Electrochemistry For Nd Electrowinning From Fluoride-oxide Molten Salts

Rare earth is the wide application of resources currently, there are abundant reserves in our country. Molten salt electrolysis is the main method of rare earth production up till the present moment, which has advantage of low cost, easy to control composition uniformity, good quality, and easy to achieve continuous. But there still have issues of high energy consumption and high emissions. Neodymium is a very typical rare earth metal, and has very important applications in the field of permanent magnet and nonferrous modified. It has the important theoretical and practical significance for studying of electrochemistry for Nd electro winning from fluoride-oxide molten salts. Some conclusions can be used in other rare earth metals. This paper studied the anode process of oxygen ions and fluoride ions in LiF-NdF3-Nd2O3 melt, Pre-electrolysis of LiF-NdF3. And cathode process of neodymium ions has been studied in LiF-NdF3 melt.Cyclic voltammetry was applied to characterize oxygen ions and fluoride ions oxidation processes in LiF-NdF3-Nd2O3 melt. The effects of the concentration of neodymium oxide, temperature, electrode area on the oxygen ion oxidation and critical potential have been discussed. The peak current density of oxygen ion oxidation displays a linearship with no more than 2.5wt% Nd2O3 in LiF-NdF3 (30wt%-70wt%) melt. The increase temperature from 950℃ to 1100℃ has significant increase in the oxygen ion oxidation current.The kinetics of the oxgen ion oxidation process in LiF-NdF3-Nd2O3 is controlled by both interfacial step and mass transfer.While the kinetics of the flouride ion oxidation process is controlled by electrochemical reaction step. The critical potential for the anode effects obtained by reverse scan is controlled by potential but independent on the electrode area. The Nd2O3 concentration and Temperature has almost no effects on the critical potential of anode effects. The starting potential for flouride ions oxidation shifts positively 0.9V as Nd2O3 concentration increases from background (0.1 wt%) to 2.5wt%. The rate of electricity quantity for oxygen ions oxidation to flouride ions oxidation per square centimeter increases with Nd2O3 concentration,and reaches about 0.9 in the melt with 2.5wt% Nd2O3.In the study of cathodic process, cyclic voltammetry and square wave been used to characterize the cathodic process of neodymium ions. And by calculating the number of electrons transferred, there are three processes Nd3+â†'Nd2+, Nd2+â†'Nd, Nd3+â†'Nd, and determining the reduction potential of each one. The kinetics of the Nd3+â†'Nd2+ process in is controlled by mass transfer. The kinetics of the Nd+â†'Nd, Nd3+â†'Nd process in is controlled by both interfacial step and mass transfer. But after neodymium metal was added into the melt, The kinetics of three process all become controlled by mass transfer.