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Separation of Zirconium--Hafnium by Nitride Precipitation

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Separation of Zirconium--Hafnium by Nitride Precipitation United States Patent [19] [li] 4,036,637 Anderson et al. BEST AVAILABLE COPY [45] July 19,1977 [54] SEPARATION OF ZIRCONIUM-HAFNIUM 3,857,919 12/1974 Hazen et al 423/73 BY NITRIDE PRECIPITATION Primary Examiner—Leland A. Sebastian [75] Inventors: Robert N. Anderson, Palo Alto; Assistant Examiner—Josephine Lloyd Norman A. Parlee, Los Altos Hills, Attorney, Agent, or Firm—Flehr, Hohbach, Test, both of Calif. Albritton & Herbert [73] Assignee: Parlee-Anderson Corporation, Menlo [57] ABSTRACT Park, Calif. A method for the separation of a light reactive metal [21] Appl. No.: 517,581 (e.g., zirconium) from a heavy reactive metal (e.g., hafnium) by forming insoluble nitrides of the metals in a [22] Filed: Oct. 24, 1974 molten metal solvent (e.g., copper) inert to nitrogen and [51] Int. C1.2 .. C22B 34/00; C01G 23/00; having a suitable density for the light metal nitride to C01G 56/00 form a separate phase in the upper portion of the solvent [52] u.s. a 75/84; 423/3; and for the heavy metal nitride to form a separate phase 423/69; 423/73 in the lower portion of the solvent. Nitriding is per- [58] Field of Search 423/3, 69, 73; 75/84 formed by maintaining a nitrogen-containing atmo- sphere over the bath. The light and heavy metals may [56] References Cited be an oxide mixture and carbothermically reduced to U.S. PATENT DOCUMENTS metal form in the same bath used for nitriding. The nitrides are then separately removed and decomposed 1,580,650 4/1926 Coster 423/73 2,793,107 5/1957 Jazwinski 75/84 to form the desired separate metals. 3,268,302 8/1966 Renner 423/73 3,794,482 2/1974 Anderson et al 75/84 16 Claims, 1 Drawing Figure U.S. Patent My 19,1977 4,036,637 •Hf 4,036,637 1 2 SEPARATION OF ZIRCONIUM-HAFNIUM BY DETAILED DESCRIPTION OF THE NITRIDE PRECIPITATION PREFERRED EMBODIMENTS I. Separation of Metal Oxides SUMMARY OF THE INVENTION AND , OBJECTS In one embodiment, an oxide of a light metal is sepa- rated from an oxide of the heavy metal, both of which It is an object of the present invention to provide a are reactive with nitrogen. As used herein, the terms method for the separation of two or more metals reac- light and heavy metals refer to relative densities of the tive with nitrogen to form nitrides of different densities nitrides of these metals with respect to each other. by a phase separation technique. 10 Thus, for example, in a mixture of zirconium oxide and It is a particular object of the invention to provide a hafinum oxide, zirconium is designated as the light method of the above type for separating zirconium and metal even though it is relatively heavy (zirconium hafnium or other mixtures of metals with similar chemi- nitride density — about 7.0 ) while hafnium is desig- cal characteristics which render them difficult to sepa- nated as the heavy metal (hafnium nitride density — rate by chemical means. 15 about 2.0). It is a further object of the invention to provide an economical method for simultaneously reducing mix- In accordance with this embodiment, carbon and the tures of metal oxides and performing the foregoing light and heavy metal oxides are reacted in contact with separation. a molten metal solent, reduced to metal form in solution In accordance with the above objects, a method is 20 and converted into nitride products insoluble in the disclosed for the separation of a light metal (e.g., zirco- molten metal solvent. The density of molten metal sol- nium) from a heavy metal (e.g. hafnium), both reactive vent is selected to be between that of the light and with nitrogen, from a mixture containing such metals. heavy metal nitrides so that the light metal nitride floats This mixture is dissolved in a molten metal solvent in a separate phase above the solvent and the heavy which does not readily form nitrides and which has a 25 metal nitride sinks in a separate phase below the same. specific gravity between the nitrides of the two metals. In the present process, the light and heavy metal The light and heavy metals are converted into nitride nitrides from separate insoluble phases in the upper and products insoluble in the solvent by maintaining a nitro- lower portions, respectively, of the solvent metal sepa- gen-containing atmosphere over the molten metal sol- rated by a liquid metal barrier ofthe solvent metal. The vent. After this nitride reaction, the light metal nitride 30 terminology of separate phases in the upper and lower floats in a separate phase above or in the upper portion solvent metal portions are intended to encompass metal of the solvent while the heavy metal nitride sinks in a nitride layers essentially free of solvent metal as well as separate phase below or in the lower