A solubility study of plutonium in carbonate solution

The Solubility experiments for Pu were measured from supersaturation direction in Na+-H+-NO3--CO32- system in the pH range of 2-13. This study was carried out under aerobic conditions at room temperature (about 25degC). The solubility of Pu in 0.1 M NaNO3 decreased with increasing pH in the low pH range, and showed constant in pH range of 10-12. In the carbonate system, the solubility of Pu increased with increasing the NaHCO3 concentration in the high pH range. In this range, the solubility was also dependent on pH, but the pH dependency of the solubility in pH range 8-10 was different from that in the pH range over 10. According to these behaviors, it was suggested that Pu carbonate or its hydroxycarbonate complex exists as dominant species in this range. From the correlating between measured pH and the pe, the redox state of aqueous species of Pu in carbonate system is different from nitrate system. The green colored precipitation was observed in the neutral to high pH range. These precipitation were not characterized, but according to other studies, it can be considered PuO2·xH2O(am). From the estimation based on chemical equilibrium for these complexes of Pu(VI), it was suggested that PuO2(OH)CO3 was the dominant species in the high pH range. (author)