Diffusion and sorption of Sr in compacted sodium montmorillonite; Multispecies modeling

Tachi, Yukio; Yotsuji, Kenji; Ito, Tsuyoshi; Suyama, Tadahiro

no journal, , 

The integrated sorption and diffusion (ISD) model was applied for systems coexisting multispecies Sr (divalent cation Sr and neutral SrSO (aq)) in compacted montmorillonite. Effective diffusion coefficients (De) and distribution coefficients (Kd) of Sr in compacted Na-montmorillonite (dry density of 800 kg/m) saturated with three types of NaSO solutions (0.05, 0.1, 0.5 M) were measured by the trough-diffusion method. The De and Kd values decreased drastically with increasing porewater salinity. The De for multispecies Sr was determined as the harmonic weight-average considering the two species distribution and their log De values, based on comparison with reactive-transport calculations using the PHREEQC. As a result, the De trend could be quantitatively express by the ISD model considering multispecies contributions. The thermodynamic sorption model considering ion exchange reactions could provide reasonable account of Kd trend as functions of salinity.