AU600541B2

AU600541B2 - A process for the production of high quality titanium dioxide by the sulfate method

Info

Publication number: AU600541B2
Application number: AU82904/87A
Authority: AU
Inventors: Gabriel Denecker; Joel Leuridan; Luc Van Royen; Domien Sluyts; Werner Verhoeven
Original assignee: Bayer Antwerpen NV
Current assignee: Bayer Antwerpen NV
Priority date: 1986-12-20
Filing date: 1987-12-18
Publication date: 1990-08-16
Anticipated expiration: 2007-12-18
Also published as: DE3643711A1; AU8290487A; EP0273244A3; FI875571A; EP0273244A2; ZA879501B; NO875071D0; FI875571A0; BR8706920A; NO875071L; JPS63166721A

Description

II_

5348-PI JGS:GS 5149T/3 4 600541

AUSTRALIA

PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Application Number: Lodged: 0 ,rr Complete Specification Lodged: Accepted: SPublished: Priority: Related Art: This document contains the amendments made under Section 49 and is correct for 1printin g.

TO BE COMPLETED BY APPLICANT i Name of Applicant: Address of Applicant: Actual Inventor: SsAddress for Service: BAYER ANTWERPEN N.V.

Kanaalsdok B 1 Kruisschans, B-2040 Antwerpen 4, Belgium Gabriel Denecker Domien Sluyts Joel Leuridan Werner Verhoeven Luc Van Royen ARTHUR S. CAVE CO.

Patent Trade Mark Attorneys Level Barrack Street SYDNEY N.S.W. 2000

AUSTRALIA

Complete Specification for the invention entitled -A IMPROVE p

D

PROCeESS. A process -fA 4&e rodccion olrf- A qoa ua(Uy u' oide by g9#e S-Aofiie Ae+od The following statement is a full description of this invention including the best method of performing it known to me:- 1 from actual invntor(s) thnntin 4. The basic application(s) referred to in paragraph 2 of this Declaration was/were the first from the actual imyntor(t). application(s) made in a Convention country in respect of the invention the subject of the application.

Atttation or lhglizaton no tr ir i. Declared at Antwerp, Belgiumthis 26th day of November 198 7 To: AYER ANTWERPEN N.V.

Le A 24 760-AU The Commissioner of Patents I s^ la 0 4 098 This invention relates to an improvement in a process for the production of high-quality titanium dioxide by the sulfuric acid digestion method comprising the steps of reacting ilmenite and/or titanium-containing slags with highly concentrated sulfuric acid, dissolving the solid digestion masses with aqueous sulfuric-acidcontaining metal sulfates and, optionally, water, reducing the trivalent iron and separating off the insoluble starting material to obtain a sulfuric acid-containing titanylsulfate solution rich in foreign metal salts (so-called black solution), hydrolyzing the black solution with subsequent separation of the titanium oxide hydrate precipitated, washing vigorously with water, drying and, optionally, calcining.

BACKGROUND OF THE INVENTION 0 4: r. I 44o 4 In the conventional production of Ti02 by the sulfate method comprising the steps of reacting ilmenite and/or titanium-containing slags with highly concentrated sulfuric acid, dissolving the solid digestion mass with water and/or dilute aqueous sulfuric acid and separating off the insoluble raw material, sulfuricacid-containing TiOSO 4 solutions are obtained which are generally contaminated to a considerable extent by Le A 24 760 2 foreign metal ions, primarily iron and also aluminium and magnesium together with relatively low concentrations of heavy metals, such as manganese, vanadium, chromium or niobium.

In addition, all the Fe I I and a small part of the Ti IV are reduced to Fe I I and Ti I I I respectively, by the addition of iron scrap either during or immediately after the dissolving step, so that the iron content increases even further.

In ilmenite-based digestion processes, some of the iron ions have to be removed from the digestion solution which contains a little Ti I I I (so-called "black solution") before the hydrolysis step. This is normally done by cooling crystallization and separation as "green salt" (FeS04'7H 2 However, the other foreign metals largely remain in the black solution. By contrast, in 20 the digestion of slag, the lower iron content means that t% "the iron compounds are not normally separated off.

German 2,620,065 describes an extraction process for the removal of Cr II I and NbV from the black solu- 8 tion. However, the Cr II I ions can be effectively extracted only by heating the black solution to temperatures of from 50 to 80 0 C coupled with long contact c. times and high concentrations of free acid.

There are no known purification processes for the removal of all foreign metals from the black solution to be hydrolyzed. Accordingly, the processes for the hydrolysis of dissolved titanylsulfate with precipitation of titanium oxide hydrate are always carried out in the presence of relatively high concentrations of foreign metals, such as iron, manganese, vanadium, 35 chromium, niobium, aluminium and magnesium.

Le A 24 760 ~~YY-arr~ln ti 3 In precipitation reactions such as these, it is known that small quantities of the coloring metals mentioned above are always co-precipitated in hydroxide or oxide hydrate form and/or may be adsorbed onto the precipitated titanium oxide hydrate. This results in a very elaborate washing process of the obtained deposits after filtration to remove the mother liquor of the hydrolysis reaction (so-called "thin acid") in which foreign metal ions are accumulated and which generally contains around to 30% sulfuric acid. This washing process is generally carried out under nascent conditions over several stages using very large quantities of water with intermediate bleaching steps to redissolve the impurities containing foreign metals.

