US 2909473 A
Description (OCR text may contain errors)
Oct. 20, 1959 R. s. DEAN E AL 2,909,473
PROCESS FOR PRODUCING TITANIUM GROUP METALS Filed-Sept. 4, 1956 n m A Cl m Zsowu; E x AVG. VALENCE Na in mi. H; svoLveo/emm 1 @zMdJ'dun 20.21% INVENTORS'.
United States Patent PROCESS FOR PRODUCING TITANIUM GROUP METALS 2 Claims. (Cl. 20464) This invention relates to the production of pure titanium group metals from their oxidic compounds such as natural. oxides or intermediate products made in refining ores of these metals. It relates in particular to the production from such oxidic compounds of a titanium group metal alloy in suitable form for an electrolytic step so contrived that pure titanium is produced together with products necessary to the step of producing titanium group metal alloy from the oxidic material.
Our invention consists of the following preferred sequential steps:
1) Reduction of the titanium group metal from its oxidic compound to a selected alloy of titanium group metal from which titanium group metal only will be dissolved by the subsequent step of anodic solution in a fused chloride cell bath, for example, an alloy of ironcopper, and titanium produced by magnesium reduction or an alloy of aluminum-iron-silicon and titanium produced by aluminum reduction.
(2) Separation of the titanium group alloy from the other reaction products, for example, acid solution of magnesium oxide and excess magnesium.
(3) Forming an anode of the titanium group metal alloy, e.g., casting, comminuting and holding it on suitable support.
(4) Selection of a fused cell bath which will dissolve titanium alone from the alloy such as a fused salt bath having a composition in the three component system NaTiCl having about 4.5-6.0% soluble titanium having an average valence of titanium to ferric sulphate of 2.1-2.5 and enough free sodium per gram of'salt to evolve 5-4.0 ml. H in acidified ferric sulphate.
, (5) Selection of a cathode inert to the fused bath, when acting as a cathode, and placed in suitable space relationship to the comminuted anode material supported on a support inert to the fused bath when connected as an anode. i
(6) Selection of a current having suitable polarity and amperage to dissolve the titanium only at the anode and form coarsely crystalline titanium at the cathode. Such as a direct current for alloys other than those of alumi num providing from 100-2000 amperes/sq. ft. on the original cathode. A direct current providing from 100 2000 amperes/sq. ft. on the original cathode with a superimposed alternating current of 60 cycles and amperage about that of the direct current for aluminum (10) Separating the anode residue from thefused cell bath.
7 (ll) Separating material in anode residue, such as copper, to recirculate to the first step. V f The production'of titanium group metal alloy accord- 2,909,173 Patented Oct. 20, 1959 2 oxidic titanium compound in the presence of an alloying metal or its reducible oxide. This alloying element may be present in the oxidic titanium compound, for example, iron or it may be added to the reduction reaction, e.g. copper. It is essential to my invention that the alloying elements be more noble than titanium in the electrolyte used for refining, since in the step of electrolytic refining the alloying elements must be recovered in the anode residue. A preferred reducing step for use in my invention consists in dispersing the oxidic compound of the element to be reduced in a molten metal having an oxide of greater negative free energy than the lowest oxide of the metal to be reduced. .For example, titanium dioxide is dispersed in molten magnesium or alumina. This dispersion takes place with partial reduction. The dispersion is then heated to a temperature and for a time to bring about substantially complete reduction of the metal of the titanium group and the alloying elements present in the oxidic material, e.g., iron and chromium. When magnesium is .used as the reducing agent I prefer to add copper to it so that the titanium group metal alloy a of reaction and-from the vessel in which the reaction formed will contain about 10% copper. The presence of this copper lowers the melting and softening point of the alloy so that it is agglomerated to larger particles and is hence more readily separated. from the other products takes place.
The reduction step produces the alloy of the titanium group metal in admixture with oxide of the reducing metal and any excess of reducing metal.
