2,935,399 United States Patent Office Patented May 3, 1960. 1. 2 cordingly, is less than that of a metal body having a lesser amount of voids or porous sections. 2,935,399 An object of this invention is to provide a method for the preparation of metal of higher purity than has METHOD FOR PREPARATION OFRHENIUM previously been available from crude rhenium metal con Ivor Eugene. Campbell, Gahanna, and Danny Mees taining potassium. - - . . . Rosenbaum, Columbus, Ohio, assignors, by mesne as Another object of this invention is a method of prepa signments, to The Battelle Development Corporation, ration of substantially pure rhenium metal, wherein the Columbus, Ohio, a corporation of Delaware rhenium metal is substantially free from impurities and No Drawing. Application November 14, 1955 10 wherein the potassium content is low enough to permit consolidation and fabrication. - Seria No. 546,781 Still another object of this invention is an improved 10 Claims. (CL, 75-84) process for recovery of a pure rhenium metal wherein impurities including potassium are eliminated or reduced 15 to a negligible amount by forming a volatile rhenium This invention relates to the preparation of substan halide, selectively volatilizing the rhenium halide, subse tially pure rhenium metal for metallurgical purposes, quently hydrolyzing the rhenium halide, and converting More particularly, this invention relates to a process for the hydrolysis product to the pure rhenium metal. the preparation of pure rhenium metal from potassium Further objects and advantages of this invention will perrhenate, or , or crude rhenium 20 be readily seen and appreciated as the same become better metal, wherein the pure rhenium metal product is sub known and understood by reference to the following de stantially free from potassium and other impurities. tailed description when considered in conjunction with Rhenium, one of the fairly recent additions to the the specific examples. - - known elements, was discovered and isolated approxi The invention is a new and novel method of prepara-: mately thirty years ago. Numerous sources of rhenium tion of substantially pure rhenium metal comprising the have been uncovered, with rhenium in small amounts combination of halogenation of a crude rhenium metal being found in the combined state in such natural ores to a rhenium halide; selective volatilization of he rhenium as molybdenite and gadolinite, and with somewhat richer halide; and conversion of the selectively volatilized rhe sources being found in some molybdenite ore concentrates nium halide to a substantially pure rhenium metal, by and influe-dust collections from copper ores containing 30 means such as hydrolysis of the rhenium halide and re molybdenite. - duction of the hydrolysis product to a substantially pure Numerous methods have been published and patented rhenium metal that for practical purposes is free of potas for the recovery of rhenium salts or metals from the nat sium. The powder size of the pure rhenium metal is such ural ores and concentrates relatively rich in rhenium, and as to lead to easy densification by methods standard to - are well known to those skilled in the art. For example, 35 the powder metallurgy art. ... U.S. Patent 2,414,965 teaches a process for rhenium re In the practice of this invention, potassium perrhenate, covery from flue dust and U.S. Patent 1911,943 teaches as sold commercially, is a suitable starting material. Al rhenium recovery from ores containing rhenium. Usu ternatively, potassium perrhenate, an important salt of ally the last step in a rhenium-recovery process involves perrhenic acid, may be prepared as a result of neutrali conversion of some rhenium compound into metallic. 40 zation of perrhenic acid with potassium or as rhenium as a powder, or as some consolidated form. a result of the reaction of potassium with per This powdered or consolidated form of metallic rhenium rhenic acid. Perrhenic acid may be prepared in several then needs to be further consolidated or compacted, as ways. One of the most common is the combination or by sintering or melting, to obtain a sound, metallic struc solution of rhenium heptoxide with . Numerous ture suitable for metallurgical purposes. . . . . other methods for the preparation of potassium perrhen In the known rhenium separation or purification meth 45 ate are known to those skilled in the art. . ods where potassium perrhenate is an intermediate prod-- Alternatively, ammonium perrhenate may be used as uct or a starting compound, there is usually a reduction the starting material. The ammonium perrhenate may step to the crude rhenium metal and this crude rhenium. be prepared by the neutralization of perrhenic acid with metal frequently has been subjected to further process ammonium hydroxide; or