Production of High Purity Rare Earth Metals by the Continuous Processing Composed of Calciothermic Reduction and Vacuum Melting.

1.初步实验差热分析表明，NdF_3在1093K开始发生钙热还原。通过热分析估算了NdF_3-CaF_2体系的相图。本文还研究了利用本实验室研制的该装置测定钕中氧含量的分析方法与流量和温度的关系。研究了不同温度、不同反应时间、不同加钙量对NdF_3钙热还原的影响。从纯度和还原比两方面考虑了获得块状钕的最佳条件，同时考虑了炉渣与金属、炉渣与坩埚的分离。真空熔炼的优化以工业生产的钕和钙为原料，在不同的温度、反应时间、初始杂质含量和搅拌条件下进行了真空熔炼的模型实验。讨论了脱除挥发性杂质的最佳条件，以及在钙热还原和真空熔炼过程中溶解的坩埚物质的沉淀。连续工艺的优化在前面实验结果的基础上，确定了连续工艺的最佳工艺条件为：在1750K下，钙的加入量为化学计量摩尔的1.2倍，进行0.9K的钙热还原；首先在1500K下搅拌真空熔炼1.2K，然后降温至略高于钕的熔点3.6K。

1. Preliminary ExperimentsDTA revealed calciothermic reduction of NdF_3 starts at 1093 K.The phase diagram of the NdF_3-CaF_2 system was estimated by thermal analysis. The analytical procedures of oxygen content in neodymium using the device in our laboratory were also studied as a function of flux and temperature.2. Optimization of Calciothermic Reduction of NdF_3Calciothermic reduction of NdF_3 were studied for various temperatures, reaction periods, and quantities of calcium addition. Optimum conditions for obtaining a lump of neodymium were considered not only based on purity and reduction ratio but also separation between slag and metal, and that between slag and crucible.3. Optimization of Vacuum MeltingUsing commercially produced neodymium and calcium, model experiments of vacuum melting were conducted for various temperatures, reaction periods, initial impurity contents, and stirring condition. Optimum conditions were discussed not only for the removal of volatile impurities but also precipitation of crucible material dissolved during the calciothermic reduction and the vacuum melting.4. Optimization of the Continuous ProcessingOn the basis of the previous experimental results, optimum conditions for the continuous processing were determined as follows : calciothermic reduction is carried out for 0.9 ks at 1750 K by the addition of calcium 1.2 times as much as the stoichiometric moles : and vacuum melting is carried out at first for 1.2 ks at 1500 K with stirring, then, by decreasing temperature down to just above the melting point of neodymium, for 3.6ks.