China Nonferrous Metallurgy

In the production process of rare earth metal praseodymium neodymium, it is easy to form nodules at the bottom of the molten salt electrolytic cell, which not only affects the continuity of production, but also affects the product quality. At present, most of the related literatures focus on the composition of nodules and the influence of electrolytic parameters on nodules. Few literatures have studied the mechanism of nodule formation. In this paper, the morphology and crystal composition of the furnace bottom nodule are analyzed. It is found that the composition of the nodule is neodymium oxide, praseodymium oxide, neodymium oxyfluoride and a small amount of neodymium fluoride and metal neodymium. The numerical simulation method was used to analyze the electrolytic flow field, and the reason for the formation of nodules at the bottom of the furnace was obtained. The main reason for the formation of nodules is that the feeding speed is too fast，and the melting point of neodymium oxyfluoride is higher than that of molten salt, and it is easy to deposit on the steps of graphite crucible to form nodules. Rare earth metals will take away a lot of heat when they leave the furnace, resulting in a large change in the temperature of the furnace bottom，and neodymium oxide is easy to precipitate in the lower temperature area and deposit on the steps of graphite crucible. The fluidity of the molten salt at the bottom of the electrolytic cell is poor, so that the products precipitated on the steps of the graphite crucible cannot be deposited with the flow of the molten salt. By controlling the feeding speed and maintaining a reasonable electrolysis temperature, excess materials or precipitated materials can be avoided to deposit on the crucible step. The growth rate of nodules can be controlled by cleaning the bottom of the furnace and the accumulated materials on the step in time.