US2288727A - Treatment of titanium-bearing materials - Google Patents

Description

July 7, 1942.

P. E. MAYER TREATMENT OF T I TANIUM BEAR ING MATERIALS Filed Nov. 13, 1939 2 SheetS Sheet l P's-es Y E. 70 name ATTORNEYS Patented July 7, 1942 TREATMENT OF TITANIUM-BEARING MATERIALS Perry E. Mayer, Collingswood, N. J., assignor to The Sherwin-Williams Company, Cleveland, Ohio, a. corporation of Ohio Application November 13, 1939, Serial No. 304,144

Claims.

This invention relates to the treatment of titanium-bearing ores for the purpose of obtaining the titanium values in the form of water soluble compounds, and more particularly to the treatment of such ores as ilmenite and rutile to convert the titanium content into soluble fluoride compounds which may be converted by well known means and methods, such as those disclosed in the Svendsen Patents 2,042,434 and 2,042,435, into titanium hydrate of such purity and characteristic properties that pure pigment rutile contains iron compounds as impurities,

whereas the ilmenite is composed of titanium and iron oxide compounds (probably in chemical combination) in varying proportions. usually contain other impurities in small amounts such as heavy metals other than iron. The iron and heavy metals must be substantially entirely removed from the resulting titanium compounds so that the resulting titanium oxide may have the required whiteness and brilliancy. The silicon which is present in the ore reacts in a manner similar to titanium in the fluoride process, and the resulting titania contains this silicon in the form of silica.

The titanium-bearing raw material is digested with the ammonium fluoride salt, which term includes the bifluoride and compounds which under the conditions of reaction form ammonium fluoride, and the titanium, silicon, iron, and

1 other heavy metal compounds react to form fluoride salts. The titanium and silicon form fluoride salts which are water-soluble under neutral or non-alkaline conditions. Because of the decomposition of at least a part of the ammonium fluoride to the bifluoride due to the instability of the ammonium fluoride at the reacting temperatures the final reaction product is non-alkaline, and the fluoride salts of titanium and silicon may be removed therefrom by leachingwith water. The iron forms a double salt with ammonium fluoride which is soluble only to a slight degree in water and even less soluble in water containing ammonium fluoride in solution. ever, this small amount of iron is suflicient to .cause titania made therefrom, withoutfurther titanium-bearing ore with an ammonium fluoride salt, in accordance with Svendsens method, it has been found in commercial practice that the control of corrosion of the apparatus is difllcult. The problem of corrosion has proven to be most acute in that part of the cyclic process dealing with the recovery of NH4F crystals or of a concentrated NHiF solution (50 to 60%) by evaporation of dilute NH4F solution (10 to obtained from the process.

I have found that the corrosive action of these NH4F or NH4F,NH4F.HF liquors can be controlled by the addition of finely pulverized ilmenite ore and carrying out the required evaporation of water vapor and NH3 fume under pressures greater than atmospheric. I have observed that concentration of dilute NH4F solutions, containing 3% or moreby weight of ilmenite, by evaporation of water vapor (steam) and NH3 fume at a pressure of from 2 to 10 atmospheres, reduces the rate of corrosion of cold rolled steel from to A the values observed when the concentration of the dilute NH4F liquors is carried out by boil- These ores ing at atmospheric pressure or under vacuum in the absence of finelypulverized ilmenite. The practice of this discovery in accordance with my invention enables the use of equipment made from the. lessexpensive corrosion-resistant alloys and greatly increases the effective life of the equipment used in the process.

Examination of the metal surfaces exposed to the action of the NH4F solution-ilmenite slurries during the simultaneous evaporation of the solution and attack of the ilmenite by the active NH4F salt at elevated pressures reveals that a coating, .probably an iron fluoride, is formed on the metal surface, which serves as a protection from further corrosive action. The formation-of this protective coating on the exposed metal surfaces and the consequent lessening of corrosion appears to be considerably facilitated by the presence of ilmenite in the NH4F solution and by the conditions resulting from carrying out the concentration-digestion step at pressures above atmospheric.

