Reaction Kinetics of Tc(Ⅶ) With Acetohydroxamic Acid in Aqueous HNO₃ Medium

The kinetics of the reaction of acetohydroxamic acid (AHA) with Tc(Ⅶ) was studied in aqueous HNO₃ medium by solvent extraction method. The results show that Tc(Ⅶ) is reduced slowly by AHA to a hydrophilic lowvalent species Tc^Ⅱ(NO)(AHA)₂H₂O⁺, which has low distribution ratio (approxamately 0.006) in 30%TBP/keroseneHNO₃ system. The UVVis spectrum of the solution after the reaction reveals that the final product has absorption peaks at 428 nm （ε＝2 559 L·mol^-1·cm^-1） and 565 nm. The apparent reaction rate equation in HNO₃ medium is r＝-dc(Tc(Ⅶ))/dt＝k′c(Tc(Ⅶ))c^1.6(AHA), t_1/2 is determined to be 16.5 h under condition of 18 ℃, c(AHA)＝1.0 mol/L and c(HNO₃)＝0.50 mol/L. The presence of Pu(Ⅳ) in the reaction system will accelerate the reduction of Tc(Ⅶ), while the distribution ratio of Pu keeps constant, which may strongly impact Tc behavior in the spent fuel reprocessing.