Actinide(IV) colloids at near-neutral pH due to reaction with dissolved silicic acid


Actinide(IV) colloids at near-neutral pH due to reaction with dissolved silicic acid

Zänker, H.; Weiss, S.; Hennig, C.; Husar, R.

A new type of actinide(IV) colloids - silica-containing U(IV), Th(IV) and Np(IV) colloids formed in near-neutral solutions of background chemicals of geogenic nature (carbonate, silicic acid, Na+) - was studied. Whereas the radiocolloids hitherto addressed in the BELBaR project are formed by the adsorption of radionuclides onto pre-existing particles, the colloids here under discussion result from a reaction of dissolved actinide(IV), An(IV), with dissolved silicic acid. An-O-Si bonds, which increasingly replace the An-O-An bonds of the amorphous actinide(IV) oxyhydroxide with increasing silica concentration, make up the internal structure of these colloids. The particles remain stable in aqueous suspension over years. A concentration of up to 10-3 M of colloid-borne An(IV) and a particle size of < 20 nm was observed. The question if such An(IV) colloids may contribute to the mobility of the actinides in the near-field or the far-field of a nuclear waste repository is discussed.

Keywords: Tetravalent actinides; silicic acid; silica; colloids; nanoparticle; nuclear waste repositories; BELBaR

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Publ.-Id: 20453