Another feature of my invention that is of great importance has to do with the recovery of chemicals used inthe process. I have found, in carrying out the cyclic process cfdigestion, boiling of the reaction mass, clarification of the titania liquor, precipitation of titania hydrate,

HOW-

and recovery of the active chemicals as described in the above-mentioned Svendsen patents, that a good' recovery of these chemicals, fluorine, and ammonia, is extremely diflicult to obtain This is due to many factors, some "of which are the escape of fume from the digester, loss of NILlF and NH: during the concentration of the dilute NH4F liquor, escape of NH: into theairwith non-condensable gases (air) introduced into the of the highly corrosive digester fumes.

system and losses due to'the extreme corrosive action of the; digester fumes and the evaporator liquors. these factors and minimized others, and thus enables the recovery, with a minimum of effort,

of a high percentage of the'active agents used in each cycle. For example, by carrying out the evaporation of dilute NH4F solution in a pressure vessel in the presence of the finely pulverized ilmenite ore, I eliminate the possibility of any fume escaping except as directed during the concentration of the solution; I prevent the access of non-condensable gases (air) to the system, and thus simplify the condensation and complete recovery of NH: fume; I decrease the losses due to corrosion, as previously described, by repressing the corrosive action of the NH4F liquor during concentration, and further, by elimination In addition to these items I have found that by my improved method I obtain a fume from the ressure vessel, during operation, containing not more than traces of NHF, whereas the fume obtained from the evaporation of dilute NH4F solution to concentrated liquor under vacuum or at atmospheric pressure as in the Svendsen method has been found in-practice to contain from 0.5 to 3% of NHiF. Such extremely dilute NH4F solutions are expensive to handle and increase the cost of the recovery system.

In performing the step of digestion of the titanium containing ore with an NH4F salt or concentrated NHLF aqueousysolution as described in the Svendsen patents an excess of the fluoride salt is'required primarily to attain high conversion ofthe titanium content'of the ore to the reaction'mass changes from .a heavy .fluid to a pasty condition and finally approaches a dry state during the course of the digestion. These physical states demand high power-requirements to provide the necessary stirring or agitation of the reaction mass and afford very poor conditions for the eflicient transfer of heat, thus making necessary very careful regulation of the heat input to prevent local overheating, loss .of active fluoride constituents by vaporization and possible freezing of the digester by fusion of thereaction mass. These latter conditions are aggravated by the large excess of NH4F salts found to be necessary to bring about complete conversion of the raw material.

I have found that these difliculties can be eliminated by the method'of attack constituting, my invention, resulting in considerable savings in time, power and heat requirements, and simplifying the control of the digestion step. By

combining the digestion step with the recovery step of evaporation of the dilute NHiF liquors obtained in the process, in accordance with the invention, I am able to secure substantially complete conversion ofthe titanium values in the raw materials to water soluble titanium fluoride compounds during theconcentration of the dilute fluoride salt solution. By combining these mul- My invention has eliminated many oftiple steps into one digestion step carried on in a pressure vessel at pressures greater than atmosphericI have found that satisfactory conversions of titanium-bearing ores can be obtained at temperatures as low as 130 C. to 140 C. The reaction mass in the pressurev vessel remains in a very liquid state throughout the conversion, thus allowing very high heat transfer and low power requirements for agitation. Heating can be accomplished very efliciently through a jacketed vessel by steam or similar means. A'further saving of heat is obtained by completing the conversion in the liquid state. thus materially deceasing the amount of water to be evaporated per cycle. Under certain conditions of operation it is possible to secure a substantially complete conversion of the titanium content of finely pulverized ilmenite ores into water soluble titanium fluoride compounds, and obtain a separation from the relatively insoluble iron fluoride compounds formed, by simple filtration, settling, or similar means without the introduction of any additional leach liquor or repulp waterinto the digested reaction mass.

The control of the attack of the active fluoride I compounds upon the titanium-bearing ore can be maintained easily by reg tionrof the several factors that have been to nd toinfluence the reaction. One of the more important of these factors is the pressure and corresponding temperature at which the reaction mass in the pressure vessel is maintained. The pressure is controlled very simply by regulating the heat'input to the jacketed reaction vessel, the fume discharge from the vessel, or both.

