FI69443C - REFERENCE TO A STRUCTURE WITH A SPECIFIC STRUCTURE OF A BLACKING UNIT - Google Patents

Description

1 69443

A process for preparing a specially structured titanium dioxide hydrate or a mixture containing it

Separated by division of application 791293.

5

The invention relates to a process for the preparation of ε-titanium dioxide hydrate or to a mixture containing more than 20%, expressed as TiO 2 and based on the total amount of TiO 2, of said β-titanium-10 dioxyhydrate having a principal maximum at 20 in the X-ray diffraction pattern of Cu-K 4. = 24.6 + 0.4 ° and 48 + 0.4 °.

The invention is characterized in that a titanium sulphate solution with a TiO 2 content of 120 to 250 g / l, a molar ratio of TiO 2 to free sulfuric acid of 1: 1 to 1: 2, a divalent iron content of 0 to 1 g Fe per gram of titanium dioxide and optionally containing trivalent titanium, hydrolysed by heating in the presence of <P-titanium dioxide dihydrate cores, separating the precipitated titanium dioxide hydrate if necessary, flocculating the colloidal titanium dioxide hydrate in solution with , washed with water to remove iron and other foreign matter and, if desired, dried.

In the thermal hydrolysis of titanium (IV) salt solutions, especially titanium-30 (IV) sulphate solutions, in which, for example, titanium dioxide pigments are prepared on a large technical scale by extraction from ilmenite or other titanium ores or other titanium-containing materials on sulfur scale. According to the sulphate method, in the presence of suitable hydrolysis nuclei, 2 69443 are usually formed titanium dioxide hydrate, which, for example, have been shown to have an anatase structure by X-ray diffraction studies (Gmelins Handbuch der anorganischen Chemie, 8th edition of System No. 1951). 229; J. Amer. Ceram. 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. Chem. 44 (1940) pages 1081-1094; J. appi. Chem. 19 (1969) pages 46-51). .

The preparation of titanium dioxide pigments from titanium (IV) sulphate solutions is carried out in such a way as to obtain titanium dioxide hydrate having an anatase or rutile structure. Such titanium dioxide hydrate 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 <4-25 radiation. This new titanium dioxide hydrate is hereinafter referred to as "^ hydrate" for short.

It is assumed that the E-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, e.g. phosphate ions.

The figure compares the X-ray diffraction pattern of the β-hydrate 35 with known hydrates having an anatase structure and a rutile structure. The given 3 69443 ma values are determined in all cases by means of a Cu-K®fcr beam. The figure shows that the β-hydrate can be distinguished, above all by its main X-ray deflection at 24.6 °, clearly from anatase (main X-ray deflection at 25.4 °) and rutile (main X-ray deflection at 27.4 °). A Brookit comparison showed that J-hydrate is also not associated with this modification. It further differs from the titanium dioxide hydrate disclosed in U.S. Patent 2,333,662, which is referred to as the "β-hydrate" and which, unlike the β-hydrate, has a main X-ray reflection at 22.3 °.

The hydrate is retained at room temperature for any length of time. Above about 350 ° C it is converted to anatase.

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

Furthermore, the precipitated, separated and washed, wet or dried <S-hydrate, unlike other TiO 2 hydrates obtained from titanium sulphate solutions, can be peptized again by the addition of sulphate ions (especially in the form of sulfuric acid) or other divalent or trivalent anions. After flocculation and separation and washing with sulfuric acid-containing mother liquor, more than 30 parts by weight per 100 parts are obtained T1O2 · 4 69443

The process according to the invention gives, β-hydrate in admixture with other TiCl 4 -hydrates. A mixture of titanium dioxide hydrate containing more than 20%, calculated as titanium oxide, based on the total amount of TiCl 2, in the form of titanium dioxide hydrate is very well suited for many purposes, in particular as an adsorbent or a collecting reagent.

The advantage of the process according to the invention is based on the fact that, by adding titanium dioxide hydrate nuclei, solutions with a higher titanium content can be used than if these nuclei are not used. In particular, solutions which are customary in the preparation of pigments can be used.

The d-titanium dioxide hydrate cores 15 are prepared, for example, by bringing a portion of the titanium sulphate stock solution in a suitable manner, e.g. by dilution, into the composition of claim 1 and hydrolysing by heating, the precipitated titanium dioxide hydrate is calculated by adding a monovalent acid or a salt thereof and the flocculated titanium dioxide hydrate having the ^ structure is removed from the solution and, if desired, washed with water.

The t-titanium dioxide hydrate cores can also be added as a colloidal solution such as that obtained in the hydrolysis of the titanium sulfate solution to prepare the t-titanium dioxide hydrate by first removing the precipitated titanium dioxide hydrate in anatase 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-35 content of the titanium sulphate solution.

