The two important oxidation states for uranium in natural environments are 4+ and 6+. Compounds containing quadrivalent uranium are insoluble in mildly acidic to alkaline conditions; whereas, those containing the linearly uranyl moiety (O=U=O)2+, are highly soluble and mobile. In solution, UO22+ forms soluble complexes with carbonate, oxalate, and hydroxide; UO22+ is also highly susceptible to adsorption either by organic matter, Fe oxyhydroxides, or precipitation with various anions, such as silicate, vanadate, arsenate, and phosphate. In ground water systems U(VI) is reduced to U(IV) if an effective reductant is present, such as H2S. Other reducing agents may be fossil plants, methane, and transported humic material. Uranium minerals display an extraordinary range structural and chemical variability, resulting from the different chemical conditions under which U minerals are formed.
Revised: November 1, 2006 |
Published: July 31, 2006
Citation
Grenthe I., E.C. Buck, J. Drozdynski, J. Drozdynski, T. Fujino, T. Albrecht-Schmitt, and S.F. Wolf. 2006.Uranium. In The Chemistry of the Actinide and Transactinide Elements, edited by Morss, LR, Edelstein, N.M., Fuger, J, Katz, J.J. 253-698. Dordrecht:Springer.PNNL-SA-43501.