US2731405A - Method of preparing electrolyte - Google Patents

Description

Jan. 17, 1956 1 R, YOUNG ET Al.

METHOD 0F PREPARING ELECTRQLYTE Filed Jan. 2l, 1955 u@ ss Nmb.

xNvEN-roRs Thomas l?. ,Voz/n Kobe/' L. Somefgme BY y ,M @M

ATToRNEYs IV E -mit United States Patent METHoD or PREPARING ELEc'rRoLYTE Thomas R. Young, Riverside, Conn., and Robert L.

Somerville, Neshanic, N. J., assignors, by mesne assignments, to Horizons Titanium Corporation, Princeton, N. J., a corporation of New Jersey Application January 21, `1953, Serial No. 332,327 4 Claims. (Cl. 2011-64) This invention relates to the electrolytic production `of metallic titanium and metallic zirconium and, more particularly, to a. cyclic method wherein `spent electrolyte from the titanium or zirconium production stage may be completely recovered and re-used in the electrolytic operation.

The production of metallic titanium and metallic zirconimn by electrolytic deposition from `a fused `salt bath containing an alkali metal-titanium or zirconium double liuoride (an alkali metal tluotitanate or iluozirconate) has `been developed to the stage where the metal so produced is of high purity. From a commercial standpoint, however, the cost of producing metal by this procedure is a serious drawback due largely to the cost of raw materials including the liuorine `component of the double .fluoride. We have now discovered that the cost of raw materials for such a process of electrolytically producing metallic titanium and metallic zirconium can be markedly reduced by appropriate choice of the diluent salt bath and by appropriate conversion of the by-products :of the electrolysis. Thus we have found that the completely cyclic handling of all by-products of the electrolysis may be .achieved without the buildup of any one .or more of the elements of the electrolytic bath. r

The success of `our recyclic operation in the .electrolytic production of metallic vtitanium or metallic zirconium from a fused salt bath is dependent upon the `use as the immediate source of the titanium or zirconium of -a :compound of such metal the anion `of which is restricted to `one or more of the elements chlorine, oxygen and carbon, by the use as `another component of the salt bath of one or more alkali metal chlorides, and advantageously `by the use `of hydrogen, as the only other extraneous raw material, for conversion of by-product chlorine from the electrolytic cell into hydrogen chloride for use in the transformation of the titanferous or Izirconiferous `source material into the corresponding alkali `metal double uoride. Thus, our invention comprises an improvement in -the proA duction of metallic titanium or metallic zirconium wherein a double iiuoride of titanium or zirconium and an alkali metal is electrolyzed `in a fused salt bath comprising this double fluoride `dissolved or otherwise contained in `an `alkali metal chloride, the-:products of the electrolysis comprising deposited metallic titanium or zirconium, evolved chlorine gas and an alkali `metal iluode-cont`aining spent electrolyte. Our improvement in such a process comprises reacting the `spent `electrolyte from the aforesaid electrolysis `with. hydrochloric acid and a titaniferous or zirconiferous source material the anion of which is cbmposed of one -or more of the `elements chlorine, oxygen and carbon with the resulting formation of an alkali metal-titanium or `zirconium double iuoride and an alkali `metal chloride which areithereafter used as `the double uoride and alkali metal components of the aforementioned `fused salt bath. .In `the presently preferred embodiment of `our invention, the .hydrochloric -acid .is rde rived by the reaction of .chlorine evolved vfrom .the electrolytic cell with extraneous hydrogen.

, 2,731,405 Patented Jan. 17, 1956 The titaniferous sources .useful in practicing our invention include oxidic compounds such as titanium dioxide, titanium carbonate and titanium oxychloride (TiOCla) and titanium carbide. Each `oit' these source materials should be supplied in as pure form as readily available in order to preclude the build up of extraneous impurities in the process. When titanium dioxide is used as the starting material, we have found it advantageous to use anatase titanium dioxide pigment, but other forms of the dioxide may be used with advantage. The oxychloride of titanium as well as the carbonate and carbide are 'available and can be used as the source of titanium without introducing into the cyclic process any component which will be built up to the detriment of the operation of the process.

