电化学方法研究铀酰离子在油/水界面的萃取转移过程

The transfer of uranyl ion at oil/water interfaces is an important issue in aqueous separation process for nuclear fuel reprocessing. The kinetic study for this process usually relies on the sampling and analysis of the bulk solution from both the aqueous and organic sides of the interface and lacks real-time monitoring tool, and the composition of the interfacial complex and the mechanism of the complexation and transfer process is not yet clear. In this project we plan to investigate this process by the electrochemical methodology at the interface between two immiscible electrolyte solutions. The current across the liquid/liquid interface will be used as a direct and real-time monitoring tool and nano-sized liquid/liquid interfaces and carefully selected supporting electrolytes will be introduced to overcome the difficulty imposed by the large iR drop due to the low polarity of the organic solvents used in nuclear fuel reprocessing. It aims to get the information about the interfacial complex formed by uranyl ion and TBP/NO3- and about the mechanism of complexation and transfer process. Moreover, the equilibrium potential across the liquid/liquid interfaces in reprocessing real system will be studied and the interfacial potential will be considered and evaluated as a factor of the distribution ratio in nuclear fuel reprocessing. By carrying out this project, we wish to establish an electrochemical methodology for ion transfer at interfaces between low-polarity organic solvent and water, which can be used in the study of ion transfer in aqueous extraction systems for nuclear fuel reprocessing and in similar systems.

铀酰离子在水/有机相界面上的转移过程是核燃料后处理水法萃取流程中的重要过程，对该过程的动力学研究一般依赖于界面附近体相溶液的取样分析，缺少直接和实时的监测手段；对其中界面络合物的组成和络合-转移机理目前还缺少一致认识。本项目拟采用液/液界面电化学方法研究这一过程，通过构筑纳米级的液/液界面和选用合适支持电解质来克服后处理体系有机溶剂极性低因而iR降过大的问题，利用伏安技术等电化学方法监测界面电化学极化情况下铀酰离子在界面的转移过程，以得到萃取剂TBP和硝酸根离子与铀酰离子形成的界面络合物的组成和络合常数，以及界面络合-转移机理。并研究实际后处理体系的液/液界面电位情况，将界面电位因素作为萃取分配比的一个影响因素加以考量。通过本项目的研究，期望建立起研究低极性有机溶剂与水形成的界面上的离子转移过程的液/液界面电化学方法，以适用于后处理萃取体系以及类似体系中离子转移过程的研究。

铀酰离子在水/有机相界面上的转移过程是核燃料后处理水法萃取流程中的重要过程，对该过程的研究传统上依赖于界面附近体相溶液的取样分析，缺少直接和实时的监测手段。本项目利用液/液界面电化学的手段，针对后处理体系有机相极性低，一般支持电解质难于溶解因而导电性不足的情况，通过筛选适用于TBP-正十二烷溶剂的支持电解质，以及拉制微米和纳米级的玻璃微管，初步研究了真实后处理溶剂体系中一些离子，包括铀酰离子等金属离子，以及硝酸根和氯离子等阴离子的界面转移过程，得到了该体系界面离子转移的电位窗口，以及控制该电位窗的离子转移过程，并比较了不同离子转移电位的差别，以及不同有机相溶剂组成的电位窗的差别；在此基础上对铀酰离子的界面转移过程进行了初步研究，观察到铀酰离子可在电位驱动下发生转移，得到了铀酰离子的转移电位，证明铀酰离子是以离子形式而非中性络合物的形式发生了转移。本项目工作的开展有助于加深对后处理溶剂萃取基本过程的理解，也有望为萃取工艺中以界面电位调节离子萃取分配比打下基础。