GB2040270A - Obtaining purified titanium compounds - Google Patents

Abstract

The invention seeks to provide a method of obtaining purified titanium compounds from an impure titanium chloride, particularly a titanium trichloride which is obtained during one step of a process for recovering titanium metal values from a titanium-bearing source (e.g. by reduction and leaching with HCl) and which still contains some impurities such as iron and vanadium compounds. According to the invention the titanium chloride is subjected to drying in an air atmosphere and further drying under a carbon monoxide atmosphere at elevated temperature, the dried compound is thereafter roasted in the presence of chlorine at an elevated temperature, the volatile impurities are separated and the desired purified titanium compounds, usually titanium dioxide and titanium tetrachloride, recovered.

Description

SPECIFICATION Obtaining purified titanium compounds The present invention relates to a novel method for obtaining purified titanium compound(s) which is of particular relevance to a process for obtaining titanium metal values from a titanium-bearing source. In one aspect, the invention is concerned with a process for recovering titanium from a titanium-bearing source such as ilmenite whereby a sharper separation of titanium from impurities contained therein may be accomplished.

Titanium in metallic form or as a compound is an important element in the chemical series. For example, titanium dioxide is utilized in paint pigments, in white rubbers and plastics, in floor coverings, glassware and ceramics, in printing inks, and as an opacifying agent in paper. Other titanium compounds are used in electronics, as fire retardants and as water-proofing agents. The metal may be used as such or in alloy form as a structural material in aircraft, jet engines, marine equipment, textile machinery, surgical instruments, orthopedic appliances, sporting equipment and food handling equipment. Heretofore in recovering the titanium from titanium-bearing sources such as ilmenite and rutile, the titanium has been subjected to separation steps which involve the formation of titanium as a compound in a valence state of +4, such compounds usually involving titanium oxide.However, when attempting to separate titanium dioxide from impurities which are also contained in the ore such as iron, the hydrolysis of the titanium dioxide at elevated temperatures usually results in relatively large amounts of iron being obtained along with the titanium.

It has now been found possible to further purify the desired titanium metal values by freeing said metal values from remaining impurities such as iron and vanadium compounds, thus rendering the obtention of relatively pure titanium in a greater yield.

According to the present invention there is provided a method of obtaining purified titanium compounds from an impure titanium chloride which comprises the steps of (a) drying the titanium chloride in an air atmosphere, (b) further drying the titanium chloride in a carbon monoxide atmosphere at an elevated temperature, (c) roasting the dried titanium chloride at an elevated temperature in the presence of chlorine, (d) separating the volatile impurities, and (e) recovering the purified titanium compound(s).

In a specific embodiment, the features of which are preferred singly and in combination, the process comprises the steps of (a) drying impure titanium trichloride in an air atmosphere at a temperature below 1 00 C., (b) further drying the titanium trichloride in a carbon monoxide atmosphere at a temperature in the range of from 250 to 7500C., (c) roasting the dry titanium trichloride at a temperature in the range of from 400" to 750"C in the presence of chlorine, (d) separating volatile iron and vanadium compounds, and (e) recovering purified titanium dioxide and titanium tetrachloride.

The present invention is especially concerned with a method of obtaining purified titanium compounds from an impure titanium chloride which has been obtained during the processing of a titanium-bearing source to obtain titanium metal values. In one method of processing, the titanium-bearing source, usually an ore such as ilmenite or rutile, which also contain other metals as contaminants, e.g. iron, vanadium, etc., is subjected to a reductive roast at an elevated temperature ranging from 600" to 9000C. in the presence of a reducing gas such as hydrogen or carbon monoxide. In the preferred embodiment, the metal-bearing source (e.g. ore) is crushed to a particle size less than 100 mesh and the reductive roast is effected at a temperature of 750"C. for a period ranging from 0.5 to 2 hours.The reducing atmosphere which is used to accomplish the purpose of the roast usually comprises a mixture of about 50 vol.% carbon monoxide and 50 vol.% hydrogen, with an excess of reductant being utilized in order to reduce the iron which is present in the system completely to the metal. Following the reductive roast of the metal-bearing source, the source is then subjected to an aqueous hydrogen chloride leach which is also effected at an elevated temperature, usually in the range of from 80" to 110"C., for a period of time usually ranging from 0.25 hour to 1 hour in duration.Upon completion of the leach step, the resulting solution is thereafter cooled to a temperature ranging from 0" to 20"C. in order to effect a crystallization or precipitation of the ferrous chloride. The cooled solution, which is maintained at 0 to 200C by external means such as an ice bath or cooling coils, is then saturated with gaseous hydrogen chloride in order to ensure complete precipitation of the iron. After subjecting the solution, which contains solid ferrous chloride and soluble titanium chloride, to the aforesaid saturation step for a period of time which may range from 0.5 to 2 hours in duration, the solution is subjected to a solid/liquid separation whereby the solid ferrous chloride crystals are separated from the soluble titanium chloride contained in the leach liquor.

