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United States Patent (19) 11 Patent Number: 5,635,146 Singh Et Al

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United States Patent (19) 11 Patent Number: 5,635,146 Singh Et Al US005635146A United States Patent (19) 11 Patent Number: 5,635,146 Singh et al. 45 Date of Patent: Jun. 3, 1997 54 METHOD FOR THE DISSOLUTION AND Tantalum, Elements, 12-17 (1992) (no month available). PURIFICATION OFTANTALUMPENTOXDE Abstract, Derwent WPI, JP 043298808A, (1992) (no month 75 Inventors: Raj P. Singh, Sayre; Michael J. available). Miller, Towanda, both of Pa. Bielecki, Use of Ion Exchange Techniques for Production of High-purity Potassium Fluorotantalate, Advances in 73) Assignee: Osram Sylvania Inc., Danvers, Mass. Extractive Metallurgy, The Institute of Mining and Metal lurgy, London, 777-788 (Apr. 17-20, 1967). 21 Appl. No.: 565,334 Carlson et al., Pure Columbium and Tantalum Oxides by Liquid-Liquid Extraction, Journal of Metals, 472-475 (Jun. 22 Filed: Nov.30, 1995 1960). (51 int. Cl. ... C01G 3500 Droeghkamp et al., Tantalum and Tantalum Compounds, 52 U.S. C. ...... ... 423/65; 423/67; 423/68; Kirk-Othmer Encyclopedia of Chemical Technology, Third 423/592; 423/593 Ed., v.22, 541-565, John Wiley & Sons (1983) no month 58 Field of Search ............................ 423/65, 67, 68, available. 423/592,593 Baram, Kinetics of Dissolution of Niobium and Tantalun Pentoxides in Hydrofluoric Acid, Journal of Applied Chem 56) References Cited istry of the USSR, 38, 2181-2188 (1965) (no month avail U.S. PATENT DOCUMENTS able). 3,072,459 1/1963 Foos et al. 423/67 Zelikman et al., Chapter III: Tantalum and Niobium, Met 3,117,833 1/1964 Pierret ......................................... 23/19 allurgy of Rare Metals, U.S. Dept. of Commerce, 99-154 3,481,694 12/1969 Hudswell et al. .. ... 423/65 (1966) (no month available). 3,712,939 1/1973 Capps et al. ....... ... 423f63 4,446,115 5/1984 Endo et al. .... ... 42.3/63 Primary Examiner-Wayne Langel 4,490,340 12/1984 Ritsko et al. .. ... 423/65 Attorney, Agent, or Firm-Robert F. Clark 4,495,158 1/1985 Ritsko et al. ...... ... 423/68 4,537,750 8/1985 Ritsko et al. ...... ... 423/65 57 ABSTRACT 4,663,130 5/1987 Bergman et al. .. ... 423/68 Amethod is disclosed for the dissolution and purification of 4,673,554 6/1987 Niwa et al. ............................... 423f63 tantalum pentoxide. The impure tantalum pentoxide is FOREIGN PATENT DOCUMENTS reacted with a potassium-containing compound to form 0034348 8/1981 European Pat. Off. ........ C22B 34/24 potassium tantalate. The potassium tantalate is optionally 024-1278 10/1987 European Pat. Off. ........ CO1G 3500 slurried with sulfuric acid and dissolved in an HF medium. 2537354A1 2/1977 Germany ....................... COG 3500 The solution is suitable for purification by conventional ion exchange or solvent extraction methods. A potassium fluo OTHER PUBLICATIONS rotantaliate precipitate may also be formed by adding KCl to Nassau et al, Quenched Metastable Glassy and Crystalline the solution. The fluorotantalate precipitate may be further Phases in the System Lithium-Sodium-Potassium Metatan processed into a pure tantalum pentoxide by suspending the talate, J. Amer. Cer. Soc., 62(1-2), 74-79 (1978) (no month precipitate in an aqueous solution optionally containing a available). chelating agent and adding ammonium hydroxide to form Borchers et al., Extractive Metallurgy of Tantalum, Extrac ammonium tantalum oxide which can then be converted to tive Metallurgy of Refractory Metals, The Metallurgical tantalum pentoxide by calcining at high temperature. Society of AIME, 110th AIME Annual Meeting, 95-106 (Feb. 22-26, 1981). 16 Claims, 1 Drawing Sheet ce: stochs: Y AYxxis ce fac. Ano Kico, EAATs':TiscA. FR320irst ForkTao, N -- - cissouToitats its self optotalsoAcu. He - SSWEHF Acces - We Acker Fis ASHARYAT ETRAckr Kaf, rescriTATE it' kNExchase I sers: PREPTAre Fict CAPATRADE LAMs was Kst-, ruRIFEDTao, SUSEs Precipit g Assis AbdohHi To - G FRATE PREATE FTER WEA try scs Act ELECTRNCRE: (HHao XXX: 3. U.S. Patent Jun. 3, 1997 5,635,146 COMBINE STOICHOMERC AMOUNTS OF Tao AND KCO, HEAT AT 550°CTO 1300°C FOR 3 TO 20 HOURS TO FORM KTao, DISSOLUTION STEP WASH AND ORYA 110°C SLURRY WITH HSO, ACID (OPTIONAL) DISSOLVE INHF ACO MEDA SOLVENT ADD KCTO FORM WASH AND ORYAT EXTRACTION OR KTaF, PRECIPITATE 110°C ION EXCHANGE SEPARATE PRECIPITATE FROM CAPACTOR GRADE LICUID AND WASH KTaF, PURIFIED Tao SUSPEND PRECIPITATEN WATER EDTACHELATING AGENT (OPTIONAL) ADD NHOHTO FORMAWHITE PRECIPTATE FESNP CACNEAT ELECTRONIC GRADE (NH), TaoH,O 900-1000°C Ta,O 5,635,146 1. 