US2556912A - Thermal process for producing pure tantalum and columbium compounds - Google Patents

Description

Patented June 12, 1951 EFICE THERMAL PROCESS FOR PRODUCING PURE COMPOUNDS TANTALUM AND 'CGLUIWBIUM Daniel Gardner, New York, N. Y.

No Drawing. Application September 14,1946,

Serial No. 697,152

10 Claims.

This invention is a n vel thermal process for producing pure tantalum and columbium and certain compounds thereof, being adapted for the conversion or reduction of certain starting materials containing these elements to yield the pure metals, or either of them, suitable for various industrial purposes. In referring to columbium it is to be understood that this is the same element also Well-known in certain countries under the alternative name of niobium.

Much of the data, and certain of the condi-- tions, relating to these two elements or metals,

referred to. The symbol R may be used to desig-- hate either or both of the metals Ta and Cb. In

this application all recited temperatures are to be understoodas those of the Centigrade system. The present invention is characterized in being directed to the production of Ta and Cb through their sulphides, and the complete process may for convenience be considered in two steps or stages, combinable to merge one into the other; and such respective steps may preliminarily be considered in a general Way as follows. The starting material may contain or consist of one or more of the following more important industrial compounds of Ta and/or Cb, namely, the pentoxide, the pentachloride and the pentafluoride; and the process hereof, thermal in character, may deal with the compound or compounds either of Ta or of Cb, or of both of these, especially when found in the same raw material or mineral. The first step then consists in the thermo-chemical treatment of the starting compound, or compound-mixture, to convert the Ta and/or Cb content thereof to the sulphide or sulphides of such element or elements. Next, in the second step or reaction, and preferably after the sulphide of Ta and/or Cb has been freed of separation may be suitably efiected at the outset or at the sulphide stage of the process.

It is believed that the present invention is novel inthe outlined process in its entirety, and as well in the sub-process involving the described first step or reaction, yielding the sulphide of the metal or metals, and also in the sub-process outlined in the second step as a practical means of reducing the sulphide to the desired metal or metals.

The general objects of the present invention are to afford the economical production of the metals Ta and/or Cb, by a process and steps which are practical and reliable, to yield the pure metal or metals. An associated object is to afford the practical conversion of the previously mentioned starting compounds of Ta and/or Cb to the sulphides thereof, and the isolation of said sulphides in pure form, irrespective of the described further steps or reactions thereon; and a further object is to afford a practical way of reducing the pure sulphide or sulphides to the metals. Other objects and advantages of the presentinvention will appear in the reading of the hereinafter following disclosure of oneor more embodiments thereof, or will be understood by those conversant with the subject. Y i

In this application the treatments of the materials and compounds of both Ta and Cb'are intimately combined and described, for the reason, among others, that said elements are in some respects closely analogous and related, both of them being in periodic group V, each of them having its more usual valence of five, both having veryhigh melting and boiling points, and both of them being found in common in certain natural compounds or minerals; and it is part of the present discovery that the intermixed compounds of the two may be treated in unison for their conversion and reduction.

'Since the general subject in discussion is relatively novel and recent, that is, having had but little intensive research and development, it is deemed appropriate to precede the description of the invention by a general outline of certain pertinent portions of the past history and available present data concerning the two elements tantalum and columbium.

Through the extensive research of Biltz & Kirchner (Berichte, vol. 43, p. 1645, 1910) the formulae of the sulphides of tantalum and of columhium (niobium) have finally been established as being TaSz and CbSz. However, numerous published assertions, starting with Rose (Pogg. Annalen, vol. 99, of 1856 and again vol. 105, of 1858) have been made, often of a very contradictory nature, believed to be due chiefly to the fact that the authors, who, although they A similar reaction, according to Rose, can be obtained by using carbon disulphide vapor or gas at a temperature around 960 C.; if a higher temperature is used, as somewhere between 1200 and 1300 the sulphide obtained is crystalline. Thus, for Ta:

Similarly, when dealing with columbium, at temperatures respectively somewhat lower, the above equations become:

Cb+2S=CbS2+147.0 Cal.

Cb+CSz=CbSz+C+1690 Cal.

The following table gives the principal data concerning the two metals and their sulphides,

namely, their molecular weights (M. W.) densities (D); melting points (M. P.); boiling points (B. P.) heats of formation (ht. f.); specific heats (sp. ht); and solubilities (sol.); using also such conventional abbreviations as d. for decomposes, sl. for slightly, exc. for excess, and ra. for ratio of B. P. to M. P.