The next step is the separation of titanium group metal alloy from the oxide of the reducing metal and any excess reducing metal. This may be accomplished in a number of ways. For example, the titanium alloymay be agglomerated by heating with a flux for the oxide formed inthe reaction or when the reducing metal is magnesium, both magnesium and magnesium oxide can be dissolved from the titanium group metal alloy by dilute acid. To prevent solutionof the titanium group metal, air must be excluded from the operation. When, for example, the reducing metal is aluminum and the alloying metal iron, an excess of aluminum may be used which maybe present without causing difliculty in the electrolytic step falls linearly from 10% at verylow oxygen to substantially none at 5% oxygen.
By use of special procedures such as superposed alternating current, alloys with combinations of higher aluminum and/or silicon and oxygen contents may be refined. Not all titanium group alloysmay be refined with equal facility. We prefer to use .alloys containing not more than 10% of the followingelements when present singly: Fe, O, N, Cr, Al, V. We have found, however,
ing to our invention is accomplished byfreducing-an that when aluminum and/ or silicon are present, the oxygen content must be kept to a lower figure to prevent difficulties in uniform and effective solution of the tita-' nium from the anode. a p u The anode from the alloys to be refined by ourproc ess is preferably made up of comminuted material which is retained on a suitable support. The refining of such comminuted material is described in detail in R. ,S. Deans co-pending application Serial No.. 470,610,; filed November 23, 1954, now Patent No. 2.7834361. E135.
invention must be selected with regard to the elements contained in the alloys and the nature of the pure titanium it is desired to produce.
In a preferred form of our invention we use the alloy in comminuted form as an anode and an electrolyte and procedure disclosed in Deans application Serial No. 600,039, filed July 25, 1956. The preferred electrolyte in this form of our invention is a single phase composition selected from the system Ti-NaCl which is defined by having a total soluble titanium content of 16%, an average valence as determined by reduction of acidified ferric sulphate of 2.052.5 and a sodium content as determined by gas evolution in acidified ferric sulphate corresponding to a hydrogen evolution of .1-6 ml. per gram of electrolyte.
In another form of our invention we use an electrolyte consisting essentially of 97% NaCl, 3% TiCl and provide means for maintaining a higher titanium valence at the cathode than at the anode. Such means may he the addition of TiCL; or C1 in the cathode area or the use of an auxiliary circuit having a graphite anode so disposed as to increase the valence of titanium at the cathode.
In either of these embodiments of our invention the titanium dissolves at the anode as chloride and diffuses into cathode zone where it is reduced by a solution of sodium formed at the cathode and diffusing into the bath. In this way the titanium is formed adherent the cathode in a mass having the structure described in the co-pending application of W. W. Gullett, Serial No. 592,543, filed June 20, 1956, now Patent No. 2,874,454.
The anode residue from the anodic solution of the titanium group alloy contains all the alloying ingredients including oxygen, nitrogen, carbon, iron, chromium, manganese, vanadium, copper and others.
It is desirable to treat this residue for the recovery of ingredients used in the initial reducing operation such as copper. This treatment may be by hydrometallurgical or pyrometallurgical processes. In certain instances, acid leaching will leave a residue of copper and titanium dioxide which may be returned to the reducing step; in other instances a fire refining step may be used to recover substantially pure copper for reuse.
The titanium group metal of our invention is recovered as bundles of coarse filamentary particles having their interstices filled with salt, preferably adhering to the cathode. The bundles of particles are broken up and leached with very dilute acid providing as the final product of our invention pure titanium group metal.
Refining in the practice of our invention takes place essentially at the anode. The concentration of sodium in the electrolyte must be such that any chlorides formed from the metallic elements alloyed with the titanium will be reduced to metal and thus not enter the electrolyte. This reduction may be regarded as a reaction with titanium, but it is no doubt an indirect one in which titanium dissolves to increase the sodium content around the anode material and the sodium in turn reduces any dissolved chlorides.
Published data on metallic chloride decomposition voltages, for example, J. Electrochem Soc. 103, 1956, p. 8, gives a value of about 3.3 volts at 800 C. for sodium and 1.8, 1.6, 1.5 for Mn, V and Cr respectively. Aluminum is not given in this compilation, but from published free energy data would be about 1.5 volts for AlCl and somewhat higher perhaps 1.8 for AlCl.
