USRE18854E

USRE18854E - Signments

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Publication number: USRE18854E
Authority: US
Publication date: 1933-05-30

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2 Sheets-Sheet l INVENTGR BY WM ATTORNEY no? @MMJ PRODUCTION QE 'IITANIUM DIOXIDE EEAEQ J. BLUMENFELD Original Filed Feb. 2

FOIL .40 ouvumatwog N GE J. BLUMENFELD M 30 1933. PRODUCTION OF TITANIUM DIOXIDE Re. 18,854

2. Shani-Sheet 2 Original Filed Feb. 2, 1928 IILQ'EN 1931K CRYSTALLOD Sauna 0H? 0 QWM. M410? INVENTOR BY M.

ATTORN EY Reissued May 30, 1933 UNITED STATES PATENT OFFICE JOSEPH BLUMENFELD, OF NEUILLY-SUR-SEINE, FRANCE, ASSIGN'OR, BY MESNE AS- SIGNMENTS, TO KREBS PIGME-NT' AND COLOR CORPORATION, OF NEWARK, NEW

JERSEY, .A' CORPORATION OF DELAWARE PRODUCTION OF TITANIUM DIOXIDE Original No. 1,795,467,-dated March 10, 1931, Serial No. 251,253, filed February 2, 1928. Application for reissue filed. April 2'6, 1932. Serial No.

This invention relates to a process for preparing titanium hydroxide or oxide by the hydrolysis of sulfuric acid solutions containing titanium at elevated temperatures.

These solutions are obtained, for instance, by the action of sulfuric acid on titaniumbearing oressuch as ilmenite, rutile, or the like. The preparation of such solutions is a Well-known step in the art and has been described by me in Patent 1,504,669. Solutions of this character usually containiron and may also contain various other impurities.

The chemical composition of the solutions in question may vary within wide limits, and the precise chemical linkage of the titanium and sulfuric acid is not completelyunderstood. From such solutions, titanyl sulfate (TiOSOQI-I O) may be crystallized under certain conditions; but at the same time some persons are of the opinion that the titanium is present in solution as the normal sulfate. Whatever the exact chemical compositions may be, the fact is that the final equilibrium of such solutions is directly proportional to the concentration of the S0 and TiO ions present.

By proper chemical treatment the sulfuric acid solutions of titanium may be caused to undergo hydrolysis, with the resultant formation of a precipitate of free titanium hydroxide or oxide and an attendant increase of free acidity of the solution. It should be noted, also, that the facts concerning the relation between titanium hydroxide and titanium dioxide are not completely known'at the present time. When titanium solutions are treated chemically in a manner that should ordinarily produce a metallic hydroxide, the resultant product apparently undergoes a transition during drying and when fully dr is found to be titanium dioxide .(TiO Hereafter, in the present specification and claims, the hydrolysis product is referred to as titanium dioxide.

subjected to hydrolysis are true solutions and possess the homogeneity which characterizescrystalloid solutions.

There is a Wide variance in the physical and chemical properties of titanium dioxide produced by hydrolysis, dependent upon the exact conditions under which the hydrolysis takes place. The object of the present invention is to provide an improved hydrolysis process, whereby titanium dioxide of consistently uniform properties may be produced rapidly and in good yield. Another object of the invention is to achieve this favorable result in a solution of relatively high concentration, so that the sulfuric acid present and formed during the process may be recovered and concentrated economically. Other objects of the invention will become apparent.

' The presence of iron in the solution to be hydrolyzed does not interfere With the reaction, but if much is present in solution the precipitated titanium dioxide is likely to become contaminated with iron. For this reason it is desirable to adjust the iron content of the solution to be hydrolyzed so that it does not contain more than 20-25 grams of iron as ferrous sulfate per liter. This may be done by simple crystallization of the ferrous sulfate, or by an improved process of refrigeration as described in my Patent N 0. 1,707,248.

