FI68088C - SAOSOM ADSORPTIONS- OCH SAMLARREAGENS ANVAENDBAR TITANDIOXIDHYDRATBLANDNING - Google Patents

Description

1 68088

Mixture of titanium dioxide hydrate useful as an adsorbent and a collecting reagent

Separated by division of application 791293.

The invention relates to a mixture containing specially structured titanium dioxide hydrate.

The invention is characterized in that the mixture contains more than 20%, expressed as TiO2 and calculated on the total amount of TiO2, of titanium dioxide hydrate, the X-ray diffraction pattern of which is taken at 10 Cu-Ket radiation with principal maxima at 2 (0-24.6 + 0.4 ° and 48 + 0.4 °.

In the thermal hydrolysis of titanium (IV) salt solutions, especially titanium (IV) sulphate solutions, in which, for example, extraction from ilmenite or other titanium ores or other titanium-containing materials with sulfuric acid on a large technical scale produces titanium dioxide pigments. according to the sulphate method, in the presence of suitable hydrolysis nuclei, titanium dioxide hydrate is usually formed, which, for example, has been shown to have an anatase structure by X-ray deflection studies (Gmelins Handbuch der anorganischen Chemie, 8th edition system no. 41 titanium (1951) page Amer. Hope.

25 Soc. part 42 No. 3 (1959) pages 127-133).

If the titanium sulfate solution is hydrolyzed by the addition of alkali, an X-ray amorphous product or a product showing the main X-ray diffraction reflection typical of anatase is usually formed (J. physic. Chein. 44 (1940) 30, pages 1081-1094; J. appi. Chem. 19 (1969), pages 46-51). .

When preparing titanium dioxide pigments from titanium (IV) sulphate solutions, it is supplied to give titanium dioxide hydrate having an anatase or rutile structure. Such titanium dioxide hydrate 35 2 68088 is hereinafter briefly referred to as "anatase hydrate" or rutile hydrate.

When studying the hydrolysis of titanium (IV) sulphate solutions, it has now been found that under certain conditions a certain titanium dioxide hydrate is formed, which differs markedly in physical and chemical properties from anatase hydrate and rutile hydrate. Titanium dioxide hydrate with a special structure was found, which is characterized in that the principal maximum appears at 2 Θ = 24.6 + 0.4 ° and 48 + 0.4 ° in the X-ray diffraction pattern obtained by Cu-K-10 radiation. This new titanium dioxide hydrate is hereinafter briefly referred to as "<£ hydrate",

It is assumed that β-hydrate is formed not only in the hydrolysis of titanium (IV) sulphate solutions, but also in the hydrolysis of solutions containing titanium (IV) salts and other polyvalent anions, for example phosphate ions.

The figure compares the X-ray diffraction pattern of the β-hydrate with known hydrates having an anatase structure and a rutile structure. The angular values given are determined in all cases by means of Cu-Kofc radiation. The figure shows that the ε-hydrate can be distinguished, above all by its main X-ray deflection at 25.6 °, clearly from anatase (main X-ray deflection at 25.4 °) and rutile (main X-ray reflex at 27.4 °). The Brockit comparison showed that ^ -hydrate is also not associated with this modification. It further differs from the titanium dioxide hydrate disclosed in U.S. Patent 2,333,662, called "N-hydrate", which, unlike N-hydrate, has a main X-ray reflection at 22.3 °.

The J-hydrate remains at room temperature for any length of time. Above about 350 ° C it becomes ana-35 again.

3 68088

Unlike anatase hydrate, which is flocculated above a certain particle size in a sulfate solution and can be removed by filtration or centrifugation, the N-hydrate is partitioned from the colloidal sulfate-5 solution and thus cannot be similarly separated from the sulfate solution. However, the β-hydrate can be flocculated with hydrochloric acid or other monovalent union acids or their salts in a sufficient concentration so that it can be separated from the non-hydrolyzed TiO 2 portion or the mother liquor in this way.

Furthermore, the precipitated, separated and washed, moist or dried β-hydrate, unlike other TiO 2 hydrates obtained from titanium sulphate solutions, can be peptized again by adding sulphate ions (especially in the form of sulfuric acid) or other divalent or trivalent anions. After flocculation and separation and washing, the sulfuric acid-containing mother liquor gives more than 30 parts by weight of T1O2 per 100 parts by weight.

Depending on the embodiment of the process, the 20? -Hydrate may be obtained in more or less pure form or as a mixture with other TiO 2 hydrates. A mixture of titanium oxide hydrate containing more than 20%, expressed as titanium dioxide and calculated on the total amount of TiO 2, in the form of titanium dioxide-dihydrate , is very well suited for many purposes, especially as an adsorbent or a collection reagent.

