US2890112A - Method of producing titanium metal - Google Patents

Description

J1me 19 c. H. WINTER, JR Y 2,89 ,1

' METHOD. OF. IERODUCING TITANIUM METAL.

Filed Oct. 15, 1954 TITANI FERROUS CREW ICARBON PREPARATION OF 6 I A v "9'2 7 A" PRIMARY ELECTROLYTIC s REDUCTION CELL STAGE SECONDARY Q2 REDUCTION STAGE Neol MgCl -CaC| ELECTROLYTE T| METAL 2 2 INVENTOR CHARLES H WINTER,JR.

ATTORNEY United States Patent O T. ce

2,890,112 Patented June 9, 1959 2,890,112 METHOD or PRODUCING TITANII' IM METAL Charles H. Winter, Jr., Wilmington, Deb, assignor to- E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Application October 15', 1954, Serial No. 462,533

' 3 Claims. (Cl. 75-845) This invention relates to the preparation of metals and alloys, and more particularly to an integrated two-step novel reduction process for producing titanium metal.

The preparation of metals by the reduction of a metal halide salt with an active reducing metal is well known. Thus, the production of titanium rnetal by reducing titanium tetrachloride with magnesium metal is described U. S. Patents 2,205,854, 2,556,763, 2,567,838, 2,607,- 674 and 2,621,121. The by-pr'oduct halide salt obtained from the reduction can be treated chemically and/or electrically to recover reducing metal and halogen values present therein. Thus, by-product magnesium chloride can beelectrolyzed to recover magnesium and chlorine values therefrom, the chlorine being useful in titanium tetrachloride production while the magnesium can be reem loyed in, the reduction step.

Many difiiculties (which result in an undesired low rate or metal production) are encountered in the single step reduction of titanium tetrachloride by magnesium due to the large amount of heat released by the reaction and the inability to efiectively control many reaction variables. It has been found that an advantageous method of alleviatirig many of these difiiculties is to carry out the reducreaction in a two-step manner; that is, the titanium tetrachloride is first reacted with a controlled amount of a reducing metal, preferably sodium, to produce a salt composition comprising a lower chloride of titanium and sodium chloride, and this salt composition is then reacted, in a second step, with the required amount of reducing metal, preferably magnesium, to obtain the desired titanium metal. The loy-product salt from this twostep process comprises a mixture of sodium chloride and magnesium chloride which disadvantageously does not lend itself to usual processes for recovery of the magneslum reducing metal and chlorine. It cannot be used ad vantageously m magnesium cell because of sodium chloride accumulation, nor can it be fed direetly to a commercial type sodium cell such as a Downs cell.

It is among the objects of this invention to overcome the above and other disadvantages of prior metal producing processes, and to provide novel and eliective methods for attaining such objects. One particular object is to provide an integrated two-step metal reduction method in which the salt by-products are effectively treated for recovery of components adapted to be recycled for reuse in the system. A further object is to provide novel means for utilizing the by-products in such integrated process "and to produce sodium for use in the initial reduction step, magnesium-calcium alloy for use in the second reduction step, and chlorine for use in the production of the metal halide reactant utilized in such process. A specific object is to produce titanium metal and alloys thereof. Other objects and advantages of the invention will be apparent from the ensuing description and the accompanying diagrammatic drawing consisting of a flow sheet arrangement illustrative or one integrated twostep reduction process in accordance with the invention.

The foregoing objects and advantages are realized in this invention which comprises initially reacting titanium tetrachloride with a regulated amount of sodium metal to form a molten titanium subchloride-sodium chloride salt composition, reacting said composition with a mag.- nesium-calcium alloy reducing agent to produce titanium metal and a molten, ternary by-product salt of said agent, separating said titanium metal and by-product salt products, subjecting the ternary by-product salt composition recovered to electrolysis in a molten salt electrolytic cell to produce sodium metal, magnesium-calcium alloy, and chlorine, and separately recycling said products of electrolysis for reuse in the process.

