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A Thermodynamic Model for Acetate, Lactate, and Oxalate Complexation with Am(III), Th(IV), Np(V), and U(VI) Valid to High Ionic Strength

Description: The organic ligands acetate, lactate, oxalate and EDTA have been identified as components of wastes targeted for disposal in the Waste Isolation Pilot Plant (WIPP) located in Southeastern New Mexico. The presence of these ligands is of concern because complexation of the actinides with the ligands may increase dissolved actinide concentrations and impact chemical retardation during transport. The current work considers the complexation of Am(III), Th (IV), Np(V), and U(W) with two of the organic ligands, acetate and lactate, in NaCl media from dilute through high concentration. A thermodynamic model for actinide complexation with the organic ligands has been developed based on the Pitzer activity coefficient formalism and the Harvie-Moller-Weare, Felmy-Weare database for describing brine evaporite systems. The model was parameterized using first apparent stability constant data from the literature. Because of complexation of other metal ions (Fe, Mg, Ni, Pb, etc.) present in the WIPP disposal room with the organic ligands, preliminary results from model calculations indicate the organic ligands do not significantly increase dissolved actinide concentrations.
Date: January 15, 1999
Creator: Bynaum, R.V.; Free, S.J. & Moore, R.C.
Partner: UNT Libraries Government Documents Department

Americium thermodynamic data for the EQ3/6 database

Description: Existing thermodynamic data for aqueous and solid species of americium have been reviewed and collected in a form that can be used with the EQ3/6 database. Data that are important in solubility calculations for americium at a proposed Yucca Mountain nuclear waste repository were emphasized. Conflicting data exist for americium complexes with carbonates. Essentially no data are available for americium solids or complexes at temperatures greater than 25{sup 0}C. 17 references, 4 figures.
Date: July 1, 1984
Creator: Kerrisk, J.F.
Partner: UNT Libraries Government Documents Department

Actinide-specific complexing agents: their structural and solution chemistry

Description: The synthesis of a series of tetracatecholate ligands designed to be specific for Pu(IV) and other actinide(IV) ions has been achieved. Although these compounds are very effective as in vivo plutonium removal agents, potentiometric and voltammetric data indicate that at neutral pH full complexation of the Pu(IV) ion by all four catecholate groups does not occur. Spectroscopic results indicate that the tetracatecholates, 3,4,3-LICAMS and 3,4,3-LICAMC, complex Am(III). The Am(IV)/(III)-catecholate couple (where catecholate = 3,4,3-LICAMS or 3,4,3-LICAMC) is not observed, but may not be observable due to the large currents associated with ligand oxidation. However, within the potential range where ligand oxidation does not occur, these experiments indicate that the reduction potential of free Am(IV)/(III) is probably greater than or equal to + 2.6 V vs NHE or higher. Proof of the complexation of americium in the trivalent oxidation state by 3,4,3-LICAMS and 3,4,3-LICAMC elimates the possibility of tetracatholates stabilizing Am(IV) in vivo.
Date: July 1, 1983
Creator: Raymond, K.N.; Freeman, G.E. & Kappel, M.J.
Partner: UNT Libraries Government Documents Department

Secondary recovery of plutonium and americium from process waste streams by solvent extraction

Description: A solvent extraction process is being evaluated for the secondary recovery of plutonium and americium from Rocky Flats waste streams. The bidentate organophosphorus compounds dihexyl-N,N-diethylcarbamylmethylene phosphonate and its dibutyl analogue have been shown to be selective extractants for the actinides from solutions of nitric acid. The results from laboratory test runs in which the organophosphorus extractants were used for processing secondary waste solutions will be presented. Solvent extractant properties and purification procedures are discussed.
Date: January 16, 1978
Creator: Hagan, P. G. & Navratil, J. D.
Partner: UNT Libraries Government Documents Department