It is known from European Application 90,692 that Ti IV ions can be recovered from aqueous solutions containing sulfuric acid and more particularly from the thin acid by extraction, with the organic extractant used containing compounds from the group of phosphonic acid diesters, phosphinic acid monoesters and phosphine oxides. To ensure an effective extract ion of the titanium content it is essential that the aqueous solution to be extracted should be highly concentrated before extraction br distilling off excess water. In the case of the black solution, however, this is not readily possible on account of the spontaneous hydrolysis to be ex- 30 pected and, in addition, leads to a highly viscous, syrupy nature of the concentrate. If this concentrate is used for extraction, large quantities of sulfuric acid are also extracted at the same time. This results

BCO

'C C C.

EC

Le A 24 760 4 4 in solutions of titanylsulfate containing sulfuric acid with an extremely high ratio of sulfuric acid to titanium dioxide (so-called "acid number") in case such an organic extract is stripped with water. It is well known that high-quality TiO 2 white pigment cannot be obtained from solutions having such high acid numbers by standard methods (Ullmanns Enzyklopidie der technischen Chemie, 4th Edition, Vol. 18, pages 576).

In addition, it is known from German 2,620,065 that Ti IV ions can also be extracted from the TiO 2 thin acid with organic solvent mixtures containing phosphonic acid monoesters and/or phosphoric acid diesters. Unfortunately, such extraction processes lead to extract phases from which the titanium can no longer be stripped with water and/or sulfuric acid. The re-extraction can only be carried out by precipitation with ammoniacal aqueous S: 20 solutions under simultaneous conversion of the organic phosphoric acid into the partly water-soluble NH4+-form.

;However, precipitation reactions in the presence of large quantities of organic components lead to organically heavily contaminated deposits which are often 25 difficult to filter and from which it is not possible to obtain high-quality TiO 2 BRIEF DESCRIPTION OF THE INVENTION S 30 The object of the present invention is to provide c a process for the production of titanium dioxide by the sulfate method which can be economically processed on an industrial scale and which is not attended by any of c C the above-described disadvantages of known processes.

Le A 24 760 I

I

5 In particular, the invention enables conversion of the black solution heavily laden with foreign ions into a hydrolyzable TiOSO 4 solution substantially free from foreign metal salts, so that the precipitation of titanium oxide hydrate may be carried out in the virtual absence of contaminating foreign metal ions.

A process has now been found which enables the black solution laden with foreign metal ions to be divided up into its components by extraction with an organic extractant. Re-extraction of the organic extract phase formed with water and/or a dilute aqueous sulfuric acid results in further separation. This process yields a substantially titanium-free aqueous sulfuric acid rich in foreign metal salts and, a concentrated sulfuricacid-containing titanylsulfate solution free from foreign metal salts which is suitable for the hydrolysis step to obtain TiO 2 In fact it has been found that substantially quantitative extraction of the titanylsulfate from the black solution may readily be obtained and that the selectivity of the extraction of titanylsulfate over sulfuric acid can significantly be increased providing extractants containing suitable organo-phosphorous compounds are contacted before and/or during extraction of the black solution with a medium-high and/or high-concentrated sulfuric acid optionally containing metal salts in such a way that extraction of the titanylsul- 30 fate may now be carried out at a significantly lower acid level.

2~i 2 C CC ta C C ftc f C cc Le A 24 760 I r~ 6- BRIEF DESCRIPTION OF THE DRAWING The Figure of the drawing is a flow chart illustrating the sequence of manipulative steps of one embodiment of this invention.

DETAILED DESCRIPTION OF THE INVENTION 4iL

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$4 I r 4 CI1 I 4: r 4a 4.

Accordingly, the present invention relates to a process for the production of high-quality titanium dioxide by the sulfuric acid digestion method comprising the steps of reacting ilmenite and/or titanium-containing slags with highly concentrated sulfuric acid, dissolving the solid digestion masses with aqueous sulfuric acid containing metal sulfates and, optionally, water, reducing the trivalent iron and separating off the in- 20 soluble starting material to obtain a sulfuric-acid-containing titanylsulfate solution rich in foreign metal salts (hereinafter referred to as the black solution), hydrolyzing the black solution with subsequent separation of the titanium oxide hydrate precipitated, washing intensively with water, drying and, optionally, calcining, whereby the black solution is contacted before hydrolysis with an organic medium hereinafter referred to as the "extractant", and re-extraction, hereinafter referred to as "stripping", of the organic phase formed with water and/or an aqueous solution containing sulfuric acid and/or titanylsulfate with ;ecycling of the organic phase obtained to the extraction stage, the sulfuric acid containing metal sulfates which remains after Le A 24 760 6h- 7 the extraction step, hereinafter referred to as the "extraction-thin acid", being used to dissolve the solid digestion mass.

