Spectroscopic and structural studies of environmentally relevant neptunyl carbonate complexes

Conference · Fri Dec 01 04:00:00 EST 1995

OSTI ID:126230

Palmer, P D; Clark, D L; Neu, M P ^[1]

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1. Los Alamos National Lab., NM (United States); and others

Carbonate and bicarbonate are common anions in many natural waters, consequently carbonate complexes of the actinides may play an important role in actinide migration from a nuclear waste repository. Due to its relatively high solubility, neptunium is the most important actinide for consideration. Carbonate complexation was examined for NpO{sub 2}{sup +} and NpO{sub 2}{sup 2+} ions using a variety of techniques including UV-Vis-NIR and NMR spectroscopics. NpO{sub 2}{sup +} carbonates have been difficult to observe by UV-Vis-NIR spectroscopy due to the formation of insoluble NaNp{sub 2}O{sub 2}(CO{sub 3}) or Na{sub 3}NpO{sub 2}(CO{sub 3}){sub 2} salts. However, by employing tetrabutylammonium as the counter cation, millimolar concentrations have been obtained and utilized for temperature dependent carbonate complexation studies by conventional UV-Vis-NIR methods. The NpO{sub 2}{sup 2+} carbonate complexes were examined as a function of pH using {sup 13}C and {sup 17}O NMR spectroscopy. The NMR data are consistent with the formation of NpO{sub 2}(CO{sub 3}){sub 3}{sup 4-} and (NpO{sub 2}){sub 3}(CO{sub 3}){sub 6}{sup 6-}. The pH dependence of the {sup 13}C NMR spectra was used to determine the equilibrium constant for the reaction: 3NpO{sub 2}CO{sub 3}{sub 3}{sup 4-} +3H{sup +}{r_reversible}(NpO{sub 2}){sub 3}(CO{sub 3}){sub 6}{sup 6-}+3HCO{sub 3}{sup -}, log K=19.7({plus_minus}0.8) (I=2.5m). This work was supported by the Yucca Mountain Site Characterization Project Office as part of the Civilian Radioactive Waste Management Program, managed by the U.S. D.O.E., YMP project office.

• OSTI ID: 126230
• Report Number(s): CONF-950402--
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
CARBONATES
CHEMICAL REACTIONS
EQUILIBRIUM
HIGH-LEVEL RADIOACTIVE WASTES
NEPTUNIUM OXIDES
NEPTUNYL COMPLEXES
RADIONUCLIDE MIGRATION
SALTS
SOLUBILITY
TUFF
UNDERGROUND DISPOSAL
YUCCA MOUNTAIN