Another important factor is the ratio of the active fluoride compounds (ammonium fluoride) to the titanium-containing material (ilmenite, rutile). I have found that I can obtain-satisfactory conversion of ilmenite by my method of attack with a much smaller excess of NHiF to ilmenite than it is necessary to use in the methods of attack at atmospheric pressure. ample, I am able to use less than 16 molecular parts (4 parts by weight of NHiF to one of ilmenite) and obtain practically complete conversion of the ilmenite to fluoride compounds. also obtained satisfactory conversion using a ratio. of'less than 12 molecular parts (3 parts by weight of NHiF to one of ilmenite). Under certain conditions I am able to. obtain satisfactory results using a ratio of 2.5 parts by weight of N H4F to one of ilmenite. This latter ratio .approaches very nearly the theoretical quantities of NH4F needed to attack and completely convert ilmenite iiito fluoride compounds according to the following equation:

Considerable economies in the operation of this cyclic process, particularly heat savings, can be made by operation of the digestion step with the smaller NHiF ilmenite ratios which are made possible by my discovery. It has been found that the concentration of the NHiF solution initially contasting the titanium-bearing material (ilmenite) For ex- I have the reactionchamber in a'variety of ways.

in the pressure vessel has a considerable influence on the subsequent pressure attack upon the ilmenite. Although the invention is not limited to an attack with NH4F solution of any particular concentration I am able by the control of other steps in the process to make available for the succeeding cycle an NHeIF solution of the optimum concentration for pressure attack in the digestion step.

I have found further, that the pressure attack method of digestion can be operated to advantage on the counter-flow principle. By this modification of the process a portion or all of the Water insoluble residue occurring from the leaching of the soluble titanium fluoride compounds can be contacted in a pressure vessel with a fresh portion of the dilute NH4F liquors available from the process and any small amounts of titanium compounds remaining in the residue be attacked-and put in solution. The liquor from this secondary reaction mass containing small amounts of soluble titanium fluoride compounds is separated from the remaining insolubles by filtration, settling, or similar means and contacted in the same or another pressure vessel with a new quantity of titanium-bearing material (ilmenite) in the primary digestion step, the liquor obtained from this step being rich in soluble titanium fluoride compounds and suitable for further treatment forthe production of titanium oxide of pigment qualities in the manner well known to the art. A division of the pressure attack digestion on the principle described enables the production of a titanium fluoride liquor well suited for further treatment in the production of titanium oxide pigment in the manner of the art and enables further a very high percentage of recovery (96 to 99+%) of the titanium content also be noted that this method of attack as just described allows the conversion process to be carried out with the minimum ratio of NH4F to ilmenite and thus provides the maximum of heat Although I prefer to use a vessel equipped with" some positive stirring device, it is not intended that the invention should be limited to the use of such type of stirring as I have found that the agitation of the slurry caused by the vigorous ebullition of fume during the attack may be sufficient to prevent the settling and baking of any of the heavier parts of the slurry.

The reacting materials may be introduced into The aqueous fluoride solution may be introduced into the pressure vessel simultaneously with the ore, or the ore may be suspended in solution of the fluoride and the suspension fed into the autoclave. My preferred method is to introduce a suspension of all of the ore with a portion of the aqueous fluoride solution into the autoclave and feed in the remainder of. the fluoride solution resecondary, according to this invention, although it is to be understood that said invention is not limited to the exact conditions set-forth in this description.

' Secondary stage Referring to Fig. 1 of the drawings, '700# of NH4F solution is charged into the steam jacketed autoclave I0, equipped with a stirrer II,

pressure gauge I2, and thermometer Well I3, by

means of the pipe I4, pump I5 and supply pipe from the titanium-bearing materials. It may I6. A fume discharge pipe is indicated at- I! and provided with a control valve I8. A discharge pipe for the slurry is indicated at I9. A charge of 125# of iron fluoride filter cake obtained from the primary digestion, hereinafter described, and containing from 8 to 16% of undigested or partially digested ilmenite is thenadded to the autoclave I0, through the manhole I9. The vessel is sealed and steam at 100# gauge pressure is admitted to the jacket by means of the pipe 20 and control valve 2I. The condensation in the jacket is discharged through the pipe 22 which is controlled by the valve 23.- When the pressure Within the autoclave reaches 75# on the gauge I2 the fume discharge valve I8 is opened and regulated to permit a continuous discharge .of vapors at 75# pressure. The stirrer II is operated while the digestion is in progress.