The reducing power of the cell bath containing sodium is best illustrated by consideration of the ternary diagram of three parameters as shown in Deans co-pending application Serial No. 600,039, filed July 25, 1956. These parameters are:
(1) Percent soluble titanium (2) Chlorine as percent soluble titanium average valence (3) Sodium as hydrogen evolved per gram in acidified ferric sulphate The determination of these parameters and their use to control the process of producing titanium is disclosed in- Deans co-pending application with R. Resnick, Serial No. 605,231, filed August 20, 1956.
The lines of equal reducing power for metallic chlorides are roughly parallel to the line xy in the ternary diagram of Deans application.
In Figure 1 we have reproduced the ternary diagram from Deans application and have shown the approximate position of the several lines in terms of metallic chloride decomposition voltages. These lines mean that any metallic chloride having a decomposition voltage below that shown on a given line will not be dissolved in the presence of active metallic titanium in a cell bath having a composition to the right of the line.
The provision of active metallic titanium in the anode material is an important part of our process. It is provided directly in many of the alloys to be refined, but in other alloys particularly those of aluminum, the residue of the alloy after the anodic solution of some of the titanium may become passive due to film formation. With such alloys comminuted crude titanium may be conveniently added to the anode material or an alternating current may be superposed on the direct current in the cell. This maintains the anode material in an active state.
It will be observed that the high titanium and sodium concentration required in the cell bath for refining from such elements as aluminum and manganese does not precipitate titanium because of the tendency of such solutions to supersaturate as set forth in Deans application, Serial No. 600,039, filed July 25, 1956.
As set forth in our co-pending application, Serial No. 601,705, filed August 2, 1956, large pure titanium crystals are formed by the difiustion of sodium from the cathode into the electrolyte just described with the formation of a supersaturated solution and crystallization therefrom of titanium.
The titanium content of the electrolyte in the cathode zone is maintained by solution of titanium from the anode material. The surface of the anode material and its space relationship to the cathode must be such as to maintain the electrolyte concentration.
EXAMPLE I In this example we take lbs. of finely ground rutile and mix it into 50 lbs. of magnesium containing 5 lbs. of copper. To accomplish the dispersion of our invention, we use a rod mill heated to 750 C. and carefully sealed from the inclusion of air. After the initial mixing we heat the rod mill to 900 C. for 1 hour while rotating.
We then cool the contents of the mill in argon and remove the reaction mixture. We treat this reaction mixture with 5% sulphuric acid in the absence of air. The insoluble residue is washed with air free water and vacuum dried. The product analyses 87% Ti, 10% copper, balance oxygen and incidental impurities. We melt this product in a graphite crucible in an induction furnace provided with an argon atmosphere, we skim otf insoluble impurities, and cast it into bars 2" diameter by 12" long. We make these bars an anode in an electrolytic cell having an electrolyte of sodium chloride to which has been added soluble titanium chloride in an amount equal to 3% Ti. The average valence of the titanium in the chloride is 2.5, and the sodium content corresponding to 0.8 ml. of H per gram. The cell is provided with an inert atmosphere, an inert cathode concentric with the anode, and an auxiliary circuit consisting of a foraminous cathode surrounding the anode and a graphite anode relatively near the cathode. The current in the main refining circuit is 500 amperes/ sq. ft. on the cathode and 2000 amperes/sq. ft. on the anode. The current in the auxiliary circuit is so adjusted that the open circuit voltage of the cell between main anode and cathode is in the reverse direction to the applied voltage. The anode goes into solution smoothly and particulate titanium is deposited at the cathode in bundles of crystals having their interstices filled with salt. The anode residue falls to the bottom of the cell from which it is recovered. We leach the anode residue with water to remove salt and fuse the leached residue in a graphite crucible with a little charcoal. We skim off the impurities and cast the copper in pigs for returning to the reducing step. We remove the titanium from the cathode and leach with dilute hydrochloric acid to obtain a particulate titanium of high purity.
