Static through-diffusion experiments were performed to study the diffusionof alkali- and alkaline earth-metals in fine-grained granite andmedium-grained Äspö-diorite. Tritiated water was used as an inert referencetracer. Radionuclides of the alkali- and alkaline earth-metals (mono- anddivalent elements which are not influenced by hydrolysis in the pH-rangestudied) were used as tracers, i.e. 22Na+, 45Ca2+ and Sr Theeffective diffusivity and the rock capacity factor were calculated byfitting the breakthrough curve to the one-dimensional solution of thediffusion equation. Sorption coefficients, Kd, that were derivedfrom the rock capacity factor (diffusion experiments) were compared with Kd determined in batch experiments using crushed material ofdifferent size fractions.

The results show that the tracers were retarded in the same order as wasexpected from the measured batch Kd. Furthermore, the largestsize fraction was the most representative when comparing batch Kdwith Kd evaluated from the diffusion experiments. The observed effectivediffusivities tended to decrease with increasing cell lengths, indicatingthat the “transport” porosity decreases with increasing sample lengths usedin the diffusion experiments.