Zusammenfassung :

Samples prepared by adding Pu(VI) to two fulvic acid solutions with a tenfold difference in fulvate concentration and to a solution with fixed pH without FA as a reference are investigated with Pu L3 XAFS. XAFS results complement our process understanding of the interactions of Pu with humic substances. Reduction of initially added PuO₂²⁺ to PuO₂⁺ and an ongoing reaction decreasing the amount of PuO₂⁺ in the solution is observed. XAFS results show that the PuO₂⁺ is further reduced by the fulvic acid to Pu(IV) identified from the XANES region. The presence of FA seems to inhibit the growth of the Pu(IV) colloids, we assume due to covering the surface of the colloids. Precipitation of PuO₂(am), which is expected at this pH value, is not observed.