METHOD FOR PRODUCING TITANIUM FLUORIDE

Abstract: A method for producing titanium fluoride comprises: a dissolution process (2), wherein iron-containing titanium material (1) is dissolved in solutions containing hydrofluoric acid (3), fluoride solutions (4) being produced; a first crystallization and separation process (8), wherein ferric fluoride is crystallized and ferric fluoride crysals (10) thus obtained are separated from the fluoride solutions by cooling the fluoride solutions, crude titanium fluoride solutions (9) being produced; a second crystallization and separation process (15), wherein ammonium fluoride salt (16) [mixed salt of (NH₄)₂ TiF₆ and (NH)₃FeF₆ ] is crystallized and separated by mixing ammonium fluoride solutions (26) with the crude titanium solutions to obtain a mixture and concentrating the mixture; a first pyrolysis process (19), wherein the ammonium fluoride salt is pyrolyzed at a temperature of from 300 to 800 ° C in a stream of dry gas after having dried the ammonium fluoride, ferric fluoride (FeF₃) in a solid state and TF₄, HF and NH₃ in a gaseous state being produced; and a condensation and separation process (22), wherein the TiF₄ HF and NH₃ in a gaseous state are condensed at a temperature of from 20 to 280° C and the TiF₄ in a solid state is separated from HF and NH₃ in a gaseous state.

Description: The present invention relates to a method for producing titanium fluoride of high purity by using iron-containing titanium ore as material. Various Methods for producing titanium fluoride (TiF₄) from iron-containing titanium materials such as ilmenite ore ( hereinafter referred to as "ilmenite" ) are reported. The following method, for example, is disclosed in a British Patent Application No.29944/72. (1) Ilmenite is oxidized until all iron content in the ilmenite becomes trivalent. The oxidized ilmenite and ferric fluoride are mixed to obtain a mixture. The ilmenite reacts with ferric fluoride in the mixture by heating, titanium fluoride ( TiF₄ ) vapor and ferric oxide ( Fe₂O₃) being produced; (2) Titanium fluoride (TiF₄) is recovered by condensing titanium fluoride (TiF₄) vapor; (3) A part of ferric oxide ( Fe₂O₃) reacts with acid ammonium fluoride (NH₄HF₂),ferric ammonium fluoride [ (NH₄)₃FeF₆ ] being produced; and (4) Ferric ammonium fluoride ( (NH₄)₃FeF₆) is pyrolyzed to ferric fluoride (FeF₃) and NH₄F, the ferric fluoride (FeF₃) and NH₄F being recycled. A solvent extraction method disclosed in a journal "Chemistry and Industry" , 57 (10), pp.387 to 392, (1983) is pointed out as another method for producing metallic titanium by obtaining titanium fluoride from ilmenite. The method is described in the journal as follows: (1) Ilmenite is dissolved in acid, aqueous solutions containing Ti-ion being produced. Ti-ion is extracted in an organic solvent out of the aqueous solutions; (2) Ti-ion is extracted by having solutions containing NH₄HF₂ come in contact with an organic solvent in which Ti-ion has been extracted, titanium ammonium fluoride ( (NH₄)₂TiF₆) being obtained; and (3) Crystals of titanium ammonium fluoride ((NH₄)₂TiF₆) are pyrolyzed in an inert gas atmosphere, titanium fluoride (TiF₄) vapor being produced. The vapor is condensed, titanium fluoride being obtained. The following shortcomings are pointed out of the British Patent Application No.29944/72. (1) The yield of titanium fluoride is as low as approximately 91% because titanium fluoride is produced by a solid phase reaction or a gas-solid reaction of ilmenite ore with ferric fluoride. (2) It is said in the British Patent Application No.29944/72 that a fluorination reaction of ilmenite ore of 150 to 250 µm in particle size with ferric fluoride of 1µm or less in particle size in a fluidized-bed furnace is desired. The reaction efficiency of ferric fluoride is decreased by an entrainment of ferric fluoride and a mixing of ferric fluoride with recovered titanium fluoride cannot be avoided because difference of the particle size between ilmenite ore powder and ferric fluoride powder grows larger. Consequently, some countermeasures are required. To overcome said difficulties, some technical solution of problems is needed. (3) There is required an oxidation of ilmenite ore as a pretreatment, a grinding of ferric fluoride and a fluidized-bed furnace capable of withstanding a temperature of from 500 to 1500° necessary for fluorination of ferric fluoride. Therefore, there are problems