2,974,007 United States Patent "lee . _ V Patented Mar. 7,1961‘,

1 “ I, 2 sure. The reaction is advantageously carried out with the exclusion of moisture ‘in an inert atmosphere, for 2,974,001 example, under nitrogen or carbon dioxide.‘ The reac PROCESS FOR THE RECOVERY OF NIOBIUM tion must, of course, be carried out at a temperature AND/OR TANTALUM FROM MIXTURES ‘OF below the decomposition temperature of the double THEIR PENTAHALIDES formed, that is to say, at‘ a temperature below about Walter ‘Scheller, Neuewelt, near Basel, Switzerland, 500° C. The speed of the reaction is fairly high at assignor to Ciba Limited, Basel,‘ Switzerland temperatures above about 300° C. It is possible to work at temperatures above 500° C., that is to say up to about No Drawing. Filed Nov. 8, 1957, Ser. No. 695,213 900° C., if the reaction is carried out under 'superatmos Claims priority, application Switzerland Nov. 13, 1956 pheric pressure, so that thedecomposition temperature of the double salt is correspondingly raised. Thus,‘ the 14 Claims. (Cl. 23-'-21) pentachloride mixture may be reacted in an apparatus, which ‘may have been previously evacuated, with ?nely This invention provides a process for the recovery of 15 powdered dry chloride, which may be diluted the anhydrous halides of niobium and tantalum from with an inert solid diluent such as carbon, and advan mixtures of their pentahalides, in which a relatively pure tageously while mechanically moving the mixture. In tantalum fraction or niobium fraction is obtained and the stead of , there may be used a mixture _N‘*44——————44a4*<444.. residual material has a relatively large concentration of of potassium ‘chloride with its double salt with niobium the other element. 1 20 or tantalum pentachloride, which mixture advantageously In the process of this invention the mixture of penta has a content of potassium chloride corresponding to the halides, especially a mixture of niobium pentachloride quantity of niobium or tantalum pentachloride present and tantalum pentachloride, is reacted with ‘a metal halide in the mixture of pentachlorides, respectively. capable of forming a double salt with tantalum penta The'pentachlorides of niobium and tantalum diluted chloride, and the tantalum-containing double salt so with an inert ‘carrier gas, such as nitrogen, may be re; formed is separated from a fraction enriched in niobium. acted at ‘300—500° C. with potassium chloride in a shaft The mixture of the pentahalides of niobium and tan furnace or tubular furnace which contains the potassium talum used as starting material can be obtained by chloride alone or diluted with .an inert solid carrier. "It methods in themselves known. Thus, for example, the is of advantage to circulate the waste gases from the mixture may be obtained by the chlorination of a mate chlorination reaction repeatedly over the potassium chlo rial which contains niobium and tantalum in oxidised ride in order to bring into reaction as much as possible or form, for example, a slag or especially a concentrate or the tantalum’ pentachloride remaining in the Waste gases. ore, which may have been after-treated to enrich it in The chemistry of the reaction leading to the formation 7 the aforesaid elements, or a mixture of the oxides of of the double salt may probably be explained in that, at these two metals, with gas and a reducing agent, 35 '?rst both potassium chloride double are formed, such as carbon. For this purpose an ordinary indus namely the double salt of niobium pentachloride and the trially available mixture of the oxides of niobium and double salt of tantalum pentachloride. The tantalum tantalum or a natural product which contains these two pentachloride double salts however are usually more elements generally in the form of their oxides, may be stable than the corresponding niobium double salts, which made into briquettes with carbon, and the briquettes entails the possibility of separating the niobium and treated with chlorine gas at 400-1000" C. in a shaft fur tantalum ‘fractions. , nace or tubular furnace. The chlorination products so Instead of carrying out the reaction to form the double obtained, which may contain considerable amounts of salts between gaseous and solid components, it may be niobium oxychloride, may be subjected to further chlorin carried out between liquid and solid components. For ation with chlorine gas in the presence of carbon, in this purpose, for example, anhydrous'potassium chloride order completely to convert the oxychlorides into penta may be'treated‘with