The formation of complexes species of the dioxouranium(VI) ion with aspartic and glutamic acids wasstudied in the pH range of 3 to 6 at 25 °C by potentiometric measurements (H+-glass electrode). Resultsgave evidence for the formation of the following species: (UO2)A0, (UO2)AH+, and (UO2)2A(OH)20 (A2- ) a glutamic or aspartic ligand). Investigations were carried out in a NaCl ionic medium at I (0.1, 0.25, 0.5,and 1.0) mol L-1. The dependence on ionic strength of the formation constants was analyzed by the specificion interaction theory (SIT) model. The formation constants at infinite dilution, obtained using this model,are log â110 ) 8.53 ( 0.03, 8.37 ( 0.05; log â111 ) 13.60 ( 0.05, 13.42 ( 0.02; and log â21-2 ) 3.31 ( 0.05,2.98 ( 0.03 for glutamate and aspartate, respectively, where indexes for the overall formation constantâpqr refer to the equilibrium pUO22+ + qA2- + rH+ ) (UO2)p(A)qHr(2p - 2q + r). The specific interactioncoefficients are also reported. A mononuclear hydroxo species (UO2)A(OH)-, of great interest for verylow naturally occurring concentrations of uranium(VI), was hypothesized, with equilibrium constant logK [(UO2)A0 + H2O ) (UO2)A(OH)-])-5.4 at t ) 25 °C and I ) 0 mol L-1. Speciation profiles for differentconcentrations of UO22+ in the presence of both amino acids are discussed.
|Numero di pagine||6|
|Rivista||Journal of Chemical and Engineering Data|
|Stato di pubblicazione||Published - 2005|
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