STUDY ON REDUCTION AND BACK EXTRACTION OF PU(Ⅳ) BY UREA DERIVATIVES IN NITRIC ACID SOLUTIONS

摘要

The reduction kinetics of Pu(Ⅳ) by hydroxyl-semicarbazide(HSC), hydroxyurea(HU) and dihydroxyurea(DHU) in nitric acid solutions were investigated separately with the kinetic equations as below: ForHSC: -d[Pu(Ⅳ)]/dt = k[Pu(Ⅳ)][HSC]~(1.06)[H~+]~(-0.43)[NO_3~-]~(-0.58), where k = 11.8 ± 1.1 (mol/L)~(-0.046)·s~(-1) at 22 °C, 1.0～2.5 mol/L HNO_3, E = 42.0 kJ/mol; For HU: -d[Pu(Ⅳ)]/dt = k[Pu(Ⅳ)]~2[HU] [H~+]~(-0.9), where k = 5853±363 (mol/L)~(-1.1)·s~(-1) at 13 °C, 1.0～3.0 mol/L HNO_3, E = 81.2 kJ/mol; And for DHU: -d[Pu(Ⅳ)]/dt = k[Pu(Ⅳ)]~2[DHU]~(0.25)[H~+]~(-1.5), where k = 1280 ± 120 (mol/L)~(0.25)·s~(-1) at 4 °C, 0.6～2.5 mol/L HNO_3, E = 89.2 kJ/mol. In addition, counter-current cascade experiments were conducted for Pu split from U in nitric acid media using three kinds of reductant, respectively. The results indicated that urea derivatives are one kind of promising salt-free reductant for U/Pu split. Furthermore, the complexing behavior of HSC with Np(Ⅳ) were also presented.