Physicochemical Models for the Behavior of Transuranic Elements in Natural Waters
Author: Vikt. L. Barsukov, M. V. Borisov
Reference: Gazette “ ГЕОХИМИЯ “ (geochemistry), 2005
ISSN: 0016-7525
Keywords: natural waters, transuranic elements
Abstract: Dissolution of solid phases of polyvalent Am, Np, and Pu in various natural waters was studied with the aid of computer thermodynamic models. The solubility of each particular phase of the transuranic elements (TUE) varies by many orders of magnitude depending on the type of water. The speciation of dissolved TUE in waters of different types is very distinctive. Free Am3+, , Pu3+, or ions dominate in some waters, whereas in other cases, the most abundant species may be hydroxo complexes, AmOH2+, , , NpO2OH0, PuOH2+, and , or carbonate, sulfate, and chloride complex ions of polyvalent TUE. Both waters and TUE phases are significantly changed during equilibration. Shifts in the pH and Eh values of water in contact with TUE phases promote partial precipitation of major components and thus change the salt composition of water. In turn, many solid TUE phases are unstable in contact with water. All Np phases are usually replaced in the models by the least soluble phase, NpO2(c), while all Pu phases are replaced by the dioxide PuO2(c). Various Am phases at the contact with various types of water are also largely transformed into a single phase: AmO2(c), Am(OH)3(c), Am carbonate, or Am hydroxycarbonate. The solubility and speciation of TUE in water reacting with the sum of Am, Np, Pu, and U solid phases are different compared with the interaction of the same water with each particular TUE. The results of our modeling can be used to elucidate the migration ability of TUE in natural waters, including the possible formation of colloidal TUE phases, and to estimate the effects of external factors, e.g., variations in R/W (integral ratio of the reacted masses of solid phase, R, and water, W) and local shifts in pH and Eh.
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