the ammonium perrhenate may steps for removal of impurities. However, the potassium be prepared from potassium perrhenate by a reduction , which is formed as a by-product in the potassium to the rhenium metal with subsequent oxidation of the perrhenate reduction, is extremely difficult if not im rhenium metal to a rhenium oxide which is treated with possible to remove completely from the crude rhenium ammonium hydroxide; or ammonium perrhenate may be metal by leaching, washing, dialysis, or by other present 55 prepared by other means well known to those skilled in day wet chemical methods. . . . . the art. w While rhenium is a relatively costly metal, it is finding Alternatively, scrap rhenium metal or crude rhenium increasing use as a special-purpose material. Many po- . metal which, as such, is not capable of fabrication may tential high-temperature applications for rhenium exist, be used as the starting material or may be used in com since, among the metals, only tungsten has a higher melt- 60 bination with crude rhenium metal obtained from nu ing point. merous starting materials. - Rhenium metal containing impurities is difficult to fab Any, or all, or combinations of any or all, of the ricate. For example, potassium in excessive amounts in rhenium materials mentioned may be used as suitable the rhenium apparently inhibits densification. For rhe alternative starting materials where it is desired to reduce nium, it appears that a minimum sintered density or ap- 65 potassium and other impurities in the rhenium metal prod proximately 70 percent of the theoretical density of the uct to a negligible amount. solid metal of 21.0 grams per cubic centimeter is needed In the practice of this invention wherein potassium for successful cold-working of the rhenium metal. perrhenate is the starting material, the first step of the . Densification is to be understood as being a measure of . process is the reduction of the potassium perrhenate to a the relative compactness of the metal body as compared crude rhenium metal. The second process step is the to the theoretical density of the solid metal. The densi 70 halogenation of the crude rhenium metal to a volatile fication of a metal body with voids or porous sections, ac rhenium halide. The third process step is the selective

ae85,899 3. 4. volatilization of the rhenium halide. The fourth process sel, circulating through the ammonium perrhenate, and step is the subsequent hydrolysis of the volatile. rhenium exiting through an exit tube. attached to the vessel. halide, and the fifth process step is the reduction of the "Vycor' is the name of a low-expansion glass consisting products of hydrolysis to rhenium metal containing only essentially of silica that is marketed and sold by the a negligible amount of potassium, and other impurities. 5 Corning Glass Company, Corning, New York. The am In the practice of this invention wherein ammonium. monium perrhenate decomposed to give ammonium hy perrhenate is the starting material, the first step is the droxide, water, and a black powder. As the heating con heating of ammonium perrhenate, in a atmos tinued, the black, powder was reduced by the hydrogen phere to obtain a crude rhenium metal. The second step atmosphere to a crude rhenium metal powder. The heat and Subsequent remaining steps of the process are the O was discontinued and the hydrogen gas flow, continued. same: as in the practice of the invention wherein potas until the vessel and product, rhenium metal, reached room sium perrhenate is the starting material. temperature; In the practice of this invention wherein scrap rhenium A chemical analysis was made of the crude rhenium metal or crude rhenium: metal having a potassium con metal powder obtained with the potassium content ana tent, which, as such, is not capable: of fabrication, or 15 lyzing .40 percent. wherein crude rhenium metal in combination with scrap Example III metal, or with metal incapable of fabrication, are the starting materials, the initial step. is the halogenation of The crude rehenium metal for this example was a com the rhenium metal to a volatile rhenium halide: The. posite mixture of crude rhenium metals prepared by the next process step and the remaining process steps are: the 20 processes as illustrated in Examples I and II. Approxi same. as the third process step and the subsequent remain mately 300 grams of cruderhenium metal powder, hav ing process steps, as in the practice of the invention ing a potassium content of .40 percent, were exposed to, wherein either potassium perrhenate or ammonium per hydrogen gas at 800° C. for two hours by passing the rhenate is the starting material. hydrogen gas through the rhenium metal powder in a In the following examples, Examples-I and II are illus 25 “Wycor” apparatus to convert any rhenium metal trative: of conventional practice, while Examples III and present to crude rhenium metal. The rhenium metal IV are illustrative of the present invention, The exam powder was: cooled to 700° C. with a purging, flow of ples: of the present invention are to be construed as merely helium gas-flowing through the apparatus. illustrative- and not as limiting the scopes of the present The helium gas inlet was closed and commercially. inyention. 