Abstract
The neodymium electrolysis produces unnecessary high emission of CF4 and C2F6. These perfluorocarbons (PFCs) are potent greenhouse gases and are not filtered or destroyed in the off-gas. A process control in analogy to the aluminum electrolysis can reduce the PFC emission to a great extend and keep the process in a green process window. Therefore, a theoretical analysis is done of the cell voltage of the industrial neodymium electrolysis in dependence on the neodymium oxide concentration in the electrolyte. The analysis shows the different contributions to the cell voltage focusing on the impact of the anodic overvoltage on the cell voltage, by which the electrolysis process can be controlled. The model of the cell voltage is evaluated by laboratory neodymium electrolysis with a similar setup as the industrial cell. The relation of the oxide concentration, the anodic current density and the cell voltage with the cell resistance are measured. The continuous off-gas measurements show the gas concentration and PFC emissions. The effect of Nd2O3 feeding on the galvanostatic electrolysis is analyzed as well. Based on the results a process control strategy is proposed similar to the aluminum electrolysis strategy. The green process window is in a narrow oxide concentration range, making a continuous and precise oxide feeding essential.
Highlights
IntroductionNeodymium as other rare earth elements is transformed to metal by oxide elec-
A process control in example of the aluminum electrolysis can be applied to the rare earth electrolysis
The theoretical analysis of the neodymium cell voltage in analogy to the aluminum electrolysis shows the impact of the different contributions but deviates from laboratory measurements
Summary
Neodymium as other rare earth elements is transformed to metal by oxide elec-. The current density should not be higher than the partial anode effect at a given oxide concentration in the electrolyte. A decrease in greenhouse gas emission over time was achieved by improvements in its process control with an appropriate feeding strategy, lowering the number and time of anode effects. The process control should manage the right amount of oxide in the electrolyte, avoiding the critical conditions of PFC formation. A similar process control is needed for the rare earth electrolysis. Foremost the neodymium electrolysis should be equipped with an automated process control because of its production quantity. The control system can be applied to the other rare earth oxide electrolysis processes as well
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