Purification of titanium trichloride

Titanium trichloride which is obtained during one step of a process for recovering titanium metal values from a titanium bearing source which still contains some impurities such as iron and vanadium compounds may be purified by drying the titanium compound in an air atmosphere, further drying under a carbon monoxide atmosphere and thereafter roasting the dried compound in the presence of chlorine at an elevated temperature to separate the impurities from the desired titanium compounds.

BACKGROUND OF THE INVENTION 
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, floor coverings, glassware and 
ceramics, painting inks, as an opacifying agent in papers, etc. The other 
titanium compounds are used in electronics, as fire retardants, 
water-proofing agents, etc. The metal may be used as such or in alloy form 
as structural material in aircraft, in jet engines, marine equipment, 
textile machinery, surgical instruments, orthopedic appliances, sporting 
equipment, food handling equipment, etc. Heretofore in recovering the 
titanium from titanium bearing sources such as ilmenite, rutile, etc., 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 also obtaining relatively large amounts of 
iron along with the titanium. 
As will hereinafter be shown in greater detail, it is now 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. 
This invention relates to a novel method for purifying titanium compounds 
during a process for obtaining titanium metal values from a titanium 
bearing source. More specifically, 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. 
It is therefore an object of this invention to provide an improvement in a 
process for the production of titanium. 
A further object of this invention is to provide a hydrometallurgical 
process for the recovery of titanium from a titanium bearing source, the 
desired titanium being obtained in a relatively purer state. 
In one aspect an embodiment of this invention resides in a process for the 
purification of a titanium chloride which comprises the steps of drying 
said titanium chloride in an air atmosphere, further drying said titanium 
chloride in a carbon monoxide atmosphere at an elevated temperature, 
roasting the dried titanium chloride at an elevated temperature in the 
presence of chlorine, separating the volatile impurities, and recovering 
the purified titanium compounds. 
A specific embodiment of this invention is found in a process for the 
purification of titanium chloride which comprises the steps of drying 
titanium trichloride in an air atmosphere at a temperature below about 
100.degree. C., further drying said titanium trichloride in a carbon 
monoxide atmosphere at a temperature in the range of from about 
250.degree. to about 750.degree. C., roasting the dry titanium trichloride 
at a temperature in the range of from about 400.degree. to about 
750.degree. C. in the presence of chlorine, separating volatile iron and 
vanadium compounds, and recovering the purified titanium dioxide and 
titanium tetrachloride. 
Other objects and embodiments will be found in the following detailed 
description of the present invention. 
As hereinbefore set forth the present invention is concerned with a process 
for the purification of a titanium chloride which has been obtained during 
the processing of a titanium bearing source to obtain titanium metal 
values. The titanium bearing source such as ores including ilmenite, 
rutile, etc., which also contain other metals such as contaminants such as 
iron, vanadium, etc., are subjected to a reductive roast at an elevated 
temperature which will range from about 600.degree. to about 900.degree. 
C. or more in the presence of a reducing gas such as hydrogen or carbon 
monoxide. In the preferred embodiment, the reductive roast is effected on 
a metal bearing source such as an ore, which has been crushed to a 
particle size less than about 100 mesh, at a temperature of about 
750.degree. C. for a period ranging from about 0.5 up to about 2 hours or 
more. The reducing atmosphere which is used to accomplish the purpose of 
the roast usually comprises a mixture of about 50% carbon monoxide and 50% 
hydrogen with an excess of reductant being utilized in order to completey 
reduce the iron which is present in the system 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 about 80.degree. to 
about 110.degree. C. for a period of time ranging from about 0.25 hours 
up to about 1 hour or more in duration. Upon completion of the leach step, 
the resulting solution is thereafter cooled to a temperature ranging from 
about 0.degree. to about 20.degree. C. in order to effect a 
crystallization or precipitation of the ferrous chloride. The cooled 
solution, which is maintained in the subambient range hereinbefore set 
forth by external means such as an ice bath, cooling coils, etc., is then 
saturated with gaseous hydrogen chloride in order to insure a 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 about 0.5 up to 
about 2 hours or more in duration, the solution is subjected to a 
solid/liquid separation whereby the solid ferrous chloride crystals are 
separated from the soluble titanium compound 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.degree. 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 solid titanium chloride 
compound 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 about 20.degree. to about 
30.degree. C. 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, cadmium, etc. 
The recovered hydrated titanium trichloride may then be purified by 
subjecting the crystals to a series of purification steps. These steps 
will include drying the hydrated titanium trichloride in an oxidizing 
atmosphere which is provided for by air, said drying being effected at 
temperatures less than about 100.degree. C. and preferably in a range of 
from about 25.degree. to about 50.degree. C. Following the drying of the 
titanium trichloride in the air atmosphere, the crystals are then 
subjected to a further drying step utilizing a carbon monoxide atmosphere, 
said drying being effected at a temperature in the range of from about 
250.degree. to about 750.degree. C. The pressure under which the further 
drying of the titanium trichloride is effected may range from about 1 to 
about 0.1 atmospheres, the drying of the crystals being effected during a 
period which may range from about 0.5 up to about 2 hours or more in 
duration, the time of drying being dependent upon the particular 
temperature and pressure which are employed during the drying step. 
Following the drying of the crystals under a carbon monoxide atmosphere the 
crystals are then roasted at a temperature in the range of from about 
400.degree. to about 750.degree. C. in the carbon monoxide atmosphere and 
in the presence of chlorine gas which is charged to the pressure resistant 
vessel employed in the reaction. In the preferred embodiment of the 
invention the combined carbon monoxide-chlorine pressure will range from 
about 1 to about 5 atmospheres. In addition, another operating parameter 
of the roasting step of the present invention involves the duration of 
said step, the roast being effected during a period of time which may 
range from about 0.5 to about 2 hours. Upon completion of the roasting 
step, the volatile impurities which comprise iron, vanadium, chromium, 
cadmium, etc., compounds which are in the form of vapors will be withdrawn 
and discharged from the operating vessel while the solids which comprise 
purified titanium tetrachloride and titanium dioxide may be recovered and 
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 hereinbefore set forth, that 
is, from about 600.degree. to about 900.degree. C. or more 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 bleaching vessel. In this 
vessel the ore is leached at an elevated temperature ranging from 
80.degree. to 110.degree. 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 
about 0.degree. to 20.degree. 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, 
centrifugal means, etc. 
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 about 20.degree. up to about 30.degree. C. or more in order 
to crystallize the titanium trichloride. The hydrated titanium trichloride 
crystals which may still contain unwanted compounds such as iron, 
vanadium, etc., compounds, is then placed in a drying apparatus and heated 
to a temperature less than about 100.degree. 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 about 400.degree. to about 750.degree. C. 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 temperature for the 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 about 600.degree. to about 
900.degree. 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 which is maintained at a temperature ranging from about 
80.degree. to about 110.degree. 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 pregnant 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 about 20.degree. to about 30.degree. C. or more. The raise in 
temperature will permit crystallization of the titanium trichloride as 
hydrated crystals. 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 about 100.degree. 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 about 250.degree. to about 750.degree. 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 about 400.degree. to about 
750.degree. 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 necessarily 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.degree. C. under an atmosphere of dry nitrogen. 
Upon reaching this roasting temperature the ore may then be roasted for a 
period of 1 hour to 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 ranging from 85.degree. to 100.degree. C. 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.degree. C. by means of an ice bath and purged 
with hydrogen chloride gas until the solution is saturated. After allowing 
the solution 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.degree. C. while maintaining the 
solution in an oxygen free atmosphere. The titanium trichloride will 
precipitate upon the temperature reaching 25.degree. C. 
Titanium tetrachloride crystals (4 grams) were then placed in a tube 
furnace and heated slowly to a temperature of 400.degree. C. under a 
carbon monoxide blanket to dehydrate. Following this the crystals were 
then subjected to a roast under chlorine gas at a temperature of 
750.degree. 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 heated to 
250.degree. 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 of 
450.degree. C. 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.degree. 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.degree. 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.