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Title: Redox behavior of Ce(IV)/Ce(III) in the presence of nitrilotriacetic acid: A surrogate study for An(I\T)/AD(III) redox behavior

Abstract

Using cyclic voltammetry, we investigated the redox behavior of Ce(IV)/Ce(III), which is a surrogate for An(IV)/An(III) (An=actinides), in a solution of nitrilotriacetic acid (NTA) at 25 C. The cyclic voltammogram of Ce in a 0.1 M NTA solution at pH 6 showed a reversible one-electron redox reaction for Ce(IV)/Ce(III) at 0.51 V vs. Ag/AgCl. This redox potential was much lower than that obtained in 1 M nitric acid, indicating that Ce(IV) was preferentially stabilized by complexation with NTA. The redox potential in the NTA solution was independent of the Ce concentration from 2 to 20 mM, NTA concentration from 5 to 200 mM and pH between 3 and 7. These results indicated that no polymerization and no additional coordination of NTA and OH{sup -} to the Ce(III)-NTA complex took place during the redox reaction. As the speciation calculation of Ce(III) in the NTA solution showed that the predominant species was Ce{sup III}(nta){sub 2}{sup 3-} (H{sub 3}nta = NTA), the redox reaction of the Ce-NTA complex was expressed by the following: Ce{sup IV}(nta){sub 2}{sup 2-} +e{sup -} Ce{sup III}(nta){sub 2}{sup 3-}. The logarithm of the stability constant of Ce{sup IV}(nta){sub 2}{sup 2-} was calculated to be 38.6 {+-} 0.8 for Imore » = 0 from the redox potential shift of Ce(IV)/Ce(III) in the NTA solution. The value was in good accordance with the stability constant of the Np{sup IV}(nta){sub 2}{sup 2-} complex, demonstrating that the aqueous coordination chemistry of Ce(IV) with NTA is quite similar to that of An(IV). These results strongly suggest that a negative shift of the Pu(IV)/Pu(III) redox potential in the NTA solution should make Pu(IV) more stable than Pu(III) even in a reducing environment.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
990253
Report Number(s):
BNL-93847-2010-JA
Journal ID: ISSN 0033-8230; RAACAP; R&D Project: EE-639-EEDA; KP1504010; TRN: US201020%%256
DOE Contract Number:  
DE-AC02-98CH10886
Resource Type:
Journal Article
Journal Name:
Radiochimica Acta
Additional Journal Information:
Journal Volume: 98; Journal Issue: 7; Journal ID: ISSN 0033-8230
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; CHEMISTRY; NITRIC ACID; NTA; POLYMERIZATION; REDOX POTENTIAL; REDOX REACTIONS; STABILITY

Citation Formats

Suzuki, Y, Francis, A, Nankawa, T, and Ohnuki, T. Redox behavior of Ce(IV)/Ce(III) in the presence of nitrilotriacetic acid: A surrogate study for An(I\T)/AD(III) redox behavior. United States: N. p., 2010. Web. doi:10.1524/ract.2010.1735.
Suzuki, Y, Francis, A, Nankawa, T, & Ohnuki, T. Redox behavior of Ce(IV)/Ce(III) in the presence of nitrilotriacetic acid: A surrogate study for An(I\T)/AD(III) redox behavior. United States. https://doi.org/10.1524/ract.2010.1735
Suzuki, Y, Francis, A, Nankawa, T, and Ohnuki, T. 2010. "Redox behavior of Ce(IV)/Ce(III) in the presence of nitrilotriacetic acid: A surrogate study for An(I\T)/AD(III) redox behavior". United States. https://doi.org/10.1524/ract.2010.1735.
@article{osti_990253,
title = {Redox behavior of Ce(IV)/Ce(III) in the presence of nitrilotriacetic acid: A surrogate study for An(I\T)/AD(III) redox behavior},
author = {Suzuki, Y and Francis, A and Nankawa, T and Ohnuki, T},
abstractNote = {Using cyclic voltammetry, we investigated the redox behavior of Ce(IV)/Ce(III), which is a surrogate for An(IV)/An(III) (An=actinides), in a solution of nitrilotriacetic acid (NTA) at 25 C. The cyclic voltammogram of Ce in a 0.1 M NTA solution at pH 6 showed a reversible one-electron redox reaction for Ce(IV)/Ce(III) at 0.51 V vs. Ag/AgCl. This redox potential was much lower than that obtained in 1 M nitric acid, indicating that Ce(IV) was preferentially stabilized by complexation with NTA. The redox potential in the NTA solution was independent of the Ce concentration from 2 to 20 mM, NTA concentration from 5 to 200 mM and pH between 3 and 7. These results indicated that no polymerization and no additional coordination of NTA and OH{sup -} to the Ce(III)-NTA complex took place during the redox reaction. As the speciation calculation of Ce(III) in the NTA solution showed that the predominant species was Ce{sup III}(nta){sub 2}{sup 3-} (H{sub 3}nta = NTA), the redox reaction of the Ce-NTA complex was expressed by the following: Ce{sup IV}(nta){sub 2}{sup 2-} +e{sup -} Ce{sup III}(nta){sub 2}{sup 3-}. The logarithm of the stability constant of Ce{sup IV}(nta){sub 2}{sup 2-} was calculated to be 38.6 {+-} 0.8 for I = 0 from the redox potential shift of Ce(IV)/Ce(III) in the NTA solution. The value was in good accordance with the stability constant of the Np{sup IV}(nta){sub 2}{sup 2-} complex, demonstrating that the aqueous coordination chemistry of Ce(IV) with NTA is quite similar to that of An(IV). These results strongly suggest that a negative shift of the Pu(IV)/Pu(III) redox potential in the NTA solution should make Pu(IV) more stable than Pu(III) even in a reducing environment.},
doi = {10.1524/ract.2010.1735},
url = {https://www.osti.gov/biblio/990253}, journal = {Radiochimica Acta},
issn = {0033-8230},
number = 7,
volume = 98,
place = {United States},
year = {Thu Jul 01 00:00:00 EDT 2010},
month = {Thu Jul 01 00:00:00 EDT 2010}
}