US3001867A - Method of refining metals - Google Patents

Description

at elevated temperature.

3,001,867 METHOD OF REFINING METALS Karl J. Korpi, Pasadena, Calif., and Raymond C. Johnson, ()rwigsburg, Pa., assignors to The Lummus Company, New York, N.Y., a corporation of Delaware Filed June 23, 1953, Ser. No. 743,736 Claims. (Cl. 75--84.1)

This invention relates to the production of high melting point metallic elements and has for an object the provision of an improved method or process for producing high-purity refractory metals. More particularly, the invention contemplates the provision of an improved method or process for producing high-purity, high melting point metallic elements, including titanium, zirconium and uranium, by the disproportionation of lower chlorides of such elements. This application is "a continuation-inpart of our co-pending application Serial Number 543,514, filed October 28, 1955, now abandoned, and entitled Method of Refining Metals.

Titanium, zirconium and uranium have becomeimportant commercial materials in view of the unusual properties which they exhibit. At present, there are several ways of recovering such metals all of which are complicated and expensive. For instance, the procedures now used for the manufacture of titanium are the follow- (1) Reduction if titanium tetrachloride or other titanium tetrahalide with either sodium or magnesium with subsequent elimination of the sodium or magnesium halide which is formed by washing or distillation.

(2) Reduction of titanium oxide with calcium hydride This procedure has not been too successful since the product is always heavily contaminated with oxygen.

(3) Thermal dissociation of a titanium tetrahalideon a hot filament under vacuum.

(4) Electrolytic recovery fromiused salts.

At the present time, the most widely used commercial method is the reduction of titanium tetrachloride with magnesium or sodium followed by subsequent distillation of the magnesium chloride or sodium chloride by-product in a vacuum. This process, popularly referred to as the Kroll process, is inherently expensive since it produces a titanium halide from a titanous ore and then reduces the halide with another substantially pure metal. In such a process, the necessary expense of the pure secondary metal establishes a very high minimum cost. Also the titanium is formed as a metallic sponge which necessitates further processing to obtain the metalin a .useable form.

As indicated, titanium, as well as the other aforementioned metals, have many unusual physical and chemical properties. In order to ,,be workable and generally useful, these metals have to be supplied in an extraordinarily pure form. Small percentages of oxygen, nitrogen, hy-

drocarbon or carbon embrittle the metal markedly so that it cannot be handled by conventional metal working procedures. Under these conditions, great care is taken'to eliminate these undesirable elements frombein-g present while the metal is being formed. While the above noted processes are illustrative of titanium recovery, they are in principle applicable to other metal recovery in pure elemental form. These processes usually involve the recovery of crystalline metals in the form of extremely small particles or a sponge form of metal. The small particles are inherently unstable and even pyrophoric, readily oxidizing in the presence of air or Water, and even 1 react with nitrogen from the air to form nitrides .of the metal.

Other difliculties -with:the treatment.- and recovery of melting point, metallic elements we have hereinafter de:

Patented Sept. 26, 1961 property of titanium, in the molten state, of'acting as a nearly universal solvent presents a major problem in handling the metal in such a state. Almost all of the impurities tolerable in other materials reduce the ductility of the high melting point metals to the degree of being unworkable.

To illustrate our process of producing high purity, high scribed our invention with regard to the treatment and recovery of titanium. I

. In accordance with .the present invention, the metal titanium is produced as a relatively high purity product of the little knownreaction of titanium monoxide with the titanium halides. Although the reactions of decomposition of sub-halides to metal and higher halides has been known,'the possibilities of. combined. titanium halide reactions have not been appreciated. Through our invention pure ductile titanium is produced in plate or ingot form, rather than in oxidizable crystals or sponge form, and at a cost substantially below that of present day methods. Further',our invention provides a relatively low temperatureprocess which can operate at substantially atmospheric pressure with a minimum of heat input and without the need for hydrogen or other costly reducing materials such as sodium or magnesium. Other objects and advantages of our invention will appear from "the following description of one form of embodiment taken in connection with the attached drawing which is asimplified flow diagram of the reaction accordingto the invention.