EXAMPLE II In this example we take 105 lbs. of Sorel slag having the following analysis and mesh size:
Equiv. .2 CI'203.20 Fe-6.4 V205-.5 3 SiO -SZ MnO-.22 Aho -65 C.06 (ho- 1.4 S.21 MgO'4.5
, 88% through 200 mesh We mix this with 50 lbs. of magnesium and in a heated rod mill as described in Example I. After reaction the product is cooled in argon and removed from the mill. We leach this with 5% sulphuric acid in the absence of air and vacuum dry the residue. This residue analyses 85% Ti, 9% Fe, 6% oxygen and incidental impurities.
We melt and cast this alloy into bars which are broken up to fragments about /2" average diameter. These fragments are placed on the bottom of an iron pot which also serves as the anode of an electrolytic cell and is provided with an inert atmosphere and an electrolyte of 90% NaCl, 10% TiCl An iron rod is disposed centrally in the pot to serve as cathode, and a DC. current corresponding to 2500 amps/sq. ft. on the rod is passed through the cell. The alloyed iron and the incidental impurities remain as anode residue on the bottom of the pot while the titanium dissolves as dichloride and particulate titanium is formed adhering to the cathode from which it is recovered by leaching with dilute hydrochloric acid. The anode residue is recovered from the bottom of the cell and is subjected to magnetic separation to remove the iron and leave a non-magnetic fraction essentially TiO which is returned to the reducing step.
EXAMPLE III In this example we use aluminum as the reducing material for the titanium oxide in Sorel slag. We use a substantial excess over the aluminum required to reduce thetitanium and iron oxides of the slag.
. 'In this example we use 100 grams slag having the analyses shown in Example II, and 150 grams aluminum.
We heat this mixture in an argon atmosphere with stirring to 1000? C. and allow the reaction mass to separate into a metallic layer and a non-metallic layer. The metallic layer contains 36% Ti, 4% Fe, 60% Al, and only small amounts of impurities. We now take this metallic layer and break it up into fragments. We heat these fragments with an excess of molten zinc in an argon atmosphere until the aluminum is dissolved leaving as a residue a titanium-iron alloy. This residue is recovered by filtration on .a Pasalt filter, and is made into anodes and refined in accordance with the previous examples. The zinc-aluminum alloy is distilled for the recovery of the two metals.
EXAMPLE IV In this example we proceed as in Example I to produce analloy of essentially. titanium and copper. We melt this alloy in afgnaphite crucible lined with lime which prevents the absorption of carbon into the alloy. We add 1% to the molten alloy in order to flux and remove certain impurities especially silicon. The molten titanium'copper alloy is bottom poured into a graphite 75 6 mold to separate it from the fluxed impurities which float. All of the operations of this example are carried out in an argon atmosphere.
The cast purified copper-titanium alloy can now be welded to other bars of the alloy to provide a continuous anode for electro-refining according to Example I. In this example, however, we provide a foraminous neutral member about A" in front of the cathode on which the bundles of titanium particles are formed. This prevents the contamination of the deposit by sealing of the cathode caused by alloying of sodium with the metal of the cathode.
EXAMPLE V In this example we make anode material from Sorel slag as in Example II. We add copper, however, to the reaction mixture in the hot rod mill so'that we obtain a product containing 78% Ti, 10% Cu, 9% Fe, and 3% oxygen. We melt this in a graphite crucible in an induction furnace with an argon atmosphere and then after cooling eomminute the mass to pass a 4 mesh screen. The comminuted material was placed in an iron basket annularly disposed around an iron rod cathode in a cylindrical cell like that disclosed in our co-pending application, Serial No. 601,705, filed August 2, 1956. The log of this example follows:
Current during operation Time from Start Amperes Ampere Hours 1 hour 20 20 2hnm's 30 30 3 hours 40 40 4ho 50 50 5hnmq 50 5O Ghours 60 60 7hours 70 Sho 80 80 Qhnnrs- 80 80 9% hours 80 40 Ano de specifications Composition- O 3.0% O-.40% Fe-- 9.0%
N .021% Cu--l0.2% Balance Ti Character-fragments Weight -10 lbs. Immersed area-3.0 sq. ft. Current density (ave.)--1.82 amps/sq. ft.