A mixture of titanium dioxide hydrates containing more than 20%, expressed as titanium dioxide and calculated on the total amount of titanium dioxide, of titanium sulphate dihydrate is prepared so that a molar ratio of titanium sulphate with a TiO2 content of up to 150 g / l to a sulfur content of free sulfur : 1 to 1: 2, the concentration of divalent iron is 0 to 1 g of iron per g of 35 titanium dioxide and, if desired, contains trihydric 4 68088 butter titanium, hydrolyzed by heating colloidal titanium dioxide hydrate flocculated by adding monovalent acid or its salt and flocculated titanium dioxide hydrated -5 on contact with the precipitated titanium dioxide hydrate, removed, washed with water to remove iron and other foreign components and, if desired, dried.

Another process for the preparation of a titanium dioxide dihydrate mixture containing more than 20%, expressed as titanium dioxide and calculated on the total amount of TiO2, of 10 f-titanium dioxide hydrate is carried out in such a way that a molar ratio of titanium sulphate with a T1O2 content of 120 to 250 g / l : 1 to 1: 2, divalent iron content 0 to 1 g Fe 15 per g T1O2 and possibly containing trivalent titanium, hydrolysed by heating in the presence of specially structured titanium dioxide hydrate cores, colloidally divided titanium dioxide hydrate flocculated by adding its monovalent acid or and the flocculated titanium dioxide hydrate together with the inseparable titanium dioxide hydrate precipitated prior to flocculation is removed, washed with water to remove iron and other foreign components and, if desired, dried.

25 The advantage of the latter procedure is that, by adding «S-titanium dioxide hydrate cores, solutions with a higher titanium content can be used than if these cores are not used. In particular, solutions which are customary in the production of pigments can be used.

The titanium dioxide hydrate cores are prepared, for example, by adding a portion of the titanium sulfate stock solution in a suitable manner, e.g., by dilution, to the above composition 35 and hydrolyzing by heating, the precipitated titanium dioxide hydrate having anatase structure is first separated is flocculated by adding a monovalent acid or a salt thereof and the flocculated titanium dioxide-5-dihydrate having the ^ structure is removed from the solution and, if desired, washed with water.

The Δ 4 -titanium dioxide hydrate cores can also be added as a colloidal solution, such as that obtained by hydrolysis of the titanium sulfate solution in the preparation of 10β-titanium dioxide hydrate, by first removing the precipitated anatase hydrate titanium dioxide hydrate before adding the monovalent acid or its salt.

The cores are generally added in an amount of 2-20%, calculated as titanium dioxide and based on the TiO2-pi-15 content of the titanium sulphate solution.

The cores can be added either before the hydrolysis of the titanium sulphate solution or at earlier stages of the process, for example during extraction or dissolution of the extraction cake.

The titanium sulphate solution can be obtained in a known manner by extracting ilmenite, but titanium ores, slag or titanium-enriched with sulfuric acid. It is possible to start from a titanium sulphate solution obtained by preparing a titanium dioxide pigment by the sulphate method. If desired, iron can be removed as iron (II) sulfate heptahydrate prior to treatment. It is essential that the titanium sulfate solution contains as few anatase cores as possible. This condition can be met by appropriate measures during extraction, extraction of the cake in solvent, reduction and / or clarification of the extraction solution. Thus, it is preferred that dilute acid be used when dissolving the extraction cake. When dissolving the extraction cake, the temperature should not rise above 60 ° C and when dissolving the extraction cake, no more liquid should be used than is necessary. A clarifier should be used for clarification, which flocculates the dissolved titanium dioxide colloidally. Suitable methods are disclosed, for example, in GB Patent 473,054 and U.S. Patent Nos. 2,413,640 and 2,413,641. A very suitable starting solution is obtained if the titanium sulfate solution prepared in a known manner is clarified with polymeric diethylaminoethyl acrylates or polyacrylamides.

The optimum TiO 2 content of the starting solution is generally determined by the iron content and the sulfur content 10. A stock solution containing 30 g / l of Fe 2+ and having a total sulphate content, calculated on the basis of SO 2, of 250 g / l and containing 0.5 g / l of Ti 2+ ions, has an optimum TiO 2 content of 100 g / l . From such a solution, assuming that the starting solution is practically free of nuclei, it is possible to obtain β-titanium dioxide hydrate cores, if desired, in the form of β-hydrate in yields of up to 90%.

If the iron content of the starting solution is low and / or the ratio of free sulfuric acid to titanium dioxide is low, the optimal TiO 2 concentration shifts to higher values (the term "free sulfuric acid" is conventionally understood as sulfuric acid which is not bound to cations other than titanium in solution).

The appropriate concentration can be adjusted during the extraction 25 and / or subsequent process steps, for example in the removal of ferrous sulphate heptahydrate. On the other hand, the iron content and the sulfuric acid content can be controlled by the quality of the titanium-containing starting material used (ilmenite, T1O2-containing slags, etc.).

