Tert-butyl Hydrazine Reduction Of Np (vi), The Dynamics In The U, Np Separation

With the development of nulear power industry,more and more attention has been given to the spent nulear fuel reprocessing.Purex process will remain predominant in the foreseenable future.Because the valence of Np,one kind of transuranium elements,is easy to interchange,the route of Np in Purex process is difficult to be controled.A lot of work has been done on the control of neptunium way in the world. One of important methods in separation of neptunium from U,Pu is selectively reducing Np(VI) to Np(V) which cannot be extracted by 30%TBP/OK,while the valence of U,Pu remains stationary.As the representatives of salt-free organic reductants,hydrazine derivatives possess such advantages as strong reductivity and high selectivity.The kinetics of the reaction of Np(VI),Pu(IV) reduction by hydrazine derivatives have been studied deeply since 1980s.The results show that it's potential for applying hydrazine derivatives as salt-free reductants in Purex process in the near future.Tert-butyl hydrazine(TBH) is a kind of hydrazine derivatives.The preliminary research results show that TBH can effectively reduce Np(VI) to Np(V).What's more,among all hydrazine derivatives ever reported in literature,the ratio of the reaction rate constants of Np(VI) reduction by TBH to that of Pu(IV) reduction by TBH is the most largest,thus it has been considered as one of promising selective reductants.In order to research systematically the kinetics of the redox reaction between TBH and Np(VI),the main contents of the work in this paper are as follows.(1) TBH is synthesized by direct alkylization in CHsOH media.The structure and composition of the product are characterized by elemental analysis,UV-Vis spectrum,IR spectrum,MS spectrum and NMR spectrum respectively.(2) The method of determining the concentration of TBH is studied in this paper.The concentration of normal-amount TBH can be determined by KIOs oxidation.The presence of HNOa in the titration media has no effect on the tritration results.The concentration of trace-amount TBH can be determined by colorimetric methodising paradimethylaminobenzaldehyde as a color reagent.The concentration of TBH is linearly dependent on the Absorbance when the concentration of TBH is 1.6xlO"3mol/L-1.5xlO"2mol/L.The relative deviation of the results compared with the result of no U(VI) are 2.5%when the concentration of U(VI)0.26g/L.(3) The kinetic study of the reaction between nitrous acid and TBH is performedjthe reaction rate equation may be expressed as follows:- dc(HNO2)/dt=kc(HNO2))c(TBH)c136 (H+)The rate constant equals S.SOxlO3 (mol/l/min"1 at 25' C and activation energy of the reaction equals to 60.7kJ/mol.(4) The kinetic study of Np(VI) reduction by tert-butyl hydrazine in nitric acid media is carried out,the reaction rate equation may be expressed as follows:-dc(Np(VI))/dt=kc(Np(VI))ca9 (TBH)/ca75 (H+)the rate constant of the reaction at 25C equals to 5.44(mol/L)-0.15min-1,the activation energy of the reaction equals to 61.2kJ/mol.The influences of NO3-,UO22+,Fe3+on the reaction rate are negligible in its concentration range studied,the reaction rate increases when the concentration of HNO25.71 X 10-3mol/L .The reaction rate increases apparently with rising temperature.(5) On the basis of batch stripping experiments and process parameters for washing Tc,the counter current cascade experiments of stripping U from organic phase and washing Np from organic phase are performed respectively.The stripping percentage of Np is 44.1% under experimental conditions.