In view of the various metals recoverable and variations of equipment which may be used to carry out our process,

the flow diagram is to be considered of generally infor-- mative nature and illustrative of process steps rather than v a limitation as to a specific metal or type of apparatus. Accordingly, in our method, titanium bearing ores such I as rutile, ilmenite and titanite or titanium dioxide-bearing slag obtained as a result of the smelting of titaniferous iron ore, are charged to pulverizer 10. These ores or slag, even in their purest state, contain iron, silicon and aluminum as regular impurities. Alkaline earth-metals,

such as calcium, are likewise commonly found in various titania rich ores. We reduce the titanium dioxide of's'uch ores with powdered carbon supplied to pulverizer 12and produce titanium contaminated with lower oxides including Ti O ,'Ti O and TiO, and titanium carbide in furnace 14. The reducing agent fed to pulverizer 12 may be derived from any known carbon source; however, in

order to limit contaminationpf the lower oxides of titanium, we prefer to-employ petroleum coke or -cha'coal.

The carbon in'the mixture serves primarily to remove the oxygen from'the titanium dioxide in the form of carbon monoxide and carbon dioxide, thereby reducing the titanium dioxide to titanium. Some'of the carbonmay react with the titanium dioxide to form titanium carbide and carbon monoxide and carbon dioxide. To prepare titanium in furnace 14, we have used a mixture of parts by weight of crushed rutile and'g27 parts by weight of crushed petroleum coke, consolidated by pressurefto a dense solid. Analysis of the rutile and petroleumcoke used by us indicated the tollowing:

' r 1 Percent Petroleum coke: Percent Volatile matter 8.81 Fixed carbon 89.86 Ash .u-d I- -a- 1133 Thefurnace 14 may be an el'ectric resistance furnace or it may be of'any typical arc, cupola or fluidiz'ed'design. In the furnace, the titanium dioxide is reduced by carbon by a series of step-Wise reactions to' produce ---low er 'oxides of titanium, elemental titanium,'and titanium carbide inaccordance'with the following chemical cquatio'ns:

(becomes favorableabout 900 1000 C.) 2) TiO +2C Ti-l-ZCO I (becomes favorable about 1500-1600 C.) 3 '"rio -1-'co- Ti0- -co V h (favorable above 100"C.) "(4) TiO +3C- TiCF-2CO I g I (becomes favorable about 900-'-1000"C.) (5) TiO+2TiC- 3Ti-l-2CO (becomes favorable abOut' ZOOO' -ZIOO C.)

A mixed'product of TiO and Tic maybe obtainedrin ifurnace: 14 by carrying out the reaction at a temperature of- 900-1100C. In presence of-excess carbon, titanium carbide will be the favored product-near 1000-'C. at' at- .zzmospheric pressure according to reactioneit. However,

lvitlisdesired to make. the maximum of-metal-and 'a miniti-mum :of carbide and lower oxides; hence the furnace ':silicon. This material is, ground=orpulverized:=in,pul-

verizer 18 for further handling.

.The pulverized titanium-titanium-monoxide mixture is rthen charged to reactor 20, which is operated under con- 'ditions to exclude oxygen, nitrogen and moisture. This reactor is preferably maintained at a temperature of between 725 C. and 1475 Cfiand at substantially atmossphericpressure. Under the conditionsof-elevated temperature and controlled-atmosphere,-the pulverizedcrude --titanium mixture introduced to the reactor is: subjected -to the action of a higher metalichloride vapor (MX entering through line 22 sc -that an exothermic reaction results. The reaction in reactor 20 is soexothermic in nature that only enough heat to start upis needed from an external source. The temperature within the reactor is controlled-by the amount of halide vapor input through line 22.

We have found that any of the halides which readily co'mbine with titanium may be used to form the halide vapor entering reactor '20 through line 22. Principally "we have formed metallic-titanium according to ourproc- ;-ess using chlorine as the combined halogen presentin the higher metallic halides-(MX and'thelower-metallic 'halide (MX p v A V For the purpose ofgeneral explanation, the metaland halide portions of all compounds illustrated in the draware represented by the symbols M and X, respecj tively with -and designatingthe-higherand lower -halideform; respectively.

The vapor in-line-22--is--principally a-higher--'halide of (MX but in; some cases may-include equflibmum amountsof lower-halides upon, reaction with "the titanium mixture charged toreactor 20 forms a liquid flower halide of titanium (MX which is removed -through line 24.