Table of properties Property alkali The above figures for the sulphides were estabished to applicants satisfaction on the basis of sulphides of highest purity. As already stated, prior workers, notwithstanding impure ingredients, found some valuable reactions, which help to explain the nature of the two sulphides. The following previously tried reactions may be cited:

Biltz & Kirchner, cited supra, proposed to obtain tantalum sulphide by acting on tantalum pentoxide with vapors of carbon disulphide, the reaction starting at 650, but this requiring a high increase in temperature to improve the yields, and being never really satisfactory. Their reaction was as follows:

Ta205+3H2S+CS2= 2'I'aSz-I-3I-I2O+CO2S+126.5 Cal.

On the other hand Rose (supra) suggested passing HZS vapors to react with Ta pentachloride TaCl5; B. P. 242, at red heat; or heating tantalum pentoxide, in a current of hydrogen charged with vapors of carbon disulphide, as follows:

Similarly, for columbium, these reactions would become:

Applicant has carefully considered these reactions and has found them to give poor yields, even when working with purest ingredients, which the quoted authors never have had at their disposal. One of the proofs of the impurity of the sulphides formerly produced is that the earlier authors disagreed even as to the color of the compounds, not to mention the more important items, such as density, structure, melting point, etc.

Still less satisfactory results have been obtained for producing columbium sulphide, where the authors cited the obtaining of an oxysulphide only, especially since the results thereof that were long ago published by Delafontaine (Arch. Sci. Phys. Nat. (2), vol. 27, p. 167, 1866).

Under the recited circumstances and absence of successful outcome, as indicated, applicant turned his attention to other ways of producing Ta and Cb sulphides and metals, guided by the following considerations: (a) tantalum and columbium sulphides are definitely stable compounds; (2)) these two sulphides must be obtained free from all possible impurities for successful final results; (0) these sulphides can be obtained in mutual mixture as well as when separated, since, as will be seen below, the best reactions for their production are rigorously similar, although the temperature data of the two sulphides are somewhat difierent; (d) both sulphides, when mixed, can be jointly reduced from the sulphide form to the mixed metals, or can be first fully separated from each other as sulphides (or even earlier) and reduced separately to the metals; (e) the two sulphides, once obtained in their purest form, are so stable, that they are attacked only by a mixture of hydrofluoric and concentrated fuming nitric acids,

a condition which in itself is absolutely technically non-existent in nature and is a strictly artificial development; (I) the two pure sulphides, recoverable in mixture or separately, may be treated as in the nature of intermediate or subproducts irrespective of the utilization to which they are put. 7

Applicant has heretofore conducted research with special reference to industrial applications of the more common hydrides, particularly when the reactions involved are of the exothermic type. Also, using carbon disulphide CS2 as a source of sulphur, as in his prior applications and patents relating to the production of light metals (magnesium, beryllium, etc.), applicant has particularly studied the reaction which occurs between carbon disulphide and a hydride, such as a saline hydride or alkaline earth hydride, for example calcium hydride CaHz; and has determined the following among other equations:

From his subsequent researches upon the compounds of Ta and/or Cb applicant has discovered that related equations are usefully available for desirable treatments of these compounds, such as the pentoxides of tantalum or columbium, or to equal or greater advantage the pentachlorides thereof (and the pentafluorides but to less advantage can also be treated). As examples the following equations are recited, useful for the conversion of Ta and/or Cb pentoxide or pentathis These reactions have the following advantages, especially when using the pentachlorides (less notably for the pentafiuorides) in accordance with the invention: (1) each of these reactions proceeds quantitatively; (2) all byproducts become volatilized, or can be otherwise easily removed; (3) the recovered products, Ta and/or Cb sulphides, are of supreme purity; temperatures of these reactions are moderate or low, not depassing or exceeding red heat (about 650 to 750) when the pentoxides are treated, and considerably lower when the pentachlorides (orpentafluorides) are treated; and this fact of operation at lower temperatures in part accounts for the extreme purity of the sulphides obtained.

In all cases the reaction atmosphere must be considered; and it should be of an inert gas, such as A or He or Ne, or at least a non-oxidizing gas such as hydrogen or a hydrocarbon, to pr clude interference with the desired reaction.