5 69443

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

The titanium sulphate solution can be obtained in a known manner by extracting ilmenite, other titanium ores, slag or titanium concentrate with sulfuric acid. It is possible to start from a titanium sulphate solution obtained by preparing a titanium dioxide pigment by means of a sulphate diluent. 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, dissolution of the extraction cake, 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 that colloidally dissolves dissolved titanium dioxide should be used for clarification. Suitable methods are described, for example, in GB Patent 473,054 and U.S. Patents 2,413,640 and 2,413,641. A very suitable starting solution is obtained if the titanium sulphate solution prepared in a known manner is clarified with polymeric diethylaminoethyl acrylates or polyacrylamides.

If the iron content of the starting solution is low and / or the ratio of free sulfuric acid to titanium dioxide is low, the optimum TiO 2 content shifts to higher values (the term "free sulfuric acid" is conventionally understood as sulfuric acid which is not bound to cations other than titanium-35 in solution).

6 69443

The appropriate concentration can be adjusted during extraction and / or subsequent process steps, e.g. 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 (manifestite, TiO 2 -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, in order to counteract 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, prior to hydrolysis, no 15 conventional nuclei are added from the outside and, for example, they do not form in solution when mixed with water. Only cores with an X-hydrate structure are added before hydrolysis.

The duration of heating is determined by the concentration of anatase-20 nuclei in the solution and the composition of the solution.

In general, the yield of ίΓ-titanium dioxide hydrate increases as the heating time increases, however, the long heating time is associated with certain disadvantages in some cases, e.g. deterioration in quality. After the addition of the 1-hydrate cores, the composition of the solution can be kept unchanged or changed, for example by evaporation or dilution, before hydrolysis.

In technically conventional titanium sulphate solutions, the f) -hydrate cores initially formed or added outside the range of analytical composition of the titanium sulphate solution, which is preferred for spontaneous nucleation, also increase further. Since in the technical preparation of titanium dioxide hydrate from sulfuric acid extraction solutions) the formation of a preferred analytical composition

II

7 69443 its area is regularly bypassed, 5-hydrate is always formed in small amounts. In addition to the rate of formation and growth of S-hydrate nuclei, the amount also depends on the number, size and growth rate of the anatase nuclei, i. the kinetics of the competitive anatase hydrate formation reaction.

In the hydrolysis, a precipitate often forms in the titanium sulphate solution, which consists mainly of anatase hydrate, while the S-hydrate 10 formed at the same time remains colloidal in solution. If a mixture of titanium dioxide hydrates consisting of both components has to be recovered, the precipitated anatase hydrate is removed only after further treatment of the hydrolyzed solution to co-precipitate the β-hydrate with it. On the other hand, if, on the other hand, it is desired to recover the J-hydrate in the most concentrated or pure form possible, the anatase hydrate precipitate is removed from the solution in a manner known per se before flocculation of the E-hydrate. Flocculation of the β-hydrate is effected 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 is required in an amount which gives their concentration in the solution in the range of 1.5 to 8, preferably 25 to 5 mol / liter.

The washing of the precipitated titanium dioxide hydrate takes place in the same way as in the preparation of titanium dioxide pigments, but a bleaching step is 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 T1O2, is that, after the addition of the monobasic acid or its salt, the titanium dioxide hydrate in the solution is separated or ammonia and washed again and / or dried.

8 69443

In neutralization, the SO 2 groups are replaced by OH groups; in which case the sulfuric acid is removed to a small extent; at the same time, however, the characteristic structure of the S-hydrate is preserved. The neutralization is preferably carried out in an aqueous suspension. The neutralized hydrate can then be washed and / or dried. The optimum pH desired in neutralization depends to some extent on the illumination conditions of the product and can be easily determined experimentally. Neutralization can be performed both before and after further processing of the product 10, e.g. before paste formation, drying and granulation. The neutralized product is particularly well suited as an adsorbent or a collecting reagent.

After the addition of the monobasic acid or its salt, the titanium dioxide hydrate flocculated in solution can be thickened by sedimentation before removal from the solution. A preferred embodiment of the method is based on the addition of a flocculant prior to the addition of the monobasic acid or its salt by flocculating titanium dioxide hydrate in solution. The flocculant must be effective in a strongly acidic solution. Suitable acylating agents 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 a substance prepared according to the invention is used as an adsorbent, it is expedient to granulate the titanium dioxide hydrate or titanium dioxide hydrate 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 hole 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.

It is characteristic of an embodiment of the invention that, before drying, solid, acid-insoluble inorganic or organic substances are added to the titanium dioxide hydrate or titanium dioxide hydrate mixture in amounts of up to 70% by weight, calculated from the total mixture thus obtained and then obtained in the total mixture.

In this way, the mechanical and / or adsorption properties and / or the adsorption kinetics of 5-titanium dioxide hydrate or an adsorbent containing this hydrate can be improved. The addition of solids can be done before mixing, flocculating, neutralizing or drying the titanium dioxide hydrate or titanium dioxide hydrate mixture. Suitable fillers are, for example, fillers used, for example, for brushes or other high-surface-area substances (see Ullmanns Encyklopädie der technischen Chemie 3rd edition, Part 13 (1962), pages 814-821 and "Chemische Technologie", published K .Winnacker and L. KUchler 3rd Edition Part 2 (1970) pages 539-545). Examples are silicon, mica, asbestos fiber and activated carbon.

