Dioxouranium(VI)-carboxylate complexes. Speciation of UO22+-1,2,3-Propanetricarboxylate system in NaClaq at different ionic strengths and at t = 25 °C

The formation constants of dioxouranium(VI) - 1,2,3-propanetricarboxylate [tricarballylate (3-), TCA] complexes were determined in NaCl aqueous solutions at 0 ≤ I / mol L-1 ≤ 1.0 and t = 25 °C, by potentiometry, ISE-[H+] glass electrode. The speciation model obtained at each ionic strength includes the following species: ML-, MLH0, ML24- and ML2H3- (M = UO22+ and L = TCA). The dependence on ionic strength of protonation constants of 1,2,3-propanetricarboxylate and of the metal-ligand complexes was modeled by the SIT (Specific ion Interaction Theory) approach and by the Pitzer equations. The formation constants at infinite dilution are [for the generic equilibrium p UO22+ + q (L3-) + r H+ = (UO22+)p(L)qHr(2p−3q+r); βpqr]: log β110 = 6.222±0.030, log β111 = 11.251±0.009, log β121 = 7.75±0.02, log β121 = 14.33±0.06. The sequestering ability of 1,2,3-propanetricarboxylate towards UOUO22+ was quantified by using a sigmoid Boltzman type equation.