Anion exclusion in crystalline rocks; The Influence of rock structure and pore network

Havlov, V.*; Zuna, M.*; Brzda, L.*; Rosendorf, T.*; Sammaljrvi, J.*; Nenonen, V.*; Siitari-Kauppi, M.*; Sasao, Eiji   ; Gvodk, L.*

Anion exclusion is a process that has been widely observed mainly with concern to clay materials. However, this process has also been observed in some types of crystalline rock. Because anion exclusion exerts the impact on migration in the most constricted parts of nanometre-scale pores, this study focused on H, Cl and I diffusion together with the characterisation of the rock pore structure of magmatic and metamorphic rocks. Both the anionic species exhibited lower diffusion coefficients than that of H, thus indicating anionic exclusion mainly in the metamorphic rocks studied. The De values for the anions in the metamorphic rocks differed from those in the magmatic rocks by around one order of magnitude. The difference between the De values for magmatic and metamorphic rocks is clearly supported by pore structure visualisation by autoradiography. Preliminary results showed decreasing accessible porosity for anionic species rather than decreasing pore diffusion coefficients.