The solid ferrous chloride crystals may then be washed with water and treated at an elevated temperature of about 400 C. whereby gaseous hydrogen chloride is removed and recycled to the saturation and precipitation step of the process, the solids which comprise ferric oxide and gangue being removed and recovered.

The pregnant leach liquor, which contains the soluble titanium chloride as well as some impurities which have not been removed in their entirety by the previous steps, is then passed to a warming stage wherein the temperature is raised to a range of from 20 to 300C. In this warming stage the soluble titanium chloride will precipitate out as hydrated titanium trichloride crystals, said crystals also containing impurities such as iron, vanadium, chromium and cadmium.

The recovered hydrated titanium trichloride is an appropriate starting material for the purification method according to the present invention.

The first step in the method according to the invention involves drying the impure titanium chloride (e.g. the hydrated titanium trichloride crystals obtained as described above) in an oxidizing atmos pherewhich is provided by air, said drying usually being effected at a temperature less than 100"C. and preferably at a temperature in the range of from 25 to 50"C.

Following the drying of the titanium chloride in the air atmosphere, it is then subjected to a further drying step utilizing a carbon monoxide atmosphere at an elevated temperature, usually at a temperature in the range of from 250 to 750"C. The pressure under which this further drying of the titanium chloride is effected is generally in the range from 1 to 0.1 atmospheres, the drying being effected during a period which usually ranges from 0.5 to 2 hours in duration, the optimum length of the period being dependent upon the particular temperature and pressure which are employed during the drying step.

Following the drying of the titanium chloride under a carbon monoxide atmosphere the crystals are then roasted at an elevated temperature, usually in the range of from 400" to 750"C., in the presence of chlorine gas which is charged to a pressure-resistant vessel which is employed in the method, and as a rule in the presence also of the carbon monoxide atmosphere. In the preferred embodiment of the invention the combined carbon monoxide-chlorine pressure is in the range from 1 to 5 atmospheres.

Another operating parameter of the roasting step is its duration which is preferably in the range from 0.5 to 2 hours.

Upon completion of the roasting step, the volatile impurities, which in the case of titanium chloride obtained from a titanium-bearing source of the type hereinbefore mentioned usually comprise iron, vanadium, chromium and cadmium compounds in the form of vapors, are withdrawn and discharged from the operating vessel while the solid residue which generally comprises purified titanium tetrach chloride and titanium dioxide is recovered and may be passed to storage.

The process for the purification of titanium chloride may be effected in any suitable manner and may comprise a batch or continuous type operation. For example, when a batch type operation is used a quantity of the ore source is placed in an appropriate apparatus such as an oven wherein it is subjected to temperatures within the range of from 600" to 900"C.

in the presence of a reductant which comprises a mixture of hydrogen and carbon monoxide gas.

After undergoing the reductive roast the ore source may then be placed in a second apparatus which comprises a leaching vessel. In this vessel the ore is leached at an elevated temperature ranging from 80" to 110 C. by contact with an aqueous hydrogen chloride leach solution. After being leached the solution is then placed in an apparatus which is maintained at subambient temperatures ranging from 0" to 20"C. whereby crystallization of the iron compounds such as ferrous chloride is effected. In addition to maintaining the temperature of the leach solution in a subambient zone the leach solution is also contacted with gaseous hydrogen chloride in order to saturate the solution and insure as complete precipitation as possible of the iron compounds.

After crystallization of the ferrous chloride the soluble titanium chloride in the leach liquor is separated from the solid ferrous chloride by conventional means such as decantation, filtration or centrifugal means.

The liquid leach liquor which has been separated is then placed in still another apparatus wherein the leach liquor is warmed to a temperature ranging from 20 up to 30"C. in order to crystallize the titanium trichloride. The hydrated titanium trichloride crystals which may still contain unwanted compounds such as iron and vanadium compounds, is then placed in a drying apparatus and heated to a temperature less than 100 C., the drying being effected in the presence of air. Thereafter the crystals are transferred to a drying oven in which they are further dried at an elevated temperature within the range hereinbefore set forth under a carbon monoxide atmosphere.After drying under the carbon monoxide atmosphere for a predetermined period of time, chlorine gas is charged to the apparatus while maintaining the temperature at a predetermined level within the range of from 400" to 75000. The action of the chlorine gas on the crystals will result in the vaporization of the volatile iron and vanadium compounds which may be vented and recovered.

After maintaining the apparatus under the predetermined carbon monoxide-chlorine pressure and tem peratureforthe desired period of time heating is discontinued, any excess pressure is vented and the solid titanium tetrachloride and/or titanium dioxide which has been formed is recovered.

It is also contemplated within the scope of this invention that the process of said invention may be effected in a continuous manner. When such a type of operation is to be employed the ore source is continuously charged to a roasting oven wherein it is subjected to a reductive roast in the presence of a reductant of the type hereinbefore set forth, said roast being effected at temperatures ranging from 600" to 900"C. After passage through the oven for a predetermined period of time the ore is continuously discharged from said oven and charged to a leaching apparatus when is maintained at a temperature ranging from 80" to 110"C. In the leaching apparatus the source is contacted with an aqueous hydrogen chloride leach solution which is also continuously charged to the apparatus.After being leached at this temperature for a predetermined period of time the leach solution is continuously withdrawn and passed to a crystallization zone which is maintained at subambient temperatures within the range hereinbefore set forth. In the crystallization zone the leach solution is contacted with gaseous hydrogen chloride which is continuously charged to the crystallization zone in order to saturate the solution and assist in the precipitation of the ferrous chloride which is present in the ore source as a contaminant or impurity. The pegnant leach liquor is continuously withdrawn from the crystallization zone and passed to a second crystallization zone wherein the leach liquor is warmed to a temperature ranging from 20 to 30"C. The raise in temperature will permit crystallization of the titanium trichloride as hydrated crys tals. After a predetermined period of time in the crystallization zone the hydrated crystals are continuously withdrawn and separated from the spent leach liquor.The solid hydrated titanium trichloride crystals are then continuously passed to a drying oven wherein they are passed through said oven in an air atmosphere while maintaining the temperature below 100"C. After continuous passage through this oven the crystals are charged to a second drying oven wherein they are subjected to a second drying step at an elevated temperature ranging from 2500 to 750"C. under a carbon monoxide atmosphere, the carbon monoxide also being continuously charged to this oven.Upon completion of the second drying step, the crystals are continuously passed under a carbon monoxide atmosphere to a roasting oven wherein they are contacted with chlorine gas while maintaining the temperature within the range of from 400" to 750"C. After passage through this roasting oven for a predetermined period of time the impurities comprising iron compounds which were not precipitated out in the previous steps as well as vanadium compounds are withdrawn in the form of vapors or gases while the desired titanium values such as titanium tetrachloride and/or titanium dioxide are continuously withdrawn and passed to storage for further treatment, if so desired.

The following examples are given for purposes of illustrating the process of this invention. However, it is to be understood that such examples are given merely for purposes of illustration and that the present invention is not limited thereto.

Example I An ilmenite ore may be crushed and sized to -100 mesh. Following this the sized ilmenite ore may then be placed in a rotary quartz tube and heated to a temperature of 750"C. under an atmosphere of dry nitrogen. Upon reaching this roasting temperature the ore may then be roasted for a period of 1 hour in a stream of reducing gas consisting of 320 ml/min. of carbon monoxide and 320 ml/min. of hydrogen. At the end of this period the ore may be cooled under a nitrogen stream until it has reached room temperature. The ore may then be leached with 300 cc of a leach solution containing concentrated hydrochloric acid, the leach being effected at temperatures rangins from 85" to 10000. under agitation for a period of 1 hour. The solution may then be allowed to cool and filtered.The pregnant leach liquor may then be placed in a flask and cooled from room temperature to about 5"C. by means of an ice bath and purged with hydrogen chloride gas until the solution is saturated. The solution is then allowed to stand for a period of 0.5 hours during which time the ferrous chloride may precipitate out. The solids may then be removed by filtration and the pregnant leach liquor containing titanium trichloride may then be warmed to a temperature of 25"C. while maintaining the solution in an oxygen free atmosphere. The titanium trichloride will precipitate upon the temperature reaching 25"C.

