EFFECT OF ION CONCENTRATION ON DIFFUSION THROUGH CLAY

The applicability of an equation that suggests the effective diffusion coefficient ofions through a charged porous medium is Linearly relate d to the square root of the concentration ofions is evaluated. Data fr om experiments on diffusion of NaCl and LiCl solutions through Na and Li bentonites were analyzed using the proposed equation. Plots of effe ctive diffusion coefficient versus square root of concentration are co nsistent with the formulation that the effective diffusion coefficient declines linearly with the square root of concentration, The analysis also indicates that effective diffusion coefficient of an ion is depe ndent on the counter ion in solution as well as that at the clay excha ngeable site. For solutions up to 0.07 meg/cc, the results further ind icate that it is feasible to combine all the porous medium characteris tics into a single factor referred to as the apparent tortuosity facto r.