Apparent Stability Constant of Zr(Ⅳ)-Hydroxyurea Complex With pH Potentiometric Titration

Hydroxyurea(HU) is a reducing and complexing agent that can be used in the PUREX process. Zr is an important fission product in the spent fuel and main element of concern in the nuclear fuel reprocessing. The decontamination of zirconium in the route of plutonium and uranium can be lowered by the complexation of hydroxyurea in the PUREX process. The complexation of Zr(Ⅳ) with hydroxyurea in the nitric acid system was investigated in this work. Under the condition of 0.3 mol/L HNO₃, the complex ratio of Zr(Ⅳ) with HU is 1∶8 obtained by Job’s method. Combining with the half-integer method, the apparent stability constants of Zr(Ⅳ) with hydroxyurea are calculated as following: lg K1≈1.59, lg K2≈1.75, lg K3≈1.88, lg K4≈1.98, lg K5≈2 09, lg K6≈2 27, lg K7≈2 51, lg K8≈3 01. Under 1 0 mol/L HNO3, the complex ratio of Zr(Ⅳ) with hydroxyurea is 1∶4, and the apparent stability constants of Zr(Ⅳ) with hydroxyurea are lg K1≈2 33, lg K2≈2 51, lg K3≈2.78, lg K4≈3.31. Under 3.0 mol/L HNO3, the complex ratio of Zr(Ⅳ) with hydroxyurea is 1∶2, and the apparent stability constants of Zr(Ⅳ) with hydroxyurea are lg K₁≈2.69 and lg K₂≈2.79.