The extractant used for the separation between titanium and foreign metals contains one or more organophosphorus compounds corresponding to the following general formula Rm(R'0)nP= 0 in which R represents straight-chain or branched-chain alkyl groups, R' represents alkyl groups R or even optionally substituted aryl groups, R and/or R' optionally contain heteroatoms such as, e 20 for example, oxygen, halogen, phosphorus, nitrogen, a* m may assume values of 1, 2 or 3 and e n may assume values of 0, 1 or 2, m n 3, S 25 and containing in all at least 12 carbon atoms, together with 3 to 15% by weight water.

Representative examples of these organophosphorus e compounds are tributyl phosphine oxide, trioctyl phos- Sphine oxide, butyl dibutylphosphonate, dibutyl butyl- S 30 phosphonate, dibutyl isobutylphosphonate, diisobutyl butylphosphonate, diisobutyl isobutylphosphonate and dic (2-ethylhexyl)-2-ethylhexylphosphonate.

Le A 24 _760 8 The organic extractant may also contain a diluent.

Suitable diluents are aromatic, aliphatic and naphthenic hydrocarbons optionally containing heteroatoms, such as for example oxygen, halogen, phosphorus. To be suitable for use in accordance with the invention, the diluent must be chemically inert and substantially insoluble in water and, when the extractant becomes charged with titanylsulfate and/or sulfuric acid, should not lead to any separation of the organic extract or to emulsion formation.

Finally, the extractant to be used for the extrac- 1 5 tion of titanylsulfate from the black solution may also contain sulfuric acid and/or titanylsulfate, for example as residues after re-extraction, optionally with subsequent aftertreatment, of the organic extract phase containing titanylsulfate and sulfuric acid or after pre- 0*e 20 treatment of the extractant with an aqueous solution Oco, containing sulfuric acid and, optionally metal salts, aont The organophosphorus compounds to be used in accordance with the invention are preferably used in dissolved form, Thus, the trialkyl phosphine oxides corresponding to the above formula are generally relatively low-melting solids and, accordingly, are generally dissolved in a liquid organophosphorus compound correspon-

S

c ding to the above-general formula and/or in an organic C diluent. By contrast, the alkyl phosphinates and the dialkyl phosphonates are generally more or less viscous liquids and, accordingly, may not only be used in combi-

S

c nation with another of the above-mentioned organophosphorus compounds and/or with an organic diluent, but also in undiluted form, depending upon viscosity.

Le A 24 760 9 The concentration of organic phosphorus compounds corresponding to the above general formula in the extractant may vary within wide limits and more especially between 5 and 95% by weight. In practice, however, concentrations of from about 35 to 90% by weight are preferred. The maximum charging of the organic phase with TiOSo 4 and/or sulfuric acid naturally decreases with increasing diluent content. In some cases, the organic extract may even separate into an upper phase rich in diluent and a lower phase poorer in diluent. Extractants co..raining at least 35% by weight of one or more dialkyl phosphonates have proved to be particularly suitable.

The ratio of extractant to black solution required for the quantitative extraction of TiOS04 is of course dependent both on the concentration of organophosphorus compounds corresponding to the above general formula in 'av 20 the extractant and on the TiOSO 4 content of the solution ocae to be extracted. The extractant used preferably contains on: from 1 to 5 moles of the organophosphorus compounds acncording to the invention per mole TiOS04 in the solution a to be extracted.

S 25 An important feature of the process according to the invention is that the concentration of sulfuric acid required for effective extraction of the titanium is adjusted by dissolving the solid digestion mass with c'c extraction thin acid and/or by partly charging the extractant with sulfuric acid before and/or during extraction of the black solution to increase the extractability of the titanium.

c c Ce.C Le A 24 760

_I

r~ i 10 Another feature of the process according to the invention is that the extraction thin acid, which corresponds both quantitatively and qualitatively to the thin acid of the conventional process, is recycled with- |i out further concentration as a medium- and/or highconcentrated sulfuric acid to the digestion reaction to dissolve the solid digestion mass.

In this embodiment, a solution containing tiLanylsulfate is obtained in which the ratio of sulfuric acid to TiO 2 hereinafter referred to as the acid number, is extremely high so that a black solution of this kind can tion thin acid recycled in accordance with the invention may vary within wide limits and, more especially, between 10 and 90%. In practice, however, the quantity i i will be limited by the solubility of iron(II) sulfate and other foreign metal sulfates and is preferably between 50 and 85%: based on the total extraction-thin acid.

'In one embodiment, the extractant is contacted with cc "a sulfuric acid of preferably medium and/or high concen- Sc 25 tration optionally containing metal salts in order to obtain a dilute or medium-high concentrated aqueous sulfuric acid solution and an organic phase partly charged i'

C

:E with sulfuric acid, this organic phase subsequently Sc. being used as extractant for the solvent extraction of titanylsulfate and, optionally, sulfuric acid from the black solution, *In another embodiment of the invention, optionally combined with the embodiment jLut described, a sulfuric c acid of medium and/or high concentration optionally con- 35 taining metal salts is introduced during the multistage Le A 24 760 ~...~riir~scirrr;.r_.ric~r ~~"UI~Ctll( 3 11 C Z r CI C C C C Cc

C

C t CC Ci C CC C C extraction of titanylsulfate and/or sulfuric acid. This S is done between the first and last stages and preferably over several stages, for example in several mixersettler stages.