30 available tank gas admitted at a rate sufficient Example I. to maintain a small positive pressure within the appa ratus as shown by the flow from the exit line of the ap Rhenium powder was prepared by the hydrogen reduc paratus. The rhenium metal powder was converted to tion of commercial potassium perrhenate in the follow rhenium pentachloride, which condensed in or near the ing manner: approximately 1000 grams of potassium per exit flow line. The rhenium metal chlorinated at a rate rhenate were reduced in a heated stainless steel vessel by 35 of approximately 150 grams per hour with all the rhenium the addition of hydrogen gas. Prior to the addition of apparently converted to the pentachloride. The cont hydrogen gas, the vessel and contents were preheated to densed rhenium pentachloride, was flamed with a hand 250 C. and this temperature was maintained for the, torch at intervals, driving the pentachloride into a col first hour of reduction. At this time- the vessel and con lecting vessel which was maintained at approximately tents were heated to 500 C. and maintained at 500° C. 40 room temperature. for approximately three hours. The reduction may be The rhenium pentachloride was hydrolyzed by adding considered completed when condensation of moisture can it slowly and cautiously to distilled water cooled to about. no longer be detected from the exiting gas. Then, the 10°. C. by an ice bath. The reaction was accompanied. vessel and contents were permitted to cool to approxi by vigorous boiling and the formation of an extremely mately room temperature and the hydrogen gas flow 45 fine particle-size precipitate. (If the hydrolysis is not stopped. The contents were removed from the vessel. carried out in cool water the yield is somewhat lower.) The product was eached with distilled water to remove The precipitate was filtered from the filtrate onto medium substantial amounts of potassium hydroxide. The prod retention filter paper. The precipitate was air-dried, and uct was then returned to the reduction vessel and reduced then dried further in a desiccator using calcium sulfate further by hydrogen gas with the vessel and contents at 50 hemihydrate as a desiccant. 1000° C. for two additional hours to obtain the crude A few grams of the dried precipitate were reduced by rhenium metal powder. The crude rhenium metal was hydrogen gas, at 600° C. in one hour to obtain the puri leached with distilled water, then leached with a dilute fied rhenium metal. Later some additional precipitate aqueous acid solution of 10 percent by was reduced at 600 C. to obtain approximately 200 volume, and then leached with additional distilled water 55 grams additional pure rhenium metal. in an effort to remove potassium from the crude rhenium. A chemical analysis was made on the purified rhenium. metal. metal and the total impurities found analyzed .05 per-. Approximately 93 percent of the rhenium was recov cent. The analysis showed a 0.00 percent potassium ered as crude rhenium metal powder. A chemical analy content. The analysis for potassium had a sensitivity Suf sis was made of the crude rhenium metal powder obtained 60 ficient to detect potassium contents, as low- as .001 per with the potassium content analyzing .50 percent. cent. Example II Example. IV The ammonium perrhenate. for this example - was pre An approximately 300-gram mixture of approximately pared from potassium perrhenate by a hydrogen reduc 65 50 percent crude rhenium metal and 50 percent Scrap. tion to the rhenium metal with subsequent oxidation of rhenium metal was converted to substantially pure rhe the rhenium metal to a rhenium oxide which was treated nium metal by-the-process of this invention. The exact with ammonium hydroxide to obtain the ammonium per impurity content of the crude rhenium metal was not rhenate. Approximately 350 grams of rhenium powder known. The crude rhenium metal had been obtained by were prepared from ammonium perrhenate. in the fol. 70 the process illustrated in Examples I and II, where in all lowing manner: 500 grams of finely divided ammonium previous runs- crude rhenium metal containing in excess perrhenate, having a potassium content of .47 percent, of .20 percent impurities was obtained. The exact im were heated gradually to 1000 C. in a closed "Vycor' purity- content of the scrap rhenium metal was not vessel with pure, dry hydrogen gas passing for approxi known. However, the scrap rhenium metal was metal mately two hours through an entrance tube into the ves- 7s incapable of fabrication because of insufficient densifi

