Sorption and diffusion of chloride (Cl-36) and uranium in conpacted sodium bentonite MX-80 were measured. No sorption was observed in the Sorption tests, however, in the diffusion tests slight sorption of uranium was noticed. The diffusivities of Cl-36 were found to be strongly dependent on the compaction of bentonite and on the salt concentration of the solution. Ion-exclusion can propably explain these phenomena.The diffusivities of uranium were also strongly dependent on the compaction of bentonite. Uranium shews features of both ion-exclusion and sorption. Farther studies are, however, needed to explain the diffusion mechanisms of uranium.

Diffusion studies were carried out with sodium and copper in sodium bentonite. The experiments were performed at room temperature and densities of the samples varied from 0.8 to 1.8 g/cm3.This paper describes the experimental methods used for the diffusion tests and gives the obtained measurement results. The evaluation of the diffusion mechanisms is at this stage preliminary, however.Diffusion of sodium seems to follow similar mechanisms as has been observed for cesium and strontium in several previous studies. The phenomena could be explained by some kind of diffusion of sorbed ions. The measured apparent diffusivities of sodium varied from 50×10−12 to 300×10−12 m2/s and the effective diffusivities from 80×10−12 to 1.6×10−9 m2/s depending on the density of bentonite and the salt concentration of water solution.Low solubility of copper caused precipitation thus interfering the diffusion experiments. However, the part of copper which did diffuse into bentonite seemed to follow the same type of mechanism as sodium. The measured apparent diffusivities of copper varied from 5×10−12 m2/s.The interaction between the cations in the circulating solutions and the sodium ion in bentonite were essential in this study.

No abstract

The nature of diffusivity and porosity in rock was studied as a function of various parameters. The phenomena of main interest were dead-end porosity, ion-exclusion and sorption. The rock types studied were rapakivi granite, granite and gneiss, and tracer techniques with 36Cl, 22Na+ and 3H (HTO) were used as a research method. A mathematical solution for outdiffusion from a porous cylinder was developed by applying a corrected form of Fick's second law for a case where part of the pores are so-called dead-end pores. With this model the theoretical curve could be closely fitted to the measured values. It was found that the rock-capacity factor is an increasing function of the ionic concentration of the solution in the case of Cl indicating ion-exclusion, while the opposite is true in the case of Na+ indicating ion-exchange type sorption. The effective diffusion coefficient was also found to vary as a function of the salinity in the case of 36Cl. In the case of 22Na, the effect was opposite and weaker. The diffusion of tritium through the rock samples was clearly higher than the diffusion of 36Cl. Part of the difference is explained by the smaller effective porosity for 36Cl. The rest can probably be explained by the steric effects on the chloride ion caused by the negatively charged pore surfaces in the narrow pores.

No abstract