<i>In situ</i> study of the synthesis of thorite (ThSiO<sub>4</sub>) under environmental representative conditions

Estevenon, Paul; Causse, Jérémy; Szenknect, Stéphanie; Welcomme, E.; Mesbah, Adel; Moisy, Philippe; Poinssot, Christophe; Dacheux, Nicolas

doi:10.1039/d0dt01790f

Cited by 8 publications

(5 citation statements)

References 36 publications

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“…This could cause the dissolution of another ceramic waste form and allow for the formation of an actinide orthosilicate, with such hypothetical conditions being similar to those used in synthesizing PuSiO 4 . These actinide orthosilicate could be formed first as colloids, which could impact the actinide mobility and allow their transport over important distances. − Thus, here we consider the possible tetravalent states of these heavy transuranic elements and their potential impact on the structural stability.…”

Section: Resultsmentioning

confidence: 99%

Thermodynamics of CeSiO₄: Implications for Actinide Orthosilicates

et al. 2020

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The mineral zircon (ZrSiO 4 : I4 1 /amd) can accommodate natural actinides, such as thorium and uranium. The zircon structure has also been obtained for several of the end member compositions of other actinides, such as plutonium and neptunium. However, the thermodynamic properties of these actinide zircon structure-types are largely unknown due to the difficulties in synthesizing these materials and handling transuranium actinides. Thus, we have completed a thermodynamic study of cerium orthosilicate, stetindite (CeSiO 4), a surrogate of PuSiO 4. For the first time, the standard enthalpy of formation of CeSiO 4 was obtained by high temperature oxide melt solution calorimetry to be-1971.9 ± 3.6 kJ/mol. Stetindite is energetically metastable with respect to CeO 2 and SiO 2 by 27.5 ± 3.1 kJ/mol. The metastability explains the rarity of the natural occurrence of stetindite and the difficulty of its synthesis. Applying the obtained enthalpy of formation of CeSiO 4 from this work, along with those previously reported for USiO 4 and ThSiO 4 , we developed an empirical energetic relation for actinide orthosilicates. The predicted enthalpies of formation of AnSiO 4 are then made with a discussion of future strategies to efficiently immobilize Pu or minor actinides in the zircon structure.

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Section: Resultsmentioning

confidence: 99%

Thermodynamics of CeSiO₄: Implications for Actinide Orthosilicates

et al. 2020

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“…Even if the formation of plutonium silicate complexes and solid plutonium silicate species (or that of other actinide or surrogate elements) has been reported, [5][6][7][8][9][10][11][12] plutonium (IV) chemistry in silicate environment remains poorly understood. Among them, Pu(OSi(OH) 3 ) 3+ was prepared between pH 0.3 and 1.4 in diluted aqueous plutonium and silicate solution and a log(β°) = 11.8 (1) value was evaluated according to equation (1).…”

Section: Introductionmentioning

confidence: 99%

Formation of plutonium(iv) silicate species in very alkaline reactive media

et al. 2021

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“…However, if the redox environment becomes strongly oxidative, a transformation from trivalent actinide silicates to the tetravalent actinide orthosilicate may occur driven by thermodynamics, such as that demonstrated in the case of A-Ce 2 Si 2 O 7 → CeSiO 4 or Ce 4.67 (SiO 4 ) 3 O → CeSiO 4 . Finally, as actinides are known to form nanoparticles in reactive silicate rich fluids, − it could enable the actinide silicate complexes or compounds to be transported in colloidal forms immense distances away from a breached canister if the particles would not settle. , …”

Section: Discussionmentioning

confidence: 99%

“…Radionuclides, especially actinides (An), when leaked from the multibarrier systems may interact with silicate-rich fluids. They could potentially form An-silicate colloids, − solid particles, ,, or An-silicate aqueous complexes , under either hydrothermal conditions presented in the early stages of the repository or ambient conditions in either the late stages of the repository or down the hydrogeological gradient. Such concerns are further justified as it has been previously demonstrated that Pu and other actinides can be transported on immense distances in the colloidal forms. − …”

Section: Introductionmentioning

confidence: 99%

High-Temperature Thermodynamics of Cerium Silicates, A-Ce₂Si₂O₇, and Ce_4.67(SiO₄)₃O

Strzelecki

Kriegsman

Estevenon

et al. 2020

ACS Earth Space Chem.

