Research on the Formation Mechanism of Impurity Carbon in Metals by the Rare Earth Molten Salt Electrolysis

Within the context of rare earth molten salt electrolysis, it is proposed that the reaction between anode gas and metal represents the primary pathway for the formation of carbon impurities in the metal. To investigate the mechanism underlying this formation process, high-temperature experiments involving both direct and indirect reaction systems were conducted. The direct reaction system examined the interaction between carbon monoxide gas and a praseodymium-neodymium metal alloy, whereas the indirect reaction system simulated the interaction between anode gas and rare earth metal during electrolysis, specifically within a carbon monoxide-electrolyte (NdF₃-LiF)-neodymium metal configuration. Direct reaction experimental results demonstrate that CO gas undergoes vigorous reactions with molten rare earth metals at 1050 ℃, leading to the formation of rare earth oxides, carbides, and elemental carbon. The indirect reaction study investigated the effects of parameters such as the CO gas injection position within the electrolyte and the reaction temperature on the carbon content in metallic neodymium. The findings revealed a significant increase in metal carbon content with increasing distance between the CO gas injection point and the molten metal surface. As the reaction temperature increases from 1050 ℃ to 1100 ℃, the carbon content in the metal exhibits a significant increase. This study investigates the carbon content in both the metal and the corresponding electrolytes during the electrolytic production of cerium and praseodymium-neodymium alloys. Furthermore, it examines the behavior of anode gases and their reaction products within the electrolyte, thereby elucidating the mechanism responsible for the formation of carbon impurities in the metal, as discussed in this paper. Research findings indicate that the carbon formation mechanism during rare earth molten salt electrolysis inhibits the reaction between anode gases and metals, thereby reducing the carbon content in rare earth metals while simultaneously improving current efficiency.