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Aqueous Dissolution and Surface Alteration Studies of Nd-bearing Zirconolite in 0.001M Citric Acid at 90°C

Published online by Cambridge University Press:  01 February 2011

Peter J. McGlinn ,
Terry McLeod ,
Gilles Leturcq ,
Zaynab Aly ,
Mark G. Blackford ,
Zhaoming Zhang ,
Huijun Li  and
Gregory R. Lumpkin
Peter J. McGlinn
Affiliation:
Materials & Engineering Science, Australian Nuclear Science & Technology Organisation, New Illawarra Road, Menai N.S.W., Australia
Terry McLeod
Affiliation:
Materials & Engineering Science, Australian Nuclear Science & Technology Organisation, New Illawarra Road, Menai N.S.W., Australia
Gilles Leturcq
Affiliation:
Commissariat de l'Energie Atomique, Marcoule, DEN/DIEC/SCDV/LEBM, BP 17171, 30207, Bagnols-sur-Ceze, France
Zaynab Aly
Affiliation:
Materials & Engineering Science, Australian Nuclear Science & Technology Organisation, New Illawarra Road, Menai N.S.W., Australia
Mark G. Blackford
Affiliation:
Materials & Engineering Science, Australian Nuclear Science & Technology Organisation, New Illawarra Road, Menai N.S.W., Australia
Zhaoming Zhang
Affiliation:
Materials & Engineering Science, Australian Nuclear Science & Technology Organisation, New Illawarra Road, Menai N.S.W., Australia
Huijun Li
Affiliation:
Materials & Engineering Science, Australian Nuclear Science & Technology Organisation, New Illawarra Road, Menai N.S.W., Australia
Gregory R. Lumpkin
Affiliation:
Materials & Engineering Science, Australian Nuclear Science & Technology Organisation, New Illawarra Road, Menai N.S.W., Australia
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Abstract

Nd-bearing zirconolite was leached at 90°C for 6 months in 0.001M citric acid, and also in deionised water, to determine the effect of organic-bearing solutions on durability. The pH of the citric acid solution was adjusted to 5 using KOH, approximating that of the water in the parallel tests, to avoid the influence of pH on chemical durability of the zirconolite.

Releases were incongruent in the tests carried out in water. Release rates of Ti, Zr and Nd were comparatively very low (commonly too low to be measured) over the first 80 days of leaching. Rates for Ca and Al were 2 to 4 orders of magnitude higher than Ti, Zr and Nd over this same period. At about 80 days, there was an anomalous decrease in pH from 6 to 4 which enhanced release rates of Ti and Nd in particular. There was development of titania crystals, and the suggestion of hydrolysed titania, on the surface after 6 months. Thermodynamic equilibrium between the leachates and hydrolysed species on the surface of the zirconolite may be the key to apparent cessation of alteration, at least during thefirst 80 days of leaching.

By contrast, zirconolite leached in 0.001M citric acid maintained release rates of Ti, Zr and Nd 2 to 4 orders of magnitude greater than those in water for the first 80 days, values sustained, within an order of magnitude, for the remainder of the leach tests. Releases were congruent. The surface of the zirconolite showed no signs of secondary phase development. This suggests complexation by citrate ions prevented control by hydrolysed species on zirconolite solubility.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 807: Symposium Scientific Basis for Nuclear Waste Management XXVII , 2003 , 219
Copyright
Copyright © Materials Research Society 2004

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References

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