Hostname: page-component-78c5997874-g7gxr Total loading time: 0 Render date: 2024-11-19T06:33:43.044Z Has data issue: false hasContentIssue false
  • English
  • Français

Oxidative alteration of Ce-rich pyrochlore: HRTEM/EELS investigation

Published online by Cambridge University Press:  10 February 2011

Huifang Xu  and
Yifeng Wang
Huifang Xu
Affiliation:
Transmission Electron Microscopy Laboratory, Department of Earth and Planetary Sciences, The University of New Mexico, Albuquerque, New Mexico 87131. [email protected]
Yifeng Wang
Affiliation:
Sandia National Laboratories, 115 North Main Street, Carlsbad, New Mexico 88220, [email protected]
Get access

Abstract

Transmission electron microscopy (TEM) and associated electron energy-loss spectroscopy (EELS) study show intergrowth of Ce4+-rich pyrochlore (metamict) and Ce3+-rich pyrochlore (partially metamict) in a Ce-rich pyrochlore from a rare earth element (REE) ore deposit of Inner Mongolia, Northern China. The partially metamict material is Ba-free and dominated by Ce3+. However, the metamict material is Ba-bearing and dominated by Ce3+,. The Ce4+-rich pyrochlore may result from radiation damage by alpha decay that also causes oxidation of Fe 2+ in titanite, and the interaction with a Ba-bearing oxidizing fluid. The oxidation of Ce3+ in the primary pyrochlore is accompanied by in the loss of REE, Ca, and Pb, a daughter product of U via alpha decay, during the alteration. However, most REE were incorporated in the alteration product, the Ce4+-rich pyrochlore. Based on EDS and EELS analyses, the chemical formulae of the partially metamict Ce3+-rich pyrochlore and metamict Ce4+-rich pyroeblore can be written as: (Ca, Ce3+, U, Pb) 2(Ti, Nb)2O7−x(OH)x, and (Ba, Ca, Ce4+, U)2 (Ti, Nb)2O7−y(OH)y, respectively. Ce is the most abundant element among all REE. It is proposed that the alteration takes place in solid-state with oxidizing fluid as a catalyst. The alteration kinetics is controlled by diffusion processes of aqueous species in metamict pyrochlore.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 556: Symposium QQ – Scientific Basis for Nuclear Waste Management XXII , 1999 , 149
Copyright
Copyright © Materials Research Society 1999

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

1. Hogarth, D. D., American Mineralogist, 62, 403–410 (1977).Google Scholar
2. Lumpkin, G. R., and Ewing, R. C., American Mineralogy, 80, 732–743 (1995).Google Scholar
3. Lumpkin, G. R., Chakoumakos, B. C., and Ewing, R. C., American Mineralogist, 71, 569–588 (1986).Google Scholar
4. Wang, P., Pan, Z., and Wong, L., Systematic Mineralogy. Geology Press, Beijing, vol.1, p.448–458 (1982).Google Scholar
5. Dosch, R. G., Hleadley, T. J., Northrup, C. J., and Hlava, P. F., Processing, microstructure, leaching, and long-term stability studies related to titanate high level waste forms. Sandia National Laboratories Report, Sandia, 82–2980, 84pp (1982).Google Scholar
6. Ringwood, A. E., Kesson, S. E., Reeve, K. D., Levins, D. M., and Ramm, E. J., Synroc, . In Lutze, W. and Ewing, R. C. eds., “Radioactive Waste Forms for the Future.” North-Holland, Amsterdam, pp. 233–334 (1988).Google Scholar
7. Begg, B. D., Vance, E. R., Day, R. A., Hambley, M., and Conradson, S. D., In Gray, W. J. and Triay, I. R. eds. “Scientific Basis for Nuclear Waste Management,” 20, 325–332 (1997).Google Scholar
8. Buck, E. C., Ebbinghaus, B., Bakel, A. J., and Bates, J. K., Characterization of a plutonium-bearing zirconolite-rich Synroc. In Gray, W. J. and Triay, I. R. eds. “Scientific Basis for Nuclear Waste Management,” 20, 1259–1266 (1997).Google Scholar
9. Vance, E. R., MRS Bulletin, vol. XIX, p. 28–32 (1994).Google Scholar
10. Vance, E. R., Jostsons, A., Stewart, M. W. A., Day, R. A., Begg, B. D., Hambley, M. J., Hart, K. P., and Ebbinghaus, B. B., In “Plutonium Future The Science.” Los Alamos National Laboratories, 19–20 (1997).Google Scholar
11. Vance, F. R., Hlart, K. P., Day, R. A., Carter, M. L., Itambley, M., Blackford, M. G., and Begg, B. D., In Gray, W. J. and Triay, I. R. eds. “Scientific Basis for Nuclear Waste Management,” 20, 341–348 (1997).Google Scholar
12. Begg, B. D., and Vance, E. R., In Gray, W. J. and Triay, I. R. eds. “Scientific Basis for Nuclear Waste Management,” 20, 333–340 (1997).Google Scholar
13. Egerton, R. F., Electron energy-loss spectroscopy in the electron microscope. Plenum Press, New York, 485 pp (1996).Google Scholar
14. Brydson, R., Sauer, H., and Engel, W., In Disko, M. M., Ahn, C. C., and Fultz, B. Eds. “Transmission electron energy loss sp ectroscopy in materials science,” p. 131–154 (1992). The Minerals, Metals and Materials Society, Warrendale, Illinois.Google Scholar
15. Garvie, L. A. J., Craven, A. J., and Brydson, R., American Mineralogist, 79, 411–425 (1994).Google Scholar
16. Spence., J. C. H., Techniques closely related to high-resolution electron microscopy. In High-Resolution Transmission Electron Microscopy and Associated Techniques, Buseck, P. R., Cowley, J. M., and Eyring, L., eds., Oxford University Press, New York, 190–243 (1988).Google Scholar
17. Xu, H.. and Garvie, L. A. J., Abstracts with Programs of Geological Society of America Annual Meeting, Salt Lake City, 400–401 (1997).Google Scholar
18. Fortner, J. A., Buck., E. C., Ellison, A. J. G., and Bates, J. K., Ultramicroscopy, 67, 77–81 (1997).Google Scholar
19. Xu, H., and Wang, Y., Journal of Nuclear Materials, 264 (in press) (1998).Google Scholar
20. IG-CAS (Institute of Geochemistry, Chinese Academy of Science) Geochemistry of Baiyun Obo REE Ore Deposits (in Chinese). Science Press, Bejing, 1988, p. 550 (1988).Google Scholar
21. Hawthone, F. C. et al., American Mineralogy, 76, 370–369 (1991).Google Scholar