An additional 300# of 20% NH4F solution is fed into the autoclave during the course of the digestion by means of pump I5 which is preferably a chemical proportioning pump. The digestion is continued until approximately 500# of water containing from 4 to 6% NH: has been vaporized and discharged through pipe IT. The supply of steam to the heating jacket is then out oil by closing valve 2| and the pressure in the autoclave allowed'to fall to normal atmospheric pressure. The total time required for this secondary digestion step is about three hours.

The temperature of the reaction mass in the au- 625#, is discharged by pipe I9 and pump 24 to a filter 25 and the fllter cake, 125#,is washed free from occluded titanium fluoride salts with.

166# of very dilute NH4F solution, which may be supplied through pipe 26, the wash liquor being allowed to pass along with the mother liquor to a storage tank 21, by closing valve 28 and opening valve 29, to make 666# of approximately 30% NH4F.NH4F.HF solution. The iron fluoride filter cake, free of ilmenite and soluble titanium fluoride compounds, is removed from fllter 25 and passed along to another step in the cyclic process for the recovery of fluorine as at 20% NH4F solution by known methods.

Primary stage The 30% acid liquor, 666#, is withdrawn from tank 21 and charged into the autoclave by means of pipe and pump I5, the valve 3| being open and the valve 32 closed. of finely pulverthe treated titania liquor.

ized ilmenite is added through the manhole i9 lar manner at 75# gauge pressure. During the reaction an additional 500# of 20% NH4F solution is fed by pump l5 into-the autoclave from the supply l6 at the same rate as fume is discharged. The heating of the autoclave is discontinued when about 891# of steam containing approximately 6% NH; has been driven ofi through pipe l1, and the pressure is then allowed to fall to atmospheric. 452# of water containing small percentages of NH4F and NH: obtained as filter washes from the general cyclic process is then added to the digested autoclave slurry and the thinned slurry is then, by means of the ,pump 24, passed through the filter 25. The filter gestion.

In order to reduce corrosion in' the apparatus it is advisable to use a second autoclave 34 which is similar in all respects to the autoclave ill with piping preferably provided in parallel arrangement so that the pumps l5 and 24 may be used for either autoclave. It will be understood, however, that each autoclave may have its own independent pumps and piping system but the arrangement shown in'Fig. L is of advantage in and the primary digestion carried out in a simito the treating system for further purification, according to the art, and conversionto titania hydrate suitable for calcination to titanium oxide having excellent pigment properties.

Itis not intended that the foregoing specific examples of the attackof ilmenite ore according tq the invention should limit the scope of said invention. I have applied the pressure attack method on several types of ilmenite ores and other titanium containing materials, and haveinvestigated the digestion of ilmenite over a range of pressures varying from atmospheric to 9 atmospheres, 135# gauge, and have obtained improved results, in comparison with prior methbds, in all cases. I have also practiced the invention in the digestion of ilmenite under conditions involving (a) changing of the relative amounts of' NH4F solution and ilmenite used or. as I! designate thisthe fluorine to ilmenite ratio, (b) changing of, the amount of fume discharged during the digestion oras I designate this-the percent of fluorine in the final digested slurry,

- (c) changing of the initial'concentration of the reducing the amount of equipment required.

With the two autoclaves the primary digestion described above may be carried out in one while the secondary'digestion is being carried out in the other, thereby greatly increasing the capacity of the plant, and after eachdigestion the autoclaves may be reversed so that they will be used alternately for the primary and secondary digestions.

The following is a second specific example to illustrate how the digestion may be carried out in one step according to this invention.

Example.--950# of 20% NH4F solution is charged to the autoclave, 100# of finely pulver-, ized ilmenite added, the vessel sealed and heated by passing steam at gauge pressure into the I jacket. When the pressure inside the autoclave has reached 754% gauge pressure corresponding to about 150 0., the fume discharge valve is opened and regulated to permit the continuous dischargeof steam and NHa'vapor at '75# pressure. A1'i additional 1000# of 20% NH4F Solution is pumped into the autoclave during the digestion at aboutthe same rate as the. fume is discharged. The digestion is completed and the heating disremaining inthe autoclave is diluted with about NH4F solutions contacting the ore during digestion, but the foregoing specific examples represent the preferred procedures. From the standpoint of operating efliciency and results the twostage digestion method as described in the first specific example is preferred.

