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Thermodynamic Stabilities of U(VI) Minerals: Estimated andObserved Relationships

Published online by Cambridge University Press:  03 September 2012

Robert J. Finch
Robert J. Finch*
Affiliation:
University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
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Abstract

Gibbs free energies of formation (ΔG°ƒ) for severalstructurally related U(VI) minerals are estimated by summing the Gibbsenergy contributions from component oxides. The estimated ΔG° f values are used to construct activity-activity (stability)diagrams, and the predicted stability fields are compared with observedmineral occurrences and reaction pathways. With some exceptions, naturaloccurrences agree well with the mineral stability fields estimated for thesystems Sio2-Cao-Uo3-UOH2O and Co2-caO-UO3-H2O providing confidence inthe estimated thermodynamic values. Activity-activity diagrams are sensitiveto small differences in ΔG° f values, and mineral compositions must be known accurately,including structurally bound H2O. The estimated ΔG° f values are not considered reliable for a few minerals for twomajor reasons: (1) the structures of the minerals in question are notclosely similar to those used to estimate the ΔG° f* values of the component oxides, and/or (2) the minerals inquestion are exceptionally fine grained, leading to large surface energiesthat increase the effective mineral solubilities.

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Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 465: Symposium II – Scienfific Basis for Nuclear Waste Management XX , 1996 , 1185
Copyright
Copyright © Materials Research Society 1997

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References

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