in high production cost and cost of equipment and in economical efficiency. Further, there are problems in the solvent extraction method that technologies of dissolution of ilmenite ore in acid and of a treatment of iron ore residual solutions containing iron after the extraction of the solvent are unknown and, moreover, the running cost of the organic solvent is high. Documents FR-A-2 073 623 discloses a method for the production of titanium fluoride whereby the Ti-containing ilmenite is directly reacted with ammonium fluoride for 2-20 hours at 120-180°C. The digest (a(NH₄)₃FeF₆/(NH₄)₂TiF₆ mixture is then pyrolized in an N₂ atmosphere at 300-900°C to give TiF₄ gas, and a solid Fe-residue. The pyrolysis step requires a large energy input due to large quantites of Fe-impurities present. It is an object of the present invention to provide a method for producing titanium fluoride wherein titanium fluoride is produced with high yield and, in addition, economically more effective than prior art methods. To accomplish said object, the present invention provides a method for producing titanium fluoride, comprising: a dissolution process, wherein iron-containing titanium material is dissolved in solutions containing hydrofluoric acid, fluoride solutions being produced; a first crystallization and separation process, wherein ferric fluoride are crystallized and the ferric fluoride crystals thus obtained are separated from the fluoride solutions by cooling the fluoride solutions, crude titanium fluoride solutions being produced; a second crystallization and separation process, wherein ammonium fluoride salt ( mixed salt of (NH₄)₂TiF₆ and (NH₄)₃FeF₆) is crystallized and separated by mixing ammonium fluoride solutions with the crude titanium solutions and concentrating said mixture; a first pyrolysis process, wherein said ammonium fluoride salt is pyrolyzed at a temperature of from 300 to 800° C in a stream of dry gas after having dried said ammonium fluoride, ferric fluoride ( FeF₃) in a solid state and TiF₄, HF and NH₃ in a gaseous state being produced; and a condensation and separation process, wherein said TiF₄, HF and NH₃ in a gaseous state are condensed at a temperature of from 20 to 280 °C and the TiF₄ in a solid state is separated from HF and NH₃ in a gaseous state. Fig.1 is a flow diagram designating a method for producing titanium fluoride of the present invention; Fig.2 is a graphical representation designating an influence of reaction time and reaction temperature on the fluorination ratio; Fig.3 is a graphical representation designating an influence of temperature on solubility of TiF₄ and FeF₃; and Fig.4 is a graphical representation designating an influence of temperature on solubility of titanium ammonium fluoride. The flow of a production process of the present invention will now be explained with specific reference to Fig.1. (1) Fluorination dissolution Hydrofluoric acid (HF sol.) of the reaction equivalent ratio of 1.1 or more is added to iron-containing titanium material 1 such as ilmenite ore ( hereinafter referred to as " ilmenite " ) and subjected to fluorination dissolution process 2 at a temperature of 40 °C or more. In Fig.2, there is indicated an influence of reaction time and rection temperature on the fluorination ratio in case of adding an amount of hydrofluoric acid by 1.2 times more than a reaction equivalent. As clearly seen from Fig.2, the higher the reaction temperature in the fluorination dissolution is, the more the time for the completion of the fluorination is shortened, the fluorination dissolution finishes almost within an hour with the range of from 60 to 90°C. During the fluorination dissolution, it is unnecessary to grind ilmenite, but ilmenite can be ground to shorten the time for dissoution thereof. (2) Crystallization and separation of ferric fluoride crystals Subsequently, fluoride solutions 4 are cooled to a fluorination dissolution temperature or less. Ferric fluoride is crystallized and the ferric fluoride crystals 10 ( FeF₃ · 4.5 H₂O ) thus obtained are separated from fluoride solutions 4 as process 8. Thus, crude titanium fluoride solutions 9 ( crude TiF₄ solutions ) are produced. Fig.3 is a graphical representation designating an influence of temperatures on solubility of TiF₄ and FeF₃. As clearly seen from Fig.3,the lower the dissolution temperature is,the lower the solubility of FeF₃ is. The lower a cooling temperature during the