2 METHOD FOR THE DISSOLUTION AND Cu, Ti, Zr, Mo, Nb, and W) at levels between 500 to 10,000 PURFICATION OF TANTALUMPENTOXDE parts permillion (ppm). Such high impurity levels would be unacceptable for use in the above electronic and phosphor TECHNICAL FIELD applications. Thus, it is necessary to purify technical grade This invention relates to methods for the processing and 5 tantalum pentoxide before it can be used. purification of tantalum-containing ores and compounds. In Unfortunately, tantalum pentoxide is extremely difficult to particular, this invention relates to methods of producing dissolve even in hydrofluoric acid, especially the crystalline high purity tantalum compounds from standard technical B-Ta-Os phase. Direct dissolution in HF requires exces grade tantalum pentoxide. sively long dissolution times and many times the amount of O HF dictated by the stoichiometry of the reaction.Thus, direct BACKGROUND ART dissolution of TaO for use in conventional purification methods like solvent extraction and ion exchange is com High purity tantalum metal and tantalum pentoxide have mercially impractical. become increasingly important to the electronics industry in The chemical reaction for the dissolution of TaCs in HF the preparation of advanced electronic materials used in the 15 can be written as: manufacture of devices such as surface acoustic wavefilters, pyroelectric infrared sensors and optoelectronic devices. High purity tantalum pentoxide is also required for the preparation of tantalate x-ray phosphors for x-ray intensifier screens. The purity of tantalum metal and tantalum pentox 20 The reaction kinetics of the dissolution of TaCs in HF ide used in the manufacture of such products should be media have been investigated by I. I. Baram, Journal of greater than 99.99% and preferably approach 99.9999%. Applied Chemistry of the U.S.S.R., V. 38,2181-88 (1965). Three major methods exist for purifying tantalum According to the reported results, only about 5.3 g of pure containing materials: distillation (or chlorination), liquid TaOs (which had been calcined at 800° C. for 3 hours) liquid solvent extraction and ion exchange. 25 could be dissolved in 1 of 14.6M HF in 4 hours at 70° C. In the distillation method, a mixture of an impure Because the dissolution reaction was reported to be first tantalum-containing material and carbon is reacted with order with respect to HF concentration, it can be estimated chlorine gas at about 600 to 800° C. Although distillation that approximately 10.8g of TaOs would have dissolved in is a well established commercial process for the purification 1 I of 29 M HF in 4 hours at 70° C., a molar ratio of 30 approximately 1200:1 HF/TaOs. Thus, it is evident that of tantalum-containing materials, it has difficulty separating under the above conditions, much more HF is required to tantalum and niobium because of the small difference in the dissolve TaOs than would be dictated by stoichiometry. boiling points of tantalum chloride (239° C.) and niobium Such a large excess of HF is not only economically unde chloride (249° C). Since niobium is a ubiquitous impurity sirable but is also likely to be hazardous. in tantalum-containing materials, solvent extraction and ion 35 Although increasing the temperature will increase the rate exchange methods are preferred over distillation when high of dissolution, the amount of HF required for dissolution is purity tantalum and tantalum pentoxide are desired. still many times the stoichiomteric amount. For example, In solvent extraction methods, an impure tantalum over a period of 3 days at 100° C., approximately 15 g of containing material is dissolved in hydrofluoric acid (HF) Ta-Os can be dissolved in 190 ml of approximately 25MHF, media and brought into contact with an organic solvent. 40 amolarratio of about 140:1 HF/TaOs, or about 10 times the Tantalum values are selectively extracted into the organic stoichiometric amount. However, using higher dissolution phase, back-extracted into aqueous solution, and precipi temperatures also increases energy consumption and the tated as tantalum hydroxide by hydrolyzing with aqueous amount of dangerous HF fumes. ammonia. The precipitated hydroxide can be converted to Therefore, it would be a significantimprovementin the art tantalum pentoxide by calcining in air. However, multiple 45 to have a method of dissolving Ta2O5 in an HF media to extraction/back-extraction cycles may be necessary to pro produce atantalum-containing solution which could be used duce the desired high purity. Examples of liquid-liquid directly in conventional solvent extraction and ion exchange solvent extraction methods are disclosed in U.S. Pat. Nos. purification methods. It would also be a significantimprove 3,117,833, 3,712.939 and 4,673,554. ment to have a method of dissolving TaOs in HF media In ion exchange methods, an impure tantalum-containing 50 which would require much less HF than needed for direct material is dissolved in HF media and then passed through dissolution of TaOs in HF media under the same conditions. an anion exchange column which selectively retainstanta lum metal values. The impurities remain in solution and are SUMMARY OF THE INVENTION discharged in the effluent. The retained tantalum values are subsequently eluted from the column and then precipitated 55 It is an object of the invention to obviate the disadvan as tantalum hydroxide as above. An example of such a tages of the prior art.
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