In order that the present invention may be appreciated, reference is made to an example showing a method of hydrolyzing in the ordinary way.

A solution of titanium containing 200 grams per liter of TiO, and 500 grams per liter of H SO free or combined with-titanium is diluted cold to a concentration of 400 grams per liter of H SO and 160 grams per liter 0 TiO This diluted solution is then heated to and maintained at a temperature of 100 C. and gives by hydrolysis the very low yield of precipitated TiO of about 30%, the timetaken to obtain this yield being about 24 hours.

I have now discovered that the speed of hydrolysis and quantitative yield of products may be increased and the quality of the precipitated TiO may be improved if the h drolysis of the crystalloid solution is car- .ried out in the presence of TiO;: in colloidal form. For example, if to the solution to be hydrolyzed as previously described there is first added about thirty grams per liter of colloidal TiO and exactly the same method of hydrolysis is adopted, a yield of about 95% TiO is obtained in about three hours.

To achieve these favorable results one may either add specially prepared colloidal titanium dioxide to the solution prior tohydrolysis,

quantity of colloidal TiO is produced in. the solution prior to any actual precipitation of TiO This latter method is the most suitable for practical use and is illustrated by the following example:

Example I The solution had the following composition:

.. Grams per liter '1i02 19a210 Fe (ferrous) 20- 25 n so. 500-550 This solution was concentrated until the sulfuric acid, free and combined with titanium (excluding the acid combinedwith the iron) was about 600 grams per liter.

100 cc. of this solution, heated to about 100 0., was added at a uniform speed with stirring over a period of 4 minutes to 100 cc. of boiling water. During the first quarter minute of the addition a turbidity was noted, but this disappeared almost immediately and or one may conduct the hydrolysis 8 itself in such a manner that an adequate 1 the solution regained its original appearance.

The temperature of the mixture was maintamed at about 103 C. and the stirring was continued. After about ten minutes tur- 1 Table 1 Grams per liter Minute of reaction Appearance of solution Tim igicolg Ptecip in solumid itated lution for T10 Clear 104 Clear 97 Clear 92 Very slight cloudiness 84 Very slight cloudiness 78 Slightly cloudy gt) 1 In the above table, the precipitated TiO was determined by the simple expedient of filtering the solution. in the filtered solution was determined by first coagulating it by adding concentrated hydrochloric acid, and then filtering.

.The data shown in Table 1 is also shown graphically in Fig. 1, where the concentration of TiO is plotted against the time during hydrolysis. Throughout the experiment, the total weight of TiO present naturally remains the same. At the first state of the reaction, all of the TiO is present in crystalloid solution. Curve A shows the progressive increase in the total amount of .TiO not in crystalloid solution. non-soluble TiO is present in colloidal form. However, when a certain point is reached i. e., at the juncture of curves A and B, the amount of colloidal material present falls oif. Curve B shows colloidal material alone, and indicates how it decreases in amount during the rest of the reaction. Obviously, the difference between curves and B shows the amount of TiO precipitated. It should be noted that Fig. 1 shows only the first few minutes of the reaction. As the hydrolysis The colloidal TiO At first all of the' or as a contract catalyst, is not minutes determines the yield and speed of hydrolysis and the quality of the resultant product. At the same time, this initial reaction is controlled by temperature, speed of mixing, and other variables.

The rapidity and high yield of the hydrolysis described in Example I is best understood in conjunction with Fig. 1, in which the course of the reaction is charted.

Under the conditions of the reaction, colloidal TiO is formed immediately on contacting the solution with water. This is shown clearly on F ig 1, for at the end of the period of introduction there is already presout about 20' grams per liter of colloidal material. At low acid concentrations, such as prevail when only a part of the solution has been added to the water, the tendency to hydrolyze is the greatest,the reaction occurring at very low temperatures.