crystallization is, the more the amount of the crystallization of ferric fluoride crystls ( FeF₃·4.5 H₂O ) 10 is. This can lighten a burden in the processes to follow. The cooling temperature in the range of from 0 to 20 °C is desirable. When the cooling temperature is higher than 20°C, the separation efficiency of ferric fluoride crystals 10 lowers. When the cooling temperature is lower than 0 °C the cooling efficiency is lower. In case Fe²⁺ and Fe³⁺ are contained in ilmenite, Fe²⁺ and Fe³⁺ also are included in fluoride solutions 4, FeF₂ and FeF₃ being produced. FeF₂ and TiF₄ produce double salt during the cooling of fluoride solutions 4. TiFeF₆ · 6H₂O together with ferric fluoride crystals 10( FeF₃ · 4.5H₂O ) is precipitated and prevents TiF₄ from being converted to solutions. Therefore, it is effective to prevent TiFeF₆ · 6H₂O from being produced by making an oxidation 5 of Fe²⁺ into Fe³⁺ before the cooling and the crystallization of ferric fluoride crystals 10 (FeF₃ · 4.5H₂O). Oxidization 5 of Fe²⁺ into Fe³⁺ is carried out by adding oxidizing agents 6 such as hydrogen peroxide solutions , ozone, air and oxygen to fluoride solutions 4 or by having said oxidizing agents come in contact with fluoride solutions 4. Iron content in fluoride solutions 7 can be reduced to a half to one tenth by making oxidation 5 of Fe²⁺ into Fe³⁺and by making crystallization and separation 8 of ferric fluoride crystals. (3) Crystallization and separation of ammonium fluoride salt Subsequently, titanium ammonium fluoride ((NH₄)₂ TiF₆) and ferric ammonium fluoride ((NH₄)₃FeF₆) are crystallized by mixing crude titanium fluoride solutions ( crude TiF₄ solutions ) obtained by making crystallization and separation 8 of ferric fluoride crystals ( FeF₃ · 4.5H₂O ) 10 with ammonium fluoride solutions (NH₄F ) 26 which is produced in the following processes. In this crystallization process, water in the mixed solutions is desired to be recovered by making evaporation and condensation 11 of the mixed solutions so as to control a water balance in the solutions. Ammonium fluoride salt crystallized by evaporation and concentration 11 of the mixed solutions turns into coarse grains,and crystallization and separation process 15 is easily carried out. As shown in Fig.4, the crystallization and separation of ammonium fluoride salt from concentrated solutions 12 can be further effectively carried out by cooling concentrated solutions 12. Crystallization and separation 15 of concentrated solutions 12 of ammonium fluoride salt obtained in this way is carried out and concentrated solutions 12 of ammonium fluoride salt are converted to ammonium fluoride salt 16 and ammonium fluoride solutions 17 containing a part of dissolved ammonium fluoride salt. Ammonium fluoride solutions 17 absorb gases 24 of ammonia (NH₃) andhydrogen fluoride (HF) produced in a condensation andseparation process which will be explained later and are mixed again, as ammonium fluoride solutions 26 (NH₄F solutions), with crude titnium fluoride solutions (crude TiF₄ solutions ) 9. Water vapor 13 obtained inevaporation and condensation process 11 is condensed and turns into condensed water. A part of the waterobtained by condensation of water vapor 13 is discharged. Remaining water 14 obtained by condensation of water vapor 13 is used for washing ferric fluoride crystals 10 (FeF₃ · 4.5H₂O) obtained in said crystallization and separation 8, TiF₄ and HF adhering to ferric fluoride crystals 10 ( FeF₃·4.5H₂O) being absorbed in the remaining water 14. Further, HF gas 32 produced inthe further successive processes and material HF gas 34 are absorbed in the remaining water 14, hydrofluoric acid 3 being produced. Hydrofluoric acid 3 is used for fluorination dissolution 2 process. Washing water is desired to be cold water to prevent the ferric fluoride crystals from dissolving during cleaning. It is very effective in preventing fluorine from being discharged out of the same circuit and, at the sametime, in reducing the cost for a measure of counterpollution and the cost for hyrogen fluoride as material to recycle water and hydrogen fluoride (HF) in the same circuit in this way. (4) Drying and pyrolyzing of ammonium fluoride salt Ammonium fluoride salt 16 being a mixed salt of titanium ammonium fluoride ( (NH₄)₂TiF₆) and ferric ammonium fluoride ( (NH₄)₃FeF₆) is subjected to drying process 8 and heated at a temperature of from 300 to 800 °C in a stream of