the molten pentachlorides or treated chlorides. The greater part of the chlorides of elements, with the pentachlorides in the presence of an inert solvent. other than niobium and tantalum, also formed during the The ‘fact that the double salts of tantalum pentachloride chlorination compounds of which elements are usually with halides of alkali metals or alkaline earth metals are present as impurities, for example, the chlorides of tita 50 more stable than those of niobium pentachloride can be nium, tin, manganese etc., may be removed, for example, utilized for re?ning the niobium pentachloride by means by so adjusting the temperature in the chlorination zone of chromatographic adsorption. As the adsorption col and the zone in which the vapours of the chlorides of umn,‘ there'is used a column of a' powdered halide of niobium and tantalum are condensed that the chlorides of an or alkaline earth metal in anhydrous the accompanying elements, whose boiling or volatiliza ' form. tion points are generally widely different from those of hydrousAs solvents solvents for which the pentachlorides vdo not react withthere the are pentachlo used the chlorides of niobium and tantalum, are separated to a considerable extent from the latter chlorides. rides' or react only to form SOlV?IiCS, and especially thionyl As metal halides which are capable of forming double vchloride, sulfur monochloride, sulfur dichloride, sulfuryl salts with tantalum pentachloride there may be mentioned .chloride or ethyl bromide. In order to remove the tanta besides thallium halides primarily the halides of alkali lum as completely as possible, it is of advantage to run the metals and alkaline earth metals, and advantageously various eluates from the chromatographic ‘separation re halides or those alkali metal chlorides and alka peatedly through the column, so that a progressively purer line earth metal chlorides whose metal ions have a diam— niobium fraction is obtained and the tantalum is retained eter greater than the ion. Especially advan in the column as the double salt. ~ ' tageous is anhydrous potassium chloride. _ In order to form the double s-alt there is used at least The reaction of the mixtures of the pentahalides of one molecular proportion of ‘alkali metal halide or %' niobium and tantalum with the halides of alkali metals molecular proportion of alkaline earth metal halide for or alkaline earth metals to obtain the tantalum-containing every molecular proportion of tantalum pentahalide pres double salts that are stable at low temperatures, that is 70 ent in the mixture. ' ' ' ' to say at temperatures up to about 500° C., may be The separation of the tantalum-containing double salt carried out under superatmosphen'c or atmospheric pres from the niobium-rich fraction olfers no special di?iculty. 2.974.901 3 4 If, the formation of the double salt is carried out by re Example 2 action between vapour and solid phases, the double salt A distilled mixture of niobium and tantalum penta remains behind as solid residue, and the vapour phase is chlorides, consisting of 4.2 grams of niobium pentachlo enriched with niobium pentachloride. If the formation ride and 0.64 gram of tantalum pentachloride (which of the double salt is carried out by reaction in the liquid corresponds to 83.8% Nb2O5 and 16.2% of Ta2O5) was phase, for example, by chromatography through a column dissolved in 200 grams of thionyl chloride, and the so of solid potassium ?uoride, the niobium pentahalide can lution was ?ltered in an inert dry atmosphere. The solu be recovered by thermal decomposition of the reaction tion was run through a column of . product which remains after distilling off the solvent, and The absoption column consisted of a layer 45 cm. high the higher melting tantalum-containing double salt, which 10 of ?nely pulverised anhydrous potassium ?uoride having remains in the column, can be recovered therefrom in a a diameter of 2 cm., and the column was conditioned with similar manner. thionyl chloride. For the purpose of regenerating the tantalum penta The solution of pentachlorides was passed through the halide from the double salt so formed, the double salt column four times at the rate of about 200 ml. per hour. may be subjected to thermal decomposition at a tempera 15 10 ml. of each solution that ran through the column ture above 500° C., and advantageously at a temperature was removed, the thionyl chloride was evaporated and within the range of 550-800° C., whereby the halide is the residue converted into oxides by ammoniacal hydrol