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RESEARCH ARTICLE
Contents Vol 6(6)

Dissolution kinetics of meta-torbernite under circum-neutral to alkaline conditions

Dawn M. Wellman A C , Bruce K. McNamara A , Diana H. Bacon A , Elsa A. Cordova A , Ruby M. Ermi A and Laken M. Top A B
+ Author Affiliations
- Author Affiliations

A Pacific Northwest National Laboratory, PO Box 999, K3-62, Richland, WA 99352, USA.

B University of Idaho, Department of Chemistry, Renfew Hall, PO Box 442343, Moscow, ID 83844, USA.

C Corresponding author. Email: dawn.wellman@pnl.gov

Environmental Chemistry 6(6) 551-560 https://doi.org/10.1071/EN09046
Submitted: 21 April 2009  Accepted: 29 October 2009   Published: 18 December 2009

Environmental context. Uranium-phosphate minerals have been identified as a long-term controlling phase that limit the mobility of uranium to groundwater in many contaminated subsurface environments. Complex, coupled processes confound the ability to isolate the rates attributed to individual processes. Results of this investigation provide the necessary information to refine current prediction on the release and long-term fate of uranium in subsurface environments.

Abstract. The purpose of this investigation was to conduct a series of single-pass flow-through (SPFT) tests to (1) quantify the effect of temperature (23–90°C) and pH (6–10) on meta-torbernite dissolution; (2) compare the dissolution of meta-torbernite to other autunite-group minerals; and (3) evaluate the effect of aqueous phosphate on the dissolution kinetics of meta-torbernite. Results presented here illustrate meta-torbernite dissolution rates increase by ~100× over the pH interval of 6 to 10, irrespective of temperature. The power law coefficient for meta-torbernite, η = 0.59 ± 0.07, is greater than that quantified for Ca-meta-autunite, η = 0.42 ± 0.12. This suggests the stability of meta-torbernite is greater than that of meta-autunite, which is reflected in the predicted stability constants. The rate equation for the dissolution of meta-torbernite as a function of aqueous phosphate concentration is log rdissol (mol m–2 s–1) = –4.7 × 10–13 + 4.1 × 10–10[PO43–].


Acknowledgements

Funding for this project was provided by the USA Department of Energy (DOE), Office of Environmental Management, EM-20 Environmental Cleanup and Acceleration (Mark Gilbertson); and by Fluor Hanford, Inc. (Jane Borghese). This work was conducted at Pacific Northwest National Laboratory, operated by Battelle for the USA Department of Energy under Contract DE-AC06–76RL01830. The authors gratefully acknowledge and thank the following individuals for their support in various aspects of this investigation: Keith Geiszler and Mike Lindberg for their planning and support of analytical work; Eric Clayton for conducting ICP-MS analyses; Igor Kutnyakov for conducting select X-ray diffraction and carbon analyses; Emily Richards for organising and assisting with single-pass flow-through testing; and Chase Bovaird for his support and assistance with various aspects of this investigation.


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