Referring to the drawing and to one adaptation of the invention, the necessary quantity of a ternary salt electrolyte composition, comprising, for example, a molten mixture of, say, 51.2% Mgcl 7.1% 02101 and 41.7% NaCl, can be charged, via a suitable inlet and from a source of supply (not shown) into an electrolytic cell 1. Said cell is conventional in design and operation and preferably comprises the sodium type cell shown at page 531 of Mantells Industrial Electrochemistry, 3rd edition. The initial heating, starting up, and operation of this type of cell is fully described at pages 532537 of that publication. In the cell 1, electrolysis at temperatures ranging from 520 C. to 900 C., of the salt composition occurs and molten sodium, molten Mg-Ca alloy, and chlorine are produced. The molten sodium and molten MgCa alloy are withdrawn from the cell through a conduit 2 into an associated storage vessel or collector 3, which, together with the conduit 2, can be suitably insulated and electrically or otherwise heated so that the vessel and conduit are maintained under a temperature of about 550650 C. In the collector 3 the two immiscible metal phases separate due to differences in den sity and form an upper molten Na layer 4 and a lower molten Ca-Mg layer 5'. Chlorine formed in the cell 1 can be stored for later use, or, as shown, is withdrawn therefrom through a line 6 and fed to a TiCl, preparation stage 7 wherein it is employed in the conventional chlorination of a titaniferous ore, such as ilmenite, at elevated temperatures in the presence of a reducing agent such as carbon, as contemplated, for example, in US. Patents Nos. 1,179,394, 2,184,884, 2,184,885, 2,184,887, 2,020 431, etc.

Pure titanium tetrachloride from stage 7 (or from any other available source) is fed via line 8 at a controlled rate to a primary reduction stage 9 wherein preparation for use in the process of a titanium subchloride intermediate (TiCI xNaCI, with x:1 -2, inclusive) is etfected. The primary reducer 9 comprises a convention- 21 type reaction vessel adapted to be maintined at tem' peratures ranging from about 550-1300" C. It is suitably provided with separate inlets through which, after apparatus purging, the TiCl; reactant from the line 8 is charged for reaction with the molten (at about C.) Na reactant fed thereto from the collector 3 through the line 10 and which is also maintained under an inert atmosphere. The titanium subchloride intermediate formed in the primary reducing stage 9 is then introduced while at a temperature of about 600 C. into a reactor equipped with an agitator, pressure releasing and purging means, and product withdrawal means provided in secondary reducing stage 12 of the system. In said stage 12, reduction of said intermediate is effected under an inert atmosphere at temperatures ranging from about 550- 950 C. with pellets of the previously formed Mg-Ca alloy from the collector 3, said alloy being fed to an inlet thereto communicating with the line 13 issuing from the bottom of said collector. Particulate titanium metal and by-product salt, MgCl +CaCl NaCl reaction products are drained from the secondary reactor and the titanium product and by-product salt are separated through conventional screening or other desired treatment. The byproduct salt is maintained in molten state and recycled, via line 14, to the cell 1 as an electrolyte feed therefor, after addition of any small amount of make-up material required to substitute for any retained in the particulate titanium metal product after the draining or separation step. The titanium metal particles recovered are removed from the stage 12 through a line 15, cooled under an inert atmosphere to approximately room temperature and are then subjected to conventional purification treatment, such as by leaching with dilute (about 5%) nitric acid. The leached product is then washed and dried to provide a highly useful form of commercial titanium met al. Vaporization or vacuum distillation to remove byproduct salts are alternative purification means.

To a clearer understanding of the invention, the following specific examples are given. These are merely illustrative and are not to be construed as limiting the scope of the invention.

Example I To an electrolytic cell in a system of the type above described there was fed, at a continuous rate of 32.5 lbs./hr., the following molten salt charge, per day 400 lbs. of magnesium chloride, 55 lbs. of calcium chloride and 325 lbs. of sodium chloride (total weight 780 lbs.). The cell was supplied with a nominal current of about 10,000 amps. at voltages between about 5.8 and 6.2 volts. The metal product, which was collected and held at 520 550 C., comprised after separating into two layers a lighter sodium layer containing 129 lbs. of sodium and a heavier magnesium-calcium layer comprising about 120 lbs. having a content of 100 lbs. of magnesium and 20 lbs. of calcium. The molten magnesium-calcium alloy solidified and because of its brittleness was easily crushed into pellets ranging from fine powder to not more than /s" in size. Sodium metal formed was held in the molten state in the storage tank at a 150 C. temperature with an inert gas blanket thereover to prevent contami' nation. During the test period 530 lbs. of chlorine was produced, of which the major portion was recovered.

