Abstract
Uranium ore concentrates (UOCs), the product of uranium mining and milling, are primarily comprised of uranium oxide (U3O8 and UO2) or peroxide (UO4·4H2O and UO4·2H2O) compounds. Following production, UOCs are typically placed in storage until they are converted to uranium hexafluoride (UF6) at a uranium conversion facility. In this study, the chemical changes responsible for an interesting hardening phenomenon observed in UOCs stored for prolonged periods was investigated to understand underlying causes. Powder X-ray diffraction and thermogravimetric analysis were used to characterize free-flowing and hardened UOC samples and revealed the hardened material had undergone hydration and oxidation as indicated by increased moisture content and the presence of metaschoepite [(UO2)4O(OH)6](H2O)5 and/or schoepite [(UO2)4O(OH)6](H2O)6. Additionally, an aging study found metaschoepite in UOCs after 3 months exposure to a high relative humidity environment. The same study found agglomerated, but not fully hardened, material in nearly all aged UOCs samples. These results suggest metaschoepite and schoepite are indicative of UOCs exposed to elevated levels of H2O during storage. Lastly, a drying/calcining study of hardened U3O8 material demonstrated a means of remediation and identified an intermediate compound of potential interest, dehydrated schoepite. Dehydrated schoepite results from heating metaschoepite or schoepite between 100 and 300 °C and indicates partial reversal of hardened U3O8 to its original condition.
Funding source: Defense Threat Reduction Agency
Award Identifier / Grant number: HDTRA1-18-1-0015
Acknowledgment
This work would not have been possible without the collaboration of ConverDyn and Honeywell Metropolis Works which provided the uranium ore concentrate samples, analytical data, and extensive working knowledge of uranium ore concentrates. We thank the Toberer Group at the Colorado School of Mines for training and use of the powder-XRD instrument. We also thank Tyler Kane and Kate Campbell of the U.S. Geological Survey for training and use of the TGA instrument. The views and conclusions expressed in this document are those of the authors and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the U.S. Government.
Author contribution: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.
Research funding: Work by JCS was supported by the Defense Threat Reduction Agency, under Grant Award no. HDTRA1-18-1-0015.
Conflict of interest statement: The authors declare no conflicts of interest regarding this article.
References
1. Hausen, D. M. Characterizing and classifying uranium yellow cakes: a background. JOM 1998, 50, 45; https://doi.org/10.1007/s11837-998-0307-5.Search in Google Scholar
2. Tsoulfanidis, N. Conversion and enrichment. In The Nuclear Fuel Cycle; American Nuclear Society: La Grange Park, IL, 2013; pp. 57–85.Search in Google Scholar
3. Odoh, S. O., Shamblin, J., Colla, C. A., Hickam, S., Lobeck, H. L., Lopez, R. A. K., Olds, T., Szymanowski, J. E. S., Sigmon, G. E., Neuefeind, J., Casey, W. H., Lang, M., Gagliardi, L., Burns, P. C. Structure and reactivity of X-ray amorphous uranyl peroxide, U2O7. Inorg. Chem. 2016, 55, 3541; https://doi.org/10.1021/acs.inorgchem.6b00017.Search in Google Scholar PubMed