By employing the counter flow principle as illustrated, I am able, most effectively, to utilize the inherent advantages of the invention resulting from attack at elevated pressures and the combination ofdigestion with the concentration of dilute NH4F liquors. I obtain by this method the most nearly complete digestion with the lowest fiuorine to ilmenite ratio, the largest heat economies, and the most eflicient use of weak filter wash liquors recovered in the process.

I have mentioned above that the extreme fluidity of the reaction mass in the autoclave, even in the final stages of digestion, enables me to obtain a very eiiicient transfer of heat at relatively low power cost for agitation. I should .gresses and shows less tendency to settle out,

thus approaching to the most favorable condition for complete reaction.

In addition to this physical condition favorable for rapid and complete digestion, there is a chemical reaction promoted by the pressure attack method that aids the rapid digestion of -the titanium-bearing ore.

This reaction is the dissociation of NHF to NH4.HF according to the equation: 2NH4F.=NI I4F.I-IF+NI-I3.-

This reaction proceeds quite slowly at temperatures below 100 C., but becomes quite rapid at higher temperatures in the neighborhood of 362# of filter wash liquors, recovered in the" process, and passed to the filter. -The iron fluoride filter cake obtained, is washed free of soluble titanium fiuoride compounds-and then transferred to another step in the process for the -150 C. I believe that the actual attack on the ilmenite ore during its digestion is carried on largelyvby the more chemically active NHAF-HF salt rather thanby the neutral NHiF salt. Hence, quickly raising the temperature of the reaction mass to about 140-150? C. and maintaining this temperature by carrying out the entire digestion under a corresponding pressure in a pressure vessel, accele'ratesthe rate of digestion by increasing the rate of formation of the active agent (NH4F.HF salt) By maintain- I digestion of the ore. of NHQF required for digestion in the Svendsen,

ing the finely pulverized ilmenite ore in a highly dispersed condition throughout the fluid reactionmass, ideal conditions are provided for the rapid digestion of said ore by the bifiuoride salt as fast as the latter is formed. The NHavapor formed by the decomposition of the NH4F salt is discharged continuously from the pressure vessel along with steam as the digestion progresses.

This explanation of the probable mechanism of the digestion reaction also accounts for the lower ratio of NH4F to ilmenite required for. digestion. According'to the chemical equations for the reactions, asrpreviously given, and subscribed to by Svendsen in his Patent No. 2,042,435,

ten molecular parts of NH4F are required to completely digest one molecular part of ilmenite,

titanium compounds from titaniferous ore, the step which consists'of mixing the .flnely ground ore with a suflicient quantity of relatively dilute a concentration of the fluoride solution by the continuous withdrawal or thevapors that are boiled off and continuous addition of sufllcient additional aqueous fluoride solution to maintain a constant reaction volume.

4. In the hereindescribed process of recovering titanium compounds from a titaniferous ore, the'step which consists oi boiling a liquid reaction mass of aqueous fluoride solution and the! finely divided ore under a pressure above atmospheric and maintaining the liquidity of the reaction mass throughout the period of the reaction by the addition of aqueous fluoride solution to replace water thatis evaporated therefrom.

one of ilmenite in order to obtain a satisfactory This considerable excess process is necessary because of the difliculty in obtaining a thorough dispersion of the reacting 5. In the hereindescribed process of recovering titanium compounds from a titaniferous ore, the step of concentrating relatively weak am-.- monium fluoride solutions by boiling the same in the presence of ilmenite and under a pressure of from 2 to 10 atmospheres.

materials in the pasty to dry reaction mass and tion and loss of appreciable quantities of unrev acted NH4F or NH4F.I'IF. 7

By carrying out the digestion under pressures greater than atmospheric, according to my invention, I prevent the vaporization of any of the active constituents, NHAF or NH4F.HF, from the reaction mass, and thus make them available for complete utilization. In addition, the complete dispersion of the reacting materials obtained in the fluid condition of the reaction massaids in securing a complete reaction with the theoretically necessary quantities of materials.