β-titanium dioxide hydrate or a mixture of titanium dioxide and hydrate containing more than 20%, as t-dioxide, based on the total amount of TiO2, ε-titanium dioxide hydrate, has an excellent adsorption capacity. In particular, it can be used as an adsorbent or a collection reagent for recovering uranium and / or other elements from dilute aqueous solutions containing these elements. It has been found that ε-hydrate 10 69443 is superior to titanium dioxide hydrates known to date due to its inherent adsorption capacity. Therefore, it is very useful as a uranium aggregating reagent in recovering it from seawater.

5 The following examples illustrate the invention in more detail.

Example 1

To a volume of 1,000 liters equipped with an exterior masonry and a leaded heating piping and a leaded stirrer, 200 liters of iron (II) sulfate heptahydrate was separated into a bulk iron-purified ilmenite extract solution containing 150 g / l of 45 g / l Fe 2+, 375 g / l total sulphate calculated as SO 2 and 0.75 g / l Ti 3+ and diluted to 300 liters with water. The composition of the solution was the analytical composition shown on page 5. The contents of the vessel were then heated to boiling point with indirect stirring by means of steam passed through the heating piping and then kept at 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 after 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 in a second vessel of 1,000 liters equipped with a masonry and a rubberized stirrer, stirring over 400 minutes with 400 liters of 30% hydrochloric acid. The β-hydrate then flocculated, and after standing overnight, the top mother liquor was removed with a spatula 11,644,43, thickening the remaining mixture to about four times the solids content. Immediately before filtration, 20 ml / l of a 2% aqueous solution of commercial polyacrylamide (Tiofloc B 21) was stirred into this suspension. In this case, the <£ hydrate could 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-10. Stirring was continued for another 10 minutes and the pH was readjusted to 7 by the addition 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 into bars by means of a press equipped with a perforated plate (hole diameter 5 mm), and the bars were dried for 12 hours at 110 ° C. The rods were then reduced to granules having a particle diameter of about 3.5 mm. The effect of the preforming then formed only a small amount of fines. About 10.5 kg of dried titanium dioxide dihydrate with a TiO 2 content of about 75% was obtained; this corresponded to about 26% yield based on the amount of T1O2 in the starting solution.

25 An X-ray diffraction study of the obtained product did not show anastase reflections and was therefore practically pure ε-hydrate.

Example 2 The same ilmenite extraction solution was used as in Example 1. A portion of this solution (30 L) was diluted as in Example 1 with water to a TiO 2 concentration of 100 g / L, heated to boiling point and boiled for 20 minutes. In this case, about 30% of the titanium in solution was hydrolyzed to the hydrate.

i2 69443

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 ε-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 the boiling point for 60 minutes. At that time, about 30% of the total T1O2 was hydrolyzed, of which 25% was 5-hydrate and 5% anatase hydrate.

The reaction mixture was diluted with water to 600 liters, whereupon the temperature dropped below 50 ° C. Removal of the anatase hydrate and flocculation and separation of the β-hydrate were performed as in Example 1. Also in the product thus obtained, no reflection of anatase-15 could be detected, but only the reflection of the 5-hydrate.

Claims (6)

A process for the preparation of </ - titanium dioxide hydrate or a mixture containing over 20%, i-titanium dioxide hydrate, designated as TiO 2 and calculated on the total amount of TiO 2, wherein the radiation exhibits principal maxima at points 2Θ = 24.6 + 0.4 ° and 48 + 0.4? can be characterized in that a titanium sulfate solution having a TiO 2 content of 120 - 250 g / l, a molar ratio of TiO 2 to free sulfuric acid of 1: 1 - 1: 2, a bivalent iron content of 0-1 g Fe per 1 g titanium dioxide and optionally containing trivalent titanium is hydrolyzed in the presence of </ - titanium dioxide dihydrate cores by heating, the precipitated titanium dioxide hydrate is separated as needed, the colloidally distributed titanium dioxide hydrate is flocculated by the addition of a monobasic acid or and the flocculated titanium dioxide hydrate, optionally together with the unspecified, pre-flocculated titanium dioxide hydrate, is removed, washed with water to remove iron and other foreign constituents, and as desired, dried. 2. A process according to claim 1, characterized in that after addition of the monobasic acid or its site, the titanium dioxide hydrate present in the solution is neutralized after separation and washing with alkali or ammonia and, if desired, then washed and washed. / or dried. 3. A process according to claim 1 or 2, characterized in that after the addition of the monobasic acid or its site, the titanium dioxide hydrate present in the solution is thickened in a flocculated form prior to separation from the solution by settling. 4. A method according to claims 1-3, characterized in that prior to the separation thereof