2,935,899 5 6 cation, and its behavior: under fabrication attempts re high as 1000 C. The particle size of the rhenium metal sembled that of rhenium metal containing sufficient potas obtained from the hydrogen reduction of the hydrolysis sium to inhibit densification. product appears to be dependent on the reduction tem The rhenium metal mixture was placed in a vessel of perature with the finer particle size obtained at the "Vycor' and the vessel and contents heated to 750 C. lower temperatures. with a purge of helium flowing through the mixture and Numerous unsuccessful attempts were made to metal vessel. The helium flow was stopped and at the same lurgically process crude rhenium metal as obtained from instant a flow of commercially available tank chlorine gas the hydrogen reduction of potassium perrhenate, as illus was supplied to the vessel and contents. The chlorine gas trated in Example I, and from the decomposition-reduc flow was continued for two hours - 15 minutes with 10 tion of ammonium perrhenate, as illustrated in Example the vessel and contents at 750° C. The rhenium metal II. In a few instances proper pressing of the crude chlorinated at a rate of approximately 150 grams per rhenium powder was achieved, but in no instance, after hour. The volatile rhenium pentachloride was collected sintering, was a densification of the powder body ob in an attached collecting vessel. tained sufficient to permit metallurgical processing and . The rhenium pentachloride was slowly and cautiously 15 fabrication, where the potassium content of these rhenium reacted with distilled water to obtain a fine particle-size metals exceeded.05 percent. The crude rhenium metals in precipitate. Three filtrations were made of the filtrate to these unsuccessful metallurgical processing attempts gen collect the precipitate. The precipitate was air-dried and erally had potassium contents ranging from 0.06 percent. then dried further in a dessicator using calcium sulfate to 0.60 percent. Varied particle-size crude rhenium hemihydrate as a dessicant. 20 powders were utilized with insufficient improvement in . The dried precipitate was reduced by hydrogen gas at densification to permit metallurgical processing. 600 C. to obtain pure rhenium metal with approximately However, rhenium metals prepared by the method of 87 percent of the theoretical yield of pure rhenium being this invention, as illustrated in Examples III and IV, with. obtained. only a very small or negligible potassium content, were Example I illustrates a conventional preparation of 25 successfully pressed, sintered, and metallurgically . crude rhenium metal from potassium perrhenate. The processed. Almost invariably, densifications from sinter crude rhenium metal after several leachings, including one ing in excess of 70 percent of theoretical density were with a dilute aqueous acid solution, still contained a sub obtained and the sintered rhenium powder body was suc stantial potassium content. . . cessfully metallurgically processed. - - Example II illustrates that a conventional method of 30 The preparation of a sintered metal rhenium body by preparation of crude rhenium metal from ammonium pressing and sintering was in accordance with known. perrhenate with a substantial potassium content gives a methods of the powder metallurgical art. The sintered rhenium metal having a substantial potassium content. and densified rhenium metal body was metallurgically Examples III and IV illustrate the method of this in processed by suitably selected cold working of the body vention wherein crude rhenium metals with a substantial 35 prior to heavier cold reductions. In the heavier cold potassium or impurity content are converted into pure reductions, annealing of the metal body was necessary rhenium metal. The potassium or total impurities in the and the amount of reduction was controlled and limited product metal are negligible for metallurgical purposes. in a stepwise procedure in that a reduction of the rheni In the step of preparing the crude rhenium metal from un metal body was made, then the body was annealed. potassium perrhenate by hydrogen reduction a maxi 40 This was then followed by subsequent reductions plus mum temperature of 500 C. is preferred. At a tempera annealings to eventually obtain the desired dimensions. ture of approximately 550 C., melting of the potassium Pure rhenium metal prepared by the process of this perrhenate is likely to occur. While the hydrogen re invention, as illustrated in Example III and IV was suc duction of