Elements bentonite effect

This example is to test the swelling effects under capillary pressures up to 10 Pa occurring in extremely low-permeable bentonite materials. For this purpose, a simple 1-D case is set up. A one meter long bentonite column is heated on the left hand side. Element discretization length is 0.01m. The initial conditions of the system are atmospheric gas pressure, full liquid saturation and a temperature of 12°C. The heater has a constant temperature of 1(X) C. Flow boundary conditions on the left side are gas pressure of 10 Pa and 15% liquid saturation. On the right side we have atmospheric pressure, full liquid saturation and no diffusive heat flux. As a consequence, a typical desaturation process of bentonite is triggered. The complete set of initial and boundary conditions and the material properties for this example was described in detail by Kolditz De Jonge (2003). 

The preference of bentonites for heavy metal ions that adsorb by cation exchange decreases in the order Cu > Pb > Zn > Cd > Mn (Lagaly, 1995). According to Lagaly, the selectivity of montmorillonite for cations generally depends on the restriction of interlayer expansion, being minimal for sodium montmorillonites. Metwally et al. (1993) found palygorskite to be more effective than montmorillonite, and very much more effective than kaolinite, for the uptake of Zn, at least under the conditions of their experiments (pH 4.5-7.0). Minerals were tailored to remove particular elements (e g., radioactive... 

There is a fairly large body of experimental data to support selection of realistic elemental diffusivities (derived from both sorption and diffusion measurements) for the bentonite backfill. Repeating the calculations with more conservative sorption distribution coefficients (generally a factor of ten smaller) has little effect on calculated releases from the geosphere, even though the near-field release profiles change somewhat. A major effect of such increased diffusivity is to allow release from the bentonite of some isotopes which otherwise decay within the near-field ( Ni, Sn, Pu, " Pu). However, these radionuclides are not dominant contributors to dose and, in any case, will decay within the far-field. 

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