The titanium higher halides function somewhatin the manner of carriers in accordance with specific reactions illustrated by the following equations:

(7) Ti PTiXi-i 2TiX The'titaniumoxides and carbideipresentin thereactor charge that donot react wi-th the higher halides under the an auxiliary reactor (not'shown) for further reactionito produce lower halides .of-titaniurn according to the following equations: (8) ==2Ti0+3TiXip TiO+4TiX t 9) :-:"I.iC-i- 3TiX C+4TiX Both" of these reactions are favorableat temperatures below about 500 0.; hence such auxiliary reactor should be operated at about 400 C." while the tetrahalide'vapor 'is introduced. Thisreactor 'should be-opera'ted batchwise so that after charging and reacting the solidtit'anium' carbide and titanium monoxidewiththe tetrahalide vapor,"such reactoris then'heated' to themelting'point of the dihalide of titanium. Under these- "conditions, *the trihalide disproportionates'todihalideand tetrahalideand '-theliquid--dihalide' may thereafter -fiow 'to reactor-30 to join the flow of liquid aiihalide inline 24. The tetrahal ide vapors may remain-in the auxiliary reactor to react with a fresh charge of titanium carbide andtitaniummonoxide 40 at the lower 9 temperatures withadditional tetrahalide added as required v The lower liquid halide (MXQ removed "from reactor -20 through line 24 is' their charged to a second reactor 30 "which contains a plurality of electric heating elements generallyindicat'edat 32. Eachlj1eating element is enclosed ina-meta1'(M) -sheath-34'andis maintained at a temperature'of from-800 C.--to 1500 C. The 'liquid poolof lowerhalide' within reactor 30 is heated by the sheathed heaters to'an average temperature of-between 725 C. andl475 C. andin this temperature range, the

'lowermetallic -halide is A thermally" disproportionated'. to formthe metal, which deposits 'on the sheaths-'or-collectors- -ina high state of purity, and to higher metallic halides (MX The decomposition of titanium dihalide to yieldnfie tallie titanium is according-to thefollowing equation: (10) zrix -mrr-i rix. "(iii inm (solid) (gas) Any titanium trihalide whichmay -bepresent isgen- .erally unstable and dissociates into titanium dihalide and titanium tetrahalide. The tetrahalide and someof the unreacted dihalide formed during the thermal disproportionation in reacto1130 is in -a.-gaseous state and is re moved through line 36 and pumped by; pump 38 to "condenser 40. In condenser 40,:thegaseous mixture is cooled to a point wherebyany titanium dihalide is condensedforreturntoreactor '30 inline 42 while the gaseous. titanium tetrahalide is r e circulated to line 22 through line 44 and. provides substantially all of the tetrahalide requirement of reactor 20.

After the initial starting up ofour process, the halide used for reacting with titanium proceeds in continuous circulation between reactors 20 and 30. Only a small amount of the higher halide (MX is necessary as makeup since the halide *"circuit' is substantially closed with accuser only small amounts of halide loss through the-formation of volatile halides of the metallic impurities in the raw material. The volatile halides are removed through line 46 to condenser 48 where the higher halide is condensed and returned through line 46 to reactor 20. The volatile halides are then removed from the system through line 50.

Within the reactor 30 there is a continuous deposition and growth of metal on the heater sheaths 34 whereby they obtain the form of an ingot. Periodically the sheaths are removed and form the pure metal product, after which a new sheath is placed over the heating element and returned to the liquid poolof lower metallic halide.

Around each heater sheath is a refractory thermal barrier 52 which acts to substantially shield the liquid 'pool of lower halide from the higher temperature of the heater while at the same time directs the liquid halide in recirculating fiow past the sheath for disproportionation.

-In some instances the heating elements may also be maintained in the vapor phase over the liquid in reactor 30 as for example where it is found that the particular lower halide used disproportionates'more rapidly as a vapor.

To illustrate a preferred embodiment of our process, operating conditions for the deposition of high purity titanium, are set forth in the following example.

Example Vaporous titanium tetrachloride (TiCl at a temperature in the neighborhood of 700 C. reacts rapidly with crushed slag (comprised of lower titanium oxides, titanium, titanium carbide and small amounts of impurities) in a bed maintained at a temperature in the neighborhood of 725 C. at atmospheric pressure to form liquid titanium dichloride, the dichloride forming a liquid pool at a point removed from the slag bed. The liquid titanium dichloride, maintained at a temperature in the neighborhood of 750 C. at atmospheric pressure, disproportionates to titanium and titanium tetrachloride vapor in the persence of a heated titanium sheath (1100 C.) immersed within the pool. The titanium tetrachloride vapor is continuously withdrawn from the space above the pool and recirculated for use as the slag halogenating media. Analysis of the titanium coating on the titanium sheath shows only slight porosity and the presence of only trace impurities.

