Solubility of plutonium(VI) carbonate in saline solutions

Among the plutonium oxidation states found to form in the environment, mobile plutonium(VI) can exist under oxidizing conditions and in waters with high chloride content due to radiolysis effects. We are investigating the solubility and speciation of plutonium(VI) carbonate under conditions relevant to natural waters and brines such as those found near some geologic radioactive waste repositories. The solid Pu(VI) phase PuO2CO3(s) was prepared and its solubility was measured in NaCl and NaClO4 solutions in a CO2 atmosphere as a function of pH and ionic strength (0.1–5.6 m). The concentration of soluble plutonium in solution was calculated from spectroscopic data and liquid scintillation counting. Spectroscopic measurements also revealed the plutonium oxidation state. The apparent solubility product of PuO2CO3(s) was determined at selected electrolyte concentrations to be, log Ks,0 = −13.95 ± 0.07 (0.1 m NaCl), log Ks,0 = −14.07 ± 0.13 (5.6 m NaCl), and log Ks,0 = −15.26 ± 0.11 (5.6 m NaClO4). Specific ion interaction theory was used to calculate the solubility product at zero ionic strength, logKs,0∘=−14.82±0.05.