The zirconiferous materials useful in practicing our invention include oxidic zirconiferous materials such as zirconium oxides, zirconium carbide and zirconium oxychloride. Thus, inasmuch as the raw materials as Well `as the chemistry of our process are substantially the same for zirconium as for titanium, we shall contine our subsequent description of the invention to the production of metallic titanium with 'the understanding, of course, that what is said in this regard applies with equal force to the .corresponding production of `metallic zirconium.

The only other raw material required in signiiicant amounts for the practice of our invention is hydrogen, `and this hydrogen may be supplied either as such or in the form of a mixture of propane and steam which, when burned in lthe presence of chlorine gas, will yield hydrogen to react with the chlorine to form hydrogen chloride.

The process of our invention will be readily understood by reference tothe accompanying flow sheet. As shown therein, an alkali metal-titanium double fluoride, such as potassium titanium fluoride (also known as potassium tiuotitanate, KzTiFs), `and at least one alkali metal chloride -such as sodium chloride are charged `to an electrolytic cell 1 as the essential components of the electrolytic bath. The cell Jis heated to maintain these salts in fused condition `in the cell. Electrolysis of the resulting bath, which may contain, for example, 2 :to 30% `by weight of the `double `iiuoride, results in the deposition at the cell cathode of metallic titanium which may be `removed in .any appropriate manner. Chlorine gas is evolved at the anode and is withdrawn from the cell and Aburned with hydrogen in a combustion -chamber 2. The resulting hydrogen chlorideis advantageously absorbed in water in an absorption tower 43, and the resulting aqueous hydrochloric acid is .delivered `to a reactor 4 wherein the alkali metal-titanium .double fluoride is produced. Spent elecxtrolyte is withdrawn from the cell either intermittently or continuously, and is delivered to the reactor 4. This spent electrolyte, which `contains an alkali metal iiuoride as its essential component, may be either cooled and -then charged directly to the reactor 41or it may be broken up into .aslurry with extraneous water or other suitable wash iiquid from another stage of the process and be delivered in this form to ithereactor4.

The .other `primary component delivered to the reactor 4 comprises the titaniferous source material such as titanium .dioxide or titanium `oxychloride. If titanium dioxide is used, it may be charged to the reactor in the form ,of d-ry titania pigment. .Of course, when the titaniferous nmaterial -is charged Lin the form of oxychloride, lesser amounts of hydrochloric acid will be required and any l,excess acid produced :from the cell chlorine maybe dis posed of or u sed .in any other desirable way. Small amounts ,of an `alkali metal chloride such as potassium chloride and arsource of Vtluorine such as hydrotluoric acid ,may also be .added to the rreactor 4 in order to `make up Vtorany mechanical loss `offthealkali metal-, chlorineand ilumine-components of the fused salt bath and thus insure 'i .a the presence in the reactor of substantially stoichiometric quantities of all essential reagents for the formation of an alkali metal-titanium double uoride.

inasmuch as the electrolysis of the fused salt bath is preferably carried out under an inert atmosphere, advantageously of a monatomic gas such as argon, the argon will be discharged from .the cell along with ythe chlorine. How ever, the argon will pass-through the combustion chamber 2 and the absorption tower 3 and can thus be returned to l the cell 1 preferably with intervening purification to remove any extraneous gas such as nitrogen from leakage or carbon dioxide from the burning of propane, or to remove a gaseous impurity introduced into the system along with the argon.

