Interaction of dioxouranium(VI) ion with EDTA at different ionic strengths

The formation of complex species of dioxouranium(VI) ion with EDTA was studied in the pH range of 1-3.5 and at 25 °C using a combination of potentiometric and spectrophotometric techniques. Results showed evidence for formation of the following species: [UO2H4EDTA]2+, [UO2H3EDTA]+, and [UO2H2EDTA]. Investigations were performed in sodium perchlorate as background electrolyte at 0.1, 0.3, 0.5, 0.7, and 1.0 mol dm− 3. The parameters based on the formation constants were calculated, and the dependences of protonation and the stability constants on ionic strength are described. The dependence on ionic strength of the formation constants was analyzed using the specific ion interaction theory (SIT) model. The stability constant values at infinite dilution, obtained using SIT model, are log β°141 = 6.77, log β°131 = 5.99 and log β°121 = 9.29, where indexes for the overall stability constant, βpqr, refer to the equilibrium pUO22+ + qH+ + rL4− ⇌ MpHqLr(2p + q − 4r). The specific interaction coefficients are also reported.