Simulation of a Through-diffusion Test

In order to verify the validity of the HA theory, we compare the numerical work with the result of a through-diffusion test for a pure smectitic clay. The HA macromodel and micro-model, i.e., the finite elements in the macro-domain and in the micro-domain, are shown in Fig. 9.2. 

We consider a diffusion/adsorption test of cesium (Cs), and the data provided are as follows The size of a clay platelet is 100 x 100 x 1. Based on experimental data of Baeyens and Bradbury (1997) the cross-section area of clay edges, which are adsorption sites, are assumed to be 35 m /g. Since the atomic radius of cesium is 3.34 A, and because of the monolayer adsorption, we set the layer thickness of the edge domain where cesium ions are adsorbed as 0.67 nm. The maximum amount of cesium adsorbed in this domain is 6.51 x 10 mol/g. The molecular number of interlayer water is given as n=2.5. The diffusion coefficient of cesium ions in the bulk water is 2x10 cm /s, and in the interlayer water is 2.62x 10 cm /sec, which is obtained from the MD simulation. The concentration of cesium at the upstream boundary, i.e., the l.h.s. surface of Fig. 9.2 (Dirichlet boundary condition) is given as Case (1) 10 mol/1, Case (2) 10 mol/1 and Case (3) 10 mol/1. 

The calculated break-through curves for Case (1) at each point of the macrodomain are shown in Fig. 9.3, where the curves corresponding to a situation without adsorption are also presented. Similarly, the curves for Cases (2) and (3) are shown 

---