Solubility of Plutonium in MgCl2 and CaCl2 Solutions in Contact with Metallic Iron

Abstract

The solubility of Pu(IV) hydrous oxide is studied at 22±2 °C under Ar atmosphere in 0.25 and 3.5 M MgCl2 (pHc¿9) and 3.5 M CaCl2 (pHc=11¿12) solutions in contact with iron powder. In alkaline 3.5¿4.0 M CaCl2 ternary Ca-Pu-OH complexes are formed and the solubility of PuO2·xH2O(s) increases from about 10-10 M at pHc=11 to 10-8¿10-7 M at pHc=12, both in the presence and absence of Fe powder. In the presence of iron the aqueous speciation is dominated by Pu(III) at pHc10. In the absence of reducing agents the aqueous speciation is dominated by Pu(V), with significant contributions of Pu(IV) complexes at pHc>10. The effect of ternary Ca-Pu(III,IV,V)-OH complexes in alkaline CaCl2 solutions can be described by assuming complex stoichiometries and experimental data from the oxidation state analogs Cm(III)/Nd(III), Th(IV) and Np(V). The ion interaction Pitzer approach is used for model calculations.JRC.E.6-Actinides researc