As a result of my experiments, I have determined that it is the presence of an adequate quantityof colloidal TiO in the mixture that causes the improved drolysis. The exact manner in which the colloidal phase promotes the precipitation is not known. Presumably, the titanium in crystalloid solution must pass through the colloidal phase before precipitation. Whether the presence of a large quantity of colloid promotes this reaction through a simple transfer, in accordance with the mass low,

known.

Example [I If the hydrolysis described under Example is repeated in the same manner except that a lesser quantity of solution is added to the water, the rate of addition remaining uniform, the hydrolysis will occur in the same way except that it will be completed in a shorter time.

In Fig. 2 there is shown a curve of hydrolysis in which 60 cubic centimeters of titanium solution was added to 100 cc. of water, as in Example I. r

Both the final yield of TiO from hydrolysis and the quality of the material for pigment purposes, after calcining, is affected by the final acidity of the solution hydrolyzed. In turn, the final acidity is, of course, and expression of the concentration at which the hydrolysis is effected. In Example III, below, a series of hydrolyses of titanium solutions at varying final acidities is shown.

Example [II Tests A, B, C and D expresesd below were all based on the introduction of a titanium solution similar to that described in Example I into 100 cc. of boiling water at a uniform rate of mixture. The data is expressed in tabular form, and it will be noted yield and rate of hythat the hydrolysis at the highest acid concentration (test D) gave the best yield.

- Final acidity Volume solu- Time of Test at end of tlon added addition hydrolysis Cubic Grams per centi'mzters Min. Sec. liter A 60 2 45 200 100 4 300 200 8 330 D 250 10 420 Analysis of mother Time of analy- -liquorg/l Test is after intro- Yield duction of T10:

Fe TlOz H2801 Hours Percent k 1%: 26.3 13 215 85 B 1% 36.8 19 297 84 CL- 1% 42. 0 23. 2 380 .85 D 2 44. 2 19. 8 410 88. 5

The TiO produced by these experiments was washed, dried and calcined at 970 (1., after which its pigment properties were tested. The TiO from test D was found to be generally superior in pigment qualities over the other samples.

Example I V r The development of an adequate colloidal phase in the solution, prior to precipitation,

depends in part on the speed with which the V titanium solution is mixed with the water. This is illustrated in the table of tests reported below. In each case, 250 cc. of the solution mentioned in Example I was added, hot, with stirring to cc. of water, and the reaction was completed as described in Example I.

Timezof gliplip sg Anallyl rsiigogffiother hours Yield of Test Tlol Per cent colloid) The table clearly indicates that most favorable results are attained with a solution of this concentration when the addition occurs at a rate of about 4-6 minutes per volume of solution added to a volume of water. Higher speeds, as in E, give lower yield and incomplete hydrolysis, due to the fact that an adequate colloidal phase is not formed. 7 If the solution is added at a speed less than the optimum, there is a gradual diminution in yield until, as in the case of I and J a considerable amount of presulfuric acid 90% ci itation occurs before all of the solution'is a ded.

In practicing my hydrolysis process I usually work with titanium solutions having a free acidity factor of about 90%; that is, solutions containing a quantity of in excess of the amount required to react with all of the titanium present to produce titanyl sulfate. The reason why solutions of this character are used is a practical one, but it has nothing to do with the present process. In the extraction of titanium from its ores, such as ilmenite, it has been found that the most rapid and satisfactory results are secured if the amount of sulfuric acid used is 90% in excess of the amount required to produce titanyl sulfate. The solutionsused for the hydrolytic precipitation of TiO are usually obtained from this source and are hence used at a free acidity predetermined by other considerations.

The factor of free acidity described in no way limits my process, which can be performed with equal satisfaction, and without change, in solutions having a free acidity factor of less than 90%. Titanium solutions practically neutral in character may be prepared if care is used, and these solutions may be hydrolyzed in the same manner. On the other hand, solutions with a free acidity factor of over 90% may also be used.

