Production of anhydrous f-element fluorides through the ionothermal treatment of f-element oxalates

Elodia Ciprian; Bryan J. Foley; Tyler L. Spano; Andrew Miskowiec; Thomas Shehee; Amy E. Hixon

doi:10.1016/j.jnucmat.2025.155983

Production of anhydrous f-element fluorides through the ionothermal treatment of f-element oxalates

Elodia Ciprian, Bryan J. Foley, Tyler L. Spano, Andrew Miskowiec, Thomas Shehee, Amy E. Hixon

Materials & Chemistry Group

Research output: Contribution to journal › Article › peer-review

Abstract

The pivotal role of uranium and plutonium fluorides in the nuclear fuel cycle, particularly in the pyrochemical reduction process, is well recognized. Traditionally, the fluorination of uranium and plutonium materials relies on the use of highly toxic and corrosive gases (e.g., HF_(g), F_2(g)). Herein, we present an alternative approach using the ionic liquid 1‑butyl‑3-methylimidazolium hexafluorophosphate ([Bmim][PF₆]_(l)) and/or hexafluorophosphoric acid (HPF_6(aq)) as fluorinating agents for the f-element oxalates M₂^III(C₂O₄)₃·9H₂O(s)M₂^III(C₂O₄)₃·9H₂O_(s) (M^III = Ce, Pu) and M^IV(C₂O₄)₂·6H₂O_(s) (M^IV = Th, U). Our findings demonstrate that [Bmim][PF₆]_(l) and HPF_6(aq) enable the ionothermal fluorination of f-element oxalates, resulting in the formation of anhydrous CeF_3(s), ThF_4(s), and UF_4(s) within 2 hours at 200 °C. This method also facilitates the partial fluorination of plutonium(III) oxalate, yielding a mixture of anhydrous PuF_3(s) and an unidentified phase. Overall, the ionothermal treatment approach offers a safer and more efficient means of producing anhydrous f-element fluorides than conventional methods involving hazardous gases. In addition, we describe the morphology of UF_4(s) materials as a function of production route and demonstrate the presence of morphological signatures that could be used during a nuclear forensic investigation.

Original language	English
Article number	155983
Journal	Journal of Nuclear Materials
Volume	615
DOIs	https://doi.org/10.1016/j.jnucmat.2025.155983
State	Published - Sep 2025

Funding

The authors would like to thank Brodie Barth for providing the thorium and uranium oxalates used in this study. This work is supported by a collaboration between the University of Notre Dame, Oak Ridge National Laboratory, and Savannah River National Laboratory under funding from the US Department of Energy, National Nuclear Security Administration, Office of Defense Nuclear Nonproliferation Research and Development.

Keywords

Cerium
Ionothermal synthesis
Morphology
Nuclear forensics
Plutonium
Thorium
Uranium

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10.1016/j.jnucmat.2025.155983

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title = "Production of anhydrous f-element fluorides through the ionothermal treatment of f-element oxalates",

abstract = "The pivotal role of uranium and plutonium fluorides in the nuclear fuel cycle, particularly in the pyrochemical reduction process, is well recognized. Traditionally, the fluorination of uranium and plutonium materials relies on the use of highly toxic and corrosive gases (e.g., HF(g), F2(g)). Herein, we present an alternative approach using the ionic liquid 1‑butyl‑3-methylimidazolium hexafluorophosphate ([Bmim][PF6](l)) and/or hexafluorophosphoric acid (HPF6(aq)) as fluorinating agents for the f-element oxalates M2III(C2O4)3·9H2O(s)M2III(C2O4)3·9H2O(s) (MIII = Ce, Pu) and MIV(C2O4)2·6H2O(s) (MIV = Th, U). Our findings demonstrate that [Bmim][PF6](l) and HPF6(aq) enable the ionothermal fluorination of f-element oxalates, resulting in the formation of anhydrous CeF3(s), ThF4(s), and UF4(s) within 2 hours at 200 °C. This method also facilitates the partial fluorination of plutonium(III) oxalate, yielding a mixture of anhydrous PuF3(s) and an unidentified phase. Overall, the ionothermal treatment approach offers a safer and more efficient means of producing anhydrous f-element fluorides than conventional methods involving hazardous gases. In addition, we describe the morphology of UF4(s) materials as a function of production route and demonstrate the presence of morphological signatures that could be used during a nuclear forensic investigation.",

