ChemInform Abstract: Coffinite, USiO<sub>4</sub>, Is Abundant in Nature: So Why Is It So Difficult to Synthesize?

Mesbah, Adel; Szenknect, Stéphanie; Clavier, Nicolas; Lozano-Rodriguez, Janeth; Poinssot, Christophe; Auwer, Christophe Den; Ewing, Rodney C.

doi:10.1002/chin.201539020

Cited by 7 publications

(17 citation statements)

References 1 publication

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“…from the Rietveld refinement (Table 2). The complete characterization of the synthesized solids has been reported by Mesbah et al, (2015) in order to confirm that only U(IV) was present in the solids. In addition, EXAFS and Raman spectroscopies were used to confirm that only U(IV)-based compounds were obtained from the synthesized and purified powders, consistent with previous reports on coffinite (Clavier et al, 2014;Dreissig et al, 2011).…”

Section: Characteristics Of the Solidsmentioning

confidence: 96%

“…Basically, the same procedure was followed; however, the pH was raised to 12.5 before buffering the pH to 8.7. Mesbah et al (2015) determined the optimal conditions in terms of pH, T, heating time and molar ratio of U:Si for the hydrothermal synthesis of coffinite.…”

Section: Synthesis Of Solid Phasesmentioning

confidence: 99%

“…More importantly, the role of silicates in this experiment is not taken into account in the evaluation of tetravalent uranium speciation. The existence of U(IV)-Si(IV) complexes is undocumented, but they could play an important role in coffinite formation (Mesbah et al, 2015). Due to similar charge and ionic radius, the analogy between U(IV) and Th can be made.…”

Section: Dissolution Experimentsmentioning

confidence: 99%

“…Mercadier et al (2011) estimate that the temperature of the mineralizing fluids in the Athabasca basin deposits (Canada), where uraninite and coffinite precipitated in the uranium front, were not higher than 50°C. Mesbah et al (2015) showed that, under appropriate conditions, small amounts of coffinite in a UO 2 plus SiO 2 (amorphous) mixture can be obtained by hydrothermal treatment at 150°C. The low yield of coffinite at low temperatures may result from slow kinetics of nucleation, but hydrothermal conditions would not be required to precipitate coffinite.…”

Section: Environmental Implicationsmentioning

confidence: 99%

“…Most importantly, the impact of silica in solution is not taken into account in the evaluation of tetravalent uranium speciation; as a result, the evaluation of UO 2 solubility in silica-rich groundwater based on the currently available thermodynamic data may not be correct. The existence of U(IV)-Si(IV) complexes is speculative, but Mesbah et al (2015) suggested that these complexes could play an important role in coffinite formation. The existence of mono-or poly-nuclear complexes of U(IV) with silicates and hydroxydes, as it was evidenced for Th by Peketroukhine et al (2002) and Rai et al (2008), would significantly increase the solubility of UO 2 under alkaline conditions and favor coffinite precipitation.…”

Section: Environmental Implicationsmentioning

confidence: 99%

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First experimental determination of the solubility constant of coffinite

Szenknect

Mesbah

Cordara

et al. 2016

Geochimica et Cosmochimica Acta

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Dissolution experiments have been performed in order to determine the solubility constant of coffinite, USiO 4. Several assemblages of phases were used in under-saturated experiments performed in 0.1 mol L-1 HCl under Ar atmosphere, as well as in air. These samples were fully-characterized and were composed of either USiO 4 , solely, or USiO 4 and additional oxide byproducts that resulted from the synthesis procedure. The solubility constant of coffinite was determined at 25°C and 1 bar (log *K S°(USiO 4 , cr) =-5.25 ± 0.05), as well as the standard free energy of formation of coffinite (Δ f G°(298 K) =-1867.6 ± 3.2 kJ mol-1), which enables one to infer the relative stability of coffinite and uraninite as a function of groundwater composition. Geochemical simulations using PHREEQC 2 software and the Thermochimie data base indicate that coffinite precipitates at 25°C under reducing conditions, at pH = 6, for H 4 SiO 4 (aq) concentration of 7 10-5 mol L-1 and U(OH) 4 (aq) concentration of 10-11 mol L-1. The Δ f G°