Much more important than the free acidity factor is the total or final acidity of the hydrolyzed solution expressed as sulfuric acid. This acidity will be equal to the free acid originally present prior to hydrolysis, plus the acid produced during the hydrolysis as the result of the precipitation of TiO In the industrial production of TiO it is naturally desired to conduct all of the operations at as high an acid concentration as possible so that the acid recovered from the process may be concentrated and re-used at a minimum expense. In fact, one of the objects of the present invention is to permit successful operations at a higher acid concentration than that known in the art.

For several practical reasons, it is desirable that the final acidity of the hydrolyzed solution should be in the neighborhood of 400 grams per liter. One of these reasons is the economical one given above. Another is based on the fact that the best recovery of the TiO is obtained at this concentration, as was shown in Example III. However, Example III also shows that my improved process is operative at final acidity concentrations below 400 grams per liter.

On the contrary, it is not advisable to operate the process at acid concentrations much above 400 grams per liter because of. the. tendency of more concentrated solution to crystallize out part of the contained titanium sulfates and a further tendency of the TiO to re-dissolve in the acid present.

. The final acidity of the hydrolysis mixture is, of course, independent of the precise quantities of titanium solution and water mixed. For example, instead of adding four parts of a mixture containing 600 grams of H SO per liter to two parts of water, the same final acidity may be produced by addmg five parts of a solution containing 480 grams of H SO per liter to one part of water.

If, instead of using the concentrated solution referred to in Example I, it is preferred to use directly the solution containing about 5 00 grams of sulphuric acid per liter of solut1on,'the proper end concentration of about 400 grams of sulphuric acid per liter may be obtained by adding the original solution to about one quarter of its volume of water. In this event, it is preferable to add the solution at a faster rate, per volume of solution added to a volume of water.

Titanium solutions originally containing considerably less than 600 grams per liter of sulfuric acid may be hydrolyzed in accordance with my process. In general, more dilute solutions are more easily hydrolyzed and at lower temperatures. On adding a small quantity of such solutions to hot water, colloidal TiO is formed in the same manner, and by the same procedure of continuing the addition gradually over a period of several minutes the production of colloidal particles of TiO prior to actual precipitation, is eifected. This fact was illustrated, indirectly, in Example III, where the final concentration of acid in the mixture was considerably less than 400 grams per liter.

However, the use of titanium solutions containing less than 500600 grams of sulfuric acid per liter, prior to admixture with water, is unnecessary and impractical in industrial operations, since the handling of larger volumes of liquid and the additional cost attendant on the concentration of very dilute acid for re-use serves no useful purpose.

While I prefer to conduct my process in the manner described in the examples by producing colloidal TiO in the solution to be hydrolyzed before actual precipitation takes place, my invention is not so limited. I may, alternatively, add colloidal TiO to a solution of titanium in sulfuric acid and then heat the mixture to cause hydrolysis. For example, I may produce a solution rich in colloidal TiO in the manner described in Example II and render such a solution stable by merely cooling it when it has reached a maximum concentration of colloidal particles, before any actual precipitation has taken place. This solution may then be mixed with a solution containing 200 grams TiO and 500 grams H SO per liter in such proportions that the mixture will contain about 30 grams per liter of colloidal TiO The mixture is then heated to a temperature of about 100 for three hours, whereupon the hydrolysis is complete.

The titanium dioxide produced by my hydrolysis process is removed from the mixture by decantation and filtered, after which it is washed to remove acid, and is dried. The dry TiO may be treated in various ways. For the preparation of pigment, it is calcined for about a half hour at a temperature of 950-1,000. The resultant product is a tough granular material which may be converted into an excellent white pigment by grinding.

While I prefer to use ordinary hot water for the purpose of hydrolyzing titanium solutions, I may, alternatively, employ dilute solutions containing titanium in place of water. Such solutions of lesser concentration of titanium are obtained, for example, as wash water from other process steps and by re-use in the manner described the loss of titanium in the plant may be avoided. In the appended claims, I have used the expression solution of lesser concentration as including both pure water and wash waters or other dilute solutions.

