Skip to main content Accessibility help
×
Home

Uranium Sequestration by Aluminum Phosphate Minerals in Unsaturated Soils

  • James L Jerden (a1)

Abstract

A mineralogical and geochemical study of soils developed from the unmined Coles Hill uranium deposit (Virginia) was undertaken to determine how phosphorous influences the speciation of uranium in an oxidizing soil/saprolite system typical of the eastern US. This paper presents mineralogical and geochemical results that identify and quantify the processes by which uranium has been sequestered in these soils. It was found that uranium is not leached from the saturated soil zone (saprolites) overlying the deposit due to the formation of a sparingly soluble uranyl phosphate mineral of the meta-autunite group. The concentration of uranium in the saprolites is approximately 1000 mg uranium per kg of saprolite. It was also found that a significant amount of uranium was retained in the unsaturated soil zone overlying uranium-rich saprolites. The uranium concentration in the unsaturated soils is approximately 200 mg uranium per kg of soil (20 times higher than uranium concentrations in similar soils adjacent to the deposit). Mineralogical evidence indicates that uranium in this zone is sequestered by a barium-strontium-calcium aluminum phosphate mineral of the crandallite group (gorceixite). This mineral is intimately inter-grown with iron and manganese oxides that also contain uranium. The amount of uranium associated with both the aluminum phosphates (as much as 1.4 weight percent) has been measured by electron microprobe microanalyses and the geochemical conditions under which these minerals formed has been studied using thermodynamic reaction path modeling. The geochemical data and modeling results suggests the meta-autunite group minerals present in the saprolites overlying the deposit are unstable in the unsaturated zone soils overlying the deposit due to a decrease in soil pH (down to a pH of 4.5) at depths less than 5 meters below the surface. Mineralogical observations suggest that, once exposed to the unsaturated environment, the meta-autunite group minerals react to form U(VI)-bearing aluminum phosphates.

Copyright

References

Hide All
1. Murakami, T., Ohnuki, T., Isobe, H. and Sato, T., American Mineralogist 82, 888 (1997).
2. Fuller, C. C., Bargar, J. R., Davis, J. A., Piana, M. J., Environmental Science and Technology 36, 158 (2002).
3. Jerden, J. L. Jr., Sinha, A. K., and Zelazny, L., Chemical Geology 199, 129 (2003).
4. Hendershot, W. H., Lalande, H. and Duquette, M., “Soil reaction and exchangeable acidity,” Soil Sampling and Methods of Analysis, ed. Carter, M. R., (Canadian Society of Soil Science, Lewis Publishers, 1993) pp. 141145
5. Schwab, R. G., Gotz, C., Herold, H. and Oliveira, N. P. De, Neues Jahrbuch f¨r Mineralogie Monatshefte, 12, 551 (1993).
6. Vochten, R. F., Van Haverbeke, L. and Van Springel, K., Mineralogical Magazine 56, 367 (1992).
7. Grenthe, I., Fuger, J., Konings, R. J. M., Lemire, R. J., Muller, A. B., Cregu, C. Nguyen-Trung, and Wanner, H., “Chemical thermodynamics of uranium,” Chemical Thermodynamics Series Volume 1, ed. Wanner, H. and Forest, I. (Elsevier, Amsterdam, 1992).

Keywords

Uranium Sequestration by Aluminum Phosphate Minerals in Unsaturated Soils

  • James L Jerden (a1)

Metrics

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed