Tbp-kerosene From Nitric Acid Extraction Of Heptavalent Technetium Kinetics

Technetium is a widely concerned element in spent fuel reprocessing because of its high fission yield and complex behaviors which may effect the separation of uranium and plutonium. Little research on extraction kinetics of technetium was reported, which is the aim of this work.A device is made according to the principle of Lewis cell for the study of technetium extraction kinetics. It can be used in research of radioactive elements extraction kinetics by simple operation, reducing the consumption of radioactive material and production of waste.The extraction kinetics behaviors of technetium in TcO₄^-/HNO₃/TBP-kerosine, TcO₄^-/HNO₃-Zr/TBP- kerosine, TcO^4-/HNO₃^-U/TBP- kerosine and TcO₄^-/HNO₃-Zr-U/TBP-kerosine system were studied by the device above. The ertaction mode is determined and the rate equation is obtained. It indicates that the extraction of technetium is controlled by diffusion mode under 136rpm of stirring speed and by chemical reaction mode above 156rpm of stirring speed.In the system of TcO₄^-/HNO₃/TBP-kerosine, when1.8mol/L≤[HNO₃]a≤5mol/L, the extraction rate equation is where V denotes the the volume of aqueous phase and S denotes interface area. The apparent extraction rate constant at 25℃is (0.205±0.031)mol^0.74·L(-0.74)·min^-1·cm^-1 and the apparent activation energy is -26.3kJ/mol.In the system of TcO₄^-/HNO₃-Zr/TBP-kerosine, when 1.8mol/L≤[HNO₃]a≤5mol/L, the rate equation is The rate constant at 25℃is (0.221±0.016)mol_-171·L_1.71·min_-1·cm_-1, and the apparent activation energy is -22.4kJ/mol.In the system of TcO₄^-/HNO₃-U/TBP-kerosine, when 1.1mol/L≤[HNO₃]_a≤5mol/L,[U]_a≤261mmol/L,[TBP]₀≤1.35mol/L, the rate equation is The rate constant at 25℃is (0.135±0.021)mol^-0.94·L^0.94·min^-1·cm^-1 , and the apparent activation energy is -12.8kJ/mol.In the system of TcO₄^-/HNO₃-Zr-U/TBP-kerosine,when 1.1mol/L≤[HNO₃]_a≤5mol/L, [U]_a≤120mmol/L, the rate equation is The apparent rate constant at 25℃Cis k_total=(1.76±0.16)mol^-0.97·L^0.97·min^-1·cm^-1, and the apparent activation energy is -10.8kJ.Mechanism of technetium extraction in some system is disscussed in this paper.The distribution of technetium under the same conditions of the four systems above is obtained. It indicates that the results are consistent with the data in relevant literature.