The Influence of Speciation on the Geospheric Migration of Radionuclides

Radionuclides in groundwater can exist as different species whose retention factors may be strongly different. For one-dimensional transport in a porous medium, we give conditions for the existence of equilibrium between two species. In most cases, these conditions are probably well fulfilled when time scales of geosphere transport are considered. In these cases, the total concentration migrates independently of a particular speciation with an effective retention factor. Such an effective retention factor can also be defined if more than two species in liquid phase are in equilibrium. As a consequence, existing radionuclide transport models can be readily used by properly redefining the retention factor.