The concentration of trivalent titanium formed in the reduction of the starting solution in the solution can be 2 g / l and in some cases even higher to ensure the absence of trivalent iron in the hydrolysis.

The hydrolysis is generally carried out simply by heating the solution to boiling point and maintaining this temperature; in this case, conventional nuclei are not added from the outside before the hydrolysis and are not formed in solution, for example when mixed with water. Only nuclei with an ε-hydrate structure can be added to en-5 nen hydrolysis.

The duration of the heating depends on the concentration of anatase nuclei in the solution, the composition of the solution and / or whether β-hydrate nuclei are added. In general, the yield of β-titanium dioxide hydrate increases as the heating time increases, however, the long heating time is in some cases associated with certain disadvantages, e.g. deterioration in quality. After the addition of the ε-hydrate cores, the composition of the solution can be kept unchanged before the hydrolysis or it can be changed, e.g.

In technically conventional titanium sulphate solutions, the β-hydrate nuclei initially formed or added outside the range of analytical composition of the titanium sulphate solution, which is preferred for spontaneous nucleation, are also further propagated. Since in the technical preparation of titanium dioxide hydrate from sulfuric acid extraction solutions for the formation of β-hydrate the formation of a preferred analytical composition is regularly bypassed, β-hydrate is always formed in small amounts. The amount depends not only on the formation and growth rate of the nuclei of the ί hydrate but also on the number, size and growth rate of the anatase nuclei, i. the kinetics of the competitive anatase hydrate formation reaction.

In hydrolysis, a precipitate often forms in the titanium sulphate solution, which consists mainly of anatase hydrate, while the β-hydrate formed at the same time remains colloidal in solution. If a mixture of titanium dioxide hydrates consisting of both components is to be recovered, the precipitated anatase hydrate is removed only after further treatment of the hydrolyzed solution to co-precipitate s 68088 S-hydrate. flocculation of the hydrate occurs by the addition of a monovalent acid or a salt thereof. Hydrochloric acid is particularly preferred, but highly water-soluble chlorides, e.g. sodium chloride, are also preferred. In general, the addition of monovalent anions requires an amount which gives a concentration in the solution of 1.5 to 8, preferably 4 to 5 moles / liter.

The washing of the precipitated titanium dioxide hydrate takes place in the same way as in the preparation of titanium dioxide pigments, but 10 bleaching steps are not necessarily required.

A preferred embodiment of the preparation of a titanium dioxide hydrate mixture containing more than 20%, expressed as titanium dioxide and calculated on the total amount of TiO2, is that after addition of a monobasic acid or a salt thereof, the or dried.

In nuetralation, SO 2 groups are replaced by OH groups; 20 then the sulfuric acid is removed up to a small amount; at the same time, however, the characteristic structure of JS hydrate is preserved. The neutralization is preferably carried out in aqueous suspension. The neutralized hydrate can then be washed and / or dried. The optimum pH desired in neutralization depends to some extent on the manufacturing conditions of the product and can be easily determined experimentally. Neutralization can be performed both before and after further processing of the product, e.g. before paste formation, drying and granulation. The neutralized product is particularly well suited as an adsorbent or a bulking reagent.

After the addition of the monobasic acid or a salt thereof, the titanium dioxide hydrate flocculated in solution can be thickened by sedimentation before removal from solution. A preferred embodiment of the process is based on the addition of flocculant before the separation of titanium dioxide hydrate flocculated in solution by the addition of a monobasic acid or a salt thereof. The flocculant must be effective in a strongly acidic solution. Suitable flocculants are, for example, polyacrylamides sold for this purpose. The flocculant is preferably added to the thickened suspension by sedimentation. The suspension thus treated can be easily filtered and the separated titanium dioxide hydrate can be easily washed.

When using the mixture according to the invention as an adsorbent, it is expedient to granulate the titanium dioxide-15-dihydrate mixture after it has been separated from the solution.

The granulation can be carried out in a known manner before or after drying, in which case granulation before drying is recommended. The granulation can be carried out, for example, in such a way that the product is formed into a paste or spray-dried, for example by extrusion through a perforated plate. It is essential that no strong shear forces are applied to the paste for extended periods of time, as this adversely affects the mechanical properties of the granulate.