The reaction between the added titaniferous source ma terial, the generated hydrochloric acid and the recirculated spent electrolyte, together with added make-up reagents, takes place in the reactor 4 upon heating this mixture to a temperature close to the boiling point of water at atmos -pheric pressure, i. e. to up to about 100 C., by means of steam coils orV the like. The resulting alkali metal `titanium double fluoride solution, such as a potassium-V titanium fluoride solution; is withdrawn from the reactor 4 and is concentrated to crystallize out of the solution both -the double iiuoride vand a portion of the contained alkali metal chloride. We have found that this result can be ob tained particularly satisfactorily in a triple effect evapo rator, but regardless of the method of separating the double fluoride and the alkali metal chloride these separated salts are passed through driers 5 and 6 and thence back to the electrolytic cell 1. yIt will be seen, accordingly, that theV only extraneous source materials for this con tinuous production of titanium metal comprises the ti taniferous source material, such as titanium dioxide, and hydrogen for the generation of hydrogen chloride from the chlorine effluent from the cell.

As pointed out hereinbefore, we have found that a triple effect evaporator may be used with particular ad vantage in the recovery of the solid alkali metal-titanium double fluoride and alkali metal chloride from the solu tion thereof withdrawn from the reactor 4. In the operation of the triple effect evaporator in accordance with our invention, the alkali metal-titanium double fluoride and alkali metal chloride solution (such, for example, as an aqueous solution of potassium titanium uoride and sodium chloride) is delivered to the third effect of the evaporator. The solution is concentrated in the third yeffect by the combination of a reduction in pressure, such as operation under a vacuum of say 27 inches of mercury, and by the heat supplied by steam which has previously been used as the heating medium for the first two effects. The liquor in the third` effect is thus concentrated at a temperature of about 50 C. with the result that potassium titanium fluoride crystals form in the liquor. The resulting slurry of thedouble fluoride is discharged from the third effect to a separator 7, and the separated double uoride is delivered to the drier 5. A portion of the mother liquor removed from the double uoride in the separatorV 7 may be'returned to the reactor 4 and the remainder of the liquor is ydelivered to the second effect of the evaporator. Inasmuch as the ysecond effect operates at a higher temperature, generally about 90 C., the further evaporation of water from the liquor introduced into the second effect from the separator 7 results in crystallization of sodium chloride. The resulting slurry is discharged from the second'effect to a separator 8 from which the separated sodium chloride is delivered to the drier 6. A

portion of the liquor separated from the sodium chloride i in the separator 8 is advantageously returned to the third effect and the remainder of this liquor is delivered to the first effect of the evaporator. Inasmuch as the heating steam for the evaporator passes through the first effect before the second and third effects, the temperature of the liquor in the first effect is raised to a still higher temperature, aboutV 130 C. Although a considerable amount of 4 water is evaporated from the liquor in the first effect, with the resulting crystallization of some sodium chloride, the resulting slurry is delivered to the second effect Where further evaporation, though at a lower prevailing operating temperature, effects more complete crystallization of sodium chloride which is then recovered in the separator 8. On the other hand, the potassium titanium fluoride contained in the aqueous phase in both of these relatively high temperature effects will remain in solution and will not crystallize from the solution to any significant extent until it is delivered to the third effect which, as noted hereinbefore, advantageously operates at a relatively low temperature of about V C.

The process of our invention may be illustrated by, but is not limited to, the following specific example thereof:

A fused salt bath composed of potassium fluotitanate and sodium chloride, in which the potassium uotitanate formed 25% of the initial weight of the bath, was electrolyzed -in an electrolytic cell maintained under an inert atmosphere of argon gas. For each rmol of potassium uotitanate that'was decomposed at the cathode, one mol of titanium was deposited on the cathode, two mols of potassiumtluoride were formed, four mols of sodium chloride were converted to four mols of sodium fluoride, and two mols of chlorine gas were evolved from the electrolyte. Chlorine gas evolved from the fused salt bath at the anode and titanium metal was deposited on the cathode. Spent electrolytedepleted in potassium fluotitanate and sodium chloride content, and containing a solution of Vhydrochloric acid.

vtion was withdrawn.

sodium fluoride and Vpotassium fluoride in an amount -stoichiometrically equivalent to the amount of potassium Yfluotitanate electrolytically decomposed by the electrolysis, was withdrawn from the electrolytic cell in the vicinityV of the cathode.

The chlorine gas evolved from the electrolytic cell was burned with hydrogen gas to form hydrogen `chloride which, in turn, was absorbed in sufficient water to form The spent electrolyte containing potassium fluoride and sodium fluoride as its essential components was allowed to cool to ambient temperature. The cooled spent electrolyte and the aqueous solution of hydrochloric acid was then introduced into `a reaction vessel maintained at about the boiling point of water by means of steam coils. Also present inthe reaction vessel was a quantity of titanium dioxide sufficient to react with the potassium fluoride and sodium fluoride content of the spentelectrolyte to form an equivalent amount of potassium fluotitanate, and sufficient water to retain the products of tbe reaction in solution.

The spent electrolyte, hydrochloric acid, and titanium dioxide in the hot aqueous medium reacted together to form soluble reaction products. The aqueous solution from the reaction vessel was then introduced into the third effect of a triple effect evaporator, the temperature of the liquor in which was maintained at about 50 C. Vapor evaporated from 4the liquor in the third effect was withdrawn therefrom by a conventional condenser and vacuum pump arrangement. Concentrated liquor from the. third effect was introduced into a separator'from which potassium fluotitanate crystallized from the solu- The crystallized potassium fluotitanate was then dried preparatory to introducing this material into the fused salt electrolyte contained in the electrolytic cell.

ride was then dried preparatory to introducing this materialinto the fused salt electrolyte.

The concentrated liquor from `the separator of thesecond effect was introduced into the first `effect which operated ata temperature of about 130 C. Vapor evaporated from the liquor in the first effect was introduced into the steam chest ofthe second effect to heat the liquor therein. Concentrated liquor from the first `effect was introduced into the second effect for further Aconcentration of its salt content.

The potassium tluotitanate obtained from the dryer associated `with the separator of the third effect and the sodium chloride `obtained .from the dryer associated with the separator of the second effect were introduced into the fused salt electrolyte being electrolyzed in the electrolytic cell. The amount of titanium which reacted with the potassium fluoride and sodium fluoride content of the spent electrolyte and with the vhydrochloric acid was stoichiometrically equivalent to the amount of potassium lluotitanate electrolytically decomposed by the cell to form titanium metal, chlorine gas and spent electrolyte containing potassium fluoride-and sodium fluoride.

Typical spent electrolytes resulting from the electrolysis of an alkali metal lluozirconate-alkali metal chloride bath are set forth in a copending application Serial No. 279,471, now Patent 2,687,340. Expressed as ions three such baths are disclosed as follows:

I II III 33.2% N a+ 53% N a* 66% K+ it' if? l? naar 52672 ci- 6% ot- 4% o Each of these spent electrolytes may be readily regenerated in accordance with our invention by reacting the spent electrolyte with HC1 obtained from all of the cell chlorine and with a titanium or, in this instance, a zirconium compound such as the carbide, carbonate or oxide, the latter being present in an amount sulicient to provide the amount of zirconium necessary to form the double fluoride of zirconium and an alkali metal when combined with the lluorine content of the spent electrolyte.

lt will be seen, accordingly, that the process of our invention makes possible the continuous production of titanium or zirconium metal by electrolysis of a fused salt bath comprising an alkali metal-titanium or zirconium double fluoride and an alkali metal chloride and that our process makes it possible to regenerate these bath component-s from the spent electrolyte without the introduction into the process, either as the titaniferous or zirconiferous source material or as the digesting medium for these materials, of any elements which would tend to accumulate in the cyclic operation which characterizes our process. The only extraneous elements introduced into our process are limited to chlorine, oxygen, carbon and hydrogen, and each of these elements ultimately is consumed in the formation of water or a permanent gas which is readily discharged from the process as outlined hereinbefore. The relatively expensive components of the system, particularly the iluorine and alkali metal components, are thus continuously recycled. The commercial appeal of the electrolytic production of titanium and zirconium metal is thereby enhanced and an integrated process is obtained in which only relatively simple forms of raw materials are required for the continuous production of these metals in a state of high purity.

