Bentonite is widely used in landfills. When bentonite is used as a material of liner

diffusion through bentonite is a very important transport mechanism. To understand the ability of retard migration of contaminant in different stress states

the diffusion coefficients of Ca2+，Cl- and Zn2+ diffusing in bentonite of different dry densities were measured. The diffusion coefficients of this study are well in the range of previously published results. With the increasing of porosity

the diffusion coefficients of Ca2+ and Cl- increase in exponential form. The estimating method of diffusion coefficient in a given range of porosity is proposed. The estimation is approximate to the measured values.