Solution coordination chemistry of uranium in the binary UO22+-SO42- and the ternary UO22+-SO42--OH- system

The structure and reaction dynamics in the systems UO22+-SO42- and UO22+-SO 42--OH- were investigated using EXAFS and O-17-NMR spectroscopy. Uranium Lm edge EXAFS indicated a bidentate coordination mode of sulfate to uranyl. I n solution, this is characterized by an U-S distance of 3.11 Angstrom. Appr oximately 5 oxygen atoms were observed in the equatorial plane at 2.39-2.43 Angstrom. The kinetics in the binary uranyl sulfate system can be describe d by four dominant exchange reactions: (1) UO22++SO(4)(2-)reversible arrow UO2SO4(k(1)), (2) U*O-2(2+)+UO(2)SO(4)reversible arrowU*O2SO4+UO22+(k(2)), (3) UO22++UO2(SO4)(2)(2-)reversible arrow 2UO(2)SO(4)(k(3)), and (4) UO2SO4 +SO42-reversible arrowUO2(SO4)(2)(2-)(k(4)). These reactions have rate cons tants indicating that the exchange is not of the simple Eigen-Wilkins type. Ternary uranyl sulfate hydroxide species were characterized by their O-17 c hemical shift and by potentiometry. There are no separate signals for the p ossible isomers of the ternary species indicating that they are in fast exc hange with each other.