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 (jl) 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 jl, the diffusion layer thickness (δ) of RE(III) was calculated using the simplified Nernst-Planck formula. Furthermore, the impacts of temperature and concentration on δ were explored. The results indicated that as the temperature declined and ions concentration increased, δ decreased. Meanwhile, the relationships between δ and temperature and concentration were also obtained.