TBP-煤油从硝酸介质中萃取七价锝的动力学研究

【作者】 王辉；

【导师】 贾永芬； 王孝荣；

【作者基本信息】 中国原子能科学研究院 ， 核燃料循环与材料， 2007， 硕士

【摘要】 锝是乏燃料后处理工艺中广泛关注的元素，因为其裂变产额高，行为复杂，对铀钚分离工艺过程的影响很大。锝的萃取行为是影响锝在Purex流程中走向的关键因素，而萃取动力学则是研究其萃取行为很重要的一个方面，不仅可以为认识过程机制提供参考，而且能够提供有实用价值的数据。关于锝萃取动力学的研究目前很少见报道，因此有必要开展这方面的研究工作。本课题在Lewis池的基础上设计加工了用于锝萃取动力学研究的恒界面萃取实验装置。该装置能有效减少物料的消耗量和废液的产生量，且运行状况良好，可以广泛的适用于放射性物质的萃取动力学研究。已报道的锝萃取热力学研究表明，在Purex流程中对锝萃取行为影响最显著的因素是硝酸浓度、锆浓度以及铀浓度。因此本课题考察了TcO₄^-／HNO₃／TBP-煤油、TcO₄^-／HNO₃-Zr／TBP-煤油、TcO₄^-／HNO₃-U／TBP-煤油以及TcO₄^-／HNO₃-Zr-U／TBP-煤油等萃取体系中锝的萃取动力学行为。通过搅拌转速、界面面积以及温度判别法表明，搅拌转速为156rpm以上时，上述四个体系中锝的萃取属于界面化学反应与相内化学反应综合控制的动力学模式。根据实验结果所建立的锝初始萃取速率方程如下：TcO₄^-／HNO₃／TBP-煤油体系中1.8mol／L≤[HNO₃]_a≤5.0mol／L时，锝的初始萃取速率方程为：式中V为水相体积，S为界面面积。25℃下表观速率常数K_Tc-HNO3=（0.205±0.031）mol.（-0.74）·L^0.74·min^-1·cm^-1，表观活化能E_a=-26.3kJ／mol。TcO₄^-／HNO₃-Zr／TBP-煤油体系中1.8mol／L≤[HNO₃]_a≤5mol／L时，锝的初始萃取速率方程为：25℃下表观速率常数K_Tc-Zr=（0.221±0.016）mol^-2.59·L^-2.59·min^-1·cm^-1，表观活化能E_a=-22.4kJ／mol。TcO₄-／HNO_3-U／TBP-煤油体系中1.1mol／L≤[HNO₃]_a≤5mol／L、[U]_a≤261mmol／L、[TBP]。≤1.35mol／L时，锝初始萃取速率方程为：25℃下表观速率常数K_Tc-U=（0.135±0.021）mol^-0.94·L^0.94·min^-1·cm^-1，表观活化能E_a=-12.8kJ／mol。TcO₄^-／HNO₃-Zr-U／TBP-煤油体系中1.1mol／L≤[HNO₃]_a≤5mol／L、[U]a≤120mmol／L时，锝初始萃取速率方程为：25℃下表观速率常数K_total=（1.76±0.16）mol^-0.97·L^0.97·min^-1·cm^-1，表观活化能E_a=-10.8kJ／mol。文中根据实验结果对锝萃取机理进行了探讨。相关热力学实验结果与已报道的锝萃取热力学研究结果相一致。更多还原

【Abstract】 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.更多还原