The quantity of sulfuric acid required to charge the extractant with sulfuric acid is of course dependent upon the extractability of the sulfuric acid which increases with increasing concentration of free sulfuric acid in the solution to be extracted. In practice, therefore, concentrations of from 40 to 96% by weight

H

2

SO

4 are preferred for the sulfuric acid solution optionally containing metal salts to be used in accordance with the invention.

Depending on the content of this acid, the quantity is selected so that from 0.1 to 1 mole and preferably from 0.2 to 0.8 mole sulfuric acid is used per mole of the organophosphorus compounds according to the invention in the extractant.

The recycling of the extraction thin acid to the digestion reac-ion of titanium-containing slags and/or ilmenite to produce a black solution of high acid number has several advantages.

Thus, it is possible in this way to reduce considerably the quantity of sulfuric acid required for substantially quantitative extraction of the titanylsulfate.

Another advantage is that, parallel with the abovementioned reduction in the quantity of sulfuric acid required, an increase is obtained in the selectivity of the extraction of titanium, particularly over sulfuric Le A 24 760

L

12 acid and vanadium, leading after re-extraction to TiOSO 4 solutions having significantly lower acid numbers and vanadium levels.

In this embodiment, the concentration of green salt will increase further, particularly in slag-based digestion processes, so that green salt will have to be crystallized from the black solution under these conditions. In practice, however, iron concentrations of from 2 to 4% by weight and from 5 to 7% by weight are respectively obtained for slag and ilmenite black solutions.

Because titanylsulfate-containing solutions with extremely high acid numbers are present, it is an important advantage of the invention that part of the iron present in the black solution may be removed as iron(II) sulfate by cooling during and/or after the extraction of titanylsulfate. In practice, the aqueous solution containing iron sulfate and foreign metals, but free from titanylsulfate, is cooled in several successive stages with simultaneous precipitation of iron(II) sulfate.

The number of stages varies mainly between 1 and 3 and is preferably 2. The cooling temperature is advantageously between 4 and 25 0 C and preferably between 7 and 150 C.

A suspensidn of iron(II) sulfate accumulates, con- 'o taining about 65 to 75% of the total iron content of the black solution and being contaminated with only up to about 0.6% by weight of foreign metals in salt form, mainly magnesium, manganese, aluminium and titanium in ppm level concentrations, Le A 24 760

I

13 The aqueous sulfuric acid solution which is obtained after the filtration of iron(II) sulfate is returned into the extraction stage.

In another embodiment, the iron(II) sulfate which accumulates during and/or after extraction is washed with extraction-thin acid and/or recrystallized before the extraction-thin acid is returned to the digestion reaction, The ratio of extraction-thin acid to iron(II) sulfate required in this embodiment varies from 5:1 to 1:1 and, more particularly, is 2:1, The iron(II) sulfate purified in this way may readily be processed.

Besides titanylsulfate and sulfuric acid, the extract phase emanating from the above-described extraction process also contains from 4 to 15% by weight dissolved water and is generally contaminated with up to about 0.1% by weight of foreign metals in salt form, primarily Fe and also Al, Mg, Mn, V, Cr in ppm level concentrations. Accordingly, another feature of the present invention is that the extract phase which is obtained during extraction of the black solution is subjected before stripping to intermediate washing, hereinafter referred to as "scrubbing", with water and/or an aqueous solution containing sulfuric acid and/or titanylsulfate.

The scrubbing step produces, on the one hand, an organic phase containing titanylsulfate and sulfuric acid which is substantially free from metal salts and, on the other hand, an aqueous sulfuric acid solution .i ct B r r c c id t' i

B

ii Le A 24 760 ~pihnaulxr 14 0 0000 O 0 0 0 00 a 00 0 o Q 0 o o a o 0 Quo o oo 0 0 0 0 O t-- 00 o 0 Q 0o0 00 0 a O 00 containing foreign metal salts and, optionally, titanium which is preferably returned to the extraction of the black solution to recover the titanium content.

The scrubbing step has a very good cleaning effect for quantitative ratios of scrubbing liquid to organic extract of from 1:50 to 1:5 and more especially from 1:30 to 1:10 and for sulfuric acid concentrations in the scrubbing liquid used of from 0 to 40% by weight and preferably from 0 to 25% by weight. If the quantity and concentration of the sulfuric acid solution used both in the extraction stage and in the scrubbing step are selected so that the aqueous solution obtained in the scrubbing contains less than 40% by weight of free sulfuric acid, part of the titanylsulfate is transferred to the aqueous solution together with the foreign metals and, optionally part of the sulfuric acid. The titanium 20 may be recovered from such a solution by recycling to the extraction of the black solution.

The organic phase freed from foreign metal salts which is obtained during the scrubbing step is then subjected to re-extraction ("stripping") by washing with 25 water and/or a dilute aqueous solution containing sulfuric acid and/or titanylsulfate. This re-extraction or stripping step produces on the one hand a TiOSO 4 solution containing sulfuric acid, but substantially free from foreign metal salts and, on the other hand, an 30 organic phase largely freed from titanylsulfate and sulfuric acid. The concentration of titanylsulfate in the aqueous phase obtained depends upon the quantitative ratio of stripping liquid to organic phase. If this ratio is adjusted to between 1:10 and 1:i, TiOS04 concentrations of from 10 to 45% by weight are generally obtained.

