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United States Patent Office Patented May 3, 1960 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 rhenium 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 ammonium perrhenate, 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 hydroxide or as rhenium as a powder, or as some consolidated form. a result of the reaction of potassium chloride 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 water. 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 oxide, 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 hydrogen 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 oxides 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.
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