ U~ (8.4 x 10 -4 to 8.4 × 10 -3 M), resulted in Kas much higher than would be predicted by our DLM model. The higher values are most likely due to the predominance of ion-exchange as the sorption mechanism in those experiments.…”

Section: Comparison With Other Datamentioning

confidence: 99%

“…Several studies have been published on the sorption of U(6+) on montmorillonite (e.g., Borovec, 1981;Tsunashima et al, 1981;Ames et al, 1983;Sikalidis et al, 1989;Zachara and McKinley, 1993;Akcay and Kurtulmus, 1995;McKinley et al, 1995). Many of these were conducted over restricted ranges of pH.…”

Section: Introductionmentioning

confidence: 99%

“…Many of these were conducted over restricted ranges of pH. For example, initial pH used in the experiments reported by Tsunashima et al (1981), Ames et al (1983), and Sikalidis et al (1989) was in the range 4 to 4.5, 7 to 9, and 3 to 4, respectively, whereas experiments by Borovec (1981) were conducted at an initial pH of 6.0. Because solution pH is a key parameter which controls the sorption of U and other actinides on mineral surfaces (e.g., Allard et al, 1984;Hsi and Langmuir, 1985;Dozol and Hagemann, 1993;Pabalan and Turner, accepted for publication; accepted for publication), it is important to have experimental data over a wide range ofpH.…”

Section: Introductionmentioning

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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