dry gas not containing water. Ammonium fluoride salt 16 is pyrolyzed by heating, as pyrolyzing process 9, FeF₃ in a state of solid 21 and TiF₄, HF and NH₃ in a state of gas 20 are produced. The pyrolyzing process proceeds with the following reaction: ( NH₄)₂ TiF₆ → TiF₄ + 2HF +2 NH₃ It is important that the dry gas does not contain water. Dry nitrogen, dry air, dry argon or the like can be used as the dry gas. When the gas contains water, TiF₄ gives rise to a hydrolysis reaction at high temperature, produces titanium oxide and this leads to a decrease of the yield of TiF₄. Heating temperature is in the range of from 300 to 800 °C. The hydrolysis reaction proceeds as follows: TiF₄+ 2H₂O → TiO₂ + 4HF When the heating temperature is lower than 300°C, TiF₄ does not sublime perfectly. When the heating temperature is higher than 800°C, FeF₃ sublimes a a little. The heating temperature is preferred to be in the range of from 400 to 600°C. (5) Condensation of titanium fluoride Titanium fluoride (TiF₄) 23 of high purity is obtained by subjecting gases 20 of TiF₄, HF and NH₃ to condensation and separation process 22 at a temperature of from 20 to 280°C in a condenser. A condensation temperature in in the range of from 20 to 280 °C. When the temperature is over 280 °C, TiF₄ sublimes completely. When the temperature is lower than 20 °C, HF liquefies. The condensation temperature is preferred to be in the range of from 50 to 100°C. Gases 24 containing HF and NH₃ after having condensed and separated titanium fluoride (TiF₄) 23 are made to be absorbed by ammonium fluoride solutions 17 which are recycled as ammonium fluoride solutions 26. (6) Pyrolysis of FeF₃ Solid 21 of FeF₃ as a residue obtained by pyrolysis 19 of ammonium fluoride salt is mixed with crystals of ferric fluoride ( FeF₃ · 4.5H₂O) 28 obtained by making crystallization and separation 8 of fluorination solutions 7 and heated at a temperature of from 600 to 1000°C with existing water. Then, FeF₃ is hydrolyzed, and iron oxide (Fe₂O₃) 31 and hydrogen fluoride (HF) 32 are produced. When the heating temperature is lower than 600 °C,the hydrolysis reaction does not take place. When the heating temperature is over 1000 °C, FeF₃ sublimes . Iron oxide (Fe₂O₃) 31 is discharged as a by-product. Hydrogen fluoride (HF)is absorbed by cleaning solutions 29 of crystals of ferric fluoride ( FeF₃ · 4.5H₂O) as mentioned above and is used again for fluorination dissolution 2 of ilmenite. As mentioned above, according to the present invention, ilmenite ore can be almost perfectly dissolved by reacting with solutions containing hydrofluoric acid at a temperature of 40°C or more, and almost all the amount of titanium content in the ilmenite ore can be extracted as titanium fluoride. Therefore, the reaction production ratio of titanium fluoride is remarkably highand the yield of titanium fluoride is 95% or more. Further, according to the present invention, there is no need of using expensive organic solvents as those used in a solvent extraction method for separating iron content from the fluorination soluions of iron-containing material. Titanium fluoride can be refined and separated at a cost lower than that in the solvent extraction method with the use of a combination of a rough separation of titanium fluoride from iron fluoride, wherein differences in solubility of titanium fluorideand iron fluoride are used, with a method of refining and separating them wherein diffrences in their sublmation temperature are used. Crystals of iron fluoride obtained by crystallization and separation process and iron fluoride produced by pyrolysis are hydrolyzed, and fluorine can be recovered as hydrogen fluoride. Ammonia and hydrogen fluoride produced by pyrolysis of ammonium fluoride salt are also recovered and fluorine, a part of which is consumed by reaction, is recycled in the same circuit. Therefore, the method of the present invention is very effective in the reduction of cost as well as in the prevention of pollution. Example-1 A mixture of 10 kg of ilmenite ore (54.9% TiO₂, 19.5% FeO and 21.6% Fe₂O₃) from West Australia and 17.9kg of 55% hydrogen fluoride solutions was agitated in a closed Teflon lined reactor at 80 °C for an hour and fluoride solutions were obtained. The fluoride solution were cooled to 35°C. 1.3 kg of 35% wt.H₂O₂ solutions were added to said fluoride solutions. Then, after fluoride solutions had been agitated for an hour, said solutions were cooled to 10 °C. In this way, 13.6 kg of a cake of FeF₃·4.5H₂ and 15.6 kg of crude TiF₄ solutions were obtained by crystallizing and separating. 