Having now described our invention with regard to the production of elemental titanium, zirconium and uranium and having given an example of a preferred embodiment of our process using titanium as the exemplified product, we desire a broad interpretation of the invention within the scope of the disclosure herein and the following claims.

We claim:

1. The method of producing a metal selected from the group consisting of titanium, zirconium and uranium by the disproportionation of a lower to form the metal and a higher chloride of the metal which comprises: halogenating a crude mixture of said metal with a higher chloride of said metal to form a lower chloride of said metal; effecting said halogenation in a first reaction zone at substantially atmospheric pressure and at a temperature above the melting point and below the boiling point of said lower chloride of the metal and above the boiling point of said higher chloride of the metal thereby to form said lower chloride of said metal in said zone; withdrawing said lower chloride as a liquid from said first reaction zone and introducing it into a second reaction zone for disproportionation therein to said metal and a higher chloride of said metal; effecting said disproportionation in said second zone at substantially atmospheric pressure in the presence of a heated body of said metal by forming a pool consisting primarily of said lower chloride around said body and maintaining chloride of the metal 7 the liquid in said pool at a temperature'above the melting point and below the boiling point of said lower chloride, said bodybeing heated to a temperature sufficient to maintain said pool temperature; depositing a substantially solid layer of disproportionated metal on said body; and recirculating the higher chloride formed during disproportionation to said first reaction zone to provide the higher chloride utilized for said halogenation. a

2. The method of producing a metal selected from the group consisting of titanium, zirconium and uranium, by the disproportionation of a lower chloride of the metal to form the metal and a higher chloride .of the'metal which'comprises: halogenating a crude mixture of said metal with a higher chloride of said metal to form a lower chloride of said metal; effecting said halogenation in a first reaction zone at substantially atmosphericpressure and at a temperature above the melting point and below the boiling point of said lower chloride of the metal and above the boiling point of said higher chloride of the metal thereby to form said lower chloride of said metal in said'zone; withdrawing said lower chloride as a liquid from said first reaction zone and introducing it into a second reaction zone for disproportionation therein to said metal and a higherchloride of said metal; effecting said disproportionation in said second zone at substantially atmospheric pressure in the presence of a heated body of said metal by forming a pool consisting primarily of said lower chloride around said body and maintaining the liquid in said pool at a temperature above the melting point and below the boiling point of said lower chloride by thermally induced circulation of said liquid up through a shield surrounding said body and over said body, said body being heated to a temperature suflicient to maintain said pool temperature; depositing a substantially solid layer of disproportionated metal on said body; and recirculating the higher chloride formed during disproportionation to said first reaction zone to provide the higher chloride utilized for said halogenation.

3. The method of producing titanium by the disproportionation of a lower chloride of titanium to form titanium and a higher chloride of titanium which comprises: halogenating a crude mixture of titanium with a higher chloride of titanium to form a lower chloride of titanium; effecting said halogenation in a first reaction zone and at a temperature above the melting point and below the boiling point of said lower chloride of titanium and above the boiling point of said higher chloride of titanium thereby to form said lower chloride of titanium in said zone; withdrawing said lower chloride as a liquid from said first reaction zone and introducing it into a second reaction zone for disproportionation therein to titanium and a higher chloride of titanium; efiecting said disproportionation in said second zone in the presence of a heated body of titanium by forming a pool of said lower chloride around said body and maintaining the liquid in said pool at a temperature above the melting point and below the boiling point of said lower chloride, said body being heated to a temperature sufiicient to maintain said pool temperature; depositing a substantially solid layer of disproportionated titanium on said body; and recirculating the higher chloride formed during disproportionation to said first reaction zone to provide the higher chloride utilized for said halogenation.

4. The method of producing zirconium by the disproportionation of a lower chloride of zirconium to form zirconium and a higher chloride of zirconium which comprises: halogenating a crude mixture of zirconium with a higher chloride of zirconium to form a lower chloride of zirconium; eltecting said halogenation in a first reaction zone and at a temperature above the melting point and below the boiling point of said lower chloride of zirconium and above the boiling point of said higher chloride of zirconium thereby to form said lower chloride of zirconium in said zone; withdrawing said lower chloride as a liquid from said first reaction zone and introducing 7 itinmaseeondreactionzonefor disproportionation there- .in;to:iirconium and. a-higher' chloride nizirconium; efiecting :said idisproportionation in said second zone in the presence rofaheated body oflzirconiumby forminga, pool ofsaid lowerschloride eroundsaid body andmaintaining the liquid in ssaid .pool nth temperature above the meltinggpointiand belowihe hoiling'point .ofsaid lower chloride, said body being heated to a temperature sufiicient to maintain: said' poiol temperature; depositing a substanti'allysolid layer :of Ilisproportionated zirconium on said body; and recirculating the higher chloride formed during disproportionation to "said first reaction zone to provide the higher chloride utilized for said halogenation.