Location-In perforated steel container dispersed annularly 3 inches from cathode Cathode specifications:
,Compositionmild steel Size--%" diameter rod Immersed area-18.85 sq. in. a Current density-407 amperes/ sq. in. Cell bath:
NaCl plus 5.05% soluble Ti Average valence of Ti to ferric sulphate-2.2
Hydrogen evolution in ferric sulphate--2.4 ml./ gram Temperature of operation: 850 C. Deposit:
Plate-.003 inch thick Salt layer- 015 inch thick Crystals1.0 inch thick Total weight of deposit-480 grams Weight of large crystals420 grams Weightof salt-50 grams Weight of fine crystals-8 grams Density large crystal deposit-2.2
Plate-98% Ti, 2% Na Fine crystals99.8% Ti Large crystals-99.99% Ti Brinell hardness large crystals melted in argon 65 EXAMPLE VI In this example we make an anode material from rutile by adding it to slightly more than its stoichiometric equivalent of aluminum held at 1500 C. in an electric furnace. Reaction is rapid, and the final product is an alloy of 90% titanium, 8% aluminum, and 2% impurities mostly silicon and iron. In order to dissolve titanium alone from this anode material it is necessary to overcome the passivity of the titanium. In this example we accomplish this by mixing with the comminuted alloy 20% of comminuted commercially pure titanium, which reacts with the cell bath to precipitate the impurities which would otherwise enter the bath/ The operation in this example is carried on in accordance with that of Example V except as follows:
NaCl plus 6.5% soluble Ti Average valence of Ti to ferric sulphate-2.1 Hydrogen evolution in ferric sulphate4.0 ml./ gram The product obtained is of the same purity and crystal structure and distribution as in Example V.
EXAMPLE VII In this example we proceed exactly as in Example VI except that we do not mix comminuted commercially pure titanium with the comminuted alloy. We superpose a 60 cycle alternating current of the same current density on the direct current passed through the cell. The operation and results are identical with those in Example VI.
EXAMPLE VIII In the co-pending application of Dean, Serial No. 592,- 089, filed June 18, 1956, it is disclosed that zirconium forms compositions in the system ZrNa-Cl which are analogous to the titanium composition used as the cell bath in Example V. I have found that a cell bath having the following description may be used: Sodium chloride plus 6.02% Zr, average valence of Zr to ferric sulphate 3.4. Hydrogen evolution in ferric sulphate 2.4 ml./ gram. I proceed with the use of this cell bath as in Example V, except that the anode has the following composition and is made by reducing ZrO with magnesium in the hot rod mill of Example I, dissolving the MgO from the reduced zirconium, sintering the zirconium at 1000 C. in argon and comminuting to fragments inch average diameter. The deposit is of the same character as that of Example V and the analysis of the large crystals is 99.99% Zr. Brinell hardness of melted button 71.
EXAMPLE IX In this example I prepare a manganese-aluminum-titanium alloy by the reaction of aluminum, manganese dioxide and titanium dioxide. The proportions are so taken that the resulting alloy contains 85% Ti, 10% Mn, Al. The alloy is prepared by heating the mixture in an electric furnace with a flux consisting of 90% CaF cryolite. We electrorefine this alloy at a temperature below the eutectoid that is in the range where only alpha titanium and the compound TiMn are present. This is necessary to obtain good refining. Manganese is more noble than titanium in fused alkalinous chlorides containing titanium chlorides and sodium in the composition ranges disclosed in Deans co-pending application, Serial No. 592,089, filed June 18, 1956. However, the manganese metal which is precipitated by titanium dissolves in it at temperatures where beta solid solution is formed. To effectively refine from manganese it is therefore'necessary to work at temperatures where no beta solid solution of titanium and manganese is stable. For the alloy of this example we have found this to be 600 C. :We therefore use an electrolyte which is molten at this temperature. The basis of this'electrolyte is 30% NaCl, 70% CaCl To this electrolyte, after deoxidation in the molten condition by adding TiO and Ti, we add the reduction mixture of 'I iCl and sodium disclosed in William W. Gulletts co-pending application. This reduction mixture contains 20% Ti as soluble Ti. 25% by weight of this mixture is added to the fused NaCl+CaCl The resulting bath contains 5% soluble Ti, average valence 2.4, hydrogen evolution in ferric sulphate 2.8 ml./ gram.
