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Henry Moll, T. Reich, Christoph Hennig, A. Roßberg, Z. Szabó, I. Grenthe

Solution coordination chemistry of uranium in the binary UO₂²⁺-SO₄^2- and the ternary UO₂²⁺-SO₄^2--OH^- system

The structure and reaction dynamics in the systems UO₂²⁺-SO₄^2- and UO₂²⁺-SO₄^2--OH^- were investigated using EXAFS and ¹⁷O-NMR spectroscopy. Uranium L_III edge EXAFS indicated a bidentate coordination mode of sulfate to uranyl. In solution, this is characterized by an U-S distance of 3.11 Å. Approximately 5 oxygen atoms were observed in the equatorial plane at 2.39-2.43 Å. The kinetics in the binary uranyl sulfate system can be described by four dominant exchange reactions: (1) UO₂²⁺ + SO₄^2- ⇔ UO₂SO₄ (k₁), (2) U^*O₂²⁺ + UO₂SO₄ ⇔ U^*O₂SO₄ + UO₂²⁺ (k₂), (3) UO₂²⁺ + UO₂(SO₄)₂^2- ⇔ 2 UO₂SO₄ (k₃), and (4) UO₂SO₄ + SO₄^2- ⇔ UO₂(SO₄)₂^2- (k₄). These reactions have rate constants indicating that the exchange is not of the simple Eigen-Wilkins type.
Ternary uranyl sulfate hydroxide species were characterized by their ¹⁷O chemical shift and by potentiometry. There are no separate signals for the possible isomers of the ternary species indicating that they are in fast exchange with each other.

Radiochimica Acta, Oldenbourg Wissenschaftsverlag

Print ISSN: 0033-8230
Volume: 88, 09/2000
Pages: 559

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