Effects of Mg, Ca, Sr and Ba on Geochemical Uranyl Speciation


Effects of Mg, Ca, Sr and Ba on Geochemical Uranyl Speciation

Geipel, G.; Bernhard, G.

The uranyl tricarbonato complex is one of the most important uranyl species under environmental conditions. The tendency to form stable metal-uranyl tricarbonato complexes was found particularly for the interaction with alkaline earth elements. However, under comparable chemical conditions the formation of these complexes is very different. While magnesium tends mainly to the formation of a MgUO2(CO3)32+ - complex, in the case of calcium the Ca2UO2(CO3)3(aq.) complex is the most stable and the formation of the CaUO2(CO3)32+ - complex is very limited. In the corresponding systems with strontium as well as for barium only the MeUO2(CO3)32+ - complex is formed. The stability constants of the MeUO2(CO3)32+ - complexes increase in the series Mg, Ca , Sr and Ba. The formation of Me2UO2(CO3)3 – complexes for Mg, Sr and Ba occurs only in a small concentration range and the formed complexes tends to precipitate. The Me2UO2(CO3)3 – complexes for Mg and Ca form stable minerals as bayleyite and liebigite. However several other mineral modifications as zellerite, fontanite, sharpite and rabbittite underline the geochemical importance of this class of compounds.
Analogous phenomena can be expected in the alkaline earth uranyl phosphate systems and first results will be presented.

Keywords: Uranium; Carbonate; Speciation

  • Contribution to proceedings
    PACIFICHEM 2005, 15.-20.12.2005, Honolulu, United States
  • Invited lecture (Conferences)
    PACIFICHEM 2005, 15.-20.12.2005, Honolulu, United States

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Publ.-Id: 7312