4. Boggs, J. E., El-Chehabi, M. The thermal decomposition of uranium peroxide, UO4·2H2O. J. Am. Chem. Soc. 1957, 79, 4258; https://doi.org/10.1021/ja01573a003.Search in Google Scholar
5. IAEA. Nuclear Forensics in Support of Investigations. IAEA Nuclear Security Series No. 2-G (Rev.1); IAEA: Vienna, 2015.Search in Google Scholar
6. Keegan, E., Kristo, M. J., Toole, K., Kips, R., Young, E. Nuclear forensics: scientific analysis supporting law enforcement and nuclear security investigations. Anal. Chem. 2016, 88, 1496; https://doi.org/10.1021/acs.analchem.5b02915.Search in Google Scholar PubMed
7. Kristo, M. J., Tumey, S. J. The state of nuclear forensics. Nucl. Instrum. Meth. B 2013, 294, 656; https://doi.org/10.1016/j.nimb.2012.07.047.Search in Google Scholar
8. Svedkauskaite-LeGore, J., Mayer, K., Millet, S., Nicholl, A., Rasmussen, G., Baltrunas, D. Investigation of the isotopic composition of lead and of trace elements concentrations in natural uranium materials as a signature in nuclear forensics. Radiochim. Acta 2007, 95, 601 https://doi.org/10.1524/ract.2007.95.10.601.Search in Google Scholar
9. Badaut, V., Wallenius, M., Mayer, K. Anion analysis in uranium ore concentrates by ion chromatography. J. Radioanal. Nucl. Chem. 2009, 280, 57; https://doi.org/10.1007/s10967-008-7404-3.Search in Google Scholar
10. Varga, Z., Wallenius, M., Mayer, K., Keegan, E., Millett, S. Application of lead and strontium isotope ratio measurements for the origin assessment of uranium ore concentrates. Anal. Chem. 2009, 81, 8327; https://doi.org/10.1021/ac901100e.Search in Google Scholar PubMed
11. Varga, Z., Wallenius, M., Mayer, K. Origin assessment of uranium ore concentrates based on their rare-earth elemental impurity pattern. Radiochim. Acta 2010, 98, 771; https://doi.org/10.1524/ract.2010.1777.Search in Google Scholar
12. Keegan, E., Wallenius, M., Mayer, K., Varga, Z., Rasmussen, G. Attribution of uranium ore concentrates using elemental and anionic data. Appl. Geochem. 2012, 27, 1600; https://doi.org/10.1016/j.apgeochem.2012.05.009.Search in Google Scholar
13. Varga, Z., Krajko, J., Penkin, M., Novak, M., Eke, Z., Wallenius, M., Mayer, K. Identification of uranium signatures relevant for nuclear safeguards and forensics. J. Radioanal. Nucl. Chem. 2017, 312, 639; https://doi.org/10.1007/s10967-017-5247-5.Search in Google Scholar
14. Schwerdt, I. J., Olsen, A., Lusk, R., Heffernan, S., Klosterman, M., Collins, B., Martinson, S., Kirkham, T., McDonald, L. W. Nuclear forensics investigation of morphological signatures in the thermal decomposition of uranyl peroxide. Talanta 2018, 176, 284; https://doi.org/10.1016/j.talanta.2017.08.020.Search in Google Scholar
15. Schwerdt, I. J., Hawkins, C. G., Taylor, B., Brenkmann, A., Martinson, S., McDonald, L. W. Uranium oxide synthetic pathway discernment through thermal decomposition and morphological analysis. Radiochim. Acta 2019, 107, 193; https://doi.org/10.1515/ract-2018-3033.Search in Google Scholar
16. May, M., Abedin-Zadeh, R., Barr, D., Carnesale, A., Coyle, P. E., Davis, J., Dorland, W., Dunlop, W., Fetter, S., Glaser, A., Hutcheon, I. D., Slakey, F., Tannebaum, B. Nuclear Forensics: Role, State of the Art, and Program Needs; American Association for the Advancement of Science and the American Physical Society: Washington, DC, 2008.Search in Google Scholar
17. Mayer, K. Expand nuclear forensics. Nature 2013, 503, 461; https://doi.org/10.1038/503461a.Search in Google Scholar