By way of review ofthe above described first step or reaction, the procedure thereof may be stated asza thermal process, which is preferably continuous by being performed with travel through the chambers of the furnace. Said step operates .to sulphidize or convert a starting compound of Ta and/or. Cb to the sulphide or sulphides thereof, said compound, in a practical aspect,- consisting of the available pentoxide and/or pentachloride and/or in some cases the pentafluoride. This step or reaction of producing the sulphidesconsists, without repeating the hereinabove set forth equations used, in mixing the starting compound in powdery condition (that is, pulverulent, granular, flaky etc.) with the following agents; (a) a sulphur agent, for which 5 fumes may be used, but preferably carbon disulphide, CS2, a liquid which under rise of temperature quickly vaporizes, and (b) a nonsulphur hydride or equivalent agent, such as a saline or an alkaline earth hydride, preferably calcium hydride Cal-I2, or, Bali-I2 or Lil-I; (or sometimes the silicides or borides may be used) also in powdery form, and then heating such mixture to a moderate temperature, of the order of several hundred degrees, e. g., in the neighborhood of 600 to 700; thereby causing the aforesaid reaction wherein the starting compound is converted to the sulphide TaSz and/or CbSz. These recovered sulphides are adapted readily to be brought to pure condition by elimination of the reaction byproducts and any impurities, as by gasification, or in the case of CaO by dissolving it in HCl.

As a following or second step or reaction the thermal treatments described may be continued for the sequential reduction of the sulphide to the metal Ta and/or Cb. By this second step the pure sulphide, still in powdery form, and which may be still hot from the previous step, is reduced to the metal by first mixing with such sulphide a suitable reducing agent as the pyro- (4) the genetic metal aluminium, also in pow'dry form;

or sometimes but less preferable can be used Mg or Be or Li. Such aluminium should be in molecular proportion, or preferably in a somewhat greater proportion, to convert surely the entire S content to aluminium sulphide A1283 in accordance with the equation hereinbelow recited. Such mixture is next brought'to a moderate temperature of about 659 or within a range, not critical, of about 150 thereabove or therebelow, thereby bringing about an exothermic reaction, with the formation of the A1283; and thereafter the temperature is progressively ele-. vated to 1550, or rather slightly thereabove, thereby. causing the A1283 to distil or sublime away, leaving behind the recovered pure metal Ta and/or Cb, which may still be in powdery form. The pyrogenetic character of the -'Al helps to elevate the temperature andkeep it high.

Supplementally,'if both of the R metals (Ta and Cb) are present in such product they may be separated from each other, for example, in one of the ways desecribed in said copending ap plication, or by the known way of converting the mixture into an oxyfluotantalate mixed with an oxyfluocolumbate, these possessing such differences in solubility as to facilitate their separa tion; followed by reconversion to the respective metals. 1

Reverting to the reduction of the sulphide or sulphides to metal, by use of Al powder, according to'Goldschmidts reaction, the equations may 6TaSz+8Al=4Al2S3+6Ta+3832 Cal.

6CbS2+8Al=4 Al2S3+6Cb+4=972 Cal.

The reduction step so characterized possesses the process value that the A12S3, which is readily attacked by moisture, has the very high heat of formation of 344.8 CaL, and melts at 1100and distills off at 1550; which latter is not merely below the boiling points of Ta and Cb butalso is well below themelting pointsthereof, 2850 and 1950". As a consequence a good temperature margin exists, ensuring the complete separation away of the A1283, which in itself is a byproduct of value and can even be used again to regenerate the S vapors or compounds needed. for the first step of the process described. Due to the high melting points of. the reduced Ta and/or Cb these elements can be maintained in powdery form during the reduction, this fact materially enhancing the effectiveness and completeness of the reduction, and yielding a final product in a most convenient condition.

The described process, considered either in its entirety or in its respective steps, may be carried on in batch manner, as in one or a succession of crucibles; or it may be preferred with travel through furnace chambers as a continuous process, between infeed and discharge, with better output. The successive steps may be overlapped to some extent, but it is better that the heat-producing agent or Al should only be fed and -mixed into the advancing materials after the Ta and/or Cb is completely converted to the sulphide and the resulting byproducts and impurities removed or allowed to pass out of the furnace. Referring to the atmosphere in the furnace, it should be free of oxygen, air or other oxygen-supplying gases for the reasons already above stated.

If it be desired to separate the conversion products, the sulphides of Ta and Cb, before reduction, the following way may be practiced.