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Section: Characteristics Of the Solidsmentioning

confidence: 96%

Section: Synthesis Of Solid Phasesmentioning

confidence: 99%

Section: Dissolution Experimentsmentioning

confidence: 99%

Section: Environmental Implicationsmentioning

confidence: 99%

Section: Environmental Implicationsmentioning

confidence: 99%

See 3 more Smart Citations

First experimental determination of the solubility constant of coffinite

Szenknect

Mesbah

Cordara

et al. 2016

Geochimica et Cosmochimica Acta

Self Cite

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Energetics of a Uranothorite (Th_1–xU_xSiO₄) Solid Solution

et al. 2016

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High-temperature oxide melt solution calorimetric measurements were completed to determine the enthalpies of formation of the uranothorite, (USiO 4 ) x −(ThSiO 4 ) 1−x , solid solution. Phase-pure samples with x values of 0, 0.11, 0.21, 0.35, 0.71, and 0.84 were prepared, purified, and characterized by powder X-ray diffraction, electron probe microanalysis, thermogravimetric analysis and differential scanning calorimetry coupled with in situ mass spectrometry, and hightemperature oxide melt solution calorimetry. This work confirms the energetic metastability of coffinite, USiO 4 , and U-rich intermediate silicate phases with respect to a mixture of binary oxides. However, variations in unit cell parameters and negative excess volumes of mixing, coupled with strongly exothermic enthalpies of mixing in the solid solution, suggest short-range cation ordering that can stabilize intermediate compositions, especially near x = 0.5.

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Stability, Composition, and Core–Shell Particle Structure of Uranium(IV)-Silicate Colloids

Neill

Morris

Pearce

et al. 2018

Environ. Sci. Technol.

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Uranium is typically the most abundant radionuclide by mass in radioactive wastes and is a significant component of effluent streams at nuclear facilities. Actinide(IV) (An(IV)) colloids formed via various pathways, including corrosion of spent nuclear fuel, have the potential to greatly enhance the mobility of poorly soluble An(IV) forms, including uranium. This is particularly important in conditions relevant to decommissioning of nuclear facilities and the geological disposal of radioactive waste. Previous studies have suggested that silicate could stabilize U(IV) colloids. Here the formation, composition, and structure of U(IV)-silicate colloids under the alkaline conditions relevant to spent nuclear fuel storage and disposal were investigated using a range of state of the art techniques. The colloids are formed across a range of pH conditions (9-10.5) and silicate concentrations (2-4 mM) and have a primary particle size 1-10 nm, also forming suspended aggregates <220 nm. X-ray absorption spectroscopy, ultrafiltration, and scanning transmission electron microscopy confirm the particles are U(IV)-silicates. Additional evidence from X-ray diffraction and pair distribution function data suggests the primary particles are composed of a UO-rich core and a U-silicate shell. U(IV)-silicate colloids formation correlates with the formation of U(OH)(HSiO) complexes in solution indicating they are likely particle precursors. Finally, these colloids form under a range of conditions relevant to nuclear fuel storage and geological disposal of radioactive waste and represent a potential pathway for U mobility in these systems.

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ChemInform Abstract: Coffinite, USiO₄, Is Abundant in Nature: So Why Is It So Difficult to Synthesize?

Abstract: Conditions are established under which coffinite can be reproducibly synthesized.

Cited by 7 publications

References 1 publication

First experimental determination of the solubility constant of coffinite

First experimental determination of the solubility constant of coffinite

Energetics of a Uranothorite (Th_1–xU_xSiO₄) Solid Solution

Stability, Composition, and Core–Shell Particle Structure of Uranium(IV)-Silicate Colloids

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ChemInform Abstract: Coffinite, USiO4, Is Abundant in Nature: So Why Is It So Difficult to Synthesize?

Abstract: Conditions are established under which coffinite can be reproducibly synthesized.

Cited by 7 publications

References 1 publication

First experimental determination of the solubility constant of coffinite

First experimental determination of the solubility constant of coffinite

Energetics of a Uranothorite (Th1–xUxSiO4) Solid Solution

Stability, Composition, and Core–Shell Particle Structure of Uranium(IV)-Silicate Colloids

Contact Info

Product

Resources

About

ChemInform Abstract: Coffinite, USiO₄, Is Abundant in Nature: So Why Is It So Difficult to Synthesize?

Energetics of a Uranothorite (Th_1–xU_xSiO₄) Solid Solution