Le A 24 760 15 If it is desired to obtain highly concentrated, for example 30 to 45% by weight, TiOSO 4 solutions, the stripped organic phase generally contains residual concentrations of from 0.3 to 3% by weight TiOS0 4 If an organic phase such as this, containing residual titanium, is returned to the extraction stage, the titanium content may be partly or completely transferred to the aqueous phase coming into contact therewith.

Accordingly, it can be of advantage to recover the residual titanium from the stripped organic phase, for which purpose the stripped organic phase is additionally scrubbed with water and/or dilute aqueous sulfuric acid optionally containing metal salts in a quantitative ratio of scrubbing liquid to organic phase of from 1:20 to 1:1. The organic extractant obtained in this step generally contains less than 0.2% by weight TiOSO 4 and may be returned to the extraction stage. The dilute aqueous scrubbing water which contains titanylsulfate and, in most cases, sulfuric acid as well may be used with advantage as scrubbing liquid both in the scrubbing step and in the re-extraction step.

Accordingly, the present invention essentially involves several solvent extractions combined with one another: an extraction, optionally in several steps, in which titanylsulfate and sulfuric acid are transferred to an organic medium, optionally a cooling crystallization stage to remove the iron(II) sulfate present, optionally a scrubbing stage to remove the co-entrained foreign metal salts and part of the co-extracted sulfuric acid and a re-extraction stage in which the titanylsulfate and the sulfuric acid are largely stripped Le A 24 760 16 off and, optionally, an aftertreatment of the stripped organic phase to recover all the titanium.

In the process according to the invention, a TiOS04 solution substantially free from metal salts is obtained on the one hand through the purification of the black solution by titanium solvent extraction and may be subsequently worked up into TiO 2 pigments by hydrolysis and calcination. On the other hand, a sulfuric acid solution substantially free from titanium is obtained which contains the full foreign metal salt content of the black solution used, but which may be recycled to the digestion reaction largely without further concentration steps to dissolve the digestion mass. In addition, an iron(II) sulfate suitable for example for the production of iron oxide pigments is also obtained. Accordingly, the dilute sulfuric acid solution (thin acid) which is 20 obtained during the hydrolysis step is substantially free from foreign metal ions. The titanium content of o this solution may be completely recovered with the sulo°ao furic acid by concentration and recycling, for example ot" c to the digestion reaction.

ts_ 25 If the Ti02 is not to be used as pigment, the calcination step may of course be omitted.

The process according to the invention is particut larly suitable for continuous working. Accordingly, it is possible to use any extraction apparatus built on the tc countercurrent principle, more especially extraction tr columns and multistage mixer/settler combinations. The theoretical number of stages under economically optimal conditions is about 5 to 10 for the combination of the Stitanylsulfate and sulfuric acid extraction, 2 to 4 for Le A 24 760 17the scrubbing step, 2 to 6 for the re-extraction step and 1 to 4 for the aftertreatment. The crystallization of the iron(II) sulfate may be carried out in suitable apparatus for cooling crystallization or vacuum crystallization.

The component processes described above may all be carried out at temperatures in the range from about to about 70 0 C. At higher temperatures, the danger of spontaneous hydrolysis of the titanylsulfate increases.

For practical reasons, in ilmenite- or slag-based digestion processes with recycling of the extraction thin acid, it is advisable to carry out the extraction of titanylsulfate and, optionally, sulfuric acid at at least 35 0 C to avoid premature separation of crystalline iron sulfate from the black solution to be used and, optionally, from the various aqueous phases of the process rich in iron sulfate. Only the cooling crystallization fits step should be carried out at lower temperatures.

In the production of TiO 2 pigments, the process according to the invention affords several advantages over conventional processes. The invention provides a process by means of which it is possible on an industrial scale to produce TiOSO 4 solutions of high titanium content which are substantially free from foreign metal salts and which have acid numbers below 2.3 or even below 1.9 with titanium yields of up to 99.5% going out from black solutions both of high and of low TiOSO 4 content and an extremely high acid number of from 3 to Le A 24 760 7 1 I f 18 Analytical composition of the TiOSO 4 solution TiOS0 4

H

2 S0 4 free Acid number Fe Al Mg Mn

V

30 to 45% by weight 10 to 20% by weight 1.7 to 2.3 (10 ppm 5 ppm 5 ppm 5 ppm (30 ppm ppm 'Il I I TiOSO 4 solutions such as these can be hydrolyzed and, after calcination of the titanium oxide hydrate, lead to particularly high-quality TiO 2 irrespective of the foreign metal content of the used titanium containing raw materials.

Another advantage is that the thin acid which accumulates during hydrolysis is substantially free from foreign metals. Accordingly, the titanium content of this aqueous acid may be completely recovered by concentration and recycling of the highly concentrated sulfuric acid obtained, for example to the digestion reaction.

A preferred embodiment of the present invention is described in the following with reference to the Figure of the accompanying drawing, in which the reference numerals used have the following meanings: 1.

2.