5c The method of producing uranium'by the disproportionation of a lower chloride of uranium to LfOI'Ill uranium and a higher chloride of uranium which comprises: halogenating a crude mixture of uranium with a "higher chloride of uranium to form a lower chloride of uranium; effecting said halogenation in a first reaction "zone and at a temperature above the melting point and "below the boiling point of said lower chloride of uranium and above the boiling point of said higher chloride of uranium thereby to .form said lower chloride of uranium inssaid zone; twithdrawing tsaidslower chloride asaliguid from said first reaction :zone and introducing .it into: second reaction .-.zone ior :disproportionation therein tto nraniumland aihigherrchloride lofnraninm; effecting said disproportionationinsaid second zone in .thepresenceloi aheated bodyofnraniumrbyiormingtalpoolofrsaidllower chloride around said body and maintaining the liquidrin said pool at atemperature above the melting point and belowrthe lboiling point .of: said lower .chloride,. said i body beingiheated to a temperature suflicient to maintainsaid pool temperature; depositing alsubstantially solid layer of .disproportionated uranium on said bcdyyand recirculating the .higher chloride formed during disproportionation to said first reaction zone to provide the higher chloride-utilized for esaid halogenation.

References Cited in thefileof this patent UNITED STATES :PATENI S 2,556,763 Maddex 'IuneI2, I951 2,670,220 .Jor'dan 'Feb.'-2-3, I954 2,706,153 Glasser Apr. 12, "1955 2,785,973 Gross Mar. 19,1957 2,890,952 Korpi et "a1. June "1 6, I959

Claims (1)

1. THE METHOD OF PRODUCING A METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM, ZIRCONIUM AND URANIUM BY THE DISPROPORTIONATION OF A LOWER CHLORIDE OF THE METAL TO FORM THE METAL AND A HIGHER CHLORIDE OF THE METAL WHICH COMPRISES: HALOGENATING A CRUDE MIXTURE OF SAID METAL WITH A HIGHER CHLORIDE OF SAID METAL TO FORM A LOWER CHLORIDE OF SAID METAL, EFFECTING SAID HALOGENATION IN A FIRST REACTION ZONE AT SUBSTANTIALLY ATMOSPHERIC PRESSURE AND AT A TEMPERATURE ABOVE THE MELTING POINT AND BELOW THE BOILING POINT OF SAID LOWER CHLORIDE OF THE METAL AND ABOVE THE BOILING POINT OF SAID HIGHER CHLORIDE OF THE METAL THEREBY TO FORM SAID LOWER CHLORIDE OF SAID METAL IN SAID ZONE, WITHDRAWING SAID LOWER CHLORIDE AS A LIQUID FROM SAID FIRST REACTION ZONE AND INTRODUCING IT INTO A SECOND REACTION ZONE FOR DISPROPORTIONATION THEREIN TO SAID METAL AND A HIGHER CHLORIDE OF SAID METAL, EFFECTING SAID DISPROPORTIONATION IN SAID SECOND ZONE AT SUBSTANTIALLY ATMOSPHERIC PRESSURE IN THE PRESENCE OF A HEATED BODY OF SAID METAL BY FORMING A POOL CONSISTING PRIMARILY OF SAID LOWER CHLORIDE AROUND SAID BODY AND MAINTAINING THE LIQUID IN SAID POOL AT A TEMPERATURE ABOVE THE MELTING POINT AND BELOW THE BOILING POINT OF SAID LOWER CHLORIDE, SAID BODY BEING HEATED TO A TEMPERATURE SUFFICIENT TO MAINTAIN SAID POOL TEMPERATURE, DEPOSITING A SUBSTANTIALLY SOLID LAYER OF DISPROPORTIONATED METAL ON SAID BODY, AND RECIRCULATING THE HIGHER CHLORIDE FORMED DURING DISPROPORTIONATION TO SAID FIRST REACTION ZONE TO PROVIDE THE HIGHER CHLORIDE UTILIZED FOR SAID HALOGENATION.

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