Thermodynamics of uranyl minerals: Enthalpies of formation of uranyl oxide hydrates

Kubatko, Karrie Ann; Helean, Katheryn B.; Navrotsky, Alexandra; Burns, Peter C.

doi:10.2138/am.2006.1856

Cited by 45 publications

(25 citation statements)

References 31 publications

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“…Thus, it appears unlikely that hydration contributes more than a small portion of the additional stabilization observed in uranyl carbonates. Similar conclusions appear to hold for uranyl oxide hydrates (Kubatko et al 2006).…”

Section: Resultssupporting

confidence: 76%

Thermodynamics of uranyl minerals: Enthalpies of formation of rutherfordine, UO2CO3, andersonite, Na2CaUO2(CO3)3(H2O)5, and grimselite, K3NaUO2(CO3)3H2O

Kubatko

Helean

Navrotsky

et al. 2005

American Mineralogist

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Enthalpies of formation of rutherfordine, UO 2 CO 3 , andersonite, Na 2 CaUO 2 (CO 3 ) 3 (H 2 O) 5 , and grimselite, K 3 NaUO 2 (CO 3 ) 3 (H 2 O), have been determined using high-temperature oxide melt solution calorimetry. The enthalpy of formation of rutherfordine from the binary oxides, ΔH r-ox , is -99.1 ± 4.2 kJ/mol for the reaction UO 3 (xl, 298 K) + CO 2 (g, 298 K) = UO 2 CO 3 (xl, 298 K). The ΔH r-ox for andersonite is -710.4 ± 9.1 kJ/mol for the reaction Na 2 O (xl, 298 K) + CaO (xl, 298 K) + UO 3 (xl, 298 K) + 3CO 2 (g, 298 K) + 5H 2 O (l, 298 K) = Na 2 CaUO 2 (CO 3 ) 3 (H 2 O) 6 (xl, 298 K). The ΔH r-ox for grimselite is -989.3 ± 14.0 kJ/mol for the reaction 1.5 K 2 O (xl, 298 K) + 0.5Na 2 O (xl, 298 K) + UO 3 (xl, 298 K) + 3CO 2 (g, 298 K) + H 2 O (l, 298 K) = K 3 NaUO 2 (CO 3 ) 3 H 2 O (xl, 298 K). The standard enthalpies of formation from the elements, ΔH f º, are -1716.4 ± 4.2, -5593.6 ± 9.1, and -4431.6 ± 15.3 kJ/mol for rutherfordine, andersonite, and grimselite, respectively. Energetic trends of uranyl carbonate formation from the binary oxides and ternary carbonates are dominated by the acid-base character of the binary oxides. However, even relative to mixtures of UO 2 CO 3 , K 2 CO 3 , and Na 2 CO 3 or CaCO 3 , andersonite and grimselite are energetically stable by 111.7 ± 10.2 and 139.6 ± 16.1 kJ/mol, respectively, suggesting additional favorable interactions arising from hydration and/or changes in cation environments. These enthalpy values are discussed in comparison with earlier estimates.

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Section: Resultssupporting

confidence: 76%

Thermodynamics of uranyl minerals: Enthalpies of formation of rutherfordine, UO2CO3, andersonite, Na2CaUO2(CO3)3(H2O)5, and grimselite, K3NaUO2(CO3)3H2O

Kubatko

Helean

Navrotsky

et al. 2005

American Mineralogist

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“…Also, schoepite is a commonly occurring UOH mineral, reported from nearly 80 localities (Plášil 2018 are closely related minerals. A transformation of schoepite to metaschoepite, connected with a loss of the H 2 O molecule from interlayer (i.e., partial dehydration), was observed in air under the room temperature (Christ and Clark 1960;O'Hare et al 1988;Finch et al 1998;Sowder et al 1999;Kubatko et al 2006). From the thermodynamic point of view the process is clearer now, however the exact mechanism remains unknown.…”

Section: Implications For Weathering Of Uo 2+xmentioning

confidence: 99%

The crystal structure of uranyl-oxide mineral schoepite, [(UO2)4O (OH)6]( H2O)6, revisited

Plášil¹

2018

Jour. Geosci.