3.

countercurrent extraction apparatus countercurrent scrubbing apparatus countercurrent stripping apparatus Le A 24 760 f I 19 4. countercurrent aftertreatment apparatus 5. apparatus for the cooling crystallization of iron sulfate 6. pipe for the black solution 7. pipe for medium- high and/or concentrated sulfuric acid 8. pipe for the extracted iron-sulfate-containing sulfuric acid solution 9. pipe for the filtrate from the crystallization of iron sulfate pipe for iron sulfate ii. pipe for the extracted sulfuric acid solution containing foreign metal salts 12. pipe for the aqueous phase obtained during scrubbing 13. pipe for the scrubbing liquid 14, pipe for the stripping liquid a 15. pipe for the washing water obtained during the o n aftertreatment S16. pipe for the TiOSO 4 solution obtained during F stripping S 25 17. pipes for water 18. pipes for water 19. pipe for the extract phase pipe for the organic scrubbing phase 21. pipe for the organic stripping phase 22, pipe for the circulating extractant.

I i It Le A 24 760 rvr 20 This embodiment of the process according to the invention is carried out as follows: The black solution 6 to be extracted and the aqueous titanium-containing phase 12 obtained during scrubbing are contacted with the organic extractant 22 in a multistage countercurrent apparatus 1. During the extraction, a medium- and/or high-concentrated sulfuric acid is optionally introduced in several partial streams 7 so that the extractant is charged with sulfuric acid in several stages to a sufficiently high level to guarantee a selective and, at the same time, quantitative extraction. A sulfuric acid solution 8 substantially free from titanium, but containing iron-II-sulfate and foreign metal salts is obtained and is separated in a multistage cooling apparatus 5 on the one hand into crystalline iron sulfate 10 and, on the other hand, into a sulfuric acid solution 9 containing foreign metal salts which is recycled to the countercurrent apparatus 1. A substantially titanium-free sulfuric acid solution 11 containing foreign metal salts is obtained.

In another multistage countercurrent apparatus 2, 25 the organic extract 19 which is obtained during extraction is subjected to scrubbing with an aqueous liquid 13, whereby an organic phase 20 substantially free from foreign metal salts is obtained.

The titanylsulfate and the sulfuric acid are 30 stripped therefrom with an aqueous liquid 14 in a multistage countercurrent apparatus 3. An organic phase 21 substantially free from titanylsulfate and sulfuric acid is obtained, which in a final step, is aftertreated with C

SC

L.CC

'CIC

C Le A 24 760

L,

-21water in a multistage countercurrent apparatus 4. The water 15 which is obtained during this aftertreatment is used as stripping liquid and/or as scrubbing liquid and the aftertreated organic phase is returned to the extraction stage 1 via 22, The following Examples are intended to illustrate the process according to the invention without limiting it in any way. The black solutions used for the Examples have the composition shown in Table 1.

Table 1 comnosition of the black solutions A B C D) E F .4 4, 4 4

H-

2 S0 4 free TiO 2 Fe Al 25 Mg

V

Cr Mn by weight) by weight) by weight) by weight) by weight) (ppm) (ppm) (ppm) 11.3 12.0 9.6 24.1 9.17 15.3 15.7 15.3 10.3 10.3 2.00 1,95 1,89 2,80 7.2 0.58 0.29 0.97 0.34 1100 411 355 249 449 1040 11 .16 8.70 6.490 0.*28 0,.35 390 236 1870 Le A 24 760 t 22 EXAMPLE 1 In 4 mixer/settler stages, a mixture of 1000 parts by weight black solution A and 1500 parts by weight

H

2 S0 4 was contacted in countercurrent at 50°C with 2095 parts by weight water-saturated dibutyl butylphosphonate (DBBP). 1684 parts by weight extracted aqueous phase and 2911 parts by weight extract phase having the following composition were obtained: Aqueous phase Extract phase

H

2

SO

4 by weight) 33.00 16.8 TiO 2 by weight) 0.090 5.20 Acid number Fe (ppm) 323 V (ppm) 231 Cr (ppm) The titanium extraction yield is 99.0%.

EXAMPLE 2 This Example shows that the selectivity of the extraction of titanium with respect to sulfuric acid and foreign metal ions can be improved by reducing the concentration of H 2 S0 4 in the solution to be extracted.

A mixture of 1000 parts by weight black solution B and 1216 parts by weight 52% sulfuric acid was extracted countercurrently at 40°C with 2097 parts by weight water-saturated DBBP in 8 mixer/settler stages.

1574 parts by weight extracted aqueous phase and 2739 S 35 parts by weight extract phase were obtained.

Le A 24 760

-C-

23 The analytical data below show that, compared with Example 1, the extract phase has a somewhat lower coni centration of sulfuric acid (acid number 3.8 as against and foreign metals. The titanium yield comprises V 96.7%.

V Aqueous phase Extract phase

H

2 S0 4 free by weight) 22.8 13.3 Ti02 by weight) 0.33 5.25 Acid number 3.8 SFe (ppm) 222 V (ppm) 135 SCr (ppm) 18 Ij 20 EXAMPLE 3 The selectivity of the extraction of titanium may also be increased by scrubbing of the extract phase.

1000 parts by weight black solution C were mixed f with 480 parts by weight of the aqueous phase II from the scrubbing step and 519 parts by weight 80% sulfuric acid. This mixture was contacted in countercurrent at 0 C with 2014 parts by weight water-saturated DBBP in 6 mixer/settler stages, giving on the one hand 1240 parts by weight extracted aqueous phase I and, on the other hand, 2773 parts by weight extract phase.

I The extract phase was subjected to scrubbing by a 4-stage extraction in countercurrent with 325 parts by weight water, resulting in the formation of 480 parts by weight aqueous phase II, which was used in the extraction of the black solution, and 2618 parts by weight organic phase III.

Le A 24 760 -L i

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-24 Phases I and III had the following analytical data: Aqueous Organic phase I phase III from extraction from scrubbing

H

2 S0 4 free by weight) 23.9 8.1 Ti02 by weight) 0.101 5.86 Acid number 2.6 Fe (ppm) (2 V (ppm) 71 Cr (ppm) By combining the extraction process with a scrubbing step, it is possible to obtain organic Ti-containing phases which, by comparison with Example 2, are characterized by comparatively low concentrations of sulfuric acid and foreign metal ions.

The titanium extraction yield is substantially quantitative despite the greatly reduced input of H 2 S0 4 However, if the input of the 80% sulfuric acid is reduced even further, the yield decreases without any significant increase in selectivity with respect to sulfuric acid: 80% H 2 S0 4 Residual TiO 2 TiO 2 yield Acid number (parts by in phase I of phase III weight) 519 0.101 by weight 99.2% 2.6 472 0.144 by weight 98.8% 2.8 456 0.272 by weight 97.7% Le A 24 760

I_

I

25 EXAMPLE 4 The extraction thin acid is used as solvent for the solid slag digestion mass.

A black solution having an extremely high acid number is thus obtained, resulting in a considerable increase in selectivity with respect to sulfuric acid and vanadium, Black solution D corresponds to a digested slag dissolved in extraction thin acid (aqueous phase I from extraction) and is characterized by a high acid number.

1000 parts by weight black solution D are contacted in countercurrent at 40 0 C in a 7-stage mixer/settler battery with 1952 parts by weight of an extractant having the following composition: DBBP 60.8 by weight Diluent free from aromatics 34.5 by weight TiO 2 0.015 by weight

H

2 0 4.5 by weight During the extraction, 479 parts by weight aqueous phase II from the scrubbing step are introduced into stage 6 and 77 parts by weight 80% H 2

SO

4 into stage 1057 parts by weight extracted aqueous phase I and 2403 parts by weight extract phase were obtained.

The extract phase is then scrubbed over 4 stages using 380 parts by weight of an aqueous solution containing 7.7% by weight TiO 2 and 15% by weight free sulfuric acid. This results in the formation of 479 parts Le A 24 760 i i.--*iuri~~t;=..ci~i~Ur7ca; I 26 by weight of an aqueous phase II, which was used in 5 stage 6 of the extraction process, and 2305 parts by weight of an organic phase III.

Phases I and III had the following analytical data: Aqueous phase I from extraction Organic phase III from scrubbing H2GO4 free by weight Ti0 2 by weight Acid number Fe by weight Al by weight Mg by weight V ppm Cr ppm Mn ppm 24.05 0.12 2.82 0.26 0.67 690 234 370 4.39 5.54 2.55 <0.0010 0.0019 0.0077 The residual TiO 2 content of the extracted aqueous phase I is thus 0.12% by weight, corresponding to a yield of 98.8%, based on the black solution.

EXAMPLE 2707 parts by weight of an organic phase III having the following composition: i 1 r a rittr r Le A 24 760

I

27

DBBP

Diluent free from aromatics

H

2 0

H

2

SO

4 free TiO 2 Acid number Fe Al Mg

V

Cr Mn approx.

approx.

49 by weight 28 by weight 7 by weight 6.31 by weight 4.14 by weight 2.72 by weight (10 ppm 5 ppm 5 ppm 5 ppm 6 ppm 1 ppm emanating from extraction of the ilmenite black solution E with subsequent scrubbing, were stripped countercurrently at 50 0 C with 277 parts by weight water in a 3-stage mixer/settler battery, resulting in the formation on the one hand of a 621 part by weight TiOSO 4 solution IV and, on the other hand, a 2363 part by weight organic phase. The organic phase was then washed with 172 parts by weight water over 4 stages, again at 500C, with formation of 288 parts by weight washing water V and 2247 parts by weight organic phase VI.

Le A 24 760 1 i

I

28

H

2

SO

4 free by weight TiO 2 by weight Acid number Fe ppm Al ppm Mg ppm V ppm TiOSO 4 solution

IV

14.54 17.63 2.02 (10 5 5 6 7 S1 Washing water

V

17.83 3.83 1 1 1 Organic phase

VI

0.11 0.05 Cr Mn ppm ppm Accordingly, the organic phase VI may readily be reused as extractant in the extraction of the black solution while the washing water V may be used both as srubbing liquid and as stripping liquid to recover the titanium content.

