Plutonium carbonate speciation changes as measured in dilute solutions with photoacoustic spectroscopy: Yucca Mountain Site Characterization Program Milestone report 3350

Technical Report · Mon May 01 04:00:00 EDT 1995

DOI:https://doi.org/10.2172/70775· OSTI ID:70775

Tait, C D; Ekberg, S A; Palmer, P D; Morris, D E

The stability fields for dilute Pu-carbonate species versus pH (8.4 to 12.0) and total carbonate concentrations (3 mM to 1.0 M) have been mapped-out using photoacoustic absorption spectroscopy (PAS). At least four different plutonium species, characterized by absorption peaks at 486, 492, 500, and 513 rim, have been found. A redox change to a Pu(VI) complex can not account for the speciation change associated with the first two spectra (486 and 492 nm peaks). Moreover, the data are consistent with what is predicted from a previous YMP milestone. This previous study was performed under very different conditions of plutonium concentration and carbonate/pH changes, and extension of these conditions to much lower Pu concentrations and to more neutral pHs was made possible with PAS spectroscopy. These new results reinforce the previous results by extending the range of direct observation and by eliminating other possibilities such as dimerization/polymerization reactions. As bicarbonate concentration is increased from .01 M to 1.0 M at pH=8.4 to 8.9, predominately [Pu(OH){sub x+1}(CO{sub 3}){sub y}]{sup 4-(x+2y)} (492 nm peak) is converted to [Pu(OH){sub x}(CO{sub 3}){sub y+l}]{sup 4-(x+2y+2)} (486 nm peak). The starting stoichiometry (x and y values) remain undetermined, but the effect of ionic strength and temperature indicate that the 486 nm species is highly charged, and therefore x+2y{ge}3. The temperature effect on the equilibrium between these two species was also investigated, with the species giving rise to the 486 nm peak reversibly losing importance at elevated (50 and 75{degrees}C temperatures).

• Research Organization: Los Alamos National Lab., NM (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 70775
• Report Number(s): LA--12886-MS; ON: DE95012118
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
40 CHEMISTRY
AQUEOUS SOLUTIONS
CARBONATES
CHEMICAL REACTIONS
GROUND WATER
HIGH-LEVEL RADIOACTIVE WASTES
PH VALUE
PLUTONIUM
RADIONUCLIDE MIGRATION
SOLUBILITY
SORPTION
TEMPERATURE DEPENDENCE
TUFF
UNDERGROUND DISPOSAL
VALENCE
YUCCA MOUNTAIN
Yucca Mountain Project