keywords = "Cerium, Ionothermal synthesis, Morphology, Nuclear forensics, Plutonium, Thorium, Uranium",

author = "Elodia Ciprian and Foley, \{Bryan J.\} and Spano, \{Tyler L.\} and Andrew Miskowiec and Thomas Shehee and Hixon, \{Amy E.\}",

note = "Publisher Copyright: {\textcopyright} 2025",

year = "2025",

month = sep,

doi = "10.1016/j.jnucmat.2025.155983",

language = "English",

volume = "615",

journal = "Journal of Nuclear Materials",

issn = "0022-3115",

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TY - JOUR

T1 - Production of anhydrous f-element fluorides through the ionothermal treatment of f-element oxalates

AU - Ciprian, Elodia

AU - Foley, Bryan J.

AU - Spano, Tyler L.

AU - Miskowiec, Andrew

AU - Shehee, Thomas

AU - Hixon, Amy E.

PY - 2025/9

Y1 - 2025/9

N2 - The pivotal role of uranium and plutonium fluorides in the nuclear fuel cycle, particularly in the pyrochemical reduction process, is well recognized. Traditionally, the fluorination of uranium and plutonium materials relies on the use of highly toxic and corrosive gases (e.g., HF(g), F2(g)). Herein, we present an alternative approach using the ionic liquid 1‑butyl‑3-methylimidazolium hexafluorophosphate ([Bmim][PF6](l)) and/or hexafluorophosphoric acid (HPF6(aq)) as fluorinating agents for the f-element oxalates M2III(C2O4)3·9H2O(s)M2III(C2O4)3·9H2O(s) (MIII = Ce, Pu) and MIV(C2O4)2·6H2O(s) (MIV = Th, U). Our findings demonstrate that [Bmim][PF6](l) and HPF6(aq) enable the ionothermal fluorination of f-element oxalates, resulting in the formation of anhydrous CeF3(s), ThF4(s), and UF4(s) within 2 hours at 200 °C. This method also facilitates the partial fluorination of plutonium(III) oxalate, yielding a mixture of anhydrous PuF3(s) and an unidentified phase. Overall, the ionothermal treatment approach offers a safer and more efficient means of producing anhydrous f-element fluorides than conventional methods involving hazardous gases. In addition, we describe the morphology of UF4(s) materials as a function of production route and demonstrate the presence of morphological signatures that could be used during a nuclear forensic investigation.

AB - The pivotal role of uranium and plutonium fluorides in the nuclear fuel cycle, particularly in the pyrochemical reduction process, is well recognized. Traditionally, the fluorination of uranium and plutonium materials relies on the use of highly toxic and corrosive gases (e.g., HF(g), F2(g)). Herein, we present an alternative approach using the ionic liquid 1‑butyl‑3-methylimidazolium hexafluorophosphate ([Bmim][PF6](l)) and/or hexafluorophosphoric acid (HPF6(aq)) as fluorinating agents for the f-element oxalates M2III(C2O4)3·9H2O(s)M2III(C2O4)3·9H2O(s) (MIII = Ce, Pu) and MIV(C2O4)2·6H2O(s) (MIV = Th, U). Our findings demonstrate that [Bmim][PF6](l) and HPF6(aq) enable the ionothermal fluorination of f-element oxalates, resulting in the formation of anhydrous CeF3(s), ThF4(s), and UF4(s) within 2 hours at 200 °C. This method also facilitates the partial fluorination of plutonium(III) oxalate, yielding a mixture of anhydrous PuF3(s) and an unidentified phase. Overall, the ionothermal treatment approach offers a safer and more efficient means of producing anhydrous f-element fluorides than conventional methods involving hazardous gases. In addition, we describe the morphology of UF4(s) materials as a function of production route and demonstrate the presence of morphological signatures that could be used during a nuclear forensic investigation.

KW - Cerium

KW - Ionothermal synthesis

KW - Morphology

KW - Nuclear forensics

KW - Plutonium

KW - Thorium

KW - Uranium

UR - https://www.scopus.com/pages/publications/105008498350

U2 - 10.1016/j.jnucmat.2025.155983

DO - 10.1016/j.jnucmat.2025.155983

M3 - Article

AN - SCOPUS:105008498350

SN - 0022-3115

VL - 615

JO - Journal of Nuclear Materials

JF - Journal of Nuclear Materials

M1 - 155983

ER -

Production of anhydrous f-element fluorides through the ionothermal treatment of f-element oxalates

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