Determination Of La(III) And Mg(II) Ion Concentrations In KCl-LiCl Melt By Molten Salt Electrochemical Method

At present,methods of tranditional detection are hysterical and destructive.At the same time,there are deficiencies in the detection process,such as cumbersome testing procedures,lengthy time and expensive detection costs,which can not match with requirements of the real-time on-line detection and remote operability in field of spent fuel molten salt electrolysis post treatment.It is significant for detection of ion concentration by molten salt electrochemical method in the post treatment of spent fuel molten salt electrolysis.In this thesis,KCl-LiCl was used as the electrolyte systemThe results of single La（Ⅲ）and Mg（Ⅱ）concentrations detected by cyclic voltammetry and chronopotentiometry were showed,the reaction of La（Ⅲ）and Mg（Ⅱ）on the W electrode was three electrons deposited by one step,and two electrons deposited by one step,respectively.The deposition potential of La（Ⅲ）relative with Ag/AgCl electrode was about-2.0 V.If the LaCl₃ concentration was less than2.29×10^-44 mol/cm³,the error of cyclic voltammogram detective method was less than3.49%.The error of chronopotentiometry detective method was less than 4.21%.Diffusion coefficient of La（Ⅲ）was 0.391×10^-55.42×10^-55 cm²/s.The depostion potential of Mg（Ⅱ）relative with Ag/AgCl electrode was about-1.9 V.If the MgCl₂ concentration was less than 4.15×10^-44 mol/cm³,the error of cyclic voltammogram detective method was less than 2.23%.The error of chronopotentiometry detective method was less than 6.58%.Diffusion coefficient of Mg（Ⅱ）was 0.0243×10^-56.37×10^-55 cm²/s.The large deviations at high concentrations may be affected by the ionic diffusion-coefficient.The detective error of cyclic voltammetry decreased from 0.42 to 10.52 percent when the diffusion-coefficient was revised by mathlab with the concentration of LaCl₃ raised from 3 wt%to 7 wt%.The detection error of the method declined from 0.51 to 5.61 percent,respectively.The results of both La（Ⅲ）and Mg（Ⅱ）concentrations detected by cyclic voltammetry and chronopotentiometry were showed in the KCl-LiCl-MgCl₂-LaCl₃eutectic salt system.the relationship between the cathode i_p and v^1/2 was linear,the result showed that the reduction process of Mg（Ⅱ）and La（Ⅲ）was controlled by the diffusion step.If the MgCl₂ concentration was between 1.22×10^-42.84×10^-4mol/cm³,the error of cyclic voltammogram detective method was less than10.13%.Under the detection of cerium ion concentration,the working electrode was affected by the deposition of magnesium,its surface state changes.the deviation is large.Under the detection of ion concentration by chronopotentiometry,if the MgCl₂concentration was between 1.12×10^-44.47×10^-44 mol/cm³,the error of chronopotentiometry detective method was less than 9.57%.Diffusion coefficient of Mg（Ⅱ）was between 0.643×10^-58.10×10^-55 cm²/s.Under the detection of LaCl₃concentration,due to the deposition process of Mg（Ⅱ）,If the LaCl₃ concentration was0.467×10^-4 mol/cm³.the error of cyclic voltammogram detective method reached28.1%.With the increasing of the ions concentration in the melt,the error expand to 82.1% furtherly.