T82 Investigating the Future of Uranium in the Geosciences: An Examination of Environmental Studies and Applications

Monday, 5 November 2012
8:00 AM - 12:00 PM
208B

SYNTHETIC GROWTH OF URANYL PHOSPHATE MINERALS AND IN SITU RAMAN DISSOLUTION STUDIES

Paper number: T82-6
Program: Technical Sessions
Time: 9:20 AM – 9:35 AM

Authors

Abstract

Meta-autunite, Ca(UO2)2(PO4)2 * 2-6 H2O, meta-torbernite, Cu(UO2)2(PO4)2 * 8 H2O, meta-ankoleite, K2(UO2)2(PO4)2 * 6 H2O, and saleeite, Mg(UO2)2(PO4)2 * 10 H2O are uranyl phosphate minerals with the autunite-type sheet structure. Uranyl phosphate minerals have been synthesized previously by simple precipitation from aqueous solution, sometimes including hydrothermal treatment. However, the solubility of uranyl phosphates in aqueous solution is very limited, and fine-grained precipitates rapidly form during aqueous syntheses. Single crystals of uranyl phosphates can be synthesized by slowly diffusing nutrients into a silica hydrogel, but the yield of crystals is low and it is difficult to remove them from the gel[1]. Inspired by Fernelius and Darling’s method of synthesizing sparingly soluble salts[2], we have shown that slow mixing by diffusion in aqueous solution gives crystals of uranyl phosphates in high yield and purity. Uranyl phosphates are synthesized using uranyl nitrate, phosphoric acid and water containing the cations necessary for the phase formation (Cu, K, Mg, and Ca). Uranyl phosphate minerals are important for understanding the genesis of uranium ore deposits, the mobility of uranium in natural systems, and for predicting and potentially controlling the mobility of uranium in contaminated sub-surface environments. In areas of uranium contamination, such as the Hanford site in Washington state, polyphosphate injection could potentially immobilize U(VI) in sparingly soluble uranyl phosphate compounds. We have examined the solubility of these minerals under different conditions using Raman spectroscopy, which is a rapid and non-destructive method for quantification of uranyl ions in solution.

[1] Locock, A. , & Burns, P. (2003). Crystal structures and synthesis of the copper-dominant members of the autunite and meta-autunite groups: Torbernite, zeunerite, metatorbernite and metazeunerite.Canadian Mineralogist, 41(2), 489-502.

[2] Fernelius, W.C. & Detling, K.D. (1934). Preparation of crystals of sparingly soluble salts Journal of Chemical Education, 11(3), 176-1978.