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Comins MB, Kaplan U, Beam J, Navarrette A, Hixon AE. Plutonium Speciation and Oxidation State Distributions in the Presence of Citrate. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2024; 58:15766-15778. [PMID: 39163648 DOI: 10.1021/acs.est.4c02803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/22/2024]
Abstract
We explored the speciation and kinetics of the Pu(VI)-citrate and Pu(III)-citrate systems (pHm = 2.5-11.0, I = 0.1 M NaCl, T = 23 °C, O2(g) < 2 ppm) using ultraviolet-visible-near-infrared (UV-vis-NIR) spectrophotometry, solvent extraction, and PHREEQC modeling. Formation constants were determined for PuO2(HcitH)(aq) (log K°1,1 = 1.09 ± 0.05) and PuO2(HcitH)(citH)3- (log K°1,2 = -0.20 ± 0.07), and evidence for (PuO2)m(citH-k)n(OH)x2m(3+k)n-x was identified under alkaline conditions. Pu(VI) species were found to be less stable in the presence of citrate than in the absence of citrate (t ≤ 168 days); the rate of reduction increased with increasing pH. The direct reduction of Pu(VI) to Pu(IV) was required to fit experimental data in the presence of citrate but did not improve the fit for Pu in the absence of citrate. We also observed increased Pu(III) stability in the presence of citrate (t ≤ 293 days), with higher concentrations of Pu(III) favored at lower pH. Finally, we provide evidence of a radiolysis-driven mechanism for the citrate-mediated reduction of plutonium that involves electron transfer from the oxidative breakdown of citrate. Our work highlights the need to investigate the redox effect of organic ligands on plutonium oxidation states under repository-relevant conditions.
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Affiliation(s)
- Matthew B Comins
- Department of Civil & Environmental Engineering & Earth Sciences, University of Notre Dame, 301 Stinson-Remick, Notre Dame, Indiana 46556, United States
| | - Ugras Kaplan
- Los Alamos National Laboratory, 1400 University Drive, Carlsbad, New Mexico 88220, United States
| | - Jeremiah Beam
- Los Alamos National Laboratory, 1400 University Drive, Carlsbad, New Mexico 88220, United States
| | - Adrianne Navarrette
- Los Alamos National Laboratory, 1400 University Drive, Carlsbad, New Mexico 88220, United States
| | - Amy E Hixon
- Department of Civil & Environmental Engineering & Earth Sciences, University of Notre Dame, 301 Stinson-Remick, Notre Dame, Indiana 46556, United States
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Comins MB, Shang C, Polly R, Skerencak-Frech A, Altmaier M, Hixon AE, Gaona X. Cm(III) speciation in the presence of citrate from neutral to hyperalkaline conditions and the effect of calcium. CHEMOSPHERE 2024; 364:143233. [PMID: 39222691 DOI: 10.1016/j.chemosphere.2024.143233] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2024] [Revised: 08/29/2024] [Accepted: 08/30/2024] [Indexed: 09/04/2024]
Abstract
We investigated the binary Cm-citrate system using time-resolved laser fluorescence spectroscopy (TRLFS), parallel factor analysis (PARAFAC), and quantum chemical calculations. Evidence collectively suggests the stepwise coordination and deprotonation of citrate alcohol groups in Cm-cit complexes with two bound citrate moieties upon increasing pH, which is supported by a bathochromic shift in emission spectra, an observed increase in lifetime measurements, and lower energy minima for citrate alcohol involvement versus hydrolysis of the Cm-citrate species. Our PARAFAC results agree with a 3-component model for the Cm-citrate system and offer pure component decompositions, yielding fraction species across the studied pH range that have a correlated slope = 1 as a function of pH. For the first time, evidence of ternary Ca-Cm-citrate complexes was revealed by TRLFS with increasing calcium concentration at fixed pHm. The formation of these ternary complexes was substantiated with density functional theory (DFT) calculations on simple model systems of the complexes. Shared citrate carboxylate groups between calcium and curium were proposed for all three ternary Ca-Cm-cit complexes based on DFT-determined Ca-O and Cm-O distances. Moreover, we found that the ternary complex with both alcohol groups deprotonated is most stable when it shares both two carboxylate and two alcohol groups between Ca and Cm. The presence of shared functional groups highlights the enhanced stability of these ternary complexes. Additional work is warranted to further constrain the stoichiometry, stability constants and dependence on ionic strength of these complexes for purposes of thermodynamic modeling of repository settings.