In the first reduction step of the process the titanium subchloride intermediate molten salt was prepared. A 10" diameter by 6' tall cylindrical steel reactor was used, having a top flange provided with inlets for sodium metal and titanium tetrachloride and a safety exit release pipe utilizable for admitting and discharging an inert purging gas to the reactor. The bottom of the reactor was closed with a hemispherical base having a bottom outlet conduit. This outlet was provided with a two-foot upward riser section connected to a catch tank held at 600 C. to insure that a two-foot level of molten salt would be retained within the reactor so that as the material was produced it would overflow at the two-foot level into such tank. The molten sodium metal was fed to the primary reactor at a rate of 75 lbs. per hour with a total of about 130 lbs. being added during a one hour and forty-five minute period. During this time there was added, at a rate of about 410 lbs/hr. about 710 lbs. of titanium tetrachloride. About 840 lbs. of molten salt was produced during this run. The material within the reactor at the two-foot level was blown into the catch tank by pressurizing the reactor with inert gas.

The resulting titanium subchloride molten intermediate salt, analyzing about 1.5 NaCl-TiCl was then reduced in the secondary stage of the process in an upright cylindrical reaction vessel provided with a demountable head, a top cylindrical portion in which the reaction was carried out, and a lower section for collecting reaction by-product. The top portion was secured to the reaction section by means of flange connections fastened together by closing means such as bolts, clamps, etc. The reaction section chamber was 2 ft. in diameter and 4 ft. in height and terminated in a conical bottom having a port and product removal valve assembly for withdrawing the products of reaction. Below this section sheet metal discs were provided which served as radiation shields and assisted in retaining heat within the reaction section while radiation to the lower portion of the reactor assembly was prevented. Below the radiation shields in the collection section a drainage screen was provided to collect particulate titanium metal product formed and allow the molten by-product salt to drain into the by-prodult collection portion of the lower section. The upper reactor section was provided with nozzles for introducing inert gas and for venting, and with means for operating a stirrer and for introducing the reactant. The magnesium-calcium alloy pellets were introduced into the reactor from a hopper through an addition line, the rate being controlled by valve means in such line. The upper portion of the reaction vessel was enclosed in a furnace adapted to be heated by conventional means such as gas burners or electrical resistors. In the reduction,-the apparatus was first purged of deleterious impurities by inert (argon) gas introduction and was then heated by the furnacing means to bring the equipment and the molten salt, added to the upper reaction section, to about 700 C. A total of 840 lbs. of molten salt intermediate was added to the reactor. The magnesium-calcium alloy pellets were then introduced to the reactor at a rate of 120 lbs. per hour, the molten salt being agitated during such introduction to submerge and disperse the reductant metal particles in such salt. During the reaction a temperature of about 800 C. was maintained by regulating the furnacing means. After 120 lbs. of alloy addition, the reactor drainage valve was opened and the titanium metal particles and by-product salts were withdrawn into the lower section of the reaction vessel. The titanium metal was collected on the screen and approximately of the by-product salts were drained therefrom into the lower by-product collection zone. After cooling, the materials were removed from the lower portion of the assembly by opening up the equipment at the lower flange. The titanium metal was removed and 260 lbs. of product comprising about 180 lbs. of titanium metal with 80 lbs. of admixed by-products was obtained. The by-product salt was drained from the product mass and was retained in the lower portion of the collection system wherein approximately 700 lbs. of salt were recovered. The 260 lbs. of product metal containing admixed by-product salt was then added to 500 gallons of 5% nitric acid solution, at a rate of 50 lbs. per hour, and leached at a temperature of 40 C. maintained by means of immersed water-cooling coils. The metal was retained in the leaching solution for 6 hours after which the solution was drained from the metal. Following draining, the metal was washed with a small volume of 2% nitric acid and then with a flowing stream of water, with the water washing being continued until the wash water gave no test for nitrate or chloride ion. The water-washed titanium particles were then drained of water as much as possible and placed in an oven to dry at a temperature of about C. The dried product weighed approximated lbs. Samples, on testing, revealed this material to be eminently suited for commercial titanium metal applications.