Noting from the table of proper-ties supra that the solubili-ties of these compounds difier it is .only; necessary to dissolveou-t one from the other. .Of-course, at the outset, the mentioned oxides, chlorides or fluorides of Ta and Cb may be anutuaily separated if desired, followed by separate sulphidizing and reduction of each metal.

I What is claimed is:

1. The thermal process for treating starting material containing a metal compound selected from the group consisting of tantalum pentoxide, columbium pentoxide, tantalum pentachloride, columbium pentachloride, tantalum pentafiuoride, columbium pentafiuoride and mixtures theerof, to convert such compound to the sulphide; said process comprising mixing with such starting material, in powdery form, a sulphidiz- .ing agent, and an alkaline-earth hydride; and in a non-oxidizing atmosphere subjecting such mixture to an elevated reaction temperature between about 609 and 750 0., thus to bring about a reaction wherein the metal compound contained in such starting material is chemically converted to the sulphide, separable from other reaction products.

,2. The process as in claim 1 and wherein the starting material contains the recited compounds of both tantalum and columbium, and during such process the mixture is treated to separate from each other the tantalum and columbium constituents.

3. The process as in claim 1 and wherein the sulphidizing agent is one selected from the group consisting of sulphur, fumes of sulphur and car bon disulphide.

4. The process as in claim 1 and wherein the sulphidizing agent is carbon disulphide.

v5. The process as in claim 1 and wherein the alkaline-earth hydride is one selected from the group consisting of calcium hydride and barium hydride, used in powdery form.

6. The process as in claim 1 and wherein the alkaline-earth hydride is calcium hydride Cal-I2.

"7. The process as in claim 1 and wherein the metal compound contained in the starting material is one selected from the group consisting of tantalum pentoxi-de and columbium pentoxide.

8. The process as in claim 1 and wherein the metal compound contained in the starting material is one selected from the group consisting of tantalum pentachloride and columbium pentachloride.

9. The thermal process for treatin starting material containing a metal compound selected from the group consisting of tantalum pentoxide and columbium pentoxide and mixtures thereof, to convert such compound to the sulphide; said process comprising mixing with such starting material as a sulphidizing agent carbon disulphide, and as an alkaline-earth hydride, calcium hydride, in an oxygen-free atmosphere and under an elevated temperature between about 600 and 750 0.; thus to bring about a reaction wherein the carbon and hydrogen constituents pass oiT in the form of gas, leaving behind the aforesaid sulphide and anhydrous calcium oxide; and thereupon separating away such calcium oxide by dissolving it in hydrochloric acid.

10. The thermal process for treating'starting material containing a metal compound selected from the group consisting of tantalum pentachloride and columbium pentachloride and rnixtures thereof, to convert such compound to the sulphide; said process comprising mixing with such starting material as a sulphidizing agent carbon disulphide, and as an alkaline-earth hydride, calcium hydride, in an oxygen-free atmos phere and under an elevated temperature between about 600 and 750 0.; thus to bring about a reaction wherein the carbon and hydrogen constituents pass off in the form of gas, leaving behind the aforesaid sulphide and calcium chloride; and thereupon separating away such calcium chloride by leaching it with water.

DANIEL GARDNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Mellor, Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 9, 1929, Longmans, Green 8: Co., New York, pages 924 and 925.

Claims (1)

1. THE THERMAL PROCESS FOR TREATING STARTING MATERIAL CONTAINING A METAL COMPOUND SELECTED FROM THE GROUP CONSISTING OF TANTALUM PENTOXIDE. COLUMBIUM PENTOXIDE, TANTALUM PENTACHLORIDE, COLUMBIUM PENTACHLORIDE, TANTALUM PENTAFLUORIDE, COLUMBIUM PENTAFLUORIDE AND MIXTURES THEREOF, TO CONVERT SUCH COMPOUND TO THE SULPHIDE; SAID PROCESS COMPRISING MIXING WITH SUCH STARTING MATERIAL, IN POWDERY FORM, A SULPHIDIZING AGENT, AND AN ALKALINE-EARTH HYDRIDE; AND IN A NON-OXIDIZING ATMOSPHERE SUBJECTING SUCH MIXTURE TO AN ELEVATED REACTION TEMPERATURE BETWEEN ABOUT 600* AND 750* C., THUS TO BRING ABOUT A REACTION WHEREIN THE METAL COMPOUND CONTAINED IN SUCH STARTING MATERIAL IS CHEMICALLY CONVERTED TO THE SULPHIDE, SEPARABLE FROM OTHER REACTION PRODUCTS.