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Affiliation(s)
- Matthew B Comins
- Department of Civil & Environmental Engineering & Earth Sciences, University of Notre Dame, 301 Stinson-Remick, Notre Dame, IN, 46556, USA.
| | - Chengming Shang
- Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal, P.O. Box 3640, Karlsruhe, 76021, Germany.
| | - Robert Polly
- Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal, P.O. Box 3640, Karlsruhe, 76021, Germany.
| | - Andrej Skerencak-Frech
- Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal, P.O. Box 3640, Karlsruhe, 76021, Germany.
| | - Marcus Altmaier
- Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal, P.O. Box 3640, Karlsruhe, 76021, Germany.
| | - Amy E Hixon
- Department of Civil & Environmental Engineering & Earth Sciences, University of Notre Dame, 301 Stinson-Remick, Notre Dame, IN, 46556, USA.
| | - Xavier Gaona
- Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal, P.O. Box 3640, Karlsruhe, 76021, Germany.
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Bai Z, Beck NB, Scheibe B, Sperling JM, Weiland A, Ruf M, Brannon JP, Rotermund BM, Gomez Martinez D, Albrecht-Schönzart TE. Investigation of Pressure Effects in the Bimetallic Transplutonium Tetrazolate Complexes [(An(pmtz) 2(H 2O) 3) 2(μ-pmtz)] 2(pmtz) 2· nH 2O (An 3+ = Cm 3+, Bk 3+, and Cf 3+). J Am Chem Soc 2024; 146:7822-7830. [PMID: 38456811 DOI: 10.1021/jacs.4c00803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/09/2024]
Abstract
Understanding the effects of pressure on actinide compounds is an integral part of safe nuclear waste storage in deep geologic repositories and provides a means of systematically altering the structure and properties. However, detailing how the effects of pressure evolve across the actinide series in the later elements is not typically undertaken because of the challenges of conducting research on these unstable isotopes. Here, a family of bimetallic actinide complexes, [(An(pmtz)2(H2O)3)2(μ-pmtz)]2(pmtz)2·nH2O (An3+ = Cm3+, Bk3+, and Cf3+, pmtz- = 5-(pyrimidyl)tetrazolate; Cm1, Bk1, and Cf1), are reported and represent the first structurally characterized bimetallic berkelium and californium compounds. The pressure response as determined from UV-vis-NIR transitions varies for Cm1, Bk1, and Cf1. The 5f → 5f transitions in Cm1 are notably more sensitive to pressure compared to those in Bk1 and Cf1 and show substantial bathochromic shifting of several 5f → 5f transitions. In the case of Bk1, an ingrowth of a metal-to-ligand charge-transfer transition occurs at elevated pressures because of the accessible Bk3+/Bk4+ couple. For Cf1, no substantial transition shifting or emergence of MLCT transitions is observed at elevated pressures because of the prohibitive energetics of the Cf3+/Cf4+ couple and reduced sensitivity of the 5f → 5f transitions to the local coordination environment because of the more contracted 5f shell versus Cm3+ and Bk3+.
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Affiliation(s)
- Zhuanling Bai
- Department of Chemistry and Nuclear Science & Engineering Center, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Nicholas B Beck
- Department of Chemistry and Nuclear Science & Engineering Center, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Benjamin Scheibe
- Department of Chemistry and Nuclear Science & Engineering Center, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Joseph M Sperling
- Department of Chemistry and Nuclear Science & Engineering Center, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Ashley Weiland
- Bruker AXS, 5465 E Cheryl Pkwy, Fitchburg, Madison, Wisconsin 53711, United States
| | - Michael Ruf
- Bruker AXS, 5465 E Cheryl Pkwy, Fitchburg, Madison, Wisconsin 53711, United States
| | - Jacob P Brannon
- Department of Chemistry and Nuclear Science & Engineering Center, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Brian M Rotermund
- Department of Chemistry and Nuclear Science & Engineering Center, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Daniela Gomez Martinez
- Department of Chemistry and Nuclear Science & Engineering Center, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Thomas E Albrecht-Schönzart
- Department of Chemistry and Nuclear Science & Engineering Center, Colorado School of Mines, Golden, Colorado 80401, United States
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DiMucci IM, Root HD, Jones ZR, Kozimor SA, MacInnes MM, Miller JL, Mocko V, Oldham WJ, Stein BW. Photochemical separation of plutonium from uranium. Chem Commun (Camb) 2022; 58:10961-10964. [PMID: 36083292 DOI: 10.1039/d2cc04225h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Plutonium-based technologies would benefit if chemical hazards for purifying plutonium were reduced. One critical processing step where improvements could be impactful is the adjustment of plutonium oxidation-states during separations. This transformation often requires addition of redox agents. Unfortunately, many of the redox agents used previously cannot be used today because their properties are deemed incompatible with modern day processing facilities and waste stream safety requirements. We demonstrated herein that photochemistry can be used as an alternative to those chemical agents. We observed that (1) Pu4+ → Pu3+ and UO22+ → U4+ photoreduction proceeded in HCl(aq) and HNO3(aq) and (2) photogenerated Pu3+(aq) and U4+(aq) could be separated using anion exchange chromatography (high yield, >90%; good separation factor, 322).
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Affiliation(s)
- Ida M DiMucci
- Los Alamos National Laboratory, P. O. Box 1663, Los Alamos, NM, 87544, USA.
| | - Harrison D Root
- Los Alamos National Laboratory, P. O. Box 1663, Los Alamos, NM, 87544, USA.
| | - Zachary R Jones
- Los Alamos National Laboratory, P. O. Box 1663, Los Alamos, NM, 87544, USA.
| | - Stosh A Kozimor
- Los Alamos National Laboratory, P. O. Box 1663, Los Alamos, NM, 87544, USA.
| | - Molly M MacInnes
- Los Alamos National Laboratory, P. O. Box 1663, Los Alamos, NM, 87544, USA.
| | - Jeffrey L Miller
- Los Alamos National Laboratory, P. O. Box 1663, Los Alamos, NM, 87544, USA.
| | - Veronika Mocko
- Los Alamos National Laboratory, P. O. Box 1663, Los Alamos, NM, 87544, USA.
| | - Warren J Oldham
- Los Alamos National Laboratory, P. O. Box 1663, Los Alamos, NM, 87544, USA.
| | - Benjamin W Stein
- Los Alamos National Laboratory, P. O. Box 1663, Los Alamos, NM, 87544, USA.
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Cho S, Kim HK, Kim TH, Cha W, Cho HR. Thermodynamic Studies on the Hydrolysis of Trivalent Plutonium and Solubility of Pu(OH) 3(am). Inorg Chem 2022; 61:12643-12651. [PMID: 35921136 DOI: 10.1021/acs.inorgchem.2c01590] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The temperature-dependent reaction properties of actinide elements are of particular interest in the safety assessment of high-level radioactive waste (HLRW) disposal systems. In this study, the hydrolysis of Pu(III) and the solubility of Pu(OH)3(am) were investigated at various temperatures (10-40 °C) in 0.1 M NaClO4. A strong reducing condition for maintaining the oxidation state of Pu(III) while slowly increasing the pH of the solution was realized by electrolysis. The formation constants of the first hydrolysis species, log *β1', and the solubility products of Pu(OH)3(am), log *Ks,0', at 10, 17, and 40 °C were experimentally determined using spectrophotometry, laser-induced breakdown detection, and radiometry. The enthalpy and entropy changes for these reactions were estimated using the van't Hoff equation. The first hydrolysis of Pu(III) is endothermic (ΔrHm° = 34.10 ± 4.48 kJ mol-1), and the dissolution of Pu(OH)3(am) is exothermic (ΔrHm° = -294.29 ± 23.05 kJ mol-1) with negative entropy changes. These thermodynamic data will contribute to improving the reliability of the safety assessment of HLRW disposal facilities and understanding the geochemical behavior of Pu under reducing or anoxic aqueous conditions at elevated temperatures.
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Affiliation(s)
- Sangki Cho
- Nuclear Chemistry Research Team, Korea Atomic Energy Research Institute, Daejeon 34057, Republic of Korea.,Department of Radiochemistry and Nuclear Nonproliferation, University of Science and Technology (UST), Daejeon 34113, Republic of Korea
| | - Hee-Kyung Kim
- Nuclear Chemistry Research Team, Korea Atomic Energy Research Institute, Daejeon 34057, Republic of Korea
| | - Tae-Hyeong Kim
- Nuclear Chemistry Research Team, Korea Atomic Energy Research Institute, Daejeon 34057, Republic of Korea
| | - Wansik Cha
- Nuclear Chemistry Research Team, Korea Atomic Energy Research Institute, Daejeon 34057, Republic of Korea
| | - Hye-Ryun Cho
- Nuclear Chemistry Research Team, Korea Atomic Energy Research Institute, Daejeon 34057, Republic of Korea.,Department of Radiochemistry and Nuclear Nonproliferation, University of Science and Technology (UST), Daejeon 34113, Republic of Korea
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Formation of mono- and binuclear complexes of Nd3+ with d-gluconate ions in hyperalkaline solutions – Composition, equilibria and structure. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2021.117047] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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