' 6.,In the hereindescribed process of recover- I ing titanium compounds from a titaniferous ore, the step which consists in the production of aqua ammonia from relatively weakv ammonium fluoride solutions by reaction with ilmenite under a pressure or from 2 to 10 atmospheres and at the boiling temperature corresponding to such pressure. A

7. The hereindescribed two-stage process -oi recovering titanium compounds from titaniferous ore, the first stage or which consists in treating Y a quantity of finely pulverized ore with amup for the water vapor and ammonia that are In the specification and claims, except where otherwise specifically stated, I intend to use the term ammonium fluoride in a generic sense to include the bi-fluoride as well as the fluoride.

Having thus described my invention, I claim: 1. In the hereindescribed process of recovering titanium compounds from titaniferous ore, the

,step which consists of treating the finely ground ore with'a reactive aqueous fluoride solution under a pressure above atmospheric and .at the boiling temperature of the reaction mass at said pressure and maintaining the reaction mass a in a highly liquid state throughout the period under a pressure above atmospheric and under conditions in which the water and ammoniathat are driven off are replaced by additional liquid to maintain the reaction .mass in a liquid state throughout the period of the reaction.

3. In the hereindescribed process oi recovering driven 01! and maintain the reacting mass in the form of a slurry, filtering the slurry, treating the filtrate to recover titanium compounds contained therein, then as the second stage of the process treating the filter cake with additional ammonium fluoride solution of about 20% concentration under a pressure of from 2 to 10 atmospheres and at the boiling temperature corresponding to such pressure, adding ammonium fluoride solution izrsuflicienf'quantity to makeup for the watervapor and ammonia that are driven iofi and maintain the'reacting mass in the 'form of a slurry, filtering the slurry, and utilizing the filtrate in the first-stage of the-treatment of another quantity-of finely pulverized one.

8. In the hereindescribed cyclic process of recovering titanium products 'irom titaniferous ores, the steps oi adding to the finely pulverized ore in a pressure vessel provided with an. agitator an aqueous solution of titanium and ammonium fluorides obtained from a previous cycle and of greater than 20% concentration and con-- taining insufliclent quantity of ammonium fluoride to effect complete digestion of-said ore. further adding, while maintaining the solution under a pressure corresponding to a boiling point above about (3., a quantity of weak ammonium fluoride liquors of less than 20 concentration to simultaneously effect partial conversion of said ore to fluorides and concentration of the weak ammonium fluoride liquors; separating the partially digested ore from the solution of ti'tanium-ammonium-fluoride and treating said partially digested ore under similar conditions with'sufflcient aqueous ammonium fluoride at about 20% concentration to effect conversion to fluorides, and separating the titanium-ammonium-fluoride solution containing more than about 20% ammonium fluoride from the solids for use in the next cycle under the conditions herein described with reference tothe first men-'- tioned aqueous solutioinfi '9. In the'hereindescribed cyclic process of re covering titanium productsfrom titani'fero'us ores; the steps of adding to the finely pulverized ore in a pressure vessel provided with an aglta- --tor an aqueous solution of titanium and amof he weak ammonium fluoride liquors, separat ing the partially digested ore from the solution of titanium-ammonium-fluoride and treating under similar-'conditions yith sufficient aqueous ammonium fluoride at about 20% concentration to eflect conversion to fluorides, and separating the titanium-ammonium-fluoride solution, containing more than about 20% ammonium fluoride from the solids for use in the next cycle under theconditions herein described with reference to the first mentioned aqueous solution.

10. In the hereindescrlbed cyclic process of recovering titanium products from titaniierous ores, the steps of adding to the finely pulverized ore in a pressure vessel provided with an agitator an aqueous solution of titanium and ammonium fluoride obtained from a previous cycle and of greater than 20% concentration and containing insufl'icient quantity of ammonium fluoride to'effect; complete digestion'of said ore,

further adding, while maintaining the solution under a pressure corresponding to a boiling point tial conversion of said ore tofluorides and concentration of the weak ammonium fluoride liquors, separating the partially digested ore from the solution of titanium-ammoniumfluoride and treating under-similar conditions with sufiicient aqueous ammonium fluoride at. about 20% concentration to effect its conversionto fluorides, separating the titanium-ammoniumfluoride solution containing more than about 20% ammonium fluoride from the solids for use in the next cycle under the conditions herein described with reference to the first mentioned aqueous solution.

PERRY E. MAYER.

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