I claim:

1. In a process for preparing titanium dioxide by combining a solution of a titanium salt with a solution of lesser concentration, the step which comprises slowly adding at an elevated temperature the titanium solution to the solution of lesser concentration while agitating the mixture so that colloidal particles of titanium compound are produced prior to actual precipitation.

2. The process of precipitating a titanium oxygen compound by hydrolysis which comprises heating to hydrolyzing temperatures a titanium salt solution which contains more colloidal titanium compound in solution at the time actual precipitation begins than a titanium salt solution containing the same amount of total titanium and total acid radicals when prepared cold and heated to the point where actual precipitation begins.

3. The process of precipitating a titanium oxygen compound by hydrolysis which comprises heating to hydrolyzing temperatures a titanium sulfate solution which contains more colloidal titanium compound in solution at the time actual precipitation begins than a titanium sulfate solution containing the same amount of total titanium and total acid radicals when prepared cold and heated to the point where actual precipitation begins.

4. In a process of preparing titanium dioxide by combining a solution of a titanium salt with a solution of lesser concentration, the steps which comprise adding the titanium salt solution to the solution of lesser concentration at an elevated temperature while agitating the mixture and regulating the rate of said addition to produce a solution which at agitating the mixture,

the time actual precipitation begins contains more colloidal titanium compound in solution than a solution containing the same amount of total titanium and total acid radicals when prepared cold and heated to the point where actual precipitation begins.

In a process of preparing titanium dioxide by combining a solution of titanium sulfate with a solution of lesser concentration, the steps which comprise adding the titanium sulfate solution to the solution of lesser concentration at an elevated temperature while agitating the mixture and regulating the rate of said addition to produce a solution which at the time actual precipitation begins contains more colloidal titanium compound in solution than a solution containing the same amount of total titanium and total acid radicals when prepared cold and heated to the point where actual precipitation begins.

6. In a process for preparing titanium dioxide by combining a solution of titanium sulfate with a solution of lesser concentration, the steps which comprise adding at an elevated temperature the titanium sulfate solution to the solution of lesser concentration, while over a period of a few minutes at such a slow rate that a colloidal titanium compound is formed in the solution in gradually increasing amounts until the completion of the addition and prior to beginning of actual precipitation.

In a method of producing-titanium dioxide which comprises mixing without difl'usion a titanium sulfate solution with a diluent, the steps of maintaining the temperature at about 100 C. and higher, adjusting the concentrations of the combining solutions to produce an acidity at the end of the hydrolysis corresponding to from about 200 to 420 grams per liter of H SO free and combined with T'iO and effecting the addition in between 2 45" and 18, and heating the mixed solution to effect hydrolysis.

8. In a process of hydrolyzing a titanium sulfate solution which produces a yield of about 85% and more of the titanium compound content of said solution and which comprises mixing without diffusion a solution of titanium sulfate with a diluent, the steps of maintaining the temperature, concentrations and rate of said combining within the range comprising temperatures in the neighborhood of 100 C. and higher, concentrations of the combining solutions to produce an acidity at the end of the hydrolysis corresponding to from about 200 to 400 grams per liter of H SO free and combined with TiO and the addition to between 2' 45" and 18', selecting and controlling the aforesaid factors to produce the above yield, and heating the mixed solution to effect hydrolysis.

9. In a process of hydrolyzing a titanium salt solution according to claim 1, the steps of combining said titanium salt solution with a combining a similar with a simllar solution solution of lesser concentration and effecting h drolysis of the mixed solution under condltions which reduce ayield of at least 85% of precipitated titanium oxygen compound, said conditions having been established by titanium salt solution of lesser concentration at various rates of addition and at various temperatures, and determining in each inunder conditions which produce a yield of at least 85% of precipitated titanium oxygen compound, said conditions having been established by combining a similar titanium sulfate solution with a similar solution of lesser concentration at various rates of addition and at various temperatures, and determinoxide which comprises as one of its steps coming in each instance. the yield of precipitated titanium oxygen'compound when boiling the mixture for three hours.