potassium perrhenate has been accomplished cessfully metallurgically processed and physical proper successfully at temperatures, slightly above 500 C., dif 45 ties of the pure rhenium metal measured. Pure rhenium ficulty has been encountered when attempting to use a metal prepared, as illustrated in Example III, was pressed 550° C. temperature. and sintered to obtain...a densification of approximately: In the step of halogenation of the crude rhenium metal, 80 percent of theoretical density. Annealed rhenium where the halogenation is a chlorination, temperatures rods (0.05, inch in diameter) from the metallurgically ranging from 600° C. to 800° C. have been used. A 50 processed rhenium. metal, prepared as illustrated in Ex temperature of 750° C. is the preferred chlorination tem ample III, gave a tensile strength of 171,000 p.s. i., an perature. The rate of chlorination appears to be de elongation of 15 percent, and, in the annealed state, a pendent on the chlorination temperature with little in Vickers hardness of less than 300 V.H.N. crease in rate of chlorination at temperatures greater than The physical properties of the pure rhenium metal, 750° C., and with rapid decreases in the rate of chlori 55 prepared by the process of this invention, after metallurgi nation at temperatures lower than approximately 600 C. cal processing are at least the equivalent and generally are: In the separation of the precipitated product of the Superior to the physical properties of rhenium obtained by: hydrolysis step, filtration time may be reduced sub any other known process. For example, Agte and his stantially by bubbling carbon dioxide gas through the coworkers in "Physical and Chemical containing the product for about 30 minutes be 60 Rhenium,'. Z. anorg. m. allgem. - Chem., 119, 129-159. fore filtering. Rhenium remaining in the filtrate may be (1931), report a tensile strength for rhenium of 70,000 recovered by treating the filtrate with a small amount p.s. i. for rhenium specimens prepared by a hot-wire depo of 30 percent solution to obtain a sition process. perrhenic acid solution which may be neutralized by The scope of possible applications for rhenium metal ammonium hydroxide to obtain ammonium perrhenate 65 has been greatly enhanced by this invention wherein which may be converted to crude rhenium metal for sub rhenium metal with improved physical properties may sequent recycling in the process of this invention. be obtained. While the exact reason for the improved In the step of hydrogen reduction of the product ob physical properties of the rhenium of this invention is tained from the hydrolysis of the volatilized rhenium unknown, it is believed and theorized that the minimiza halide, it is preferred that the temperature be raised step 70 tion of potassium and other impurities in the rhenium has wise to a maximum temperature of approximately 600 permitted the obtaining of the improved properties. C. and that the maximum reduction temperature be While the specific procedures and examples given have maintained for a sufficient period of time to accomplish been only of the chlorination of the crude rhenium metal the reduction. Successful reductions of the hydrolysis as the preferred treatment, it is to be understood that this product have been made at maximum temperatures as 75 invention is not so limited and, that, as will be obvious

2935,899 8. to others: skilled in the art, a member, selected from the 2. The methods of claim. 1. in which the halogen is: group consisting of fluorine, chlorine, and bromines of fluorine. group VII of the periodictable may be used in the halo-. 3. The method of claim 1 in which the halogen is: genation step. These members of group VII of the chlorine. periodic table are commonly known as halogens and the 5. 4. The method of claim 1 in which the: halogen is generic reaction of a member of the group with rhenium bromine. to give a rhenium halide is known as halogenation. 5. The method of claim 1 in which the halogen is: It is to be understood that rhenium halide as used in chlorine and in which the method includes the prepara the specification and claims is inclusive - of all volatile tion of the crude rhenium metal containing potassium halides or volatile complex halides of rhenium and fluo 0. by a hydrogen reduction of potassium perrhenate. rine, chlorine, and/or bromine. It is to be understood 6. The method of claim 1 in which the halogen is that-the-term rhenium chloride as used in the specification chlorine and in which the method includes the prepara and the claims is intended to include all volatile rhenium tion of the crude rhenium metal containing potassium . Rhenium-chlorine binary compounds corre by a hydrogen reduction of ammonium perrhenate con sponding to several oxidation states are