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In this paper a method for producing niobium from columbite was proposed by the authors. The columbite used contained 51.20 Nb_2O_5,16.53 Ta_2O_5,6.06 TiO_2,2.50 WO_3,2.62 SnO_2,1.08 SiO_2,14.79 FeO, and 5.21 wt. % MnO. Before producing the metal niobium, it was necessary to extract pure niobium compound from ore. The first step of decomposing the ore to prepare a mixture of niobium and tantalum pentaoxide was attempted by means of the fusion with alkali fluxes. The second step of separating niobium from tantalum was proposed for the solvent extraction. Niobium pentaoxide obtained was converted to pure compound such as K_2NbF_7. The last step of producing of niobium was carried out by electrolysis of the fused salt mixture. The conditions to be preferred for the above step are given as follows : (1) Fusion with sodium hydroxide and sodium peroxide. It was preferred to use a mixture of sodium hydroxide and sodium peroxide as flux for columbite. The optimum fusion mixture was found to be 1 part of-100 mesh ground ore, 2 parts of NaOH, and 0.5 part of Na_2O_2. The alkali mixture was preliminarily heated in a nickel crucible to above the melting temperature and the ground ore was added in small portions so that a gentle reaction might proceed. After the addition of the ore the temperature was kept at 600℃ for 40 to 60 minutes. The solidified melt was digested with hot water. The insoluble sodium niobate and tantalate were separated from most of soluble impurities, particularly, tungusten and tin. The niobate and tantalate were decomposed by hydrochloric acid which dissolved manganese and iron eventually. It was relatively difficult to remove titanium. The yield of the mixture of niobium and tantalum pentaoxide from columbite was about 90%.(2) Solvent extraction with MIBK-HF-H_2SO_4. The preparation of the pregnant solution was made by dissolving the mixture of both pentaoxides in 56% HF solution. The pregnant solution composed of 20.40 Nb_2O_5,5.48 Ta_2O_5,1.20 TiO_2,0.42 SnO_2,0.45 FeO+MnO, and 22.89g HF per 100g of solution. This solution was adjusted to contain 100g of total pentaoxides with various acidities of HF and H_2SO_4. The equilibrated MIBK phase with 6.8N HF-7 N H_2SO_4 solution was capable of extracting 62.81g Nb_2O_5,and 22.28g Ta_2O_5 per liter. The stripping solution adjusted to 0～2 N HF and 0～2 N H_2SO_4 was used for recovering niobium and tantalum in the usual manner. The niobium pentaoxide extracted contained 8～9% Ta_2O_5,and tantalum pentaoxide 20～40% Nb_2O_5. Therefore it was necessary to repeat the extraction for preparing pure niobium compound.(3) Electrolysis of K_2NbF_7 with alkali halides. Pure niobium metal was prepared by the electrolysis of fused salts of K_2NbF_7 and NaCl, and the eutectic mixture of NaCl and KCl. Before the electrolysis, the liquidus curves of pseudo-binary system of K_2NbF_7 and KCl, and that of K_2NbF_7 and NaCl were determined. Thereafter the electrolysis was performed on the composition of 20% K_2NbF_7 in NaCl at 800℃, and in NaCl-KCl eutectic mixture at 750℃. In a run of NaCl mixture the dendritic cathode deposit was obtained for 450-600A/dm^2 of the cathode current densities. On the other hand a coarse deposit was obtained from the eutectic mixture of NaCl and KCl on the same condition as above. The general trend in the electrolysis showed that the current efficiency was about 20% for 20% K_2NbF_7 in NaCl at 800℃, and 10% for 20% K_2NbF_7 in NaCl-KCl eutectic mixture at 750℃.

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