Anode processes for Nd electrowinning from LiF-NdF3-Nd2O3 melt

• Oxidation of oxygen ions processes include adsorption and gas evolution of oxidation products.
• During adsorption process, the peak current density and the peak potential of oxidation of oxygen ions increase linearly with the increase of Nd2O3 concentration.
• During the adsorption process, the kinetics of the oxygen ions oxidation is controlled by both electrochemical reaction step and mass transfer. During the gas evolution, the oxidation of oxygen ions process is controlled by electrochemical reaction step.
• The critical potential by reverse scan is independent of the electrode area, but depends on electrode area by positive scan.
• The temperature between 950 °C to 1050 °C has more effects on the oxygen ions oxidation current but almost no effects on the critical potential of anode effects. At 950 °C, after the critical potential relatively big current peaks involving formaiton of perflouride compounds occurs.

ABSTRACTCyclic voltammetry was applied to characterize oxidation processes of oxygen ions and fluoride ions on a graphite electrode in LiF-NdF3-Nd2O3 melt. The effects of the concentration of Nd2O3, temperature, electrode area on the oxidation of oxygen ions and critical potential have been discussed. Oxidation processes of oxygen ions include adsorption and gas evolution of oxidation products, which is proved by the the smooth and fluctuant cyclic voltammograms. During adsorption process, both the peak current density and the peak potential of oxidation of oxygen ions increase with the increase of Nd2O3 concentration. The peak current density of oxidation of oxygen ions displays a linearity within 2.5wt% Nd2O3 in the melt. The kinetics of the oxidation of oxygen ions is controlled by both electrochemical reaction step and mass transfer. During gas evolution, the oxidation process of oxygen ions is controlled by electrochemical reaction step. Oxidation of flouride ions starts from the critical potential. The critical potential by reverse scan is independent of the electrode area, but depends on electrode area by positive scan. Increasing temperature causes significantly increased the adsoprtion current density for oxidation of oxygen ions. At 950 °C, after the critical potential relatively big current peaks involving formaiton of perflouride compounds occurs after the cirtical potential.