Natural analogue approaches to prediction of long-term behaviour of Ca2UO5∙2-3H2O X-phase: case study from Tulul Al Hammam site, Jordan

The Tulul Al Hammam area in central Jordan is an advantageous natural analogue site to study long-term U(VI) retention in ~ 1 Ma old U-bearing combustion metamorphic marbles with clinker-like mineralogy exposed to prolonged supergene alteration for at least ~ 100 kyr. The marbles contain abundant gr...

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Bibliographic Details
Published in:Arabian journal of geosciences 2017-12, Vol.10 (23), p.1-14, Article 512
Main Authors: Sokol, E.V., Kokh, S.N., Khoury, H.N., Seryotkin, Yu.V., Goryainov, S.V., Novikova, S.A., Sokol, I.A.
Format: Article
Language:English
Subjects:
Aluminum
Analytical methods
Calcium
Case studies
Clinker
Earth and Environmental Science
Earth science
Earth Sciences
Electron microprobe
Impurities
Iron
Microtexture
Mineralogy
Original Paper
Oxides
Radioactive waste disposal
Radioactive wastes
Raman spectroscopy
Single crystals
Spectroscopy
Stability
Uranium
Waste disposal
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Summary:The Tulul Al Hammam area in central Jordan is an advantageous natural analogue site to study long-term U(VI) retention in ~ 1 Ma old U-bearing combustion metamorphic marbles with clinker-like mineralogy exposed to prolonged supergene alteration for at least ~ 100 kyr. The marbles contain abundant grains of high-temperature (ca. 800–850 °C) primary double Ca-U(VI) oxides (mainly Ca 3 UO 6 and CaUO 4 ), which are commonly replaced by hydrated calcium uranates with various impurities (Si, Fe, Al and F). A more hydrous natural analogue of X-phase (Ca 2 UO 5 ·2-3H 2 O) occurs as a predominant secondary U compound after primary Ca-U(VI) oxides. The phase was studied by single-crystal XRD, SEM/EDX and electron microprobe (EPMA) analyses and Raman spectroscopy. It is a non-crystalline phase with a specific finger-like microtexture consisting of thin (no wider than 1–2 μm) lamellar particles. Its Raman spectrum shows a single strong band at 706–713 cm −1 , sometimes coexisting with up to three weak diffuse bands (ν ~ 390, ~ 540 and 1355–1400 cm −1 ). The find of the natural X-phase (Ca 2 UO 5 ·2-3H 2 O) is evidence of its long-term stability in a natural environment. It proves explicitly that the compound Ca 2 UO 5 ·nH 2 O is a solubility-limiting phase in aged cements. The results have implications for geological disposal of radioactive wastes.
ISSN:1866-7511
1866-7538
DOI:10.1007/s12517-017-3305-5