known. In a like taining potassium. - manner, rhenium fluoride includes all volatile rhenium 7. A. method for obtaining a substantially free-from fluorides and volatile. complex fluorides and rhenium pctassium, purified rhenium metal powder for metallur bromide includes all volatile rhenium bromides or volatile . gical consolidation and fabrication from a crude rhenium complex-bromides. metal containing potassium, the method comprising: ex While the specific: procedures and examples given have 20 posing the crude rhenium metal containing potassium illustrated the conversion of the selectively volatilized to a halogen selected from the group consisting of fluo rhenium halide to a substantially pure rhenium metal by rine, chlorine, and bromine at an elevated temperature the preferred method of hydrolysis of the selectively volas sufficient to form and to volatilize a rhenium halide to tilized rhenium halide and reduction of the hydrolysis. form a volatilization product; transferring the volatiliza product to a substantially pure rhenium metal, it is to be tion product in a gaseous state to a situs other than the understood that this invention is not so limited. Other situs of the formation of the rhenium halide; contacting. means known to those skilled in the art may be used. the-transferred volatilization product with water to form. For example, the selectively volatilized rhenium halide. a rhenium hydrolysis product; and reducing the rhe may be converted to a substantially pure rhenium metal by: nium hydrolysis product with hydrogen to provide the hydrogen reduction, or by conversion to an oxide fol 30 substantially free-from-potassium, purified rhenium metal lowed by subsequent reduction, or by other means well powder. known to those skilled in the art. 8. The method of claim 7 in which the halogen is: This invention permits the preparation of a pure rhe chlorine and the rhenium halide is a rhenium chloride. nium metal of adequate purity for metallurgical pur 9. The method of claim 8 in which the rhenium chlo poses. The potassium and other impurities in the puri ride is rhenium pentachloride and in which the method fied rhenium metal are held to a negligible quantity, thus includes the preparation of the crude rhenium metal facilitating the consolidation of the purified metallic rhe containing potassium by reducing potassium perrhenate nium to a sound, metallic structure for metallurgical pur with hydrogen. poses and permitting the obtaining of improved physical 10. The method of claim 8 in which the rhenium properties in the sound, metallic structure. 40 chloride is rhenium pentachloride and in which the While a preferred method has been shown and de method includes the preparation of the crude rhenium scribed, it will be obvious to those skilled in the art metal containing potassium by reducing an ammonium that various changes and modifications may be made perrhenate containing potassium with hydrogen. without departing from the invention in its broadest as pects and the appended claims are intended to cover all References Cited in the file of this patent such changes, and modifications as follow, within the true spirit and scopes of the invention. UNITED STATES PATENTS What is claimed is: 1,829,756 Noddack et al. ------Nov. 3, 1931 1. A method for obtaining. a. substantially free-from 2,594,370 Warburton ------. Apr. 29, 1952. potassium, purified rhenium metal powder for metallur 50 2,670,270 Jordan -----rur r man as a any Feb. 23, 1954 gical consolidation and fabrication from a crude rhe FOREIGN PATENTS nium metal containing potassium, the method compris ing: preparing a volatilization product by exposing the 575,801 Germany ------nea--as-gen mean May 3, 1933 crude- rhenium metal containing potassium to a halogen 680,710 Great Britain ------pur murve a Oct. 8, 1952. selected from the group consisting of fluorine, chlorine, OTHER REFERENCES and bromine at an elevated temperature-sufficient to form Van Arkel: Chem. Abstracts, vol. 28, p. 5011 (1934). and to volatilize, a rhenium halide transferring the vola Thorpe's Dictionary of Applied Chemistry, 4th ed., tilization product in a gaseous state- to a situs other than vol. X, 1950, pp. 517, 518, 521-524. the situs of the preparation of the volatilization product; Battelle Technical Review, July 1954, page 77. condensing the transferred volatilization product; con 60 Hampel: Rare Metals Handbook, pages 352-359, pub tacting the condensed volatilization product with water to form a rhenium hydrolysis product; and reducing the lished 1954 by Reinhold Pub. Corp., N.Y. rhenium hydrolysis product with hydrogen to provide Hampel: Rare Metals Handbook, pp. 360-361, pub the substantially free-from-potassium, purified rhenium lished 1954 by Reinhold Pub. Corp., N.Y. metal powder. 65