18. Tracy, C. L., Chen, C. H., Park, S., Davisson, M. L., Ewing, R. C. Measurement of UO2 surface oxidation using grazing-incidence X-ray diffraction: implications for nuclear forensics. J. Nucl. Mater. 2018, 502, 68; https://doi.org/10.1016/j.jnucmat.2018.01.052.Search in Google Scholar
19. Donald, S. B., Dai, Z. R. R., Davisson, M. L., Jeffries, J. R., Nelson, A. J. An XPS study on the impact of relative humidity on the aging of UO2 powders. J. Nucl. Mater. 2017, 487, 105; https://doi.org/10.1016/j.jnucmat.2017.02.016.Search in Google Scholar
20. Tamasi, A. L., Boland, K. S., Czerwinski, K., Ellis, J. K., Kozimor, S. A., Martin, R. L., Pugmire, A. L., Reilly, D., Scott, B. L., Sutton, A. D., Wagner, G. L., Walensky, J. R., Wilkerson, M. P. Oxidation and hydration of U3O8 materials following controlled exposure to temperature and humidity. Anal. Chem. 2015, 87, 4210; https://doi.org/10.1021/ac504105t.Search in Google Scholar
21. Tamasi, A. L., Cash, L. J., Mullen, W. T., Pugmire, A. L., Ross, A. R., Ruggiero, C. E., Scott, B. L., Wagner, G. L., Walensky, J. R., Wilkerson, M. P. Morphology of U3O8 materials following storage under controlled conditions of temperature and relative humidity. J. Radioanal. Nucl. Chem. 2017, 311, 35; https://doi.org/10.1007/s10967-016-4923-1.Search in Google Scholar
22. Wilkerson, M. P., Hernandez, S. C., Mullen, W. T., Nelson, A. T., Pugmire, A. L., Scott, B. L., Sooby, E. S., Tamasi, A. L., Wagner, G. L., Walensky, J. R. Hydration of α-UO3 following storage under controlled conditions of remperature and relative humidity. Dalton Trans. 2020 49, 10452; https://doi.org/10.1039/d0dt01852j.10.1039/D0DT01852JSearch in Google Scholar
23. ASTM International. Standard Test Method for Determination of Impurities in Nuclear Grade Uranium Compounds by Inductively Coupled Plasma Mass Spectrometry; ASTM International: West Conshohocken, PA, 2018.Search in Google Scholar
24. ASTM International. Standard Test Method for Uranium by Iron (II) Reduction in Phosphoric Acid Followed by Chromium (VI) Titration in the Presence of Vanadium; ASTM International: West Conshohocken, PA, 2017.Search in Google Scholar
25. ASTM International. Standard Test Methods for Total Sulfur in the Analysis Sample of Coal and Coke; ASTM International: West Conshohocken, PA, 2007.Search in Google Scholar
26. Hoekstra, H. R., Siegel, S. The uranium-oxygen system: U3O8-UO3. J. Inorg. Nucl. Chem. 1961, 18, 154; https://doi.org/10.1016/0022-1902(61)80383-7.Search in Google Scholar
27. Dawson, J. K., Wait, E., Alcock, K., Chilton, D. R. Some aspects of the system uranium trioxide-water. J. Chem. Soc. 1956, 3531. https://doi.org/10.1039/jr9560003531.Search in Google Scholar
28. Finch, R. J., Hawthorne, F. C., Ewing, R. C. Structural relations among schoepite, metaschoepite and dehydrated schoepite. Can. Mineral. 1998, 36, 831.Search in Google Scholar
29. Sowder, A. G., Clark, S. B., Fjeld, R. A. The transformation of uranyl oxide hydrates: the effect of dehydration on synthetic metaschoepite and its alteration to becquerelite. Environ. Sci. Technol. 1999, 33, 3552; https://doi.org/10.1021/es9901516.Search in Google Scholar
30. Nipruk, O. V., Knyazev, A. V., Chernorukov, G. N., Pykhova, Y. P. Synthesis and study of hydrated uranium(VI) oxides, UO3·nH2O. Radiochemistry 2011, 53, 146; https://doi.org/10.1134/s1066362211020044.Search in Google Scholar