obtained as a sublimate. The thermal decomposition of ysis. After the fourth passage through the column it was the double salt may also be carried out under reduced washed with 200 grams of fresh thionyl chloride. pressure. By using two “moving beds,” one bed being 20 In the following table are given the proportions of maintained, for example, at a temperature within the pentachlorides present in the solution after each passage, range of 280-500" C. for double salt formation and the which were measured by spectographic methods, and also other bed, for example, at a temperature within the range in the thionyl chloride used for washing the column, the of 550-800° C., for thermally decomposing the double quantities of pentachlorides being calculated as oxides. salt, the process can be carried out in a continuous man 25 ner, so that there is obtained, on the one hand, a fraction Percent Percent enriched in niobium and, on the other, a tantalum penta N bZOS 'I'aaOs halide. By applying the potassium chloride to an inert solid carrier material or by diluting the potassium chlo Initial mixture ____ -. 83. 8 16. 2 ride with such a material, for example, carbon, the risk 30 After ?rst passage... 96. G 3. 1 After second passage 98. 9 1. 1 of caking can be avoided. After third passage... 99. 3 0.7 The alkali metal halide or alkaline earth metal halide After fourth passage . . _ . _ _ _ _ _ . _ _ t _ _ _ _ . . . . ._ 99. 9 0. 1 which remains behind after the thermal decomposition of Washing liquid ...... _. 99. 9 0. 1 the double salt can be reused directly in the process. Thus, the practically pure or highly enriched pentahalides 35 It will be seen that the tantalum is preferentially can be recovered from the mixture of halides in a cyclic absorbed on the potassium ?uoride. After evaporating process, and it is only necessary to supply to the process the thionyl chloride from the eluates the residue con the quantities of niobium and tantalum halides consumed sisted mainly of the potassium ?uoride double salt of and, when necessary, to replace any loss of alkali metal niobium pentachloride. By heating the double salt in an halide, or alkaline earth metal halide and, when the sepa inert atmosphere at 550—800‘’ C. there could be obtained ration is carried out by subjecting a solution to chro niobium pentachloride substantially free from tantalum matography, to make good any de?ciency of solvent. or NbCl3F2. In order further to purify the pentahalides of niobium Example 3 and tantalum obtained by the process they may be dis 27 parts by weight of niobium pentachloride, 21 parts tilled or sublimed. However, the halides obtained by the 45 by weight of tantalum chloride and 3.75 parts by weight sublimation which accompanies the thermal decomposi of potassium ?uoride were heated for 21/2. hours under Lion of the double salts are usually so highly enriched re?ux. Then all products volatile up to about 300° C. that they are suf?ciently pure for many industrial uses. were driven off without the use of a fractionating attach The process of the present invention is especially ad ment. There were obtained 25.3 parts of distillate, and .vantageous for the puri?cation of niobium pentachloride. 26.33 parts of a yellow melt remain behind as residue. The following examples illustrate the invention: The results given in the following table show that the Example 1. potassium ?uoride reacted preferentially with tantalum pentachloride to form a double salt and that the niobium A mixture of niobium pentachloride and tantalum pentachloride became enriched in the distillate. pentachloride, which contained 36.5% of niobium calcu 55 Percent Percent lated as Nb2O5 and 63.5% of tantalum calculated as Ta2O5, Nbzos T3205 was passed in a current of dry nitrogen through a layer

about 40 cm. long of dry granular potassium chloride. Composition of starting material ______. _ 50. 7 49. 3 The potassium chloride was maintained at 300° C. Composition of distillate ______.r ... 81. 5 18. 5 The sublimate condensed from the gaseous mixture Distillation residue ______22. 0 78. 0 leaving the potassium chloride layer contained 92.0% of niobium calculated as Nb2O5 and 8.0%rof tantalum cal What is claimed is: culated as Ta2O5. In a series of experiments the change l. A process for the separation of niobium and tanta ‘in composition of the sublimate at progressively higher 65 lum values from mixtures of their pentachlorides com temperatures within the absorption layer of potassium prising the steps of reacting under anhydrous and oxygen» chloride was determined, and the results are given in the free conditions a mixture of such pentachlorides with following table: a metal halide, the metal being a member selected from the group consisting of an alkali metal and an alkaline 70 earth metal and said metal ion having a diameter larger Temperature of the K01 350° 0. 