Mass Transfer Process by Diffusion of RE(III) (RE=La, Pr) in Eutectic LiCl-KCl Salt

Mass transfer is an important link in the entire electrode process. To investigate mass transfer process by diffusion of trivalent rare Earth ions in molten LiCl-KCl system, the electroreduction mechanism, mass transfer kinetics and diffusion layer thicknesses of RE(III) (RE = La and Pr) were studied by a series of electrochemical methods. It was found that RE(III) underwent one-step reduction reaction with the exchange of 3-electron and reversible processes. The diffusion coefficients (D) of RE(III) and limiting current densities (j l ) for RE(III)/RE pair were measured at different temperatures and concentrations by cyclic voltammetry and chronoamperometry, respectively. Based on the results of D and j l , the diffusion layer thickness (delta) of RE(III) was calculated using the simplified Nernst-Planck formula. Furthermore, the impacts of temperature and concentration on delta were explored. The results indicated that as the temperature declined and ions concentration increased, delta decreased. Meanwhile, the relationships between delta and temperature and concentration were also obtained.