portion of the layers of insoluble nitride particles dispersed in solvent solvent. This technique is highly effective for separating metal in the interstices. In either situation, the presence relatively light zirconium metal from relatively heavy 35 of the liquid metal solvent barrier permits a clean sepa- hafnium metal. These metals are dissolved in molten ration between the floating and sunk metal nitride lay- copper solvent and subjected to a nitrogen atmosphere. ers. The zirconium forms an insoluble nitride which floats in The disclosure of our aforementioned U.S. Pat. No. the upper portion of the copper in a separate phase 3,794,482, is incorporated at this point by reference. while the hafnium forms a nitride which sinks in a sepa- 40 Briefly summarized, it discloses a technique for carbo- rate phase to the lower portion of the copper. thermically reducing an oxide of a "reactive" metal The above two metal nitride phases may be separated defined as a metal which readily reacts with carbon to from the molten metal solvent and formed into the form a corresponding metal carbide. This reduction is corresponding metals by a number of different tech- performed in a molten metal solvent which prevents the niques. For example, either the light or heavy metal 45 formation of carbides so that the reduction product is nitrides may be removed from contact with the molten molten metal. The molten metal solvent is specified as solvent and placed in contact with fres solvent metal one that lowers the activity of the reduced reactive and decomposed to metal form by lowering the nitro- metal formed during the reduction raction to a level gen partial pressure; while the residual metal nitride below that required for the reactive metal to form a remaining in contact with the solvent metal is corre- 50 carbide under the reaction conditions prevailing in the spondingly reduced to metal form by lowering the ni- system. Such molten metal solvent is capable of forming trogen partial pressure over the mixture. stable intermetallic compounds with the reactive metal. The present process is particularly effective for the During this carbothermic reduction, the partial pressure carbothermic reduction of a mixture of metal oxides in of the carbon monoxide present over the reaction mix- the presence of carbon in a molten solvent and perform- 55 ture is maintained at a level below the equilibrium value ing the foregoing nitriding separation upon the reduced for the reaction mixture as the reduction of the metal metals as part of the same overall reaction. Thus, the oxide takes place. carbon and nitrogen-contaning atmosphere would be The above patent also discloses a method for carrying present simultaneously in the reaction vessel. out the carbothermic reduction in the presence of the Further objects and features of the present invention 60 nitrogen-containing atmosphere. The overall reaction will appear from the following description and accom- which takes place in the solution is represented by the panying drawing in which the preferred embodiments following generalized formula: are set forth in detail. MO;(i) + 2C (s) +hN2(g) = MN (j) + 2CO (g) (1) BRIEF DESCRIPTION OF THE DRAWING 65 The single FIGURE is a schematic view of apparatus In the above and other equations employed herein, M suitable for carrying out the process of the present in- represents reactive metal, (s) and (g) repesent solid and vention. gaseous components, respectively. 4,036,637 3 4 Reaction (1) is the underlying reaction for the separa- solvent contained in a suitable reaction vessel together tion technique ofthe present invention in which the with at least a stoichiometric amount of a carbon source light and heavy metal oxides are converted to corre- material. The carbon from the carbon source material sponding insoluble light and heavy metal nitrides in a preferably is added in moderate excess, e.g., 0.1 to 10% molten metal solvent having a density selected to be 5 or more above this stoichiometric requirement. Suitable between that of the two nitride products. carbon source materials include particulate carbon The method of this invention has utility for separating black, lamp black, charcoal, coke, graphite, petroleum the oxides of a wide variety of light and heavy metal gases, wood products and the like, oxides so long as the reactive metals react readily with To contain the various molten metal solutions em- carbon to form the corresponding metal carbides and 10 ployed in accordance with the present invention, an the reduced metals react readily with nitrogen to form inert material, preferably graphite, is employed. Other the corresponding nitrides. This assumes the availability inert, refractory materials may be employed such as of an appropriate molten metal solvent. Suitable reac- boron nitride and beryllium nitride.
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