We claim:

l. In the production of ametal of the group consisting of titanium and zirconium wherein a fused salt bath consisting essentially of an alkali metal chloride and a double fluoride of an alkali metal and a metal of the group consisting of titanium and zirconium in electrolytically decomposed with (l) the resulting production of an electrodeposit of said metal on a cathode, (2) the evolution of chlorine gas at an anode and (3) the formation ot' a spent electrolyte consisting essentially of at least one alkali metal fluoride; the improvement which comprises regenerating `material suitable for reuse as the fused salt bath in the aforesaid electrolytic process from said evolved chlorine and said spent electrolyte as follows: reacting the evolved chlorine with hydrogen to form hydrogen chloride; heating to upto about C. an aqueous solution of the spent electrolyte and said hydrogen chloride and a compound of said metal from the group consisting of compounds of the said metal and at least one element of the group consisting of oxygen and carbon in which the relative amounts of alkali metal, halogen and metal values present are substantially the stoichiometric amounts necessary to produce the desired double fluoride of an alkali metal and the metal of the group consisting of titanium and zirconium and recovering said double fluoride and said alkali chloride produced in said heated solution for reuse in a repetition ofthe electrolysis.

2. In the production of a metal of the group consisting of titanium and zirconium wherein a fused salt bath consisting essentially of an alkali metal chloride and a double fluoride of an alkali metal and a metal of the group consisting of titanium and zirconium is electrolytically decomposed with (l) the resulting production of an electrodeposit of said metal on a cathode, (2)) the evolution of chlorine gas at an anode and (3) the formation of a spent electrolyte consisting essentially of at least one alkali metal fluoride; the improvement which comprises regenerating material suitable for reuse as the fused salt bath in the aforesaid electrolytic process from said evolved chlorine and said spent electrolyte as follows: reacting the evolved chlorine with hydrogen to form hydrogen chloride; heating to up to about 100 C., an aqueous solution of the spent electrolyte and said hydrogen chloride and an oxide of said metal in which the relative amounts of alkali metal, halogen and metal values present are substantially in the stoiclliometric proportions necessary for the formation of a double fluoride of said metal and an alkali metal and an alkali metal chloride and recovering said double fluoride and said alkali chloride from said heated aqueous solution for reuse in a repetition of the electrolysis.

3. In the production of a metal of the group consisting of titanium and zirconium wherein a fused salt bath consisting essentially of sodium chloride and a double fluoride of potassium and a metal of the group consisting of titanium and zirconium is electrolytically decomposed with (l) the resulting production of the electrodeposit of said metal on a cathode, (2) the evolution of chlorine gas at an anode and (3) the formation of a spent electrolyte consisting essentially of alkali metal and halide ions; the improvement which comprises regenerating material suitable for reuse as the fused sait bath in the aforesaid electrolytic process from said evolved chlorine and said spent electrolyte as follows: reacting the evolved chlorine with hydrogen to form hydrogen chloride; heating to up to about 100 C., an aqueous solution of the spent electrolyte and said hydrogen chloride and an oxido of said metalV in which the relative amounts of alkali metal, halogen and metal values present are substantially in the stoichiometric proportions necessary for the formation of a double fluoride of said metal and an alkali metal and an alkali metal chloride and recovering said double fluoride and said alkali chloride for reuse in a repetition of the electrolysis.

4. In the production of a metal of the group consisting of titanium and zirconium wherein a fused salt bath consisting essentially of an alkali metal chloride and a double fluoride of an alkali metal and a metal of the group consisting of titanium and zirconium is electrolytically decomposed with l) the resulting production of an electrodeposit of said metal on a cathode, (2) the evolution of chlorine gas at an anode and (3) the formation of a. spent electrolyte consisting essentially of at least one ava-1,405

7 alkali metal fluoride; the improvement which comprises regenerating material. suitable for reuse as the fused salt ybath in the aforesaid electrolytic process from said evolved chlorine with hydrogen to form hydrogen chloride; heating to up to about 100 C., an aqueous solution of the spent electrolyte and said hydrogen chloride and a compound of said metal from the group consisting of compounds of said metal and at least one of the following carbon and oxygen, in which the relative amounts of alkali metal, halogen and metal of the group consisting of titanium and zirconium present are Substantially the stoichiometric proportions necessary for the formation of anaqueous medium containing a double fluoride of said metal and an alkali metal and an alkali metal chloride; charging the aqueous medium to the third effect of a triple effect evaporator and therein concentrating the aqueous medium to an extent sufficient to promote crystallization therefrom of the double fluoride; crystallizing the double fluoride, recovering the crystallized double iluoride Vfrom the effluent from the third effect of the evaporator; delivering the remaining aqueous medium to the References Cited in the tile of this patent UNITED STATES PATENTS 1,801,661 Collngs Apr. 2l, 1931 2,144,339 Laist lan. 17, 1939 Y 2,687,340 Wainer Aug. 24, i954 FOREIGN PATENTS 574,832 Great Britain g Ian. 22, 1946 OTHER REFERENCES Journal of Applied Chemistry (U. S. S. RJ, vol. i3, 1940, pages 51 thru 55; paper by Sklarenko et al.

Claims (1)

1. IN THE PRODUCTION OF A METAL OF THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM WHEREIN A FUSED SALT BATH CONSISTING ESSENTIALLY OF AN ALKALI METAL CHLORIDE AND A DOUBLE FLUORIDE OF AN ALKALI METAL AND A METAL OF THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM IN ELECTROLYTICALLY DECOMPOSED WITH (1) THE RESULTING PRODUCTION OF AN ELECTRODEPOSIT OF SAID METAL ON A CATHODE, (2) THE EVOLUTION OF CHLORINE GAS AT AN ANODE AND (3) THE FORMATION OF A SPENT ELECTROLYTE CONSISTING ESSENTIALLY OF AT LEAST ONE ALKALI METAL FLUORIDE; THE IMPROVEMENT WHICH COMPRISES REGENERATING MATERIAL SUITABLE FOR REUSE AS THE FUSED SALT BATH IN THE AFORESAID ELECTROLYTIC PROCESS FROM SAID EVOLVED CHLORINE AND SAID SPENT ELECTROLYTE AS FOLLOWS: REACTING THE EVOLVED CHLORINE WITH HYDROGEN TO FORM HYDROGEN CHLORIDE; HEATING TO UP TO ABOUT 100* C. AN AQUEOUS SOLUTION OF THE SPENT ELECTROLYTE AND SAID HYDROGEN CHLORIDE AND A COMPOUND OF SAID METAL FROM THE GROUP CONSISTING OF COMPOUNDS OF THE SAID METAL AND AT LEAST ONE ELEMENT OF THE GROUP CONSISTING OF OXYGEN AND CARBON IN WHICH THE RELATIVE AMOUNTS OF ALKALI METAL, HALOGEN AND METAL VALUES PRESENT ARE SUBSTANTIALLY THE STOICHIOMETRIC AMOUNTS NECESSARY TO PRODUCE THE DESIRED DOUBLE FLUORIDE OF AN ALKALI METAL AND THE METAL OF THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM AND RECOVERING SAID DOUBLE FLUORIDE AND SAID ALKALI CHLORIDE PRODUCED IN SAID HEATED SOLUTION FOR REUSE IN A REPETITION OF THE ELECTROLYSIS.

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