Hostname: page-component-586b7cd67f-rdxmf Total loading time: 0 Render date: 2024-11-29T07:28:05.272Z Has data issue: false hasContentIssue false
  • English
  • Français

Leaching Behaviour of Zirconolite in 0.001M Citric Acid at 90°C Under Various Flow Regimes

Published online by Cambridge University Press:  21 March 2011

Peter J. McGlinn ,
Thierry Advocat ,
Gilles Leturcq ,
Terry I. McLeod ,
Zaynab Aly  and
Patrick Yee
Peter J. McGlinn
Affiliation:
Institute of Materials & Engineering Science, Australian Nuclear Science & Technology Organisation, New Illawarra Road, Menai, N.S.W., Australia
Thierry Advocat
Affiliation:
Commissariat de l'Energie Atomique, Marcoule, DEN/DTCD, BP 17171, 30207 Bagnols-sur-Ceze, France
Gilles Leturcq
Affiliation:
Commissariat de l'Energie Atomique, Marcoule, DEN/DTCD, BP 17171, 30207 Bagnols-sur-Ceze, France
Terry I. McLeod
Affiliation:
Institute of Materials & Engineering Science, Australian Nuclear Science & Technology Organisation, New Illawarra Road, Menai, N.S.W., Australia
Zaynab Aly
Affiliation:
Institute of Materials & Engineering Science, Australian Nuclear Science & Technology Organisation, New Illawarra Road, Menai, N.S.W., Australia
Patrick Yee
Affiliation:
Institute of Materials & Engineering Science, Australian Nuclear Science & Technology Organisation, New Illawarra Road, Menai, N.S.W., Australia
Get access

Abstract

Nd-bearing zirconolite was leached at 90°C for 157 days in 0.001M citric acid under single-pass-flow-through conditions (modified MCC-4 protocol). Three different flow rates were used, ranging in an order of magnitude from 10 mL per day to 100 mL per day, to determine the effect of the rate of leachant replenishment on the durability of the zirconolite. Results of previous studies on the role of complexing agents on the leaching behaviour of single-phase zirconolite have been included in the discussion.

The pH of the citric acid solution was adjusted to 5 using KOH, mimicking that of the water in the parallel tests, to avoid the influence of pH on chemical durability of the zirconolite.

Simulated groundwater containing 0.001M citric acid at 90°C led to congruency in elemental releases and a diminution of release rate with time of about an order of magnitude, reaching virtual constancy after about 50 to 60 days to a level of about 10−5 g m−2 day−1. The most significant finding was that the elemental release rates of Nd, Ti and Zr (and Ca and Al where detected) were similar for all flow rates. Clearly, varying flow rate by up to an order of magnitude had no effect on elemental releases i.e. there is no solubility limit control on releases at 0.001M citric acid concentration.

An important finding of previous studies using identical leaching protocols with 0.001M citric acid, and inferred in our latest investigations reported here, was that there is no secondary layer development at the surface of the zirconolite to affect leach rates. In contrast, parallel tests carried out in deionised water instead of citric acid showed that hydroxides form in situ on the zirconolite surface, effectively forming hydrolysed zirconolite. This controls further dissolution of the zirconolite matrix due to the solubility limit being reached with respect to the hydrolysed phases rather than with zirconolite. Complexation by citrate ions prevents such control by hydrolysed species on zirconolite solubility.

Even under the more aggressive conditions imposed in these studies (0.001M citric acid), and regardless of flow rate of the leachant, elemental releases from zirconolite are very low for a candidate wasteform and demonstrate its attributes as a ceramic-based wasteform for the containment of actinides.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 932: Symposium – Scientific Basis for Nuclear Waste Management XXIX , 2006 , 61.1
Copyright
Copyright © Materials Research Society 2006

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. Vance, E.R., Begg, B.D., Day, R.A. and Ball, C.J., in Scientific Basis for Nuclear Waste Management, Mat. Res. Symp. Proc., Vol. 353 (1995).Google Scholar
2. Ebbinghaus, B., Konynenburg, R. Van, Vance, E. and Allender, J., in Waste Management proc. USA (1998).Google Scholar
3. Jostsons, A., Vance, E.R., Mercer, D.J. and Oversby, V.M., Scientific Basis for Nuclear Waste Management XVIII, Kyoto, Japan, October 23-27, 1994, pp. 775–781 (2004).Google Scholar
4. Ringwood, A.E., Kesson, S.E., Reeve, K.D., Levins, D.M. and Ramm, E.J., “Synroc”, Radioactive Waste Forms for the Future, ed. Lutze, W. and Ewing, R.C. (Elsevier, 1988), pp 233–334.Google Scholar
5. Leturcq, G., Advocat, T., Hart, K., Berger, G., Lacombe, J., and Bonnetier, A., American Mineralogist, 86, pp. 871–880 (2001).Google Scholar
6. Leturcq, G., PhD thesis, University of Toulouse III, France, 207 p.(1998).Google Scholar
7. Leturcq, G., McGlinn, P.J., Barbé, C., Blackford, M.G. and Finnie, K.S., Applied Geochemistry, 20, Issue 5, pp. 899–906 (2005).Google Scholar
8. Materials Characterization Center, Nuclear Waste Materials Handbook – Test Methods. DOE/TIC-11400 (1986).Google Scholar
9. McGlinn, P.J., McLeod, T., Leturcq, G., Aly, Z., Blackford, M.G., Zhang, Z., Li, H., Lumpkin, G.R., Scientific Basis for Nuclear Waste Management XXVII, Kalmar, Sweden, 15-19 June 2003, pp. 219–224 (2004).Google Scholar
10. McGlinn, P.J., McLeod, T., Aly, Z., Zhang, Z., Advocat, T., Blackford, M.G., Li, H., Leturcq, G., In the Proceedings of ‘Atalante 2004 Intern. Conf. on Science for the Future Nuclear Fuel Cycles’, Nîmes, France, June 21-24, 2004. Paper P3-18.Google Scholar
11. Sillén, L.G. and Martell, A.E., Stability Constants of Metal-Ion Complexes, Special Publication, The Chemical Society, London, No. 17 (1964); No. 25 (1971).Google Scholar