Investigation of actinide(IV)-silica colloids at near-neutral pH

Knowledge of the migration and mobility of actinides is an important issue to predict potential release of radiotoxic elements from nuclear waste repositories. Under the reducing conditions expected for the disposal zone, the tetravalent form of the actinides An (An = Th, U, Np) is predominant. Due to the low solubility at neutral pH, An(IV) are considered as immobile under these conditions. Nevertheless, high environmental mobility has been found. This fact is obviously related with the formation of An(IV) eigencolloids or the sorption on other colloids.
We report some examples of investigated colloids of An(IV) ( An= Th, U, Np): An(IV) silica colloids.
The main characteristic properties (eg. particlesize distribution, longterm monitored time stability, surfacecharge) of these colloids are presented.