According to one embodiment, the mixture according to the invention is prepared by adding to the titanium dioxide hydrate mixture, before drying, solid, acid-insoluble inorganic or organic substances in amounts of up to 70% by weight, based on the total mixture thus obtained, and then, if desired, after granulation. , dried. In this way, the mechanical and / or adsorption properties and / or the adsorption kinetics of the adsorbent containing <S-titanium dioxide hydrate can be improved. The addition of solids can be done before mixing, flocculating, neutralizing or drying the titanium dioxide hydrate mixture. Suitable fillers are, for example, fillers used, for example, in coatings or other high-surface-area substances (see Ullmanns Encyklopädie der 5 technischen Chemie 3rd edition, Part 13 (1962), pages 814-821 and "Chemische Technologie", published by K. Winnacker and L. Kiichler 3rd Edition Part 2 (1970) pages 539-545). Examples are silicon, mica, asbestos fiber and activated carbon.

A mixture of 10-titanium dioxide hydrate containing more than 20%, based on the total amount of TiO 2, of titanium dioxide, 4-titanium dioxide hydrate, has an excellent adsorption capacity. In particular, it can be used as an adsorbent or a collecting reagent for recovering uranium-15 and / or other elements from dilute aqueous solutions containing these elements. It has been found that β-hydrate is superior to titanium dioxide hydrates known to date due to its inherent adsorption capacity. Therefore, it is very useful as a uranium collection reagent in recovering it from seawater.

The following examples illustrate the invention in more detail.

Example 1 25 A vessel with an external masonry and a leaded heating piping and a leaded stirrer with a volume of 1,000 liters was charged with 200 liters of iron (II) sulfate heptahydrate by separating most of the iron-purified ilmenite-30 leach solution containing 150 g / l. TiO 2, 45 g / l Fe 2+, 375 g / l total sulphate calculated as SO 2 and 0.75 3+ 4 g / l Ti and diluted with water to 300 liters. The composition of the solution was the analytical composition shown on page 6. The contents of the vessel were then heated to boiling point 35 with stirring indirectly through the heating piping through 11,68088 steam and kept at the boiling point for about 30 minutes. The steam supply was then stopped and the mixture was diluted with cold water to 600 liters, dropping the temperature to 62 ° C. The presence of a small amount of anatase nuclei in the extraction solution could not be avoided, so that a certain amount of anatase hydrate was formed in the hydrolysis, which, however, was only about 5% of the total amount of titanium dioxide. This anatase hydrate separated from the solution during standing for 70 hours.

The above, only slightly turbid brown solution containing ε-hydrate of about 50% of the total amount of TiO 2 in colloidal distribution was removed. To 500 liters of this solution was added a second vessel with a masonry and rubberized stirrer with a volume of 15,000 liters, stirring for 60 minutes with 400 liters of 30% hydrochloric acid. In this case, the β-hydrate flocculated and, after standing overnight, the mother liquor at the top was removed with a spatula, thickening the remaining mixture to about four times the solids content. Immediately before filtration, this suspension was stirred with 20 ml / l of a 2% aqueous solution of commercial polyacrylamide (Tiofloc B 21). The ^ hydrate could then be filtered and washed without difficulty.

The iron-washed filter cakes were kneaded with water in the cold to mix well and 10% sodium hydroxide solution was added slowly until pH 7. Stirring was continued for another 10 minutes and the pH was readjusted to 7 by the addition of 30 ml of fresh sodium hydroxide solution. The suspension was then well flocculated and could be filtered and washed without difficulty without the addition of a flocculant. The paste thus obtained was pressed by means of a press equipped with a perforated plate (hole diameter 5 mm)

35 rods and the rods were dried at 110 ° C for 12 hours

i2 6 80 8 8 li at temperature. The rods were then reduced to granules with a particle diameter of about 3.5 mm. As a result of the preforming, only a small amount of fine material was formed. About 10.5 kg of dried titanium dioxide-5 dihydrate with a TiO 2 content of about 75% was obtained; this corresponded to a yield of about 26% based on the amount of TiO 2 in the starting solution.

X-ray diffraction studies of the obtained product did not show anastase reflections, and thus the product was practically pure ε-hydrate.

Example 2 The same ilmenite extraction solution as in Example 1 was used. A portion of this solution (30 L) was diluted as in Example 1 with water to a TiO 2 ~ pi-15 content of 100 g / L, heated to boiling point and kept at reflux for 20 minutes. At this time, about 30% of the titanium in solution was hydrolyzed to the β-hydrate.

Another portion of the extraction solution was evaporated in vacuo to a TiO 2 content of 250 g / l. One hundred liters of this concentrated solution was mixed with the β-hydrate-containing reaction mixture contained in the first part of the ilmenite extract solution, the mixture was heated to reflux with stirring and kept at boiling point for 60 minutes. At that time, about 30% of the total TiO 2 was hydrolyzed, of which 25% was hydrate and 5% was anatase hydrate.

The reaction mixture was diluted with water to 600 liters, whereupon the temperature dropped below 50 ° C. Removal of anatase-30 hydrate and flocculation and separation of β-hydrate were performed as in Example 1. Also in the product thus obtained, no anatase reflection could be detected, but only β-hydrate reflection.