400° 0. 450° 0. 500° 0. than that of the sodium ion, and thereby selectively form ing a double salt with the tantalum pentachloride frac Composition of the sublimate' tion, and separating the tantalum-containing double salt Percent NbaOr...... 87.1 73.5 49 0 36. 5 Percent TazOr ..... -_ 12.9 26.15. 51 0 63. 5 from the mixture thereby enriched in niobium. 76 '2. A process for the separation of niobium and tanta v2,974,007 5 6 lum values from mixtures of their pentachlorides com sium chloride and potassium ?uoride, thereby selectively prising the steps of reacting under anhydrous and ogygen forming a double salt with the tantalum pentachloride free conditions a mixture of such pentachlorides with a fraction, separating the tantalum-containing double salt metal halide selected from the group consisting of potas from the mixture thereby enriched in niobium, and heat sium chloride and potassium ?uoride, thereby selectively 5 ing the tantalum-containing double salt to a temperature forming a double salt with the tantalum pentachloride within the range of 550°-800° C. in order to regenerate fraction, and separating the tantalum-containing double the tantalum pentachloride. salt from the mixture thereby enriched in niobium. 12. A process for the recovery of a highly concen- .' 3. A process as claimediu clairn'2 wherein the forma 10 trated niobium fraction from a mixture of the. pentachlo tion of the double salt is carried out under superat rides of niobium and tantalum comprising contacting a. mospheric pressure and below the decomposition tem solution of said mixture in an inert solvent with an an perature of the double salt under the pressure used. hydrous solid halide selected from the group consisting 4. A process as claimed in claim 1 wherein the re of alkali metal halides and alkaline earth metal halides, action is carried out batch-wise and at least one molecu and separating the resulting solution vfrom the solid lar proportion of the alkali metal halide is added for 15 halide. every molecular proportion of tantalum pentachloride 13. A process as claimed in claim 12 wherein thionyl present in the mixture of pentachlorides. chloride is the inert solvent. 5. A process as claimed in claim 1 wherein the reac 14. A process for the separation of niobium and tan tion is carried out batch-wise and at least 2/s molecular talum values from mixtures of their pentachlorides com proportion of alkaline earth metal halide is added for 20 prising the steps of reacting under anhydrous and oxygen every molecular proportion of tantalum pentachloride free conditions a mixture of such pentachlorides with present in the mixture of pentachlorides. potassium ?uoride, thereby selectively forming a double 6. A process as claimed in claim 2, wherein the forma salt with the tantalum pentachloride fraction, and sepa tion of the double salt is carried out at a temperature rating the tantalum-containing double salt from the mix not exceeding 500° C. 25 lture thereby enriched in niobium. 7. A process as claimed in claim 6, wherein the forma tion of the double salt is carried out under atmospheric References Cited in the ?le of this patent pressure within the range of 300°” C. to 500° C. 8. A process as claimed in claim 2, wherein the double UNITED STATES PATENTS salt is formed by reacting the pentachloride vapour with 3° 2,816,816 Jackson et al ______.. Dec. 17, 1957 solid potassium chloride. 9. A process as claimed in claim 8, wherein the penta OTHER REFERENCES chloride vapour is diluted with an inert gas. ‘Thorpe: “Dictionary of Applied Chemistry,” 4th ed., 10. A process according to claim 9 wherein the inert 35 vol. III, pp. 310-311, published by Longrnans, Green and gas is nitrogen. Co. N.Y., 1939. 11. A process for the separation of niobium and tan Friend: “Textbook of ,” vol. VI, talum values from mixtures of their pentachlorides com part III, pp. 128, 129, 188, published by Charles Gri?in prising the steps of reacting under anhydrous and oxygen & Co., Ltd., London, England, 1929. free conditions a mixture of such pentachlorides with a 40 Williams: “An Introduction to Chromatography,” pp. metal halide selected from the group consisting of potas 2, 4, 5, published by Chemical Pub. Co., N.Y., 1947.