Hostname: page-component-586b7cd67f-vdxz6 Total loading time: 0 Render date: 2024-11-25T20:38:56.924Z Has data issue: false hasContentIssue false
  • English
  • Français

Dissolution of A2Ti2O7 (A = Y3+, Gd3+, or Lu3+) Pyrochlore by Experiment at pH = 2, T = 90°C: Evidence for Solubility Control Using a Linear Free Energy Model

Published online by Cambridge University Press:  21 March 2011

J. P. Icenhower ,
B. P. McGrail ,
W. J. Weber ,
B. D. Begg ,
N. J. Hess ,
E. A. Rodriguez ,
J. L. Steele ,
C. F. Brown  and
and M. J. O'Hara
J. P. Icenhower
Affiliation:
Pacific Northwest National Laboratory, Richland, WA 99352, U.S.A.
B. P. McGrail
Affiliation:
Pacific Northwest National Laboratory, Richland, WA 99352, U.S.A.
W. J. Weber
Affiliation:
Pacific Northwest National Laboratory, Richland, WA 99352, U.S.A.
B. D. Begg
Affiliation:
ANSTO, PMB1, Menai, New South Wales 2234, Australia.
N. J. Hess
Affiliation:
Pacific Northwest National Laboratory, Richland, WA 99352, U.S.A.
E. A. Rodriguez
Affiliation:
Pacific Northwest National Laboratory, Richland, WA 99352, U.S.A.
J. L. Steele
Affiliation:
Pacific Northwest National Laboratory, Richland, WA 99352, U.S.A.
C. F. Brown
Affiliation:
Pacific Northwest National Laboratory, Richland, WA 99352, U.S.A.
and M. J. O'Hara
Affiliation:
Pacific Northwest National Laboratory, Richland, WA 99352, U.S.A.
Get access

Abstract

We performed a series of dissolution experiments with well-characterized pyrochlore ceramics with the formula A2Ti2O7, where A = Y3+, Gd3+, or Lu3+ in H2O- and D2Obased solutions [pH(D) = 2] at 90°C. Normalized log10 dissolution rates (g·m−2·d−1) in H2O-based solutions increase from Lu2Ti2O7 (−3.2 to –3.3) to Gd2Ti2O7 (−2.6 to –2.9), to Y2Ti2O7 (−1.9 to –2.0). Rates in D20-based solutions are indistinguishable from rates in H2O, indicating that release of elements is probably not diffusion controlled. A recent dissolution model, based on ligand-exchange reactions, suggests that the rate of reaction should increase in inverse order of the cation field strength: Lu < Y < Gd (where the cation denotes the appropriate pyrochlore composition), which is not observed. Evaluation of the thermodynamic stability of the three solids was performed using a linear free-energy model and reported free energies of formation. The calculations indicate that reactivity should follow in the progression Lu < Gd < Y, as observed in the dissolution experiments. Our data indicates, therefore, that dissolution models based on ligand-exchange reactions may not be strictly applicable to simple pyrochlore minerals.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 713: Symposium JJ – Scientific Basis for Nuclear Waste Management XXV , 2002 , JJ6.2
Copyright
Copyright © Materials Research Society 2002

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. Cochran, S. G., Dunlop, W. H., Edmunds, T. A., MacLean, L. M., and Gould, T. H., Fissile Materials Disposition Program Final Immobilization form Assessment and Recommendation, Lawrence Livermore National Laboratory, UCRL-ID-128705, Livermore, California, (1997).Google Scholar
2. Casey, W. H. and Ludwig, C., in Chemical Weathering Rates of Silicate Minerals, edited by White, A. F. and Brantely, S. L. (Min. Soc. Am., 1995) pp. 87–117.Google Scholar
3. Leturcq, G., Advocat, T., Hart, K., Berger, G., Lacombe, J., Bonnetier, A., Am. Min. 86: 871–880 (2001).Google Scholar
4. Klee, W. E., Weitz, G., J. Inorg. Nucl. Chem. 31: 2367–2372 (1969).Google Scholar
5. Begg, B. D., Weber, W. J., Devanathan, R., Icenhower, J. P., Thevuthasen, S., McGrail, B. P., Ceram. Trans. 107: 553–560 (2000).Google Scholar
6. Jantzen, C. M., Clarke, D. R., Morgan, P. E. D., Harker, A. B., J. Am. Ceram. Soc. 65(6): 292–300 (1982).Google Scholar
7. Knauss, K. G., Dibley, M. J., Boucier, W. L., Shaw, H. F., Appl. Geochem. (2001) (in press).Google Scholar
8. Shannon, R. D., Acta Cryst. A, 32: 751 (1976).Google Scholar
9. Sverjensky, D. A., Molling, P.A., Nature 358: 231–234 (1992).Google Scholar
10. Wagman, D. B.et al., The NBS Tables of Chemical and Thermodynamic Properties, vol. 11, suppl. 2 (NBS, Washington D.C.) (1982).Google Scholar
11. Wang, Y., Xu, H., in Scientific Basis for Nuclear Waste Management XXIII, edited by Smith, R. W., Shoesmith, D. W. (Mat. Res. Soc. Symp. Proc. 608, Boston, 2000), pp. 367–372.Google Scholar