Diffusion of lead ions trough the Poznan Clay (Neogene) and through glacial clay

Two main kinds of migration through clays can be distinguished: advection and diffusion. The main force for advective flow is the water pressure gradient, while ionic concentration gradients drive diffusion. In compacted clays the hydraulic permeability is very low, therefore the diffusion process predominates. Clays can be considered as waste repositories. This paper shows characteristics of the diffusion process and the application of this process to modelling of waste migration in clays. Additionally, a new calculation method for the apparent diffusion coefficient using the finite-difference method is given. Experimental, values of the apparent diffusion coefficient Dapp for Poznan Clay and glacial clay are respectively 2.2_2.6 _ 10-12 m2/s and 2.6_4.4 _ 10-12 m2/s