Effect of Gallium Oxide on Phase Assemblage in Apatite and Whitlockite Hosts for Waste Immobilization

Abstract

To immobilize halide and actinide ions present in specific ILW waste a process has been developed that uses mineral phases as the host material. The mechanism of substitution of gallium into these phases will have a large effect on the phase assemblage. This will inevitably affect the total amount of halide that can be immobilized in to total phase mixture.

The full simulated waste stream composition containing varying concentrations (1–40 wt.%) of gallium oxide was studied. Also nominal compositions for gallium doped fluorapatites (Ca10-1.5xGax)F2(PO4)6 (x = 0, 0.25, 0.5, 0.75, 1.0) and gallium doped whitlockites Ca9Gay(PO4)6+y (x = 0.2, 0.4, 0.6, 0.8, 1.0) were prepared at 750–1050 °C.

These were studied by powder x-ray diffraction (XRD) to determine the phase assemblage and solid solution limits of gallium in the apatite and whitlockite phases. It was found that a complete solid solution was formed between whitlockite, Ca3(PO4)2, and Ca9Gay(PO4)6+y. In the nominal apatite compositions it was found that gallium did not substitute into the apatite structure but was instead partitioned over Ca9Gay(PO4)6+y, gallium phosphate, and unreacted gallium oxide. At higher temperatures gallium suppressed the formation of the apatite phase and was largely partitioned into the Ca9Gay(PO4)6+y phase whereas at lower temperature the majority was present as unreacted Ga2O3. In the full DCHP compositions it was found that gallium is likely to be partitioned over a number of phases including apatite, cationdoped whitlockite and gallium phosphate.

This is a preview of subscription content, access via your institution.

References

  1. 1

    I.W. Donald, B.L. Metcalfe and R.N.J. Taylor, J. Mater. Sci., 32, 5851 (1997).

    CAS  Article  Google Scholar 

  2. 2

    I.W. Donald, B.L. Metcalfe, R.D. Scheele and D.M. Strachan ., Proc. 10th. Int. Congress on Ceramics, Part D, 2002, pp. 233–240.

  3. 3

    I.W. Donald, B.L. Metcalfe, S.K. Fong, L.A. Gerrard, D.M. Strachan and R.D. Scheele, J. Nuc. Mater., 361, 78–93 (2007).

    CAS  Article  Google Scholar 

  4. 4

    B.L. Metcalfe, I.W. Donald, R.D. Scheele and D.M. Strachan ., Scientific Basis For Nuclear Waste Management XXVIII, Edited by J. M. Hanchar, S. Stroes-Gascoyne and L. Browning (Mat. Res. Soc. Symp. Proc., 824, Warrendale PA 2004) pp. 255–260.

    Google Scholar 

  5. 5

    J.C. Elliot . Structure and Chemistry of the Apatites and Other Calcium Orthophosphates, (Elsevier, Amsterdam, 1994) pp. 34–52 and 63-110.

    Google Scholar 

  6. 6

    K. Yoshida, H. Hyuga, N. Kondo, H. Kita, M. Sasaki, M. Mitamura, K. Hashimoto and Y. Toda, J. Am Ceram. Soc., 89, 688–690 (2006).

    CAS  Article  Google Scholar 

  7. 7

    Bruker AXS, “DIFFRACPLUS Evaluation Package Release 2006 – EVA V.12.

  8. 8

    A.C. Larson and R.B. Von Dreele, Los Alamos National Laboratory Report LAUR, 2000, 86–748.; B.H. Toby, J. Appl. Cryst., 2001, 34, 210-213.

Download references

Author information

Affiliations

Authors

Corresponding author

Correspondence to A. Gerrard Lee.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Lee, A.G., Shirley, K.F., Brian, L.M. et al. Effect of Gallium Oxide on Phase Assemblage in Apatite and Whitlockite Hosts for Waste Immobilization. MRS Online Proceedings Library 1107, 339 (2008). https://doi.org/10.1557/PROC-1107-339

Download citation