Finally, the TiOSO 4 solution IV was worked up by hydrolysis, filtration, washing, drying and calcination into a TiO 2 pigment of particularly high quality which had the following foreign metal contents: 1 I Fe Al Mg 3 ppm (4 ppm (1 ppm

V

Cr 3 ppm 2 ppm Mn (1 ppm TiOSO 4 solutions such as these may also be used for the production of high-purity titanium oxide hydrate or titanium dioxide products which may in turn serve as starting material for the production of inorganic titanates.

Le A 24 760 ~rj;l(n~l ar~- i rarr~-ariin~oI~l 29 EXAMPLE 6 This Example demonstrates that, in the case of black solutions of high iron content, most of the iron content may be recovered as green salt during the extraction of TiOS04.

2620 parts by weight of an organic phase VII having the following composition: DBBP approx. 49 by weight Diluent free from aromatics approx. 28 by weight

H

2 0 approx, 7 by weight H2SO 4 free 14.12 by weight TiO 2 0.37 by weight are contacted in countercurrent in a 4-stage mixer/settler battery with 1338 parts by weight of a black solution F and 424 parts by weight of 80% sulfuric acid, resulting in the formation of, on the one hand, 2691 parts by weight of an organic extract phase and, on the other hand, 1691 parts by weight of an aqueous phase containing iron sulfate.

After cooling at 7 0 C in a 2 stage cooling apparatus, the aqueous phase gives 1691 parts by weight of a suspension containing iron sulfate which is filtered off, giving 244 parts by weight of a crystalline iron sulfate and 1447 parts by weight of an aqueous phase VIII which is returned to the extraction stage.

Le A 24 760 *1! The phase VIII and the iron sulfate have the following analytical data: Fe Ti02

V

Al Mg Mn Cr by weight by weight ppm ppm ppm ppm ppm Iron sulfate Aqueous phase VIII 20.52 1.53 0.064 0.52 19 127 2300 1890 18 The yield of Fe in the iron sulfate corresponds to based on the black solution.

Le A 24 760

Claims

2. A process as claimed in Claim 1, characterized in that part of the extraction thin acid, preferably from to 85% of the total quantity, is recycled to dissolve the solid digestion mass.
3. A process as claimed in Claim 1 or 2, characterized in that, after extraction of titanylsulfate, iron(II) sulfate is crystallized out from aqueous solution obtained by cooling and separated off, and filtrate accumulating being returned to the extraction stage.
4. A process as claimed in one or more of Claims 1 to 3, characterized in that cooling is carried out in 0077h/ABD C) 43~c~ <p A'R o 32 *19 000 0 *oa t 0Qrt 0*00 o 0 4, o a .4. several stages at temperatures of from 4 to 25°C and preferably at temperatures of from 7 to A process as claimed in one or more of Claims 1 to 4, characterized in that the extractant is contacted before and/or during extraction with an at least 40% by weight sulfuric acid optionally containing metal salts.
6. A process as claimed in Claim 1 or 5, characterized in that the extractant contains one: or more organophosphorus compounds corresponding to the following general formula Rm(R'O) P=0 in Which R represents straight-chain or branched-chain alkyl groups R represents alkyl radicals R or even optionally substituted aryl groups, R and/or R" optionally contain heteroatoms, such as for example oxygen, halogen, phosphorus, nitrogen, m may assume values of 1, 2 or 3 and n may assume values of 0, 1 or 2 with m n 3 and containing in all at least 12 carbon atoms, together with from 3 to 15% by weight water.
7. a process as claimed in Claim 6, characterized in that the organophosphorus compounds are diluted with aromatic, aliphatic and/or naphthenic hydrocarbons optionally containing heteroatoms, such as oxygen, halogen or phosphorus.
8. A process as claimed in one or more of Claims 1 to 7, characterized in that the extractant contains from 1 to 5 moles of the organophosphorus compounds per mole titanylsulfate to be extracted.
9. A process as claimed in one or more of Claims 1 to 8, characterized in that the concentration of organo- phosphorus compounds in the extractant is from 5 to 077h/ABD 33 by weight and preferably from 35 to 90% by weight. A process as claimed in onie or more of Claims 5 to 9, characterized in that from 0.1 to 1 mole and preferably from 0.2 to 0.8 mole sulfuric acid.is used per mole organo-phosphorus compound.
11. A process as claimed in one or more of Claims 1 to characterized in that the extract phase accumulating during extraction of the black solution is subjected before stripping to intermediate washing, hereinafter referred to as scrubbing, with water or an aqueous solution containing sulfuric acid or titanylsu.fate. wil 12. A process as claimed in Claim 11, characterized in that the aqueous sulfuric acid solution which accumulates I during scrubbing is recycled to the extraction of the black solution. S' 13. A process as claimed in one or more of Claims 1 to o 12, characterized in that, before it is recycled to the extraction stage, the organic phase largely free from i titanylsulfate and sulfuric acid which accumulates during the stripping step is aftertreated by scrubbing with water and/or a dilute aqueous sulfuric acid solution optionally containing metal salts.
14. A process according to Claim 1 and substantially as :herein described with reference to any one of the foregoing examples thereof. A product produced by the process of any one of the jl preceding claims. DATED this 30th day of May, 1990. BAYER ANTWERPEN N.V. By Its Patent Attorneys ARTHUR S. CAVE CO. 0077h/ABD A7 ^/|bL _I