Titanium tetrachloride crystals (4 grams) were subjected to a drying step in an airatmosphere at 45"C. and then placed in a tube furnance and heated slowly to a temperature of 400"C. under a carbon monoxide blanket. Following this the crystals were then subjected to a roast under chlorine gas at a temperature of 750"C. for a period of 1 hour. At the end of this 1 hour heating was discontinued and the crystals-were allowed to cool while maintaining the charge of chlorine gas. The residue which remained was analyzed and found to consist of 71 % titanium, less than 0.1% iron and 0.05% vanadium. An X-ray analysis of the residue disclosed a strong rutile and weak anatase pattern.

Example II In this example 10 grams of titanium trichloride which is prepared in a manner similar to that set forth in Example I above was subjected to a drying step in an air atmosphere at 40 C. and then heated to 250 C. and dried under a blanket of carbon monoxide. Following this the charge was chlorinated for 15 minutes to remove ferrous chloride. The tube furnace and charge were then heated to a temperature of45000. under a carbon monoxide blanket and upon reaching this temperature were then chlorinated by the addition of chlorine gas for a period of 1 hour. When heating to a temperature of 250"C. and chlorinating, a small amount of copper colored crystals were blown out of the tube furnace while black crystals were formed in the furnace. The titanium trichloride turned brown upon the first chlorination while further heating at the elevated temperature caused a large build up of the copper colored crystals, which turned black from opening the furnace. Analysis of the black crystals showed that there was 0.01% titanium, 30% iron, with less than 0.001% vanadium present in the crystals. In addition, an X-ray analysis of the crystals showed that they were amorphous in form. At the end of the 1 hour chlorination at 450 C., the residue was a light brown solid. Analysis of the solid residue showed it to be 64% titanium,1.8% iron and 0.1 % vanadium while the X-ray analysis disclosed a strong rutile pattern plus an anatase pattern.

Claims (14)

1. A method of obtaining purified titanium compound(s) from an impure titanium chloride which comprises the steps of: (a) drying the titanium chloride in an air atmosphere; (b) further drying the titanium chloride in a carbon monoxide atmosphere at an elevated temperature; (c) roasting the dried titanium chloride at an elevated temperature in the presence of chlorine; (d) separating the volatile impurities; and (e) recovering the purified titanium compound(s).

2. A method as claimed in claim 1 wherein the drying of the titanium chloride in an air atmosphere is effected at a temperature below 10000.

3. A method as claimed in claim 1 or 2 wherein the drying of the titanium chloride in a carbon monoxide atmosphere is effected at a temperature in the range of from 250 to 7500C.

4. A method as claimed in claim 3 wherein the drying in a carbon monoxide atmosphere is effected for 0.5 to 2 hours at 0.1 to 1 atmosphere pressure.

5. A method as claimed in any of claims 1 to 4 wherein the roasting of the dried titanium chloride in the presence of chlorine is effected at a temperature in the range of from 400" to 7500C.

6. A method as claimed in any of claims 1 to 5 wherein the roasting of the dried titanium chloride is effected in a carbon monoxide atmosphere under combined carbon monoxide-chlorine pressure of from 1 to 5 atmospheres.

7. A method as claimed in claim 5 or 6 wherein the roasting of the dried titanium chloride is effected for from 0.5 to 2 hours.

8. A method as claimed in any of claims 1 to 7 wherein the purified titanium compounds comprise titanium dioxide and titanium tetrachloride.

9. A method as claimed in any of claims 1 to 8 wherein the titanium chloride is titanium trichloride.

10. A method as claimed in claim 9 wherein the titanium trichloride has been obtained in the processing of a titanium-bearing ore to recover titanium metal values.

11. A method of obtaining purified titanium compound(s) from impure titanium chloride carried out substantially as herein before described.

12. A process for recovering titanium metal values from a titanium-bearing source comprising subjecting the titanium-bearing source to a reductive roast at from 600 to 900"C in the presence of a reducing gas, subjecting the roasted material to an aqueous hydrogen chloride leach at an elevated temperature, cooling the resulting solution to 0 to 20"C to effect crystallization/precipitation of ferrous chloride whilst retaining titanium chloride in solution, saturating the cooled solution with gaseous hydrogen chloride, separating crystallized/precipitated matter from the residual solution, warming the residual solution to 20 to 300C to crystallize/precipitate hydrated titanium trichloride, separating the crystallized/precipitated titanium trichloride and obtaining purified titanium compound(s) from it by method as claimed in any of claims 1 to 9.

13. A process for recovering titanium metal values from a titanium-bearing source carried out substantially as described in either of the foregoing Examples I and II.

14. Purified titanium compounds when obtained by a method as claimed in any of claims 1 to 11.