Journal Article
Radiochimica Acta, vol. 96, iss. 9-11, pp. 599-605, 2009
Authors
Zheming Wang, K. B. Wagnon, C. C. Ainsworth, Chongxuan Liu, Kevin M. Rosso, K. J. Frederickson
Abstract
Abstract
In this paper, the reduction rate of uranyl complexes with hydroxide, carbonate, EDTA, and desferriferrioxamine B (DFB) by anthraquinone-2,6-disulfonate (AH2DS) is studied by stopped-flow kinetic technique under anoxic atmosphere. The apparent reaction rates varied with ligand type, solution pH, and U(VI) concentration. For each ligand, a single largest pseudo −1st order reaction rate constant, k
obs, within the studied pH range was observed, suggesting the influence of pH-dependent speciation on the U(VI) reduction rate. The maximum reaction rate found in each case followed the order of OH−>CO3
2−>EDTA>DFB, in reverse order of the trend of the thermodynamic stability of the uranyl complexes and ionic sizes of the ligands. The pH-dependent rates were modeled using a second-order rate expression that was assumed to be dependent on a single U(VI) complex and an AH2DS species. By quantitatively comparing the calculated and measured apparent rate constants as a function of pH, species AHDS3− was suggested as the primary reductant in all cases examined. Species UO2CO3(aq), UO2HEDTA−, and (UO2)2(OH)2
2+ were suggested as the principal electron acceptors among the U(VI) species mixture in each of the carbonate, EDTA, and hydroxyl systems, respectively.