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Lanthanide disilicates and oxyapatites have potential roles in high temperature applications as thermal (TBC) and environmental barrier coatings (EBC), or possible alteration phases in geological nuclear waste respositories. However, those Ce 3+-bearing silicates have only been limitedly studied. In this work we performed detailed structural and thermodynamic investigations on ACe 2 Si 2 O 7 (tetragonal, P4 1) and Ce 4.67 (SiO 4) 3 O (hexagonal, P6 3 /m). The high temperature structural behaviors and coefficients of thermal expansion were determined by in situ high temperature synchrotron X-ray diffraction (HT-XRD) implemented with Rietveld analysis and thermogravimetric analysis coupled with differential scanning calorimetry (TGA-DSC). ACe 2 Si 2 O 7 was found to be stable in N 2 and air up to ~1483 K with an isotropic thermal expansion (α a = 12.3 × 10-6 K-1 and α c = 12.4 × 10-6 K-1). Ce 4.67 (SiO 4) 3 O had a slow partial oxidation between 533 K and 873 K to a new nonstoichemitric phase Ce 3+ 1.67-x Ce 4+ x Ce 3+ 3 (SiO 4) 3 O 1+0.5x , followed by a thermal decomposition to CeO 2 and SiO 2 at ~1000 K. By using high temperature oxide melt solution calorimetry at 973 K with lead borate as solvent, we determined, for the first time, the standard enthalpy of formation of ACe 2 Si 2 O 7 (-3825.1 ± 6.0 kJ/mol) and Ce 4.67 (SiO 4) 3 O (-7391.3 ± 9.5 kJ/mol). These thermodynamic paramters were compared with those of CeO 2 , CeSiO 4 , and other silicate oxyapatites for examining their chemical stability in high temperature environments relevent for aeronautical applications, mineral formation, and nuclear fuel cycle.

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In situ study of the synthesis of thorite (ThSiO₄) under environmental representative conditions

Abstract: Thorite, (ThSiO4 ) with Zircon type structure, is one of the most abundant natural sources of thorium on earth. Generally, actinides are known to form nanoparticles in silicate medium, though...

Cited by 8 publications

References 36 publications

Thermodynamics of CeSiO₄: Implications for Actinide Orthosilicates

Thermodynamics of CeSiO₄: Implications for Actinide Orthosilicates

Formation of plutonium(iv) silicate species in very alkaline reactive media

High-Temperature Thermodynamics of Cerium Silicates, A-Ce₂Si₂O₇, and Ce_4.67(SiO₄)₃O

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In situ study of the synthesis of thorite (ThSiO4) under environmental representative conditions

Abstract: Thorite, (ThSiO4 ) with Zircon type structure, is one of the most abundant natural sources of thorium on earth. Generally, actinides are known to form nanoparticles in silicate medium, though...

Cited by 8 publications

References 36 publications

Thermodynamics of CeSiO4: Implications for Actinide Orthosilicates

Thermodynamics of CeSiO4: Implications for Actinide Orthosilicates

Formation of plutonium(iv) silicate species in very alkaline reactive media

High-Temperature Thermodynamics of Cerium Silicates, A-Ce2Si2O7, and Ce4.67(SiO4)3O

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In situ study of the synthesis of thorite (ThSiO₄) under environmental representative conditions

Thermodynamics of CeSiO₄: Implications for Actinide Orthosilicates

Thermodynamics of CeSiO₄: Implications for Actinide Orthosilicates

High-Temperature Thermodynamics of Cerium Silicates, A-Ce₂Si₂O₇, and Ce_4.67(SiO₄)₃O