ABSTRACTThe chemical behavior of actinide elements in tank solutions, in soil, and
in groundwater is dependent upon the chemical species that form when aqueous
solutions come in contact with the actinide compounds. In particular the
chemical speciation of the reduced actinide oxidation states (III and IV)
are important, for example, to DOE waste tank processing and, more
generally, to nuclear waste disposal issues. Predicting the solubility of
the actinides in these solutions requires identification of the strong
aqueous complexes, such as carbonates and organic chelating agents, that can
form in aqueous solution.Previous speciation work has often relied on indirect techniques such as
potentiometric titrations or solubility measurements. Recent XAS experiments
determine directly the speciation of the Th carbonato species of seven
solutions under a range of carbonate concentrations and pH conditions. The
presence of the pentacarbonato complex is confirmed and the complex's
stability at low carbonate concentrations is determined. These experimental
results support a proposed thermodynamic model that describes the solubility
of Th(IV) hydrous oxide in the aqueous Na+-HCO3--CO32--OH--ClO4--H2O system extending to high concentrations at 25°C.
This model is relatively simple in that only two aqueous species are
included Th(OH)3CO3- and Th(CO3)56-.
Synthesis and Characterization of New Homo- and Heteronuclear Schiff Base Complexes