11.4 kg of crystals of FeF₃·4.5H₂O and 6.5 kg of washing solutions were obtained by washing the cake of FeF₃·4.5H₂O with 4.3 kg of cold water of 5°C. In Table 1, there are indicated the composition of the crude TiF₄ solutions, the washing solutions and FeF₃·4.5H₂O, Ti content and the ratio of migration of Ti in ore. Weight (kg) TiF₄ (%) FeF₃ (%) HF (%) Ti content(%) and amount(kg) Ratio of migration of Ti in ore (%) Crude TiF₄ solutions 15.6 44.1 3.0 5.7 17.0 2.65 80.5 99.0 Washing solutions 6.5 24.1 2.8 3.2 9.4 0.61 18.5 FeF₃·4.5H₂O 11.4 0.70 49.4 0.1 0.27 0.03 1.0 As shown in Table 1, 99.0 wt.% of Ti contained in ilmenite ore migrated to the crude TiF₄ solutions and the washing solutions. Subsequently, 16.6 kg of ammonium fluoride solutions ( 37.6 wt.% of NH₄F and 18.8 wt.% of Ti (NH₄)F₆) containing dissolved Ti(NH₄)₂F₆ at 20°C were mixed with mixture of the crude TiF₄ solutions and the washing solutions. The mixture thus obtained was concentrated under reduced pressure, being agitated at 80 °C. After 11.9 kg of water had been evaporated from the mixture, the mixture was cooled to 20°C. Then, 14.8 kg of ammonium fluoride salt was obtained by filtering and separating said ammonium fluoride from the mixture and by drying said ammonium fluoride at 105° C for 5 hours. The composition of said ammonium fluoride salt is indicated in Table 2. Composition Content (%) (NH₄)₂TiF₆ 90.4 (NH₄)₃FeF₆ 9.6 Subsequently, said ammonium fluoride salt was put in a hastelloy pyrolysis reactor and heated to 400°C in a stream of dry nitrogen gas. Outlet gas containing pyrolysis gas was sent to a condenser, whose temperature was at 80 °C. 8.2 kg of TiF₄ was recovered in said condenser. 8.2 kg of TiF₄ corresponds to 98 wt.% titanium fluoride in 14.8 kg of ammonium fluoride salt. As a result, 96 wt.% of Ti in ilmenite ore was recovered in the form of TiF₄. The outlet gas of the condenser was absorbed in filtrate obtained by filtering and separating ammonium fluoride salt from the mixture, and the gas was recycled again in the pyrolysis reactor after dehumdication of the gas. 0.6 kg of FeF₃ remaining in the pyrolysis reactor was mixed with 11.4 kg of crystals of FeF₃·4.5.H₂O obtained by cooling and crystallization 4.4kg of Fe₂O₃ was obtained as a residue by subjecting said mixture to a heat treatment at 700°C with the use of air as carrier gas. Outlet gas produced during the heat treatment was sent to the condenser of 5°C and 7.6kg of hydrofluoric acid liquid containing 3.3 kg of hydrogen fluoride was obtained. Example-2 Titanium ammonium fluoride was dried at 105° C for 20 hours. After 100.0 g of dried titanium ammonium fluoride had been charged into a tubular furnace, the inside of said tubular furnace was heated to approximately 500 ° C by passing, at a rate of 1 liter per min., the air which had been dried by being passed through a calcium chloride tube. Outlet gas of said tubular furnace was sent to the condenser whose temperature has been arranged to be at 50 ° C, and 61.5 g of titanium fluoride was recovered. The ratio of recovery was 98%. For comparison, a test was conducted with the use of air, as a control, which had not been passed through calcium chloride tube, that is, air in the atmosphere. Firstly, titanium ammonium fluoride was dried at 105° C for 20 hours. After 100.0 g of dried titanium ammonium fluoride had been charged into a tubular furnace, the inside of said tubular furnace was heated to approximately 500 ° C in a stream of the atmospheric air. Outlet gas was sent to a condenser whose temperature was arranged to be at 50° C. In consequence, 48.0 g of titanium fluoride was recovered and 9.8 g of titanium oxide remained in the furnace. The ratio of recovery of titanium fluoride was 77%. Example-3 14.8 kg of ammonium fluoride salt,whose composition is indicated in Table 2 and which was controlled in the same manner as Example-1, was put in the hastelloy pyrolysis reactor and was heated to 400 ° C in a stream of the dry air dried by being passed through calcium chloride tube. Outlet gas containing pyrolized gas was sent to a condenser whose temperature was arranged at 80 ° C and 8.2 kg of TiF₄ was recovered. In case the dry air was used as dry gas, 98% titanium fluoride in 14.8 kg of ammonium fluoride salt could be recovered.