Example II An electrolysis of a molten salt composition of sodium chloride, magnesium chloride and calcium chloride was conducted similar to that of Example I to produce molten sodium, molten magnesium-calcium alloy, and chlorine. The metals recovered were utilized to produce sponge t tanium metal. In the primary stage, the reduction of titanium tetrachloride was conducted in a cylindrical iron reactor 24 inches in diameter and 48 inches high disposed within an electrically heated furnace and fitted with necessary means for purging of contaminants, adding reactants, draining the by-product salt in the secondary stage, and a valved line leading to an associated by-product condenser. During the reduction steps the furnacing means was not activated and the reactor was cooled by "forcing a rapid flow of air through the furnace structure about the exterior of the reactor by means of a fan blower. 80 lbs. per hour of titanium tetrachloride were reduced in the reactor at a temperature about 900 C. by sodiummetal fed thereto ata rate of .14 lbs. per hour. From this reduction a molten salt intermediate of titanium subchloride and sodium chloride was obtained at a rate .of about 94 lbs. per-hour. After 10 hours of operation, 940 lbs. of suchintermediate was produced- At the end of the first reduction step, the temperature of the molten salt was reduced to about 600 C. To this batch of molten intermediate salt was added 135 lbs. of the magnesiumvcalci-um alloyproduced in the system, this alloy being fed in at a rate (about 50 ;lbs..-per hour) 7 to keep the molten -salt ,reaction temperature at about 850 C. During the second reduction step, cooling air was also passed over th furnace exterior to cool the walls of the reactor- The product from this reaction consisted of mixed byproduct salt of sodium chloride, magnesium chloride and calcium chloride and sponge titanium metal. After addition of the final amount of magnesium-calcium alloy, the reactor drainage valve was opened and the molten by-product salts were drained from the reactor. About 800 lbs, of molten salt was recovered t ay-drainage to about 80% of that produced by the reaction. The drainage valve was then closed and the valve to the distillation condenser was opened and the vacuum system activated. The furnacing means was then activated and the temperature of the reaction vessel stabilized at 1000 C. In consequence of the resulting distillation, the titanium metal sponge product was purilied to produce high-grade titanium metal sponge, the residual by-produc't salt being collected in the distillation condenser. The recovered by-product salt was added to that recovered by drainage from the reactor and the mixture was utilized as the 'cell feed for electrolytic recovery of its chlorine and reducing metal content.

While the invetnion has been specifically illustrated by the examples illustrative of an integrated process utilizing a two-step reduction and with electrolysis of the mixed by-product salt to produce the two metal reduction reactants, recourse to modifications thereof is contemplated. Continuous reduction of titanium tetrachloride by sodium in the first step can be followed by continuous reduction of the titanium subchloride, sodium chloride intermediate salt by the magnesium-calcium alloy or batch operation of either or both of the reduction steps may be practiced. Varied types of metal product can be obtained by this process in that the titanium metal can be recovered in the form of particles, as titanium sponge metal, or as a shaped ingot of titanium metal associated with by-product salt. A critical item in the process is the recovery and electrolytic dissociation of the mixed by-product salts into the metals required for reduction of the titanium chloride, and chlorine. An important essential of my novel process involves the preparation of the reducing metals required in my two-step reduction method from the by-product salts collected from the second step. The molten salt electrolyte used consists of a ternary composition of sodium chloride, magnesium chloride, and calcium chloride, which is extremely useful because, advantageously, by electrolysis a two-phase metallic system can be produced. The metallic electrolytic product on separating into the two-phase system provides an upper metallic sodium phase and a heavier lower calcium-magnesium alloy phase. This arises from the fact that calcium forms alloys with magnesium and a eutectic with magnesium containing 16.3% calcium melting at 516 C., which is about 75 C. below the normal operating temperature of a sodium-type cell such as a Downs cell. The reasons why this alloy is immiscible with sodium at cell temperatures appear to be: (a) magnesium and sodium are practically immiscible at 65W alc um is. sol b e :in sodium 10 the extent of only 5% at 600 ;C., andtel partition of calcium is largely toward the magnesium-rich phase.