11. In a process of preparing titanium dibining a solution of a titanium salt with a diluent, the steps which comprise mixing-the titanium salt solution with the diluent while agitating the mixture and-regulating the rate and conditions of mixing to produce a substantial amount of titanium compound in colloidal solutionprior to actual precipitation and heating the solution to eflect hydrolysis.

12. In a process of preparing titanium dioxide which comprises as one of its steps combining a solution of titanium sulfate with a diluent, the steps which comprise mixing the titanium sulfate solution with the diluent while agitating the mixture and regulating the rate and conditions of mixing to produce a substantial amount of titanium compound in colloidal solution prior to actual precipitation and heating the solution to effect hydrolysis.

13. In a process of preparing titanium dioxide by combining a solution of titanium sulfate with a solution of lesser concentration, the steps which comprise adding at an elevated temperature and titanium sulfate solution to the solution of lesser concentration while agitating the mixture and regulating the rate of said addition to produce at least 20 grams per liter of titanium compound in colloidal solution prior to actual precipitation.

14. In aprocess of preparing titanium dioxide by combining a solution of titanium sulfate with a solution of lesser concentration, the steps which comprise adding at an elevated temperature the titanium sulfate solution to the solution of lesser concentration while agitating the mixture and regulating'the'rate of saidaddition to produce at least 16% of the total titaniumcompound present in colloidal form prior to actual precipitation. r

15. The process for the production of titanium dioxide which comprises slowly of titanium, containing about 600 rams per liter of acid and about 220 grams 0 titanium dioxide, to 40% of'its volume of water at an elevatedtemperature over a period of about 10 minutes, and heating said mixture until precipitation is effected.

16. The process for producing colloidal TiO, particles in a titanium sulfuric acid solution which comprises slowly adding said solution'to a solution of lesser concentration at an elevated temperature and agitating the mixture during said addition.

17. The process for preparing titanium dioxide by-combining four parts of a solution containing approximately 200 grams Ti-Og and 500 grams I-LSO; per

liter with one part of water which comprises adding the titanium solution to the water at an elevated temperature so thatcolloidal articles of TiO are produced, the mixture eing meanwhile agitated, and heating the mixture until precipitation is'eflected.

18. The process for producing hydrolyti cally precipitated titanium dioxide which comprises slowly combining a titanium sulfatesolution with a diluent at an elevated temperature, the mixture meanwhile being agitated to neity, where y colloidal titanium dioxide is slowly reserve a substantial homogeformed in a solution of slowly'increasing concentration of sulfate mm, and

heating the completed admixture until hydrolysis is substantially complete.

19. The process for producing hydrolytically precipitated titanium dioxide which comprises slowly adding a titanium sulfate solution to a diluent, at an elevated temperar ture, the mixture being agitated to promote homogeneity, and heating the completed mixture until hydrolysis is plete.

20. In a process of preparing titanium dioxide by combining a solution containing a titanium salt with adiluent at an elevated temperature, the steps which comprise adding a concentrated solution of titanium sulfate to the diluent while agitating the mixture at such a rate that after the initial turbidity, the solution will remain clear for about 10 minutes after the addition is completed. v I

21. In a process of preparing titanium dioxide by combining a solution containing a titanium salt with a diluent at an elevated substantially comadding with agitation a sulfuric acid solution temperature, the steps which comprise adding a concentrated solution of titanium sulfate to the diluent While agitating the mixture at such a rate that after the initial turbidity, the solution will remain clear for about 10 minutes after the initial turbidity had disappeared.

witness whereof, I affix my signature. JOSEPH BLUMENFELD.