Claims: A method for producing titanium fluoride,comprising: a dissolution process (2), wherein iron-containing titanium material (1) is dissolved in solutions containing hydrofluoric acid (3), fluoride solutions (4) being produced; characterized by a first crystallization and separation process (8), wherein ferric fluoride is crystallized and ferric fluoride cristals (10) thus obtained are separated from the fluoride solutions by cooling the fluoride solutions, crude titanium fluoride solutions (9) being produced; a second crystallization and separation process (15), wherein ammonium fluoride salt (16) [mixed salt of (NH₄)₂ TiF₆ and (NH₄)₃FeF₆] is crystallized and separated by mixing ammonium fluoride solutions (26) with the crude titanium solutions to obtain a mixture and concentrating said mixture; a first pyrolysis process (19), wherein said ammonium fluoride salt is pyrolyzed at a temperature of from 300 to 800 ° C in a stream of dry gas after having dried said ammonium fluoride, ferric fluoride ( FeF₃) in a solid state and TiF₄, HF and NH₃ in a gaseous state being produced; and a condensation and separation process (22), wherein the TiF₄, HF and NH₃ in a gaseous state are condensed at a temperature of from 20 to 280°C and the TiF₄ in a solid state is separated from HF and NH₃ in a gaseous state . The method of claim 1, characterized by further comprising an oxidation process (5), wherein divalent iron-ion in the fluoride solutions is oxidized into trivalent iron-ion by blowing oxidizing agent (6) in the fluoride solutions obtained in the dissolution process; and said oxidized fluoride solutions being sent to the first crystallization and separation process in which crude titanium fluoride solutions are produced. The method of claim 1 or 2,characterized by further comprising a second pyrolysis process(30), wherein the ferric fluoride crystals obtained in the first crystallization and separation process and the ferric fluoride obtained in the first pyrolysis process are hydrolyzed at a temperature of from 600 to 1000 °C, iron oxide (31) (Fe₂O₃) and HF (32) being produced. The method of claim 1, 2 or 3, characterized in that the ammonium fluoride solutions to be mixed in the second crystallization and separation process include solutions which are produced by having the HF · NH₃ (24) gas obtained in said condensation and separation process absorbed in ammonium fluoride solutions (17) containing a dissolved portion of the ammonium fluoride salt obtained in said second crystallization and separation process. The method of any one of claims 1 to 4, characterized in that the dissolution of titanium material in solutions containing hydrofluoric acid in said dissolution process includes dissolution of titanium material at a reaction temperature of from 60 to 90 °C. The method of any one of claims 1 to 5, characterized in that the cooling of the fluoride solutions in said first crystallization and separation process includes cooling the fluoride solutions at a temperature of from 0 to 20 °C. The method of any one of claims 1 to 6, characterized in that said second crystallization and separation process includes mixing ammonium fluoride solutions with said crude titanium fluoride solutions to obtain a mixture, evaporating and concentrating the mixture, ammonium fluoride salt [mixed salt of (NH₄)₂TiF₆ and ( NH₄)₃FeF₆] being crystallized and separated. The method of any one of claims 1 to 7, characterized in that the second crystallization and separation process includes mixing ammonium fluoride solutions with said crude titanium fluoride solutions to obtain a mixture; evaporating and concentrating the mixture by evaporating and cooling the mixture; ammonium fluoride salt [mixed salt of ( NH₄)₂ TiF₆ and (NH₄)₃ FeF₆] being crystallized and separated. The method of any one of claims 1 to 8, characterized in that the heating in said first pyrolysis process includes heating at a temperature of from 400 to 600 °C in a stream of dry gas selected from the group consisting of dry nitrogen, dry air and dry argon. The method of any one of claims 1 to 9, characterized in that said condensation and separation process includes condensation and separation at a temperature of from 50 to 100°C.

Inventors: HINAMI, TOSHIO C/O PATENT & LICENSE AND, KAWAWA, TAKAHO C/O PATENT & LICENSE AND, NAKAHARA, KEISUKE C/O PATENT & LICENSE AND, YOSHIKOSHI, HIDEYUKI C/O PATENT & LICENSE AND, Hinami, Toshio c/o Patent &amp; License and, Kawawa, Takaho c/o Patent &amp; License and, Nakahara, Keisuke c/o Patent &amp; License and, Yoshikoshi, Hideyuki c/o Patent &amp; License and
Applicants: NKK CORPORATION
Application year: 1988
Main classification: C01G23
IPC codes: C01G23, C22B34