Other factors of importance relative to the metal product compositions include theqfollowing: alloys of calcium containing 70-100% magnesium have melting points which lie in the range of no higher than 620-650 C. The composition 84% magnesium and 16% calcium is the eutectic and has a melting point of 516 C. At 520 C., which is about the temperature preferred .for separating the two immiscible metal phases, sodium will dissolve less than 5% calcium metal. The melting point of the sodium-calcium alloys rise rapidly and at 6% calcium the melting point is about 620 C.

-The-electrolytic cell molten salt composition electrolyte will contain only a very small quantity of magnesium chloride because magnesium electrolyzes from a magnesium chloride-calcium chloride-sodium chloride electrolyte preferentially, and also magnesium chloride is reduced to magnesium by both sodium and calcium. Therefore, the equilibrium bath existing in the electrolytic cell contains very little magnesium chloride. For this reason, it is :essential to have a continuous flow of electrolyte into the cell to provide the .very small amount of magnesium chloride required in the electrolyte and to provide the amount of magnesium required to make the magnesium-calcium alloy which has a melting point in the range suitable for the operation of the cell. The calcium chloride to sodium chloride ratio in the electrolyte within the usual operating range will not have a serious 'eifect upon the term perature of operation of the cell since the melting .points of compositions from 50-80% calcium chloride are less than 640 C. and a eutectic exists at 68% calcium chloride with a melting point of 500 C.

Asnoted, the separation of the 'two immiscible metal phases from the electrolysis product occurs because of difierences in density. At the preferred separation temperature of about 520 C. it is estimated that the density of the preferred 84% magnesium, 16% calcium heavier alloy is about 1.5 and that the nearly pure sodium layer would be about 0.8. This provides a very satisfactory density difference and therefore leads to rapid separation into two layers. The two layers may be separated by decanting or siphoning oh the upper lighter layer of sodium or draining out the heavier lower layer of the magnesium-calcium alloy.

In the electrolytic dissociation of the mixed by-product salts, several factors are critical. It is necessary that the cell feed of by-product salt be made continuous because of the fact that the electrolyte during cell operation will contain a very low concentration of magnesium chloride which must be supplied continuously thereto. The by-product salt may be fed to the cell molten or as solid lumps. The cell must operate above a temperature of 520 C. The molten metal riser and catch tank must be maintained above 520 C. Several commercial type cells adapted for use in the process are discussed at pages 530-538 of the above Industrial Electro Chemistry, 3rd edition, publication, with the Downs cell and German Knapsack sodium cell being specifically shown. In both of these cases, recourse to simple modifications thereof, consisting of heating and insulating the metal riser and catch tank and installing an electrolyte feed line into the chlorine dome are the only factors necessary to effect utilization of a standard type cell in the invention.

My integrated process obtains the benefits derived from a two-step process which are essentially associated with reaction rates in commercial apparatus, the single step reduction process being limited because of the excessive amount of heat released by the reaction of titanium tetrachloride with magnesium. The use of the two-step process also allows many modifications in reduction conditions thereby permitting varied types of product to be produced. The problems arising because 7 of the mixed by-product salts havebeen'solved by the improved electrolytic stepinmy process.