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New single-crystal X-ray diffraction experiments have revealed that the crystal structure of schoepite, one of the more common U-oxide minerals, is centrosymmetric, rather than acentric as reported in the past. Schoepite is orthorhombic, space group Pbca, a = 16.7810 (5), b = 14.7044(4), c = 14.2985(5) Å, with V = 3528.22(19) Å 3 and Z = 8. Its structure was solved by charge-flipping algorithm and refined to an agreement index (R) of 4.7 % for 4662 unique reflections collected using microfocus X-ray source. Schoepite structure, in line with its previous determination, is based upon U-O-OH sheets of the fourmarierite topol ogy and an interlayer filled only by molecular H 2 O. The complexity calculations show that the difference in complexity values between schoepite, [(UO 2 ) 4 O(OH) 6 ](H 2 O) 6 , and metaschoepite, [(UO 2 ) 4 O(OH) 6 ](H 2 O) 5 , are much smaller (about 100 bits/cell) then considered previously (about 1000 bits/cell). Such small difference is in line with the easy transformation of schoepite to metaschoepite under ambient conditions and a joint occurrence of both minerals. The online version of this article (doi: 10.3190/jgeosci.252) contains supplementary electronic material. who reported that schoepite is orthorhombic, P2 1 ca, with a = 14.337(3), b = 16.813(5), c = 14.731(4) Å, V = 3551(2) Å 3 , Z = 4; the chemical formula was given as [(UO 2 ) 8 O 2 (OH) 12 ](H 2 O) 12 , with Z = 4. Recently, we have undertaken new studies on the structures of schoepite-related minerals (Plášil et al. 2017; Olds et al. 2018), which revealed several issues, among them the fact that all related studied structures are centrosymmetric. Thus, it prompted our re-examination of the schoepite structure. Experimental SampleThe schoepite crystal used in this study was recovered from a specimen stored in the collections of the Royal Museum for Central Africa in Tervuren (Belgium): n° RGM2708. This specimen originates from the Shinkolobwe mine, the Haut-Katanga Province, Democratic Republic of Congo. The specimen is composed of a massive mixture of uranyl-oxide minerals. On the surface and fissures, there are yellow tabular to prismatic crystals of schoepite (described originally as paraschoepite) (Fig. 1), reddish-orange needle-like curite and bipyramidal soddyite. It should be noted that we found no evidence for paraschoepite on the specimen (cf. Christ and Clark 1960).

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“…Recent assessment of the thermodynamics of metaschoepite and β-UO 2 (OH) 2 by Kubatko et al (2006) concluded that metaschoepite (and probably schoepite) may be metastable under all conditions. At 298.15 K, the Gibbs free energy for the reaction UO 3 ·2H 2 O (metaschoepite) = β-UO 2 (OH) 2 + H 2 O(l) is Overall, these calculations based on calorimetric results give little energy difference between metaschoepite, "dehydrated schoepite," and β-UO 2 (OH) 2 , which suggests that kinetic effects probably play a major role in controlling the paths by which "dehydrated schoepite" forms (Fig.…”

Section: Occurrences Of Paulscherreritementioning

confidence: 99%

Paulscherrerite from the Number 2 Workings, Mount Painter Inlier, Northern Flinders Ranges, South Australia: "Dehydrated schoepite" is a mineral after all

Brugger

Meisser²,

Ansermet³

et al. 2011

American Mineralogist

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Paulscherrerite, UO 2 (OH) 2 , occurs as an abundant dehydration product of metaschoepite at the Number 2 Workings at Radium Ridge, Northern Flinders Ranges, South Australia. The mineral name honors the contribution of Swiss physicist Paul Scherrer to mineralogy and nuclear physics. Individual paulscherrerite crystals are tabular, reaching a maximum of 500 nm in length. Paulscherrerite has a canary yellow color and displays no fluorescence under UV light. Chemically, paulscherrerite is a pure uranyl hydroxide/hydrate, containing only traces of other metals (<1 wt% in total). Bulk (mg) samples always contain admixtures of metaschoepite (purest samples have ~80 wt% paulscherrerite). A thermogravimetric analysis corrected for the presence of metaschoepite contamination leads to the empirical formula UO 3 ·1.02H 2 O, and the simplified structural formula UO 2 (OH) 2 . Powder diffraction shows that the crystal structure of paulscherrerite is closely related to that of synthetic orthorhombic α-UO 2 (OH) 2 . However, splitting of some X-ray diffraction lines suggests a monoclinic symmetry for type paulscherrerite, with a = 4.288(2), b = 10.270(6), c = 6.885(5) Å, β = 90.39(4)°, V = 303.2(2) Å 3 , Z = 4, and possible space groups P2, P2 1 , P2/m, or P2 1 /m.Paulscherrerite-like material was synthesized using various methods, including heating metaschoepite in water at 150 °C and slow hydration of UO 3 (am) in air; material synthesized using hydrothermal techniques displayed peak splitting indicative of monoclinic symmetry. Paulscherrerite has been reported under the name "dehydrated schoepite" as an early weathering product of uraninite/pitchblende in several deposits, such as Shinkolobwe, Zaire; Nopal I deposit, Mexico; and the granitic pegmatites of New Hampshire, U.S.A.

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Thermodynamics of uranyl minerals: Enthalpies of formation of uranyl oxide hydrates

Cited by 45 publications

References 31 publications

Thermodynamics of uranyl minerals: Enthalpies of formation of rutherfordine, UO2CO3, andersonite, Na2CaUO2(CO3)3(H2O)5, and grimselite, K3NaUO2(CO3)3H2O

Thermodynamics of uranyl minerals: Enthalpies of formation of rutherfordine, UO2CO3, andersonite, Na2CaUO2(CO3)3(H2O)5, and grimselite, K3NaUO2(CO3)3H2O

The crystal structure of uranyl-oxide mineral schoepite, [(UO2)4O (OH)6]( H2O)6, revisited

Paulscherrerite from the Number 2 Workings, Mount Painter Inlier, Northern Flinders Ranges, South Australia: "Dehydrated schoepite" is a mineral after all

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