Aqueous Complexation of Thorium(IV), Uranium(IV), Neptunium(IV), Plutonium(III/IV), and Cerium(III/IV) with DTPA

Aqueous complexation of Th(IV), U(IV), Np(IV), Pu(III/IV), and Ce(III/IV) with DTPA was studied by potentiometry, absorption spectrophotometry, and cyclic voltammetry at 1 M ionic strength and 25 degrees C. The stability constants for the 1:1 complex of each trivalent and tetravalent metal were calculated. From the potentiometric data, we report stability constant values for Ce(III)DTPA, Ce(III)HDTPA, and Th(IV)DTPA of log beta(101) = 20.01 +/- 0.02, log beta(111) = 22.0 +/- 0.2, and log beta(101) = 29.6 +/- 1, respectively. From the absorption spectrophotometry data, we report stability constant values for U(IV)DTPA, Np(IV)DTPA, and Pu(IV)DTPA of log beta(101) = 31.8 +/- 0.1, 32.3 +/- 0.1, and 33.67 +/- 0.02, respectively. From the cyclic voltammetry data, we report stability constant values for Ce(IV) and Pu(III) of log beta(101) = 34.04 +/- 0.04 and 20.58 +/- 0.04, respectively. The values obtained in this work are compared and discussed with respect to the ionic radius of each cationic metal.