I claim as my invention: V 1.'An integratedprocess for producing titanium metal which comprises reacting titanium tetrachloride in a primary reduction stage of the process and at temperatures ranging from SSQ-IBOO-YC. with a regulated amount of sodium metal to produce a molten titanium subchloridesodium chloride salt composition, reacting said composition in a secondary reduction stage at temperatures ranging from 550950 C. and under an inert atmosphere with a magnesiiun-ca'lcium alloy reducing agent to produce particulate titanium metal and a molten ternary byproduct salt NaClCaCl MgCl separating the titanium metal product from said molten ternary by-product and subjecting the-latter in molten state to electrolysis in a molten salt electrolytic cell to produce molten sodium metal, molten magnesium-calcium alloy, and chlorine, and collecting and separating said molten sodium and magnesium-calcium alloy and reemploying as reactants the sodium recovered from said cell in said primary stage and the magnesium-calcium alloy recovered therefrom in said secondary stage of the process.

2. An integrated process for producing titanium metal by the reduction of titanium tetrachloride, comprising initially reducing at temperatures ranging from 550- 1300 C. said titanium tetrachloride with sodium to produce a titanium subchloride intermediate molten salt, thereafter reacting said intermediate at temperatures ranging firom 550950 C. and under an inert atmosphere with a calcium-magnesium alloy to produce particulate titanium met-a1 and a ternary MgCl -CaCl NaCl byproduct, electrolyzing the latter in molten state in a modified molten sodium type cell to produce sodium metal and molten magnesium-calcium alloy, collecting and separating said molten sodium and magnesium-calcium alloy, and reemploying as reactants said sodium metal in said initial reduction of titanium tetrachloride and said alloy in the reduction of said intermediate.

3. An integrated cyclic process for preparing'titanium metal which comprises reacting sodium with TiCl in a closed primary reactor at temperatures ranging from 550-1300 C. to form a titanium subchloride intermediate corresponding to the formula TiCl ,,xNaC1 in which x equals 1-2, inclusive, thereafter reacting said intermediate, at temperatures ranging from about 550- 950 C., in a closed secondary reactor with CaMg alloy to produce particulate titanium metal and a ternary MgCl -CaCl 'NaCl by-product salt, recovering said titanium metal product from said salt'and subjecting the recovered" product to purification, subjecting said byproduct salt to electrolysis in molten state to produce molten sodiurnand a molten CaMg alloy, collecting and separating said'molten Na and Mg-Ca alloy, and recycling said sodium electrolysis product as a reactant to said primary reactor and said C-aMg a-lloy electrolysis product as a reactant to said secondary reactor.

References Cited in the file of this patent UNITED STATES PATENTS 1,882,525 Siecke Oct. 11, 1932 2,073,631 Gilbert Mar. 16, 1937 2,374,762 McNitt May 1, 1945 2,390,548 McNitt Dec. 11, 1945 2,607,674 Winter Aug. 19, 1952 2,621,121 Winter Dec. 9, 1952 I FOREIGN PATENTS 686,845 Great Britain Feb. 4, 1953 694,921 Great Britain July 29, 1953 OTHER REFERENCES Werner et a1.: Australasian Institute of Mining and Metallurgy, The Extraction of Titanium, Proceedings New Series, Nos. 158-9, 1950. Pages 79, 80.

Claims (1)

1. AN INTEGRATED PROCESS FOR PRODUCING TITANIUM METAL WHICH COMPRISES RECTING TITANIUM TETRACHLORIDE IN A PRIMARY REDUCTION STAGE OF THE PROCESS AND AT TEMPERATURES RANGING FROM 550-1300*C. WITH A REGULATED AMOUNT OF SODIUM METAL TO PRODUCE A MOLTEN TITANIUM SUBCHLORIDESODIUM CHLORIDE SALT COMPOSITION, REACTING SAID COMPOSITION IN A SECONDARY REDUCTION STAGE AT TEMPERATURES RANGING FROM 550-950*C. AND UNDER AN INERT ATMOSPHERE WITH A MAGNESIUM-CALCIUM ALLOY REDUCING AGENT TO PRODUCE PARTICULATE TITANIUM METAL AND A MOLTEN TERNARY BYPRODUCT SALT NACI-CACI2-MGCI2, SEPARATING THE TITANIUM METAL PRODUCT FROM SAID MOLTEN TERNARY BY-PRODUCT AND SUBJECTING THE LATTER IN MOLTEN STATE TO ELECTROLYSIS IN

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