31. Leinders, G., Bes, R., Pakarinen, J., Kvashnina, K., Verwerft, M. Evolution of the uranium chemical state in mixed-valence oxides. Inorg. Chem. 2017, 56, 6784; https://doi.org/10.1021/acs.inorgchem.7b01001.Search in Google Scholar
32. Sanyal, K., Khooha, A., Das, G., Tiwari, M. K., Misra, N. L. Direct determination of oxidation states of uranium in mixed-valent uranium oxides using total reflection X-ray fluorescence X-ray absorption near-edge spectroscopy. Anal. Chem. 2017, 89, 871; https://doi.org/10.1021/acs.analchem.6b03945.Search in Google Scholar
33. Ohashi, H., Noda, E., Morozumi, T. Oxidation of uranium-dioxide. J. Nucl. Sci. Technol. 1974, 11, 445; https://doi.org/10.1080/18811248.1974.9730692.Search in Google Scholar
34. Rousseau, G., Desgranges, L., Charlot, F., Millot, N., Niepce, J. C., Pijolat, M., Valdivieso, F., Baldinozzi, G., Berar, J. F. A detailed study of UO2 to U3O8 oxidation phases and the associated rate-limiting steps. J. Nucl. Mater. 2006, 355, 10; https://doi.org/10.1016/j.jnucmat.2006.03.015.Search in Google Scholar
35. Sinkov, S. I., Delegard, C. H., Schmidt, A. J. Preparation and Characterization of Uranium Oxides in Support of the K Basin Sludge Treatment Project; Pacific Northwest National Lab. (PNNL): WA, 2008.10.2172/940228Search in Google Scholar
36. Guillaumont, R., Fanghanel, T., Neck, V., Fuger, J., Palmer, D. A., Grenthe, I., Rand, M. H. Chemical Thermodynamics Vol. 5: Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium, and Technetium; Elsevier: Issy-les-Moulineaux, 2003.Search in Google Scholar
37. O’Hare, P. A. G., Lewis, B. M., Nguyen, S. N. Thermochemistry of uranium compounds XVII. Standard molar enthalpy of formation at 298.15 K of dehydrated schoepite UO3·0.9H2O. Thermodynamics of (schoepite + dehydrated schoepite + water). J. Chem. Thermodyn. 1988, 20, 1287; https://doi.org/10.1016/0021-9614(88)90165-6.Search in Google Scholar
38. Vieillard, P. Thermodynamics of hydration in minerals: how to predict these entities. In Thermodynamics - Fundamentals and Its Application in Science; IntechOpen Limited: London, 2012; pp. 339–370.10.5772/51567Search in Google Scholar
39. Icenhour, A. S., Toth, L. M., Luo, H. M. Water sorption and gamma radiolysis studies for uranium oxides. Nucl. Technol. 2004, 147, 258; https://doi.org/10.13182/nt04-a3530.Search in Google Scholar
40. Guo, X., Wu, D., Ushakov, S. V., Shvareva, T., Xu, H., Navrotsky, A. Energetics of hydration on uranium oxide and peroxide surfaces. J. Mater. Res. 2019, 34, 3319; https://doi.org/10.1557/jmr.2019.192.Search in Google Scholar
41. Guo, X., Wu, D., Xu, H. W., Burns, P. C., Navrotsky, A. Thermodynamic studies of studtite thermal decomposition pathways via amorphous intermediates UO3, U2O7, and UO4. J. Nucl. Mater. 2016, 478, 158; https://doi.org/10.1016/j.jnucmat.2016.06.014.Search in Google Scholar
42. Peakall, K. A., Antill, J. E. Oxidation of uranium dioxide in air at 350-1000°C. J. Nucl. Mater. 1960, 2, 194; https://doi.org/10.1016/0022-3115(60)90051-9.Search in Google Scholar
43. Sato, T. Thermal decomposition of uranium peroxide hydrates. J. Appl. Chem. 1976, 26, 207; https://doi.org/10.1002/jctb.5020260408.Search in Google Scholar
Supplementary material
The online version of this article offers supplementary material (https://doi.org/10.1515/ract-2020-0044).
© 2020 Walter de Gruyter GmbH, Berlin/Boston