I place the comminuted manganese-titanium-aluminum alloy in an iron anode basket and refine in accordance with Example V. I obtain on the cathode pure titanium which when melted in argon has a Brinell hardness of 70.
EXAMPLE X In this example we take 240 lbs. of Sorel slag of the composition given in Example II. We mix this with 55 lbs. of granulated Al and compact into pellets. We place these pellets together with 10 lbs. CaF and 1 lb. cryolite in a closed graphite crucible and heat to 1750 C. There is formed a regulus which analyzes:
Insol. mostly Al O 6% And a slag containing most of the A1 0 formed in the reaction This regulus is comminuted to form an anode product which is refined in accordance with the procedure of Example V, except that the direct current is periodically reversed for one (1) second out of every five (5). The titanium in the anode product is completely dissolved and the cathode deposit is identical with that of Example V.
EXAMPLE XI We proceed as in Example V, except that the electrolyte is 65% SrCl and 35% NaCl in place of the NaCl in Example V. The control parameters of soluble titanium, average valence, and hydrogen evolution are substantially the same as in Example V. The temperature of operation is 750 C. The log of operation and the results are substantially the same except that the plate formed contains Sr in place of Na.
What is claimed is:
1. Process of producing a substantially oxygen-free titanium group metal of high purity from an impure oxidic compound of the titanium group metal containing a substantial amount of iron, which comprises reacting the impure oxidic compound With magnesium, at a temperature above the melting point of magnesium, out of access to air, under conditions to produce a frangible crude alloy consisting essentially of from 5 to 10% by weight of iron, 3 to 5% by weight of interstitial oxygen and the balance titanium group metal, separating said crude alloy from associated reaction products, comminuting the frangible crude alloy, and electrorefining the comminuted alloy by making the same an anode in an electrolytic cell provided with a cathode and containing a cell bath consisting essentially of molten sodium chloride containing dissolved therein from 3 to 7% of titanium group metal, as chlo ride, having a valence of 2.0-2.6 and 0.l-3.0% dissolved metallic sodium and electrolyzing at a cathode current density of 400-2500 amperes per square foot to produce coarse crystals of pure titanium group metal adherent to the cathode.
2. Process of producing substantially oxygen-freetitanium of high purity from Sorel slag which comprises reacting the Sorel slag with magnesium, in the app oximate ratio of 5 parts by weight of magnesium to an amount of the Screl slag corresponding to 8 parts by weight of TiO out of access to air and at a temperature above the melting point of magnesium, whereby to produce a frangible crude alloy consisting essentially of from 5 to 10% by weight of iron, 3 to 5% by weight of interstitial oxygen and titanium the remainder, comminuting the frangible crude alloy, and electrorefining the comrninuted alloy by making the same an anode in an electrolytic cell provided with a cathode and containing a cell bath consisting essentially of molten sodium chloride containing dissolved therein from 3 to 7% of titanium group metal, as chloride, having a valence of 2.0-2.6 and (ll-3.0% dissolved metallic sodium and electrolyzing at a cathode current density of 4002500 amperes per square foot to produce coarse crystals of pure titanium adherent to the cathode.
5 References Cited in the file of this patent UNITED STATES PATENTS 1,534,709 Holt Apr. 21, 1925 2,734,856 Schultz et a1. Feb. 14, 1956 2,757,135 Gleave et al July 31, 1956 10 2,817,631 Gullett Dec. 24, 1957 UNITED STATES PATENT O.F.F ICE CERTIFICATE OF CORRECTION Patent "No, 2,909,473 Q October 20, 1959 Reginald vSc. Dean et al0 It is herebycertifie'd that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.
Column 2, line '72, strike out now Patent Noo 2 78x8610" and insert instead a period after "November 23, 1954;"a
Signed and sealed this 10th day of May 1%0a Attest:
H. ,AXLINE ROBERT C WATSON