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Title: Electrochemical and spectroscopic evidence on the one-electron reduction of U(VI) to U(V) on magnetite

Abstract

Reduction of U(VI) to U(IV) on mineral surfaces has been considered as a one-step two electron process. However, stabilized U(V), with no evidence of U(IV), found in recent studies indicates U(VI) can undergo a one electron reduction to U(V) without further progression to U(IV). We investigated the mechanisms of uranium reduction by reducing U(VI) electrochemically on a magnetite electrode at pH 3.4 . The one electron reduction of U(VI) was first confirmed using the cyclic voltammetry method. Formation of nano-size uranium precipitates on the surface of magnetite at reducing potentials and dissolution of the solids at oxidizing potentials were observed by in situ electrochemical AFM. XPS analysis of the magnetite electrodes polarized in uranium solutions at voltages from 0.1 ~ 0.9 V (vs. Ag/AgCl) showed the presence of only U(V) and U(VI). The highest amount of U(V) relative to U(VI) was prepared at 0.7 V, where the longest average U–Oaxial distance of 2.05 ± 0.01 Å was evident in the same sample revealed by EXAFS analysis. The results demonstrate that the electrochemical reduction of U(VI) on magnetite only yields U(V), even at a potential of 0.9 V, which favors the one-electron reduction mechanism. U(V) did not disproportionate but stabilized onmore » magnetite through precipitation of mixed-valence state U(VI)/U(V) solids.« less

Authors:
 [1];  [2];  [3];  [1];  [1];  [1]
  1. Univ. of Michigan, Ann Arbor, MI (United States)
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  3. Argonne National Lab. (ANL), Argonne, IL (United States)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1203902
Report Number(s):
PNNL-SA-108945
Journal ID: ISSN 0013-936X; KC0302060
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Environmental Science and Technology
Additional Journal Information:
Journal Volume: 49; Journal Issue: 10; Journal ID: ISSN 0013-936X
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
uranium; magnetite; reduction; electrochemstry

Citation Formats

Yuan, Ke, Ilton, Eugene S., Antonio, Mark R., Li, Zhongrui, Cook, Peter J., and Becker, Udo. Electrochemical and spectroscopic evidence on the one-electron reduction of U(VI) to U(V) on magnetite. United States: N. p., 2015. Web. doi:10.1021/acs.est.5b00025.
Yuan, Ke, Ilton, Eugene S., Antonio, Mark R., Li, Zhongrui, Cook, Peter J., & Becker, Udo. Electrochemical and spectroscopic evidence on the one-electron reduction of U(VI) to U(V) on magnetite. United States. doi:10.1021/acs.est.5b00025.
Yuan, Ke, Ilton, Eugene S., Antonio, Mark R., Li, Zhongrui, Cook, Peter J., and Becker, Udo. Tue . "Electrochemical and spectroscopic evidence on the one-electron reduction of U(VI) to U(V) on magnetite". United States. doi:10.1021/acs.est.5b00025.
@article{osti_1203902,
title = {Electrochemical and spectroscopic evidence on the one-electron reduction of U(VI) to U(V) on magnetite},
author = {Yuan, Ke and Ilton, Eugene S. and Antonio, Mark R. and Li, Zhongrui and Cook, Peter J. and Becker, Udo},
abstractNote = {Reduction of U(VI) to U(IV) on mineral surfaces has been considered as a one-step two electron process. However, stabilized U(V), with no evidence of U(IV), found in recent studies indicates U(VI) can undergo a one electron reduction to U(V) without further progression to U(IV). We investigated the mechanisms of uranium reduction by reducing U(VI) electrochemically on a magnetite electrode at pH 3.4 . The one electron reduction of U(VI) was first confirmed using the cyclic voltammetry method. Formation of nano-size uranium precipitates on the surface of magnetite at reducing potentials and dissolution of the solids at oxidizing potentials were observed by in situ electrochemical AFM. XPS analysis of the magnetite electrodes polarized in uranium solutions at voltages from 0.1 ~ 0.9 V (vs. Ag/AgCl) showed the presence of only U(V) and U(VI). The highest amount of U(V) relative to U(VI) was prepared at 0.7 V, where the longest average U–Oaxial distance of 2.05 ± 0.01 Å was evident in the same sample revealed by EXAFS analysis. The results demonstrate that the electrochemical reduction of U(VI) on magnetite only yields U(V), even at a potential of 0.9 V, which favors the one-electron reduction mechanism. U(V) did not disproportionate but stabilized on magnetite through precipitation of mixed-valence state U(VI)/U(V) solids.},
doi = {10.1021/acs.est.5b00025},
journal = {Environmental Science and Technology},
issn = {0013-936X},
number = 10,
volume = 49,
place = {United States},
year = {2015},
month = {5}
}