Diffusion and sorption of U(VI) in compacted bentonite studied by a capillary method

Abstract

Diffusion and sorption of U(VI) in compacted bentonite were studied using a capillary method. The experiments were carried out at room temperature in 0.1 M NaClO 4 solutions at pH 7.0 ± 0.1. Effects of contact time, solution concentration and bentonite bulk density on diffusion were also investigated. The results fit the Fick's second law very well and are in good agreement with the literature data for similar bentonite dry densities [3]. The K d values from capillary method are in most cases lower than those from batch experiments. The interlaminary space of the compacted bentonite contributes significantly to the sorption of uranium. The apparent diffusion coefficient D a of diffusion derived from the experiments are used to simulate its diffusion in compacted bentonite and the results indicate that several meters of compacted bentonite is enough to prevent the diffusion of from the repository to the environment.

Sorption of Radiocaesium onto Powdered and Compacted Rectorite Studied by Batch and Capillary Methods

“…From Figure 5, it is clear that the K d values calculated from the D e value for HTO and the D a value for the Cs + ion were much larger than those deduced from n 0 and n slice 1 . Wang et al (2005b) studied the diffusion of U(VI) in compacted bentonite and found similar results. The data listed in Table 1 indicate that the D e value for the Cs + ion was much higher than that of HTO, thereby suggesting that the diffusion of the Cs + ion was mainly dominated by surface diffusion (Yu and Neretnieks 1997;Wang and Liu 2004d).…”

“…The data listed in Table 1 indicate that the D e value for the Cs + ion was much higher than that of HTO, thereby suggesting that the diffusion of the Cs + ion was mainly dominated by surface diffusion (Yu and Neretnieks 1997;Wang and Liu 2004d). Equation (7) can only be used when the diffusion mechanism of the radionuclide is the same as that of HTO (Wang et al 2005b).…”

“…The sorption, desorption, migration and diffusion of radionuclides in the backfill materials (such as clays and bentonite) has been a topic of extensive studies during the past few decades. The distribution coefficient derived via the batch technique (Xu et al 2006a;Wang et al 2004a;Montavon et al 2004), the dispersion coefficient derived from column experiments (Wang and Liu 2005a;Jedináková-Křižová 1998), the diffusion coefficient in compacted clay minerals (Xu et al 2006b;Wang et al 2005b) and the desorption properties of radionuclides (Wang et al 2005c(Wang et al , 2006Geckeis et al 2002) are all important parameters for the evaluation of the behaviour of radionuclides in the natural environment. Compacted clay is a candidate as a buffer material in the geological disposal of high-level radioactive wastes because of its low hydraulic conductivity, high swelling and sealing ability, and large sorption capacity (Bucher and Müller-Vonmoos 1989).…”

“…Compacted clay is a candidate as a buffer material in the geological disposal of high-level radioactive wastes because of its low hydraulic conductivity, high swelling and sealing ability, and large sorption capacity (Bucher and Müller-Vonmoos 1989). The distribution coefficient and diffusion coefficient are important for the evaluation of the pollution potential of radionuclides to the natural environment (Wang et al 2004b(Wang et al , 2005d.…”

A Network Model for Diffusion in Media with Partially Resolvable Pore Space Characteristics

“…Sorption of diffusing species changes the pore space in Opalinus clay and may have a significant beneficial impact on the long-term diffusivity (Wang et al 2005). The macroscopic diffusivity of the system with and without sorption is different (Korichi et al 2010).…”